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Re: Capacitor Charging Question

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  • wilf_nv
    If you are using a 5V solar cell operating at 3.2V or less, the solar cell current will be nearly constant and the cap charging time equation becomes
    Message 1 of 14 , Dec 31, 2006
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      If you are using a 5V solar cell operating at 3.2V or less, the solar
      cell current will be nearly constant and the cap charging time
      equation becomes

      dT=C*dV/Isc

      According to your experiment, using a 1380L (3.2V) with the 4700uF
      cap the time between pops is about 30 secs.

      That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)

      The energy stored in the cap with 4700uF charged to 3.2V (which is
      completely discharged into the load) is 0.5V*V*C =0.024J

      Let's see how that works for the 1F cap with the 1381C trigger.

      Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset voltage),
      the initial charging time from 0V to the operating voltage (2.4V) is
      1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J of stored
      energy.

      After reaching the 2.4V operating voltage and using approximantly the
      same discharge energy per pop of 0.024J (10mA * 1sec) with the 1F
      capacitor voltage dropping dV=10mV every pop, the charging time
      between pops is 1F * 0.01V / 0.0005A = 20 seconds which is faster
      that the 4700uF case because once initialized, the solar cell
      operates constantly at 2.4V nearer to its maximum power point.

      wilf

      --- In beam@yahoogroups.com, Gary Tolley <grogyan@...> wrote:
      >
      > Tk,
      > There is a formula to calculate the charge time of a cap.
      > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
      > or
      > http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capchg.html
      >
      > ater a quick search on google.
      >
      > Gary T
      >
      >
      > >OK, I have a working solarpopper based on Wilfs "Photopopper v8"
      > >circuit posed back in September. Slick circuit...simple and
      elegant.
      > >
      > >I have a Radio Shack 4700uF 35v capacitor...it is massive but I
      > >figured it would be OK for testing purposes. With this capacitor
      and
      > >a 1381L as indicated in the plans, it works and charges very
      quickly
      > >and drives the 6mm motors just fine.
      > >
      > >As a test, I wanted to see what a 1381C (2.4v) and the 1.0F 2.5v
      > >Aerogel Super Capacitor would do. I have a few of these so it is
      > >worth checking out because they are tiny. This capacitor is MUCH
      > >smaller and if I could drive the 6mm motors from the 2.4v, then it
      > >might be something worth implementing.
      > >
      > >Here is the deal...the 1F capacitor takes FOREVER to charge. Maybe
      I
      > >am confused on my basic electronics but shouldn't a 1F capacitor
      > >charge in a bit more than double the time as the 4700uF capacitor?
      > >
      > >Under an incandecent bulb I did the following...I tested both the
      > >4700uF and 1F with the 1381C triggering at 2.4v. The 4700uF was
      > >triggering rather rapidly (several times per minute)...I am not
      sure
      > >the 2.4v will be adequate to drive the motors but that is not the
      > >point right now...the 1F took about 90 minutes to charge. It was
      > >painfully long. Just how much more capacity does the 1F have?
      > >
      > >Can someone shed some light on why the 1F is taking so long to
      charge?
      > >
      > >tk
      > >
      > >
      >
    • kinkyme360
      Wow...that is some good information. The math seems to bear out my observations which is good, but the cool thing is that once the 1F gets charged, it will
      Message 2 of 14 , Jan 1, 2007
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        Wow...that is some good information. The math seems to bear out my
        observations which is good, but the cool thing is that once the 1F
        gets charged, it will fire pretty quick afterwards. If there is a
        design that can live on only 2.4 volts then this could be
        interesting.

        2.4 volts seems pretty weak...not enough to really drive the motors
        well. Is it possible to put 2 1F 2.5 capacitors in series and use the
        1381L (3.2 volts) or higher trigger? Dividing the charge between the
        two, keeping both under the 2.5v rating but reaping the benefit of
        the added discharge voltage? Yea, it would take quite awhile to
        initially charge but might perform well afterwards.

        Sorry if these are obvious questions...I am electronically
        challenged. I took basic electronics in high school nearly 20 years
        ago and that's it. One of these days I'm going to blow something up
        but it will be fun getting there!

        tk






        --- In beam@yahoogroups.com, "wilf_nv" <wrigter@...> wrote:
        >
        > If you are using a 5V solar cell operating at 3.2V or less, the
        solar
        > cell current will be nearly constant and the cap charging time
        > equation becomes
        >
        > dT=C*dV/Isc
        >
        > According to your experiment, using a 1380L (3.2V) with the 4700uF
        > cap the time between pops is about 30 secs.
        >
        > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)
        >
        > The energy stored in the cap with 4700uF charged to 3.2V (which is
        > completely discharged into the load) is 0.5V*V*C =0.024J
        >
        > Let's see how that works for the 1F cap with the 1381C trigger.
        >
        > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset voltage),
        > the initial charging time from 0V to the operating voltage (2.4V)
        is
        > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J of
        stored
        > energy.
        >
        > After reaching the 2.4V operating voltage and using approximantly
        the
        > same discharge energy per pop of 0.024J (10mA * 1sec) with the 1F
        > capacitor voltage dropping dV=10mV every pop, the charging time
        > between pops is 1F * 0.01V / 0.0005A = 20 seconds which is faster
        > that the 4700uF case because once initialized, the solar cell
        > operates constantly at 2.4V nearer to its maximum power point.
        >
        > wilf
        >
        > --- In beam@yahoogroups.com, Gary Tolley <grogyan@> wrote:
        > >
        > > Tk,
        > > There is a formula to calculate the charge time of a cap.
        > > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
        > > or
        > > http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capchg.html
        > >
        > > ater a quick search on google.
        > >
        > > Gary T
        > >
        > >
        > > >OK, I have a working solarpopper based on Wilfs "Photopopper v8"
        > > >circuit posed back in September. Slick circuit...simple and
        > elegant.
        > > >
        > > >I have a Radio Shack 4700uF 35v capacitor...it is massive but I
        > > >figured it would be OK for testing purposes. With this capacitor
        > and
        > > >a 1381L as indicated in the plans, it works and charges very
        > quickly
        > > >and drives the 6mm motors just fine.
        > > >
        > > >As a test, I wanted to see what a 1381C (2.4v) and the 1.0F 2.5v
        > > >Aerogel Super Capacitor would do. I have a few of these so it is
        > > >worth checking out because they are tiny. This capacitor is MUCH
        > > >smaller and if I could drive the 6mm motors from the 2.4v, then
        it
        > > >might be something worth implementing.
        > > >
        > > >Here is the deal...the 1F capacitor takes FOREVER to charge.
        Maybe
        > I
        > > >am confused on my basic electronics but shouldn't a 1F capacitor
        > > >charge in a bit more than double the time as the 4700uF
        capacitor?
        > > >
        > > >Under an incandecent bulb I did the following...I tested both the
        > > >4700uF and 1F with the 1381C triggering at 2.4v. The 4700uF was
        > > >triggering rather rapidly (several times per minute)...I am not
        > sure
        > > >the 2.4v will be adequate to drive the motors but that is not the
        > > >point right now...the 1F took about 90 minutes to charge. It was
        > > >painfully long. Just how much more capacity does the 1F have?
        > > >
        > > >Can someone shed some light on why the 1F is taking so long to
        > charge?
        > > >
        > > >tk
        > > >
        > > >
        > >
        >
      • wilf rigter
        Hi tk With two 1F caps in series, which gives you a combined cap of 0.5F @ 5V, and a 1381L (3.2V) trigger, the initial charging time with a solar cell
        Message 3 of 14 , Jan 1, 2007
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          Hi tk
           
          With two 1F caps in series, which gives you a combined cap of 0.5F @ 5V,  and  a 1381L (3.2V) trigger, the initial charging time with a solar cell supplying 0.5mA constant current 
           
          dT (charging  time)=Capacitance*dV(voltage change) /Isc(solar cell current)
           
          0.5F * 3.2V / 0.5ma  = 3200 seconds = 53 minutes
           
          Note that, with a Ge diode in series with the solar cell and charged up to 3.2V, the cap should hold that voltage for quite a while in the dark (i.e. overnight) and won't take long to start popping when the light comes back on.
           
          btw what solar cell are  you using?
           
          Now consider the discharge cycle.  If each pop from the 0.5F sol;ar popper is assumed to be equivalent to a 4700uf cap discharging completely from 3.2V to 0V and depending on the timing cap and the load, such an equivalent  pop might be 15mA (average) * 3.2V * 0.5 sec during which the capacitor voltage drops 15mV.
           
          The recharge time between pops would be:
           
          0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the popping time would be 
           
          wilf
           
           
          ----- Original Message -----
          Sent: Monday, January 01, 2007 11:54 AM
          Subject: [beam] Re: Capacitor Charging Question

          Wow...that is some good information. The math seems to bear out my
          observations which is good, but the cool thing is that once the 1F
          gets charged, it will fire pretty quick afterwards. If there is a
          design that can live on only 2.4 volts then this could be
          interesting.

          2.4 volts seems pretty weak...not enough to really drive the motors
          well. Is it possible to put 2 1F 2.5 capacitors in series and use the
          1381L (3.2 volts) or higher trigger? Dividing the charge between the
          two, keeping both under the 2.5v rating but reaping the benefit of
          the added discharge voltage? Yea, it would take quite awhile to
          initially charge but might perform well afterwards.

          Sorry if these are obvious questions... I am electronically
          challenged. I took basic electronics in high school nearly 20 years
          ago and that's it. One of these days I'm going to blow something up
          but it will be fun getting there!

          tk

          --- In beam@yahoogroups. com, "wilf_nv" <wrigter@... > wrote:
          >
          > If you are using a 5V solar cell operating at 3.2V or less, the
          solar
          > cell current will be nearly constant and the cap charging time
          > equation becomes
          >
          > dT=C*dV/Isc
          >
          > According to your experiment, using a 1380L (3.2V) with the 4700uF
          > cap the time between pops is about 30 secs.
          >
          > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)
          >
          > The energy stored in the cap with 4700uF charged to 3.2V (which is
          > completely discharged into the load) is 0.5V*V*C =0.024J
          >
          > Let's see how that works for the 1F cap with the 1381C trigger.
          >
          > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset voltage),
          > the initial charging time from 0V to the operating voltage (2.4V)
          is
          > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J of
          stored
          > energy.
          >
          > After reaching the 2.4V operating voltage and using approximantly
          the
          > same discharge energy per pop of 0.024J (10mA * 1sec) with the 1F
          > capacitor voltage dropping dV=10mV every pop, the charging time
          > between pops is 1F * 0.01V / 0.0005A = 20 seconds which is faster
          > that the 4700uF case because once initialized, the solar cell
          > operates constantly at 2.4V nearer to its maximum power point.
          >
          > wilf
          >
          > --- In beam@yahoogroups. com, Gary Tolley <grogyan@> wrote:
          > >
          > > Tk,
          > > There is a formula to calculate the charge time of a cap.
          > > http://ourworld. compuserve. com/homepages/ Bill_Bowden/ rc.htm
          > > or
          > > http://hyperphysics .phy-astr. gsu.edu/hbase/ electric/ capchg.html
          > >
          > > ater a quick search on google.
          > >
          > > Gary T
          > >
          > >
          > > >OK, I have a working solarpopper based on Wilfs "Photopopper v8"
          > > >circuit posed back in September. Slick circuit...simple and
          > elegant.
          > > >
          > > >I have a Radio Shack 4700uF 35v capacitor... it is massive but I
          > > >figured it would be OK for testing purposes. With this capacitor
          > and
          > > >a 1381L as indicated in the plans, it works and charges very
          > quickly
          > > >and drives the 6mm motors just fine.
          > > >
          > > >As a test, I wanted to see what a 1381C (2.4v) and the 1.0F 2.5v
          > > >Aerogel Super Capacitor would do. I have a few of these so it is
          > > >worth checking out because they are tiny. This capacitor is MUCH
          > > >smaller and if I could drive the 6mm motors from the 2.4v, then
          it
          > > >might be something worth implementing.
          > > >
          > > >Here is the deal...the 1F capacitor takes FOREVER to charge.
          Maybe
          > I
          > > >am confused on my basic electronics but shouldn't a 1F capacitor
          > > >charge in a bit more than double the time as the 4700uF
          capacitor?
          > > >
          > > >Under an incandecent bulb I did the following... I tested both the
          > > >4700uF and 1F with the 1381C triggering at 2.4v. The 4700uF was
          > > >triggering rather rapidly (several times per minute)...I am not
          > sure
          > > >the 2.4v will be adequate to drive the motors but that is not the
          > > >point right now...the 1F took about 90 minutes to charge. It was
          > > >painfully long. Just how much more capacity does the 1F have?
          > > >
          > > >Can someone shed some light on why the 1F is taking so long to
          > charge?
          > > >
          > > >tk
          > > >
          > > >
          > >
          >

        • kinkyme360
          I m using the solar cell that comes with the old Solarbotics Solarpopper 4.2 kit but I do have other options. I have some of the new Russian-made cells
          Message 4 of 14 , Jan 1, 2007
          • 0 Attachment
            I'm using the solar cell that comes with the old Solarbotics
            Solarpopper 4.2 kit but I do have other options.

            I have some of the new Russian-made cells Solarbotics has for sale.
            For some odd reason they sent me one with the Miller circuit etched
            on the back and one did not. It also seems odd that the non-etched
            one says 6.7v @ 15mA on the back...they state that it is very
            efficient but on their website they have one the same exact size
            rated at 6.7v @ 31mA

            I also have several 3v 22mA thin-film cells I could use. They are
            lighter but have a larger footprint.

            I'm going to try out the dual caps and diode and see how it runs.

            thanx again...tk



            --- In beam@yahoogroups.com, "wilf rigter" <wrigter@...> wrote:
            >
            >
            > Hi tk
            >
            > With two 1F caps in series, which gives you a combined cap of 0.5F
            @ 5V, and a 1381L (3.2V) trigger, the initial charging time with a
            solar cell supplying 0.5mA constant current
            >
            > dT (charging time)=Capacitance*dV(voltage change) /Isc(solar cell
            current)
            >
            > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
            >
            > Note that, with a Ge diode in series with the solar cell and
            charged up to 3.2V, the cap should hold that voltage for quite a
            while in the dark (i.e. overnight) and won't take long to start
            popping when the light comes back on.
            >
            > btw what solar cell are you using?
            >
            > Now consider the discharge cycle. If each pop from the 0.5F sol;ar
            popper is assumed to be equivalent to a 4700uf cap discharging
            completely from 3.2V to 0V and depending on the timing cap and the
            load, such an equivalent pop might be 15mA (average) * 3.2V * 0.5
            sec during which the capacitor voltage drops 15mV.
            >
            > The recharge time between pops would be:
            >
            > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the popping
            time would be
            >
            > wilf
            >
            >
            > ----- Original Message -----
            > From: kinkyme360
            > To: beam@yahoogroups.com
            > Sent: Monday, January 01, 2007 11:54 AM
            > Subject: [beam] Re: Capacitor Charging Question
            >
            >
            > Wow...that is some good information. The math seems to bear out
            my
            > observations which is good, but the cool thing is that once the
            1F
            > gets charged, it will fire pretty quick afterwards. If there is a
            > design that can live on only 2.4 volts then this could be
            > interesting.
            >
            > 2.4 volts seems pretty weak...not enough to really drive the
            motors
            > well. Is it possible to put 2 1F 2.5 capacitors in series and use
            the
            > 1381L (3.2 volts) or higher trigger? Dividing the charge between
            the
            > two, keeping both under the 2.5v rating but reaping the benefit
            of
            > the added discharge voltage? Yea, it would take quite awhile to
            > initially charge but might perform well afterwards.
            >
            > Sorry if these are obvious questions...I am electronically
            > challenged. I took basic electronics in high school nearly 20
            years
            > ago and that's it. One of these days I'm going to blow something
            up
            > but it will be fun getting there!
            >
            > tk
            >
            > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
            > >
            > > If you are using a 5V solar cell operating at 3.2V or less, the
            > solar
            > > cell current will be nearly constant and the cap charging time
            > > equation becomes
            > >
            > > dT=C*dV/Isc
            > >
            > > According to your experiment, using a 1380L (3.2V) with the
            4700uF
            > > cap the time between pops is about 30 secs.
            > >
            > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)
            > >
            > > The energy stored in the cap with 4700uF charged to 3.2V (which
            is
            > > completely discharged into the load) is 0.5V*V*C =0.024J
            > >
            > > Let's see how that works for the 1F cap with the 1381C trigger.
            > >
            > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset
            voltage),
            > > the initial charging time from 0V to the operating voltage
            (2.4V)
            > is
            > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J of
            > stored
            > > energy.
            > >
            > > After reaching the 2.4V operating voltage and using
            approximantly
            > the
            > > same discharge energy per pop of 0.024J (10mA * 1sec) with the
            1F
            > > capacitor voltage dropping dV=10mV every pop, the charging time
            > > between pops is 1F * 0.01V / 0.0005A = 20 seconds which is
            faster
            > > that the 4700uF case because once initialized, the solar cell
            > > operates constantly at 2.4V nearer to its maximum power point.
            > >
            > > wilf
            > >
            > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@> wrote:
            > > >
            > > > Tk,
            > > > There is a formula to calculate the charge time of a cap.
            > > > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
            > > > or
            > > > http://hyperphysics.phy-
            astr.gsu.edu/hbase/electric/capchg.html
            > > >
            > > > ater a quick search on google.
            > > >
            > > > Gary T
            > > >
            > > >
            > > > >OK, I have a working solarpopper based on Wilfs "Photopopper
            v8"
            > > > >circuit posed back in September. Slick circuit...simple and
            > > elegant.
            > > > >
            > > > >I have a Radio Shack 4700uF 35v capacitor...it is massive
            but I
            > > > >figured it would be OK for testing purposes. With this
            capacitor
            > > and
            > > > >a 1381L as indicated in the plans, it works and charges very
            > > quickly
            > > > >and drives the 6mm motors just fine.
            > > > >
            > > > >As a test, I wanted to see what a 1381C (2.4v) and the 1.0F
            2.5v
            > > > >Aerogel Super Capacitor would do. I have a few of these so
            it is
            > > > >worth checking out because they are tiny. This capacitor is
            MUCH
            > > > >smaller and if I could drive the 6mm motors from the 2.4v,
            then
            > it
            > > > >might be something worth implementing.
            > > > >
            > > > >Here is the deal...the 1F capacitor takes FOREVER to charge.
            > Maybe
            > > I
            > > > >am confused on my basic electronics but shouldn't a 1F
            capacitor
            > > > >charge in a bit more than double the time as the 4700uF
            > capacitor?
            > > > >
            > > > >Under an incandecent bulb I did the following...I tested
            both the
            > > > >4700uF and 1F with the 1381C triggering at 2.4v. The 4700uF
            was
            > > > >triggering rather rapidly (several times per minute)...I am
            not
            > > sure
            > > > >the 2.4v will be adequate to drive the motors but that is
            not the
            > > > >point right now...the 1F took about 90 minutes to charge. It
            was
            > > > >painfully long. Just how much more capacity does the 1F have?
            > > > >
            > > > >Can someone shed some light on why the 1F is taking so long
            to
            > > charge?
            > > > >
            > > > >tk
            > > > >
            > > > >
            > > >
            > >
            >
          • wilf_nv
            Hmmm... so the 0.5ma current I derived from your timing measurements is very low compared to the rated output current of the cell. Keep in mind that the rated
            Message 5 of 14 , Jan 1, 2007
            • 0 Attachment
              Hmmm... so the 0.5ma current I derived from your timing measurements
              is very low compared to the rated output current of the cell. Keep in
              mind that the rated currrent is measured in very bright light. Can
              you measure current during charging to confirm the value and that it
              is not low because of some other problem?


              --- In beam@yahoogroups.com, "kinkyme360" <tskunka@...> wrote:
              >
              > I'm using the solar cell that comes with the old Solarbotics
              > Solarpopper 4.2 kit but I do have other options.
              >
              > I have some of the new Russian-made cells Solarbotics has for sale.
              > For some odd reason they sent me one with the Miller circuit etched
              > on the back and one did not. It also seems odd that the non-etched
              > one says 6.7v @ 15mA on the back...they state that it is very
              > efficient but on their website they have one the same exact size
              > rated at 6.7v @ 31mA
              >
              > I also have several 3v 22mA thin-film cells I could use. They are
              > lighter but have a larger footprint.
              >
              > I'm going to try out the dual caps and diode and see how it runs.
              >
              > thanx again...tk
              >
              >
              >
              > --- In beam@yahoogroups.com, "wilf rigter" <wrigter@> wrote:
              > >
              > >
              > > Hi tk
              > >
              > > With two 1F caps in series, which gives you a combined cap of
              0.5F
              > @ 5V, and a 1381L (3.2V) trigger, the initial charging time with
              a
              > solar cell supplying 0.5mA constant current
              > >
              > > dT (charging time)=Capacitance*dV(voltage change) /Isc(solar
              cell
              > current)
              > >
              > > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
              > >
              > > Note that, with a Ge diode in series with the solar cell and
              > charged up to 3.2V, the cap should hold that voltage for quite a
              > while in the dark (i.e. overnight) and won't take long to start
              > popping when the light comes back on.
              > >
              > > btw what solar cell are you using?
              > >
              > > Now consider the discharge cycle. If each pop from the 0.5F
              sol;ar
              > popper is assumed to be equivalent to a 4700uf cap discharging
              > completely from 3.2V to 0V and depending on the timing cap and the
              > load, such an equivalent pop might be 15mA (average) * 3.2V * 0.5
              > sec during which the capacitor voltage drops 15mV.
              > >
              > > The recharge time between pops would be:
              > >
              > > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the
              popping
              > time would be
              > >
              > > wilf
              > >
              > >
              > > ----- Original Message -----
              > > From: kinkyme360
              > > To: beam@yahoogroups.com
              > > Sent: Monday, January 01, 2007 11:54 AM
              > > Subject: [beam] Re: Capacitor Charging Question
              > >
              > >
              > > Wow...that is some good information. The math seems to bear out
              > my
              > > observations which is good, but the cool thing is that once the
              > 1F
              > > gets charged, it will fire pretty quick afterwards. If there is
              a
              > > design that can live on only 2.4 volts then this could be
              > > interesting.
              > >
              > > 2.4 volts seems pretty weak...not enough to really drive the
              > motors
              > > well. Is it possible to put 2 1F 2.5 capacitors in series and
              use
              > the
              > > 1381L (3.2 volts) or higher trigger? Dividing the charge
              between
              > the
              > > two, keeping both under the 2.5v rating but reaping the benefit
              > of
              > > the added discharge voltage? Yea, it would take quite awhile to
              > > initially charge but might perform well afterwards.
              > >
              > > Sorry if these are obvious questions...I am electronically
              > > challenged. I took basic electronics in high school nearly 20
              > years
              > > ago and that's it. One of these days I'm going to blow
              something
              > up
              > > but it will be fun getting there!
              > >
              > > tk
              > >
              > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
              > > >
              > > > If you are using a 5V solar cell operating at 3.2V or less,
              the
              > > solar
              > > > cell current will be nearly constant and the cap charging
              time
              > > > equation becomes
              > > >
              > > > dT=C*dV/Isc
              > > >
              > > > According to your experiment, using a 1380L (3.2V) with the
              > 4700uF
              > > > cap the time between pops is about 30 secs.
              > > >
              > > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)
              > > >
              > > > The energy stored in the cap with 4700uF charged to 3.2V
              (which
              > is
              > > > completely discharged into the load) is 0.5V*V*C =0.024J
              > > >
              > > > Let's see how that works for the 1F cap with the 1381C
              trigger.
              > > >
              > > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset
              > voltage),
              > > > the initial charging time from 0V to the operating voltage
              > (2.4V)
              > > is
              > > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J of
              > > stored
              > > > energy.
              > > >
              > > > After reaching the 2.4V operating voltage and using
              > approximantly
              > > the
              > > > same discharge energy per pop of 0.024J (10mA * 1sec) with
              the
              > 1F
              > > > capacitor voltage dropping dV=10mV every pop, the charging
              time
              > > > between pops is 1F * 0.01V / 0.0005A = 20 seconds which is
              > faster
              > > > that the 4700uF case because once initialized, the solar cell
              > > > operates constantly at 2.4V nearer to its maximum power point.
              > > >
              > > > wilf
              > > >
              > > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@> wrote:
              > > > >
              > > > > Tk,
              > > > > There is a formula to calculate the charge time of a cap.
              > > > > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
              > > > > or
              > > > > http://hyperphysics.phy-
              > astr.gsu.edu/hbase/electric/capchg.html
              > > > >
              > > > > ater a quick search on google.
              > > > >
              > > > > Gary T
              > > > >
              > > > >
              > > > > >OK, I have a working solarpopper based on
              Wilfs "Photopopper
              > v8"
              > > > > >circuit posed back in September. Slick circuit...simple
              and
              > > > elegant.
              > > > > >
              > > > > >I have a Radio Shack 4700uF 35v capacitor...it is massive
              > but I
              > > > > >figured it would be OK for testing purposes. With this
              > capacitor
              > > > and
              > > > > >a 1381L as indicated in the plans, it works and charges
              very
              > > > quickly
              > > > > >and drives the 6mm motors just fine.
              > > > > >
              > > > > >As a test, I wanted to see what a 1381C (2.4v) and the
              1.0F
              > 2.5v
              > > > > >Aerogel Super Capacitor would do. I have a few of these so
              > it is
              > > > > >worth checking out because they are tiny. This capacitor
              is
              > MUCH
              > > > > >smaller and if I could drive the 6mm motors from the 2.4v,
              > then
              > > it
              > > > > >might be something worth implementing.
              > > > > >
              > > > > >Here is the deal...the 1F capacitor takes FOREVER to
              charge.
              > > Maybe
              > > > I
              > > > > >am confused on my basic electronics but shouldn't a 1F
              > capacitor
              > > > > >charge in a bit more than double the time as the 4700uF
              > > capacitor?
              > > > > >
              > > > > >Under an incandecent bulb I did the following...I tested
              > both the
              > > > > >4700uF and 1F with the 1381C triggering at 2.4v. The
              4700uF
              > was
              > > > > >triggering rather rapidly (several times per minute)...I
              am
              > not
              > > > sure
              > > > > >the 2.4v will be adequate to drive the motors but that is
              > not the
              > > > > >point right now...the 1F took about 90 minutes to charge.
              It
              > was
              > > > > >painfully long. Just how much more capacity does the 1F
              have?
              > > > > >
              > > > > >Can someone shed some light on why the 1F is taking so
              long
              > to
              > > > charge?
              > > > > >
              > > > > >tk
              > > > > >
              > > > > >
              > > > >
              > > >
              > >
              >
            • kinkyme360
              You ask a very good question...I might be able to measure the current if I knew how. ;-) I have a basic analog Radio Shack multimeter...I m not sure how to
              Message 6 of 14 , Jan 2, 2007
              • 0 Attachment
                You ask a very good question...I might be able to measure the current
                if I knew how. ;-) I have a basic analog Radio Shack multimeter...I'm
                not sure how to measure current with it.

                I tried out the dual 1F cap and sure enough, once the thing gets
                charged, it triggers at a very regular interval. I seem to have some
                loss of charge when idle...perhaps I need a bigger diode? I'm using a
                1N914 right now.

                tk


                --- In beam@yahoogroups.com, "wilf_nv" <wrigter@...> wrote:
                >
                > Hmmm... so the 0.5ma current I derived from your timing
                measurements
                > is very low compared to the rated output current of the cell. Keep
                in
                > mind that the rated currrent is measured in very bright light. Can
                > you measure current during charging to confirm the value and that
                it
                > is not low because of some other problem?
                >
                >
                > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                > >
                > > I'm using the solar cell that comes with the old Solarbotics
                > > Solarpopper 4.2 kit but I do have other options.
                > >
                > > I have some of the new Russian-made cells Solarbotics has for
                sale.
                > > For some odd reason they sent me one with the Miller circuit
                etched
                > > on the back and one did not. It also seems odd that the non-
                etched
                > > one says 6.7v @ 15mA on the back...they state that it is very
                > > efficient but on their website they have one the same exact size
                > > rated at 6.7v @ 31mA
                > >
                > > I also have several 3v 22mA thin-film cells I could use. They are
                > > lighter but have a larger footprint.
                > >
                > > I'm going to try out the dual caps and diode and see how it runs.
                > >
                > > thanx again...tk
                > >
                > >
                > >
                > > --- In beam@yahoogroups.com, "wilf rigter" <wrigter@> wrote:
                > > >
                > > >
                > > > Hi tk
                > > >
                > > > With two 1F caps in series, which gives you a combined cap of
                > 0.5F
                > > @ 5V, and a 1381L (3.2V) trigger, the initial charging time
                with
                > a
                > > solar cell supplying 0.5mA constant current
                > > >
                > > > dT (charging time)=Capacitance*dV(voltage change) /Isc(solar
                > cell
                > > current)
                > > >
                > > > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
                > > >
                > > > Note that, with a Ge diode in series with the solar cell and
                > > charged up to 3.2V, the cap should hold that voltage for quite a
                > > while in the dark (i.e. overnight) and won't take long to start
                > > popping when the light comes back on.
                > > >
                > > > btw what solar cell are you using?
                > > >
                > > > Now consider the discharge cycle. If each pop from the 0.5F
                > sol;ar
                > > popper is assumed to be equivalent to a 4700uf cap discharging
                > > completely from 3.2V to 0V and depending on the timing cap and
                the
                > > load, such an equivalent pop might be 15mA (average) * 3.2V *
                0.5
                > > sec during which the capacitor voltage drops 15mV.
                > > >
                > > > The recharge time between pops would be:
                > > >
                > > > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the
                > popping
                > > time would be
                > > >
                > > > wilf
                > > >
                > > >
                > > > ----- Original Message -----
                > > > From: kinkyme360
                > > > To: beam@yahoogroups.com
                > > > Sent: Monday, January 01, 2007 11:54 AM
                > > > Subject: [beam] Re: Capacitor Charging Question
                > > >
                > > >
                > > > Wow...that is some good information. The math seems to bear
                out
                > > my
                > > > observations which is good, but the cool thing is that once
                the
                > > 1F
                > > > gets charged, it will fire pretty quick afterwards. If there
                is
                > a
                > > > design that can live on only 2.4 volts then this could be
                > > > interesting.
                > > >
                > > > 2.4 volts seems pretty weak...not enough to really drive the
                > > motors
                > > > well. Is it possible to put 2 1F 2.5 capacitors in series and
                > use
                > > the
                > > > 1381L (3.2 volts) or higher trigger? Dividing the charge
                > between
                > > the
                > > > two, keeping both under the 2.5v rating but reaping the
                benefit
                > > of
                > > > the added discharge voltage? Yea, it would take quite awhile
                to
                > > > initially charge but might perform well afterwards.
                > > >
                > > > Sorry if these are obvious questions...I am electronically
                > > > challenged. I took basic electronics in high school nearly 20
                > > years
                > > > ago and that's it. One of these days I'm going to blow
                > something
                > > up
                > > > but it will be fun getting there!
                > > >
                > > > tk
                > > >
                > > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                > > > >
                > > > > If you are using a 5V solar cell operating at 3.2V or less,
                > the
                > > > solar
                > > > > cell current will be nearly constant and the cap charging
                > time
                > > > > equation becomes
                > > > >
                > > > > dT=C*dV/Isc
                > > > >
                > > > > According to your experiment, using a 1380L (3.2V) with the
                > > 4700uF
                > > > > cap the time between pops is about 30 secs.
                > > > >
                > > > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A (0.5mA)
                > > > >
                > > > > The energy stored in the cap with 4700uF charged to 3.2V
                > (which
                > > is
                > > > > completely discharged into the load) is 0.5V*V*C =0.024J
                > > > >
                > > > > Let's see how that works for the 1F cap with the 1381C
                > trigger.
                > > > >
                > > > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset
                > > voltage),
                > > > > the initial charging time from 0V to the operating voltage
                > > (2.4V)
                > > > is
                > > > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88 J
                of
                > > > stored
                > > > > energy.
                > > > >
                > > > > After reaching the 2.4V operating voltage and using
                > > approximantly
                > > > the
                > > > > same discharge energy per pop of 0.024J (10mA * 1sec) with
                > the
                > > 1F
                > > > > capacitor voltage dropping dV=10mV every pop, the charging
                > time
                > > > > between pops is 1F * 0.01V / 0.0005A = 20 seconds which is
                > > faster
                > > > > that the 4700uF case because once initialized, the solar
                cell
                > > > > operates constantly at 2.4V nearer to its maximum power
                point.
                > > > >
                > > > > wilf
                > > > >
                > > > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@> wrote:
                > > > > >
                > > > > > Tk,
                > > > > > There is a formula to calculate the charge time of a cap.
                > > > > >
                http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
                > > > > > or
                > > > > > http://hyperphysics.phy-
                > > astr.gsu.edu/hbase/electric/capchg.html
                > > > > >
                > > > > > ater a quick search on google.
                > > > > >
                > > > > > Gary T
                > > > > >
                > > > > >
                > > > > > >OK, I have a working solarpopper based on
                > Wilfs "Photopopper
                > > v8"
                > > > > > >circuit posed back in September. Slick circuit...simple
                > and
                > > > > elegant.
                > > > > > >
                > > > > > >I have a Radio Shack 4700uF 35v capacitor...it is
                massive
                > > but I
                > > > > > >figured it would be OK for testing purposes. With this
                > > capacitor
                > > > > and
                > > > > > >a 1381L as indicated in the plans, it works and charges
                > very
                > > > > quickly
                > > > > > >and drives the 6mm motors just fine.
                > > > > > >
                > > > > > >As a test, I wanted to see what a 1381C (2.4v) and the
                > 1.0F
                > > 2.5v
                > > > > > >Aerogel Super Capacitor would do. I have a few of these
                so
                > > it is
                > > > > > >worth checking out because they are tiny. This capacitor
                > is
                > > MUCH
                > > > > > >smaller and if I could drive the 6mm motors from the
                2.4v,
                > > then
                > > > it
                > > > > > >might be something worth implementing.
                > > > > > >
                > > > > > >Here is the deal...the 1F capacitor takes FOREVER to
                > charge.
                > > > Maybe
                > > > > I
                > > > > > >am confused on my basic electronics but shouldn't a 1F
                > > capacitor
                > > > > > >charge in a bit more than double the time as the 4700uF
                > > > capacitor?
                > > > > > >
                > > > > > >Under an incandecent bulb I did the following...I tested
                > > both the
                > > > > > >4700uF and 1F with the 1381C triggering at 2.4v. The
                > 4700uF
                > > was
                > > > > > >triggering rather rapidly (several times per minute)...I
                > am
                > > not
                > > > > sure
                > > > > > >the 2.4v will be adequate to drive the motors but that
                is
                > > not the
                > > > > > >point right now...the 1F took about 90 minutes to
                charge.
                > It
                > > was
                > > > > > >painfully long. Just how much more capacity does the 1F
                > have?
                > > > > > >
                > > > > > >Can someone shed some light on why the 1F is taking so
                > long
                > > to
                > > > > charge?
                > > > > > >
                > > > > > >tk
                > > > > > >
                > > > > > >
                > > > > >
                > > > >
                > > >
                > >
                >
              • wilf_nv
                You should invest in a digital multimeter (
                Message 7 of 14 , Jan 4, 2007
                • 0 Attachment
                  You should invest in a digital multimeter (<$20) which is far
                  more sensitive than a basic needle type meter and which will
                  avoid influencing the circuit you are measuring.

                  In general, the meter is set to the DC ma Current range and the
                  leads are connected to com and ma. The meter leads are then
                  inserted between the +V of the battery and the positive (Vcc)
                  bus of the circuit. Be sure to return the meter setting to
                  DC Volts after you finish the current measurements.

                  wilf

                  --- In beam@yahoogroups.com, "kinkyme360" <tskunka@...> wrote:
                  >
                  > You ask a very good question...I might be able to measure the
                  current
                  > if I knew how. ;-) I have a basic analog Radio Shack
                  multimeter...I'm
                  > not sure how to measure current with it.
                  >
                  > I tried out the dual 1F cap and sure enough, once the thing gets
                  > charged, it triggers at a very regular interval. I seem to have
                  some
                  > loss of charge when idle...perhaps I need a bigger diode? I'm using
                  a
                  > 1N914 right now.
                  >
                  > tk
                  >
                  >
                  > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                  > >
                  > > Hmmm... so the 0.5ma current I derived from your timing
                  > measurements
                  > > is very low compared to the rated output current of the cell.
                  Keep
                  > in
                  > > mind that the rated currrent is measured in very bright light.
                  Can
                  > > you measure current during charging to confirm the value and that
                  > it
                  > > is not low because of some other problem?
                  > >
                  > >
                  > > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                  > > >
                  > > > I'm using the solar cell that comes with the old Solarbotics
                  > > > Solarpopper 4.2 kit but I do have other options.
                  > > >
                  > > > I have some of the new Russian-made cells Solarbotics has for
                  > sale.
                  > > > For some odd reason they sent me one with the Miller circuit
                  > etched
                  > > > on the back and one did not. It also seems odd that the non-
                  > etched
                  > > > one says 6.7v @ 15mA on the back...they state that it is very
                  > > > efficient but on their website they have one the same exact
                  size
                  > > > rated at 6.7v @ 31mA
                  > > >
                  > > > I also have several 3v 22mA thin-film cells I could use. They
                  are
                  > > > lighter but have a larger footprint.
                  > > >
                  > > > I'm going to try out the dual caps and diode and see how it
                  runs.
                  > > >
                  > > > thanx again...tk
                  > > >
                  > > >
                  > > >
                  > > > --- In beam@yahoogroups.com, "wilf rigter" <wrigter@> wrote:
                  > > > >
                  > > > >
                  > > > > Hi tk
                  > > > >
                  > > > > With two 1F caps in series, which gives you a combined cap of
                  > > 0.5F
                  > > > @ 5V, and a 1381L (3.2V) trigger, the initial charging time
                  > with
                  > > a
                  > > > solar cell supplying 0.5mA constant current
                  > > > >
                  > > > > dT (charging time)=Capacitance*dV(voltage change) /Isc(solar
                  > > cell
                  > > > current)
                  > > > >
                  > > > > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
                  > > > >
                  > > > > Note that, with a Ge diode in series with the solar cell and
                  > > > charged up to 3.2V, the cap should hold that voltage for quite
                  a
                  > > > while in the dark (i.e. overnight) and won't take long to start
                  > > > popping when the light comes back on.
                  > > > >
                  > > > > btw what solar cell are you using?
                  > > > >
                  > > > > Now consider the discharge cycle. If each pop from the 0.5F
                  > > sol;ar
                  > > > popper is assumed to be equivalent to a 4700uf cap discharging
                  > > > completely from 3.2V to 0V and depending on the timing cap and
                  > the
                  > > > load, such an equivalent pop might be 15mA (average) * 3.2V *
                  > 0.5
                  > > > sec during which the capacitor voltage drops 15mV.
                  > > > >
                  > > > > The recharge time between pops would be:
                  > > > >
                  > > > > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the
                  > > popping
                  > > > time would be
                  > > > >
                  > > > > wilf
                  > > > >
                  > > > >
                  > > > > ----- Original Message -----
                  > > > > From: kinkyme360
                  > > > > To: beam@yahoogroups.com
                  > > > > Sent: Monday, January 01, 2007 11:54 AM
                  > > > > Subject: [beam] Re: Capacitor Charging Question
                  > > > >
                  > > > >
                  > > > > Wow...that is some good information. The math seems to bear
                  > out
                  > > > my
                  > > > > observations which is good, but the cool thing is that once
                  > the
                  > > > 1F
                  > > > > gets charged, it will fire pretty quick afterwards. If
                  there
                  > is
                  > > a
                  > > > > design that can live on only 2.4 volts then this could be
                  > > > > interesting.
                  > > > >
                  > > > > 2.4 volts seems pretty weak...not enough to really drive
                  the
                  > > > motors
                  > > > > well. Is it possible to put 2 1F 2.5 capacitors in series
                  and
                  > > use
                  > > > the
                  > > > > 1381L (3.2 volts) or higher trigger? Dividing the charge
                  > > between
                  > > > the
                  > > > > two, keeping both under the 2.5v rating but reaping the
                  > benefit
                  > > > of
                  > > > > the added discharge voltage? Yea, it would take quite
                  awhile
                  > to
                  > > > > initially charge but might perform well afterwards.
                  > > > >
                  > > > > Sorry if these are obvious questions...I am electronically
                  > > > > challenged. I took basic electronics in high school nearly
                  20
                  > > > years
                  > > > > ago and that's it. One of these days I'm going to blow
                  > > something
                  > > > up
                  > > > > but it will be fun getting there!
                  > > > >
                  > > > > tk
                  > > > >
                  > > > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                  > > > > >
                  > > > > > If you are using a 5V solar cell operating at 3.2V or
                  less,
                  > > the
                  > > > > solar
                  > > > > > cell current will be nearly constant and the cap charging
                  > > time
                  > > > > > equation becomes
                  > > > > >
                  > > > > > dT=C*dV/Isc
                  > > > > >
                  > > > > > According to your experiment, using a 1380L (3.2V) with
                  the
                  > > > 4700uF
                  > > > > > cap the time between pops is about 30 secs.
                  > > > > >
                  > > > > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A
                  (0.5mA)
                  > > > > >
                  > > > > > The energy stored in the cap with 4700uF charged to 3.2V
                  > > (which
                  > > > is
                  > > > > > completely discharged into the load) is 0.5V*V*C =0.024J
                  > > > > >
                  > > > > > Let's see how that works for the 1F cap with the 1381C
                  > > trigger.
                  > > > > >
                  > > > > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset
                  > > > voltage),
                  > > > > > the initial charging time from 0V to the operating
                  voltage
                  > > > (2.4V)
                  > > > > is
                  > > > > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's 2.88
                  J
                  > of
                  > > > > stored
                  > > > > > energy.
                  > > > > >
                  > > > > > After reaching the 2.4V operating voltage and using
                  > > > approximantly
                  > > > > the
                  > > > > > same discharge energy per pop of 0.024J (10mA * 1sec)
                  with
                  > > the
                  > > > 1F
                  > > > > > capacitor voltage dropping dV=10mV every pop, the
                  charging
                  > > time
                  > > > > > between pops is 1F * 0.01V / 0.0005A = 20 seconds which
                  is
                  > > > faster
                  > > > > > that the 4700uF case because once initialized, the solar
                  > cell
                  > > > > > operates constantly at 2.4V nearer to its maximum power
                  > point.
                  > > > > >
                  > > > > > wilf
                  > > > > >
                  > > > > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@> wrote:
                  > > > > > >
                  > > > > > > Tk,
                  > > > > > > There is a formula to calculate the charge time of a
                  cap.
                  > > > > > >
                  > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
                  > > > > > > or
                  > > > > > > http://hyperphysics.phy-
                  > > > astr.gsu.edu/hbase/electric/capchg.html
                  > > > > > >
                  > > > > > > ater a quick search on google.
                  > > > > > >
                  > > > > > > Gary T
                  > > > > > >
                  > > > > > >
                  > > > > > > >OK, I have a working solarpopper based on
                  > > Wilfs "Photopopper
                  > > > v8"
                  > > > > > > >circuit posed back in September. Slick
                  circuit...simple
                  > > and
                  > > > > > elegant.
                  > > > > > > >
                  > > > > > > >I have a Radio Shack 4700uF 35v capacitor...it is
                  > massive
                  > > > but I
                  > > > > > > >figured it would be OK for testing purposes. With this
                  > > > capacitor
                  > > > > > and
                  > > > > > > >a 1381L as indicated in the plans, it works and
                  charges
                  > > very
                  > > > > > quickly
                  > > > > > > >and drives the 6mm motors just fine.
                  > > > > > > >
                  > > > > > > >As a test, I wanted to see what a 1381C (2.4v) and the
                  > > 1.0F
                  > > > 2.5v
                  > > > > > > >Aerogel Super Capacitor would do. I have a few of
                  these
                  > so
                  > > > it is
                  > > > > > > >worth checking out because they are tiny. This
                  capacitor
                  > > is
                  > > > MUCH
                  > > > > > > >smaller and if I could drive the 6mm motors from the
                  > 2.4v,
                  > > > then
                  > > > > it
                  > > > > > > >might be something worth implementing.
                  > > > > > > >
                  > > > > > > >Here is the deal...the 1F capacitor takes FOREVER to
                  > > charge.
                  > > > > Maybe
                  > > > > > I
                  > > > > > > >am confused on my basic electronics but shouldn't a 1F
                  > > > capacitor
                  > > > > > > >charge in a bit more than double the time as the
                  4700uF
                  > > > > capacitor?
                  > > > > > > >
                  > > > > > > >Under an incandecent bulb I did the following...I
                  tested
                  > > > both the
                  > > > > > > >4700uF and 1F with the 1381C triggering at 2.4v. The
                  > > 4700uF
                  > > > was
                  > > > > > > >triggering rather rapidly (several times per
                  minute)...I
                  > > am
                  > > > not
                  > > > > > sure
                  > > > > > > >the 2.4v will be adequate to drive the motors but that
                  > is
                  > > > not the
                  > > > > > > >point right now...the 1F took about 90 minutes to
                  > charge.
                  > > It
                  > > > was
                  > > > > > > >painfully long. Just how much more capacity does the
                  1F
                  > > have?
                  > > > > > > >
                  > > > > > > >Can someone shed some light on why the 1F is taking so
                  > > long
                  > > > to
                  > > > > > charge?
                  > > > > > > >
                  > > > > > > >tk
                  > > > > > > >
                  > > > > > > >
                  > > > > > >
                  > > > > >
                  > > > >
                  > > >
                  > >
                  >
                • kinkyme360
                  Cool...a coworker well versed in electronics and I went through this earlier today with his multimeter. We were getting 2.5 microamps under a bright halogen
                  Message 8 of 14 , Jan 4, 2007
                  • 0 Attachment
                    Cool...a coworker well versed in electronics and I went through this
                    earlier today with his multimeter. We were getting 2.5 microamps
                    under a bright halogen light. The cell is rated at 15 milliamps so
                    something is amiss either with the cell, the capacitors or my
                    understanding. I am betting on the latter! ;-)

                    His thought is that the process of charging the capacitor wasn't
                    drawing the current from the cell. Thus the low readings. I'm not
                    sold on that theory.

                    I was planning on connecting the cell directly to a load and
                    performing the same test. I will also try that Russian cell with
                    similar ratings to use as a comparison.

                    Overall, the thing works well under 50w desk lamp once charged so I
                    am very pleased so far. I added buzzers instead of motors for giggle
                    and it is VERY annoying. Buzzing every few seconds!

                    I'm planning out the circuit board so I can take the next step and go
                    from the breadboard to actual bot. If I feel ambitious I may try
                    adding a secondary circuit that is dark activated...so if things go
                    pitch black, it becomes a simple pummer. I'm using 2 1F capacitors so
                    I might as well take advantage.

                    I'm getting some good ideas...I've been spending alot of time
                    absorbing the on-line information and processing the great help from
                    the kind folks here in the group.

                    thanks!

                    tk



                    --- In beam@yahoogroups.com, "wilf_nv" <wrigter@...> wrote:
                    >
                    >
                    > You should invest in a digital multimeter (<$20) which is far
                    > more sensitive than a basic needle type meter and which will
                    > avoid influencing the circuit you are measuring.
                    >
                    > In general, the meter is set to the DC ma Current range and the
                    > leads are connected to com and ma. The meter leads are then
                    > inserted between the +V of the battery and the positive (Vcc)
                    > bus of the circuit. Be sure to return the meter setting to
                    > DC Volts after you finish the current measurements.
                    >
                    > wilf
                    >
                    > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                    > >
                    > > You ask a very good question...I might be able to measure the
                    > current
                    > > if I knew how. ;-) I have a basic analog Radio Shack
                    > multimeter...I'm
                    > > not sure how to measure current with it.
                    > >
                    > > I tried out the dual 1F cap and sure enough, once the thing gets
                    > > charged, it triggers at a very regular interval. I seem to have
                    > some
                    > > loss of charge when idle...perhaps I need a bigger diode? I'm
                    using
                    > a
                    > > 1N914 right now.
                    > >
                    > > tk
                    > >
                    > >
                    > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                    > > >
                    > > > Hmmm... so the 0.5ma current I derived from your timing
                    > > measurements
                    > > > is very low compared to the rated output current of the cell.
                    > Keep
                    > > in
                    > > > mind that the rated currrent is measured in very bright light.
                    > Can
                    > > > you measure current during charging to confirm the value and
                    that
                    > > it
                    > > > is not low because of some other problem?
                    > > >
                    > > >
                    > > > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                    > > > >
                    > > > > I'm using the solar cell that comes with the old Solarbotics
                    > > > > Solarpopper 4.2 kit but I do have other options.
                    > > > >
                    > > > > I have some of the new Russian-made cells Solarbotics has for
                    > > sale.
                    > > > > For some odd reason they sent me one with the Miller circuit
                    > > etched
                    > > > > on the back and one did not. It also seems odd that the non-
                    > > etched
                    > > > > one says 6.7v @ 15mA on the back...they state that it is very
                    > > > > efficient but on their website they have one the same exact
                    > size
                    > > > > rated at 6.7v @ 31mA
                    > > > >
                    > > > > I also have several 3v 22mA thin-film cells I could use. They
                    > are
                    > > > > lighter but have a larger footprint.
                    > > > >
                    > > > > I'm going to try out the dual caps and diode and see how it
                    > runs.
                    > > > >
                    > > > > thanx again...tk
                    > > > >
                    > > > >
                    > > > >
                    > > > > --- In beam@yahoogroups.com, "wilf rigter" <wrigter@> wrote:
                    > > > > >
                    > > > > >
                    > > > > > Hi tk
                    > > > > >
                    > > > > > With two 1F caps in series, which gives you a combined cap
                    of
                    > > > 0.5F
                    > > > > @ 5V, and a 1381L (3.2V) trigger, the initial charging time
                    > > with
                    > > > a
                    > > > > solar cell supplying 0.5mA constant current
                    > > > > >
                    > > > > > dT (charging time)=Capacitance*dV(voltage change) /Isc
                    (solar
                    > > > cell
                    > > > > current)
                    > > > > >
                    > > > > > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
                    > > > > >
                    > > > > > Note that, with a Ge diode in series with the solar cell
                    and
                    > > > > charged up to 3.2V, the cap should hold that voltage for
                    quite
                    > a
                    > > > > while in the dark (i.e. overnight) and won't take long to
                    start
                    > > > > popping when the light comes back on.
                    > > > > >
                    > > > > > btw what solar cell are you using?
                    > > > > >
                    > > > > > Now consider the discharge cycle. If each pop from the
                    0.5F
                    > > > sol;ar
                    > > > > popper is assumed to be equivalent to a 4700uf cap
                    discharging
                    > > > > completely from 3.2V to 0V and depending on the timing cap
                    and
                    > > the
                    > > > > load, such an equivalent pop might be 15mA (average) * 3.2V
                    *
                    > > 0.5
                    > > > > sec during which the capacitor voltage drops 15mV.
                    > > > > >
                    > > > > > The recharge time between pops would be:
                    > > > > >
                    > > > > > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA the
                    > > > popping
                    > > > > time would be
                    > > > > >
                    > > > > > wilf
                    > > > > >
                    > > > > >
                    > > > > > ----- Original Message -----
                    > > > > > From: kinkyme360
                    > > > > > To: beam@yahoogroups.com
                    > > > > > Sent: Monday, January 01, 2007 11:54 AM
                    > > > > > Subject: [beam] Re: Capacitor Charging Question
                    > > > > >
                    > > > > >
                    > > > > > Wow...that is some good information. The math seems to
                    bear
                    > > out
                    > > > > my
                    > > > > > observations which is good, but the cool thing is that
                    once
                    > > the
                    > > > > 1F
                    > > > > > gets charged, it will fire pretty quick afterwards. If
                    > there
                    > > is
                    > > > a
                    > > > > > design that can live on only 2.4 volts then this could be
                    > > > > > interesting.
                    > > > > >
                    > > > > > 2.4 volts seems pretty weak...not enough to really drive
                    > the
                    > > > > motors
                    > > > > > well. Is it possible to put 2 1F 2.5 capacitors in series
                    > and
                    > > > use
                    > > > > the
                    > > > > > 1381L (3.2 volts) or higher trigger? Dividing the charge
                    > > > between
                    > > > > the
                    > > > > > two, keeping both under the 2.5v rating but reaping the
                    > > benefit
                    > > > > of
                    > > > > > the added discharge voltage? Yea, it would take quite
                    > awhile
                    > > to
                    > > > > > initially charge but might perform well afterwards.
                    > > > > >
                    > > > > > Sorry if these are obvious questions...I am
                    electronically
                    > > > > > challenged. I took basic electronics in high school
                    nearly
                    > 20
                    > > > > years
                    > > > > > ago and that's it. One of these days I'm going to blow
                    > > > something
                    > > > > up
                    > > > > > but it will be fun getting there!
                    > > > > >
                    > > > > > tk
                    > > > > >
                    > > > > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                    > > > > > >
                    > > > > > > If you are using a 5V solar cell operating at 3.2V or
                    > less,
                    > > > the
                    > > > > > solar
                    > > > > > > cell current will be nearly constant and the cap
                    charging
                    > > > time
                    > > > > > > equation becomes
                    > > > > > >
                    > > > > > > dT=C*dV/Isc
                    > > > > > >
                    > > > > > > According to your experiment, using a 1380L (3.2V) with
                    > the
                    > > > > 4700uF
                    > > > > > > cap the time between pops is about 30 secs.
                    > > > > > >
                    > > > > > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A
                    > (0.5mA)
                    > > > > > >
                    > > > > > > The energy stored in the cap with 4700uF charged to
                    3.2V
                    > > > (which
                    > > > > is
                    > > > > > > completely discharged into the load) is 0.5V*V*C
                    =0.024J
                    > > > > > >
                    > > > > > > Let's see how that works for the 1F cap with the 1381C
                    > > > trigger.
                    > > > > > >
                    > > > > > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C reset
                    > > > > voltage),
                    > > > > > > the initial charging time from 0V to the operating
                    > voltage
                    > > > > (2.4V)
                    > > > > > is
                    > > > > > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's
                    2.88
                    > J
                    > > of
                    > > > > > stored
                    > > > > > > energy.
                    > > > > > >
                    > > > > > > After reaching the 2.4V operating voltage and using
                    > > > > approximantly
                    > > > > > the
                    > > > > > > same discharge energy per pop of 0.024J (10mA * 1sec)
                    > with
                    > > > the
                    > > > > 1F
                    > > > > > > capacitor voltage dropping dV=10mV every pop, the
                    > charging
                    > > > time
                    > > > > > > between pops is 1F * 0.01V / 0.0005A = 20 seconds which
                    > is
                    > > > > faster
                    > > > > > > that the 4700uF case because once initialized, the
                    solar
                    > > cell
                    > > > > > > operates constantly at 2.4V nearer to its maximum power
                    > > point.
                    > > > > > >
                    > > > > > > wilf
                    > > > > > >
                    > > > > > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@>
                    wrote:
                    > > > > > > >
                    > > > > > > > Tk,
                    > > > > > > > There is a formula to calculate the charge time of a
                    > cap.
                    > > > > > > >
                    > > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
                    > > > > > > > or
                    > > > > > > > http://hyperphysics.phy-
                    > > > > astr.gsu.edu/hbase/electric/capchg.html
                    > > > > > > >
                    > > > > > > > ater a quick search on google.
                    > > > > > > >
                    > > > > > > > Gary T
                    > > > > > > >
                    > > > > > > >
                    > > > > > > > >OK, I have a working solarpopper based on
                    > > > Wilfs "Photopopper
                    > > > > v8"
                    > > > > > > > >circuit posed back in September. Slick
                    > circuit...simple
                    > > > and
                    > > > > > > elegant.
                    > > > > > > > >
                    > > > > > > > >I have a Radio Shack 4700uF 35v capacitor...it is
                    > > massive
                    > > > > but I
                    > > > > > > > >figured it would be OK for testing purposes. With
                    this
                    > > > > capacitor
                    > > > > > > and
                    > > > > > > > >a 1381L as indicated in the plans, it works and
                    > charges
                    > > > very
                    > > > > > > quickly
                    > > > > > > > >and drives the 6mm motors just fine.
                    > > > > > > > >
                    > > > > > > > >As a test, I wanted to see what a 1381C (2.4v) and
                    the
                    > > > 1.0F
                    > > > > 2.5v
                    > > > > > > > >Aerogel Super Capacitor would do. I have a few of
                    > these
                    > > so
                    > > > > it is
                    > > > > > > > >worth checking out because they are tiny. This
                    > capacitor
                    > > > is
                    > > > > MUCH
                    > > > > > > > >smaller and if I could drive the 6mm motors from the
                    > > 2.4v,
                    > > > > then
                    > > > > > it
                    > > > > > > > >might be something worth implementing.
                    > > > > > > > >
                    > > > > > > > >Here is the deal...the 1F capacitor takes FOREVER to
                    > > > charge.
                    > > > > > Maybe
                    > > > > > > I
                    > > > > > > > >am confused on my basic electronics but shouldn't a
                    1F
                    > > > > capacitor
                    > > > > > > > >charge in a bit more than double the time as the
                    > 4700uF
                    > > > > > capacitor?
                    > > > > > > > >
                    > > > > > > > >Under an incandecent bulb I did the following...I
                    > tested
                    > > > > both the
                    > > > > > > > >4700uF and 1F with the 1381C triggering at 2.4v. The
                    > > > 4700uF
                    > > > > was
                    > > > > > > > >triggering rather rapidly (several times per
                    > minute)...I
                    > > > am
                    > > > > not
                    > > > > > > sure
                    > > > > > > > >the 2.4v will be adequate to drive the motors but
                    that
                    > > is
                    > > > > not the
                    > > > > > > > >point right now...the 1F took about 90 minutes to
                    > > charge.
                    > > > It
                    > > > > was
                    > > > > > > > >painfully long. Just how much more capacity does the
                    > 1F
                    > > > have?
                    > > > > > > > >
                    > > > > > > > >Can someone shed some light on why the 1F is taking
                    so
                    > > > long
                    > > > > to
                    > > > > > > charge?
                    > > > > > > > >
                    > > > > > > > >tk
                    > > > > > > > >
                    > > > > > > > >
                    > > > > > > >
                    > > > > > >
                    > > > > >
                    > > > >
                    > > >
                    > >
                    >
                  • wilf_nv
                    Go step by step. Measure the solar cell current by itself just across the cell terminals. Then add a discharged cap in series (observe cap polarity) and
                    Message 9 of 14 , Jan 4, 2007
                    • 0 Attachment
                      Go step by step. Measure the solar cell current by itself just across
                      the cell terminals. Then add a discharged cap in series (observe cap
                      polarity) and measure again. That should give the same reading,
                      observe the reading after the cap has charged to near the threshold.
                      Should be the same reading. Now add the solar engine. Any change?
                      Add the motor. Any change? Observe what you find at each step and
                      you can pinpoint where things go wrong. Mind you the popping every
                      few seconds sounds promising and there may not be any problem.

                      wwilf

                      --- In beam@yahoogroups.com, "kinkyme360" <tskunka@...> wrote:
                      >
                      > Cool...a coworker well versed in electronics and I went through
                      this
                      > earlier today with his multimeter. We were getting 2.5 microamps
                      > under a bright halogen light. The cell is rated at 15 milliamps so
                      > something is amiss either with the cell, the capacitors or my
                      > understanding. I am betting on the latter! ;-)
                      >
                      > His thought is that the process of charging the capacitor wasn't
                      > drawing the current from the cell. Thus the low readings. I'm not
                      > sold on that theory.
                      >
                      > I was planning on connecting the cell directly to a load and
                      > performing the same test. I will also try that Russian cell with
                      > similar ratings to use as a comparison.
                      >
                      > Overall, the thing works well under 50w desk lamp once charged so I
                      > am very pleased so far. I added buzzers instead of motors for
                      giggle
                      > and it is VERY annoying. Buzzing every few seconds!
                      >
                      > I'm planning out the circuit board so I can take the next step and
                      go
                      > from the breadboard to actual bot. If I feel ambitious I may try
                      > adding a secondary circuit that is dark activated...so if things go
                      > pitch black, it becomes a simple pummer. I'm using 2 1F capacitors
                      so
                      > I might as well take advantage.
                      >
                      > I'm getting some good ideas...I've been spending alot of time
                      > absorbing the on-line information and processing the great help
                      from
                      > the kind folks here in the group.
                      >
                      > thanks!
                      >
                      > tk
                      >
                      >
                      >
                      > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                      > >
                      > >
                      > > You should invest in a digital multimeter (<$20) which is far
                      > > more sensitive than a basic needle type meter and which will
                      > > avoid influencing the circuit you are measuring.
                      > >
                      > > In general, the meter is set to the DC ma Current range and the
                      > > leads are connected to com and ma. The meter leads are then
                      > > inserted between the +V of the battery and the positive (Vcc)
                      > > bus of the circuit. Be sure to return the meter setting to
                      > > DC Volts after you finish the current measurements.
                      > >
                      > > wilf
                      > >
                      > > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                      > > >
                      > > > You ask a very good question...I might be able to measure the
                      > > current
                      > > > if I knew how. ;-) I have a basic analog Radio Shack
                      > > multimeter...I'm
                      > > > not sure how to measure current with it.
                      > > >
                      > > > I tried out the dual 1F cap and sure enough, once the thing
                      gets
                      > > > charged, it triggers at a very regular interval. I seem to have
                      > > some
                      > > > loss of charge when idle...perhaps I need a bigger diode? I'm
                      > using
                      > > a
                      > > > 1N914 right now.
                      > > >
                      > > > tk
                      > > >
                      > > >
                      > > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                      > > > >
                      > > > > Hmmm... so the 0.5ma current I derived from your timing
                      > > > measurements
                      > > > > is very low compared to the rated output current of the cell.
                      > > Keep
                      > > > in
                      > > > > mind that the rated currrent is measured in very bright
                      light.
                      > > Can
                      > > > > you measure current during charging to confirm the value and
                      > that
                      > > > it
                      > > > > is not low because of some other problem?
                      > > > >
                      > > > >
                      > > > > --- In beam@yahoogroups.com, "kinkyme360" <tskunka@> wrote:
                      > > > > >
                      > > > > > I'm using the solar cell that comes with the old
                      Solarbotics
                      > > > > > Solarpopper 4.2 kit but I do have other options.
                      > > > > >
                      > > > > > I have some of the new Russian-made cells Solarbotics has
                      for
                      > > > sale.
                      > > > > > For some odd reason they sent me one with the Miller
                      circuit
                      > > > etched
                      > > > > > on the back and one did not. It also seems odd that the non-
                      > > > etched
                      > > > > > one says 6.7v @ 15mA on the back...they state that it is
                      very
                      > > > > > efficient but on their website they have one the same exact
                      > > size
                      > > > > > rated at 6.7v @ 31mA
                      > > > > >
                      > > > > > I also have several 3v 22mA thin-film cells I could use.
                      They
                      > > are
                      > > > > > lighter but have a larger footprint.
                      > > > > >
                      > > > > > I'm going to try out the dual caps and diode and see how it
                      > > runs.
                      > > > > >
                      > > > > > thanx again...tk
                      > > > > >
                      > > > > >
                      > > > > >
                      > > > > > --- In beam@yahoogroups.com, "wilf rigter" <wrigter@> wrote:
                      > > > > > >
                      > > > > > >
                      > > > > > > Hi tk
                      > > > > > >
                      > > > > > > With two 1F caps in series, which gives you a combined
                      cap
                      > of
                      > > > > 0.5F
                      > > > > > @ 5V, and a 1381L (3.2V) trigger, the initial charging
                      time
                      > > > with
                      > > > > a
                      > > > > > solar cell supplying 0.5mA constant current
                      > > > > > >
                      > > > > > > dT (charging time)=Capacitance*dV(voltage change) /Isc
                      > (solar
                      > > > > cell
                      > > > > > current)
                      > > > > > >
                      > > > > > > 0.5F * 3.2V / 0.5ma = 3200 seconds = 53 minutes
                      > > > > > >
                      > > > > > > Note that, with a Ge diode in series with the solar cell
                      > and
                      > > > > > charged up to 3.2V, the cap should hold that voltage for
                      > quite
                      > > a
                      > > > > > while in the dark (i.e. overnight) and won't take long to
                      > start
                      > > > > > popping when the light comes back on.
                      > > > > > >
                      > > > > > > btw what solar cell are you using?
                      > > > > > >
                      > > > > > > Now consider the discharge cycle. If each pop from the
                      > 0.5F
                      > > > > sol;ar
                      > > > > > popper is assumed to be equivalent to a 4700uf cap
                      > discharging
                      > > > > > completely from 3.2V to 0V and depending on the timing cap
                      > and
                      > > > the
                      > > > > > load, such an equivalent pop might be 15mA (average) *
                      3.2V
                      > *
                      > > > 0.5
                      > > > > > sec during which the capacitor voltage drops 15mV.
                      > > > > > >
                      > > > > > > The recharge time between pops would be:
                      > > > > > >
                      > > > > > > 0.5F * 0.015V / 0.5ma = 15 seconds and with I(sc)=30mA
                      the
                      > > > > popping
                      > > > > > time would be
                      > > > > > >
                      > > > > > > wilf
                      > > > > > >
                      > > > > > >
                      > > > > > > ----- Original Message -----
                      > > > > > > From: kinkyme360
                      > > > > > > To: beam@yahoogroups.com
                      > > > > > > Sent: Monday, January 01, 2007 11:54 AM
                      > > > > > > Subject: [beam] Re: Capacitor Charging Question
                      > > > > > >
                      > > > > > >
                      > > > > > > Wow...that is some good information. The math seems to
                      > bear
                      > > > out
                      > > > > > my
                      > > > > > > observations which is good, but the cool thing is that
                      > once
                      > > > the
                      > > > > > 1F
                      > > > > > > gets charged, it will fire pretty quick afterwards. If
                      > > there
                      > > > is
                      > > > > a
                      > > > > > > design that can live on only 2.4 volts then this could
                      be
                      > > > > > > interesting.
                      > > > > > >
                      > > > > > > 2.4 volts seems pretty weak...not enough to really
                      drive
                      > > the
                      > > > > > motors
                      > > > > > > well. Is it possible to put 2 1F 2.5 capacitors in
                      series
                      > > and
                      > > > > use
                      > > > > > the
                      > > > > > > 1381L (3.2 volts) or higher trigger? Dividing the
                      charge
                      > > > > between
                      > > > > > the
                      > > > > > > two, keeping both under the 2.5v rating but reaping the
                      > > > benefit
                      > > > > > of
                      > > > > > > the added discharge voltage? Yea, it would take quite
                      > > awhile
                      > > > to
                      > > > > > > initially charge but might perform well afterwards.
                      > > > > > >
                      > > > > > > Sorry if these are obvious questions...I am
                      > electronically
                      > > > > > > challenged. I took basic electronics in high school
                      > nearly
                      > > 20
                      > > > > > years
                      > > > > > > ago and that's it. One of these days I'm going to blow
                      > > > > something
                      > > > > > up
                      > > > > > > but it will be fun getting there!
                      > > > > > >
                      > > > > > > tk
                      > > > > > >
                      > > > > > > --- In beam@yahoogroups.com, "wilf_nv" <wrigter@> wrote:
                      > > > > > > >
                      > > > > > > > If you are using a 5V solar cell operating at 3.2V or
                      > > less,
                      > > > > the
                      > > > > > > solar
                      > > > > > > > cell current will be nearly constant and the cap
                      > charging
                      > > > > time
                      > > > > > > > equation becomes
                      > > > > > > >
                      > > > > > > > dT=C*dV/Isc
                      > > > > > > >
                      > > > > > > > According to your experiment, using a 1380L (3.2V)
                      with
                      > > the
                      > > > > > 4700uF
                      > > > > > > > cap the time between pops is about 30 secs.
                      > > > > > > >
                      > > > > > > > That means Isc must be 0.0047F * 3.2V / 30 = 0.0005A
                      > > (0.5mA)
                      > > > > > > >
                      > > > > > > > The energy stored in the cap with 4700uF charged to
                      > 3.2V
                      > > > > (which
                      > > > > > is
                      > > > > > > > completely discharged into the load) is 0.5V*V*C
                      > =0.024J
                      > > > > > > >
                      > > > > > > > Let's see how that works for the 1F cap with the
                      1381C
                      > > > > trigger.
                      > > > > > > >
                      > > > > > > > Using C=1F and Isc = 0.5ma and dV=2.4V (the 1381C
                      reset
                      > > > > > voltage),
                      > > > > > > > the initial charging time from 0V to the operating
                      > > voltage
                      > > > > > (2.4V)
                      > > > > > > is
                      > > > > > > > 1F * 2.4V / 0.0005A = 4800 seconds = 80 min. That's
                      > 2.88
                      > > J
                      > > > of
                      > > > > > > stored
                      > > > > > > > energy.
                      > > > > > > >
                      > > > > > > > After reaching the 2.4V operating voltage and using
                      > > > > > approximantly
                      > > > > > > the
                      > > > > > > > same discharge energy per pop of 0.024J (10mA * 1sec)
                      > > with
                      > > > > the
                      > > > > > 1F
                      > > > > > > > capacitor voltage dropping dV=10mV every pop, the
                      > > charging
                      > > > > time
                      > > > > > > > between pops is 1F * 0.01V / 0.0005A = 20 seconds
                      which
                      > > is
                      > > > > > faster
                      > > > > > > > that the 4700uF case because once initialized, the
                      > solar
                      > > > cell
                      > > > > > > > operates constantly at 2.4V nearer to its maximum
                      power
                      > > > point.
                      > > > > > > >
                      > > > > > > > wilf
                      > > > > > > >
                      > > > > > > > --- In beam@yahoogroups.com, Gary Tolley <grogyan@>
                      > wrote:
                      > > > > > > > >
                      > > > > > > > > Tk,
                      > > > > > > > > There is a formula to calculate the charge time of
                      a
                      > > cap.
                      > > > > > > > >
                      > > > http://ourworld.compuserve.com/homepages/Bill_Bowden/rc.htm
                      > > > > > > > > or
                      > > > > > > > > http://hyperphysics.phy-
                      > > > > > astr.gsu.edu/hbase/electric/capchg.html
                      > > > > > > > >
                      > > > > > > > > ater a quick search on google.
                      > > > > > > > >
                      > > > > > > > > Gary T
                      > > > > > > > >
                      > > > > > > > >
                      > > > > > > > > >OK, I have a working solarpopper based on
                      > > > > Wilfs "Photopopper
                      > > > > > v8"
                      > > > > > > > > >circuit posed back in September. Slick
                      > > circuit...simple
                      > > > > and
                      > > > > > > > elegant.
                      > > > > > > > > >
                      > > > > > > > > >I have a Radio Shack 4700uF 35v capacitor...it is
                      > > > massive
                      > > > > > but I
                      > > > > > > > > >figured it would be OK for testing purposes. With
                      > this
                      > > > > > capacitor
                      > > > > > > > and
                      > > > > > > > > >a 1381L as indicated in the plans, it works and
                      > > charges
                      > > > > very
                      > > > > > > > quickly
                      > > > > > > > > >and drives the 6mm motors just fine.
                      > > > > > > > > >
                      > > > > > > > > >As a test, I wanted to see what a 1381C (2.4v) and
                      > the
                      > > > > 1.0F
                      > > > > > 2.5v
                      > > > > > > > > >Aerogel Super Capacitor would do. I have a few of
                      > > these
                      > > > so
                      > > > > > it is
                      > > > > > > > > >worth checking out because they are tiny. This
                      > > capacitor
                      > > > > is
                      > > > > > MUCH
                      > > > > > > > > >smaller and if I could drive the 6mm motors from
                      the
                      > > > 2.4v,
                      > > > > > then
                      > > > > > > it
                      > > > > > > > > >might be something worth implementing.
                      > > > > > > > > >
                      > > > > > > > > >Here is the deal...the 1F capacitor takes FOREVER
                      to
                      > > > > charge.
                      > > > > > > Maybe
                      > > > > > > > I
                      > > > > > > > > >am confused on my basic electronics but shouldn't
                      a
                      > 1F
                      > > > > > capacitor
                      > > > > > > > > >charge in a bit more than double the time as the
                      > > 4700uF
                      > > > > > > capacitor?
                      > > > > > > > > >
                      > > > > > > > > >Under an incandecent bulb I did the following...I
                      > > tested
                      > > > > > both the
                      > > > > > > > > >4700uF and 1F with the 1381C triggering at 2.4v.
                      The
                      > > > > 4700uF
                      > > > > > was
                      > > > > > > > > >triggering rather rapidly (several times per
                      > > minute)...I
                      > > > > am
                      > > > > > not
                      > > > > > > > sure
                      > > > > > > > > >the 2.4v will be adequate to drive the motors but
                      > that
                      > > > is
                      > > > > > not the
                      > > > > > > > > >point right now...the 1F took about 90 minutes to
                      > > > charge.
                      > > > > It
                      > > > > > was
                      > > > > > > > > >painfully long. Just how much more capacity does
                      the
                      > > 1F
                      > > > > have?
                      > > > > > > > > >
                      > > > > > > > > >Can someone shed some light on why the 1F is
                      taking
                      > so
                      > > > > long
                      > > > > > to
                      > > > > > > > charge?
                      > > > > > > > > >
                      > > > > > > > > >tk
                      > > > > > > > > >
                      > > > > > > > > >
                      > > > > > > > >
                      > > > > > > >
                      > > > > > >
                      > > > > >
                      > > > >
                      > > >
                      > >
                      >
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