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Re: NSLU2 using 7805s and a 12V battery

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  • bullfrog528
    Hi Must admit I m somewhat rusty on my electronics theory. Regulators are rated with suitable heatsinks fitted.They are very derated without heatsinks. Various
    Message 1 of 15 , May 3, 2008
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      Hi

      Must admit I'm somewhat rusty on my electronics theory. Regulators
      are rated with suitable heatsinks fitted.They are very derated
      without heatsinks. Various problems here - the regulator has to
      disapate a 7V drop as well as the actual current drawn. There is a
      way to use a 78xx regulator with an external transistor to boost
      current.

      See page 22 of the datasheet below for a 7805 which shows a typical
      cct.

      http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf

      A large Watt rated resistor between the 12V and the input to the
      regulator may also help, but regulation might become an issue as the
      volt drop across the resistor would increase as current increased.

      Jeremy (Bullfrog528)




      --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@...>
      wrote:
      >
      >
      > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to
      an old wifi
      > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805
      voltage
      > regulators.
      > So far, I've tried a few different regulators (rated 1 or 1.5
      amps), and
      > when I turn the NSLU2 on, after about 30 seconds, the regulators
      are too hot
      > to touch and soon shut themselves down.
      > I'm not sure what the problem is.
      > Just to try, I connected it with a single 7805 (1 amp), which
      immediately
      > shut itself off.
      >
      > I connected the regulators in parallel with each other to provide
      up to 3
      > amps (more than the NSLU2 power supply), so I figured that I
      wouldn't need
      > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
      strangely?
      > How many people out there have tried this?
      >
      > (For those wondering, this is for a robotics project for school,
      and the
      > NSLU2 is running Debian)
      > --
      > View this message in context: http://www.nabble.com/NSLU2-using-
      7805s-and-a-12V-battery-tp17030363p17030363.html
      > Sent from the Nslu2 - General mailing list archive at Nabble.com.
      >
    • mackowiakp
      This is the worst way to make proper 5 V supply from 12 V battery, because 60% of power from battery is chaned in to heat not in to power necessery to supply
      Message 2 of 15 , May 3, 2008
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        This is the worst way to make proper 5 V supply from 12 V battery,
        because 60% of power from battery is chaned in to heat not in to power
        necessery to supply NSLU. The solution is to use DV/DV converter. You
        can buy such converter for example in ELFA internet shop. Just
        www.elfa.se and choose the language most usefull for You. And than try
        to find DV/DV converter model DC/DC THD12-1211 by TRACO Power. This is
        expensive solution but it resolve Your problem for century.



        --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@...> wrote:
        >
        >
        > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to an
        old wifi
        > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805 voltage
        > regulators.
        > So far, I've tried a few different regulators (rated 1 or 1.5 amps), and
        > when I turn the NSLU2 on, after about 30 seconds, the regulators are
        too hot
        > to touch and soon shut themselves down.
        > I'm not sure what the problem is.
        > Just to try, I connected it with a single 7805 (1 amp), which
        immediately
        > shut itself off.
        >
        > I connected the regulators in parallel with each other to provide up
        to 3
        > amps (more than the NSLU2 power supply), so I figured that I
        wouldn't need
        > heatsinks for them. Am I wrong, or is my NSLU2 just behaving strangely?
        > How many people out there have tried this?
        >
        > (For those wondering, this is for a robotics project for school, and the
        > NSLU2 is running Debian)
        > --
        > View this message in context:
        http://www.nabble.com/NSLU2-using-7805s-and-a-12V-battery-tp17030363p17030363.html
        > Sent from the Nslu2 - General mailing list archive at Nabble.com.
        >
      • Klaus Ruebsam
        Efil, 12V-5V=7V 7V*1A=7W (heat!!) 7V*1.5A=10.5W (even more heat!!) ... when I turn the NSLU2 on, after about 30 seconds, the regulators are too hot to touch
        Message 3 of 15 , May 3, 2008
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          Efil,

          12V-5V=7V

          7V*1A=7W (heat!!)
          7V*1.5A=10.5W (even more heat!!)

          >So far, I've tried a few different regulators (rated 1 or 1.5 amps), and
          when I turn the NSLU2 on, after about 30 seconds, the regulators are too hot
          to touch and soon shut themselves down.

          They are rated 1 or 1.5A as long as you take care on proper cooling
          (heatsink).

          >I'm not sure what the problem is.

          You quite likely forgot the hitsink for the regulator

          > I connected the regulators in parallel with each other to provide up to 3
          amps (more than the NSLU2 power supply), so I figured that I wouldn't need
          heatsinks for them. Am I wrong, or is my NSLU2 just behaving strangely?

          Conneting them in parallel makes a shortage on their output. Never ever do
          that!!! It is OK to do so with transistors, but not with power regulators
          that have protection circuits in them.


          I would search for a DC/DC-converter that converts your 12V down to 5V but
          without converting the voltage difference into heat. Those DC/DC-comvertrs
          actuaklly comnvert the input DC into an AC, route it through a transformer
          and rectify it again. The loss within the transformer is little compared to
          the loss you would have in a normal regulator (with ist proper heatsink
          attached!!!).

          Best regards,

          Klaus
        • bullfrog528
          Is there any particular reason your trying to run this off a 12Volt battery? If you need 12V to run the rest of the project.You could have two 6Volt batteries
          Message 4 of 15 , May 3, 2008
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            Is there any particular reason your trying to run this off a 12Volt
            battery?

            If you need 12V to run the rest of the project.You could have two
            6Volt batteries in series use the the 12V to run whatever it is and
            tap 6V out from the link between the two and regulate that down to
            5Volts. The lower battery will discharge quicker mind.


            |------ 12v ---> to rest of project
            []6volt batt
            |------6V ----> to 5volt reg and onto nslu2
            []6volt batt
            |______ov


            As they say there is always more than one way to string a cat.

            Bullfrog

            --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@...>
            wrote:
            >
            > Hi
            >
            > Must admit I'm somewhat rusty on my electronics theory. Regulators
            > are rated with suitable heatsinks fitted.They are very derated
            > without heatsinks. Various problems here - the regulator has to
            > disapate a 7V drop as well as the actual current drawn. There is a
            > way to use a 78xx regulator with an external transistor to boost
            > current.
            >
            > See page 22 of the datasheet below for a 7805 which shows a
            typical
            > cct.
            >
            > http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf
            >
            > A large Watt rated resistor between the 12V and the input to the
            > regulator may also help, but regulation might become an issue as
            the
            > volt drop across the resistor would increase as current increased.
            >
            > Jeremy (Bullfrog528)
            >
            >
            >
            >
            > --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@>
            > wrote:
            > >
            > >
            > > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to
            > an old wifi
            > > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805
            > voltage
            > > regulators.
            > > So far, I've tried a few different regulators (rated 1 or 1.5
            > amps), and
            > > when I turn the NSLU2 on, after about 30 seconds, the regulators
            > are too hot
            > > to touch and soon shut themselves down.
            > > I'm not sure what the problem is.
            > > Just to try, I connected it with a single 7805 (1 amp), which
            > immediately
            > > shut itself off.
            > >
            > > I connected the regulators in parallel with each other to
            provide
            > up to 3
            > > amps (more than the NSLU2 power supply), so I figured that I
            > wouldn't need
            > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
            > strangely?
            > > How many people out there have tried this?
            > >
            > > (For those wondering, this is for a robotics project for school,
            > and the
            > > NSLU2 is running Debian)
            > > --
            > > View this message in context: http://www.nabble.com/NSLU2-using-
            > 7805s-and-a-12V-battery-tp17030363p17030363.html
            > > Sent from the Nslu2 - General mailing list archive at Nabble.com.
            > >
            >
          • efilvasers
            Thanks for all your responses. I m using a 12V battery because it s what I happened to have on hand. The NSLU2, three Arduinos, and a few various ICs and LEDs
            Message 5 of 15 , May 3, 2008
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              Thanks for all your responses.

              I'm using a 12V battery because it's what I happened to have on hand.
              The NSLU2, three Arduinos, and a few various ICs and LEDs need the 5
              volts, while the wifi router needs 12, and all the motors use 9 (the
              actual robot itself is made with LEGO).

              As for solving this problem, I googled around a bit and found a
              solution for connecting 78xx's in parallel; it involves diodes on the
              outputs to isolate them, and one between their ground pins and the
              real ground to cancel out the voltage drop.

              The other solution I am considering is from the datasheet that
              bullfrog528 linked me to; on page 23, adding a PNP power transistor
              and 3 ohm resistor.

              I'll try both of these later tonight once I get myself to RadioShack.
              I neglected to mention before that this project is already about one
              day late and I don't have the time to wait for orders to ship.

              --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@...> wrote:
              >
              > Is there any particular reason your trying to run this off a 12Volt
              > battery?
              >
              > If you need 12V to run the rest of the project.You could have two
              > 6Volt batteries in series use the the 12V to run whatever it is and
              > tap 6V out from the link between the two and regulate that down to
              > 5Volts. The lower battery will discharge quicker mind.
              >
              >
              > |------ 12v ---> to rest of project
              > []6volt batt
              > |------6V ----> to 5volt reg and onto nslu2
              > []6volt batt
              > |______ov
              >
              >
              > As they say there is always more than one way to string a cat.
              >
              > Bullfrog
              >
              > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@>
              > wrote:
              > >
              > > Hi
              > >
              > > Must admit I'm somewhat rusty on my electronics theory. Regulators
              > > are rated with suitable heatsinks fitted.They are very derated
              > > without heatsinks. Various problems here - the regulator has to
              > > disapate a 7V drop as well as the actual current drawn. There is a
              > > way to use a 78xx regulator with an external transistor to boost
              > > current.
              > >
              > > See page 22 of the datasheet below for a 7805 which shows a
              > typical
              > > cct.
              > >
              > > http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf
              > >
              > > A large Watt rated resistor between the 12V and the input to the
              > > regulator may also help, but regulation might become an issue as
              > the
              > > volt drop across the resistor would increase as current increased.
              > >
              > > Jeremy (Bullfrog528)
              > >
              > >
              > >
              > >
              > > --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@>
              > > wrote:
              > > >
              > > >
              > > > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to
              > > an old wifi
              > > > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805
              > > voltage
              > > > regulators.
              > > > So far, I've tried a few different regulators (rated 1 or 1.5
              > > amps), and
              > > > when I turn the NSLU2 on, after about 30 seconds, the regulators
              > > are too hot
              > > > to touch and soon shut themselves down.
              > > > I'm not sure what the problem is.
              > > > Just to try, I connected it with a single 7805 (1 amp), which
              > > immediately
              > > > shut itself off.
              > > >
              > > > I connected the regulators in parallel with each other to
              > provide
              > > up to 3
              > > > amps (more than the NSLU2 power supply), so I figured that I
              > > wouldn't need
              > > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
              > > strangely?
              > > > How many people out there have tried this?
              > > >
              > > > (For those wondering, this is for a robotics project for school,
              > > and the
              > > > NSLU2 is running Debian)
              > > > --
              > > > View this message in context: http://www.nabble.com/NSLU2-using-
              > > 7805s-and-a-12V-battery-tp17030363p17030363.html
              > > > Sent from the Nslu2 - General mailing list archive at Nabble.com.
              > > >
              > >
              >
            • oabroad
              One option worth considering is a switching regulator. These have the huge advantage that they are efficient so don t create all that waste heat and could
              Message 6 of 15 , May 4, 2008
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                One option worth considering is a switching regulator. These have the
                huge advantage that they are efficient so don't create all that waste
                heat and could halve the current drain from the battery.

                If you can get hold of one you could do worse than get the Texas
                instruments TPS5430EVM-173 evaluation module, I've seen it priced at
                £7.99 and is supplied configured as a 5v 3A regulator. Failing that
                I've got a design for a 5V 1A switch reg that can be built on
                stripboard for a BOM cost of about £2.50 last time I costed it.


                --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@...>
                wrote:
                >
                > Thanks for all your responses.
                >
                > I'm using a 12V battery because it's what I happened to have on
                hand.
                > The NSLU2, three Arduinos, and a few various ICs and LEDs need the 5
                > volts, while the wifi router needs 12, and all the motors use 9 (the
                > actual robot itself is made with LEGO).
                >
                > As for solving this problem, I googled around a bit and found a
                > solution for connecting 78xx's in parallel; it involves diodes on
                the
                > outputs to isolate them, and one between their ground pins and the
                > real ground to cancel out the voltage drop.
                >
                > The other solution I am considering is from the datasheet that
                > bullfrog528 linked me to; on page 23, adding a PNP power transistor
                > and 3 ohm resistor.
                >
                > I'll try both of these later tonight once I get myself to
                RadioShack.
                > I neglected to mention before that this project is already about one
                > day late and I don't have the time to wait for orders to ship.
                >
                > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@> wrote:
                > >
                > > Is there any particular reason your trying to run this off a
                12Volt
                > > battery?
                > >
                > > If you need 12V to run the rest of the project.You could have two
                > > 6Volt batteries in series use the the 12V to run whatever it is
                and
                > > tap 6V out from the link between the two and regulate that down
                to
                > > 5Volts. The lower battery will discharge quicker mind.
                > >
                > >
                > > |------ 12v ---> to rest of project
                > > []6volt batt
                > > |------6V ----> to 5volt reg and onto nslu2
                > > []6volt batt
                > > |______ov
                > >
                > >
                > > As they say there is always more than one way to string a cat.
                > >
                > > Bullfrog
                > >
                > > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@>
                > > wrote:
                > > >
                > > > Hi
                > > >
                > > > Must admit I'm somewhat rusty on my electronics theory.
                Regulators
                > > > are rated with suitable heatsinks fitted.They are very derated
                > > > without heatsinks. Various problems here - the regulator has to
                > > > disapate a 7V drop as well as the actual current drawn. There
                is a
                > > > way to use a 78xx regulator with an external transistor to
                boost
                > > > current.
                > > >
                > > > See page 22 of the datasheet below for a 7805 which shows a
                > > typical
                > > > cct.
                > > >
                > > > http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf
                > > >
                > > > A large Watt rated resistor between the 12V and the input to
                the
                > > > regulator may also help, but regulation might become an issue
                as
                > > the
                > > > volt drop across the resistor would increase as current
                increased.
                > > >
                > > > Jeremy (Bullfrog528)
                > > >
                > > >
                > > >
                > > >
                > > > --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@>
                > > > wrote:
                > > > >
                > > > >
                > > > > I'm trying to run my NSLU2 (with a 1GB flash drive, connected
                to
                > > > an old wifi
                > > > > router) from a 12 volt SLA rechargeable battery (5Ah) using
                7805
                > > > voltage
                > > > > regulators.
                > > > > So far, I've tried a few different regulators (rated 1 or 1.5
                > > > amps), and
                > > > > when I turn the NSLU2 on, after about 30 seconds, the
                regulators
                > > > are too hot
                > > > > to touch and soon shut themselves down.
                > > > > I'm not sure what the problem is.
                > > > > Just to try, I connected it with a single 7805 (1 amp), which
                > > > immediately
                > > > > shut itself off.
                > > > >
                > > > > I connected the regulators in parallel with each other to
                > > provide
                > > > up to 3
                > > > > amps (more than the NSLU2 power supply), so I figured that I
                > > > wouldn't need
                > > > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
                > > > strangely?
                > > > > How many people out there have tried this?
                > > > >
                > > > > (For those wondering, this is for a robotics project for
                school,
                > > > and the
                > > > > NSLU2 is running Debian)
                > > > > --
                > > > > View this message in context: http://www.nabble.com/NSLU2-
                using-
                > > > 7805s-and-a-12V-battery-tp17030363p17030363.html
                > > > > Sent from the Nslu2 - General mailing list archive at
                Nabble.com.
                > > > >
                > > >
                > >
                >
              • Philip Pemberton
                ... OK, this is going to be a long post, mainly because I don t like saying that something is going wrong, I also like saying exactly *why* it s going wrong
                Message 7 of 15 , May 4, 2008
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                  efil vasers wrote:
                  > So far, I've tried a few different regulators (rated 1 or 1.5 amps), and
                  > when I turn the NSLU2 on, after about 30 seconds, the regulators are too hot
                  > to touch and soon shut themselves down.

                  OK, this is going to be a long post, mainly because I don't like saying that
                  something is going wrong, I also like saying exactly *why* it's going wrong
                  and how I came to the conclusion. If you've seen Big Bang Theory, think
                  'Sheldon with slightly better social skills' :)

                  Two things that could cause this:

                  You're trying to drop too much power over the 7805s.
                  ----------------------------------------------------
                  7805s are linear regulators (and horribly inefficient ones at that, but
                  they're cheap and pretty much the 'jellybean standard' so everyone uses them).
                  That means that any voltage drop has to be dissipated in the form of heat...
                  So let's do the math:

                  Your input voltage is 13.8V (assuming a fully charged SLA battery). You're
                  using 7805s, so your output is 5V. That means a voltage drop of 8.8V by virtue of:
                  13.8V - 5.0V = 8.8V

                  You're also dumping a peak of 2A over the the regulators (though ~1A typical;
                  the USB ports are rated for 500mA each for a total of 1A). That's 17.6 Watts:
                  8.8V * 2A = 17.6W

                  Or with the USBs 'open' (nothing connected), we assume 1A because:
                  2A - (500mA * 2) = 1A

                  Thus:
                  8.8V * 1A = 8.8W

                  So your regulators have to dissipate between 8.8 and 17.6 Watts of energy as
                  heat. And probably more than that because of internal inefficiencies. That's a
                  lot of heat!

                  Your heatsink isn't big enough
                  ------------------------------
                  You need to get rid of 17.6W of heat, and keep the temperature of the chip die
                  itself below the thermal cutoff point (70 Celsius if I remember correctly). I
                  honestly can't remember the calculations for heatsinks off the top of my head,
                  but you can probably find them in 'The Art of Electronics' by Horowitz and
                  Hill. Or on the internet.

                  OK, so your possible solutions would be:
                  - A switching regulator. These are pretty much turn-key these days, but you
                  have to be careful with them. Good PCB layout is essential, heatsinking less
                  so. Also, because you're not wasting as much energy as heat, your battery will
                  last longer.
                  - A bigger heatsink. Probably something about the size of a PC processor
                  heatsink, with a fan, and drilled to take your regulator. You'll need some
                  thermal grease and an insulator pad too.
                  - A pre-regulator. Add another regulator in front of the 7805 to
                  pre-regulate the 12V down to 8V, then feed the 8V to the 7805. Still horribly
                  inefficient, but you're distributing the load over two separate chips, which
                  reduces the heat output per chip.

                  > I connected the regulators in parallel with each other to provide up to 3
                  > amps (more than the NSLU2 power supply), so I figured that I wouldn't need
                  > heatsinks for them. Am I wrong, or is my NSLU2 just behaving strangely?
                  > How many people out there have tried this?

                  You shouldn't parallel 7805s. One chip will end up with a lower voltage than
                  the others (due to internal tolerances), and that'll take most of the load.
                  Result being that it ends up getting roasted, then when it eventually blows
                  you get a cascading failure of all the other 7805s. Lots of fun, involving
                  burned plastic, melted silicon and smoke that really isn't good for your
                  health or the chips'.

                  You can add an external pass transistor though -- though it's been ages since
                  I've done it. I do recall it involves a 10-ohm resistor and a beefy PNP
                  transistor though. Cost is likely to be more than a switcher, though.

                  Thanks,
                  --
                  Phil. | (\_/) This is Bunny. Copy and paste Bunny
                  ygroups@... | (='.'=) into your signature to help him gain
                  http://www.philpem.me.uk/ | (")_(") world domination.
                • efilvasers
                  oabroad: a schematic and parts list would be great. I ve been fiddling with other ways; if I don t have the parts to make a switching regulator, I ll probably
                  Message 8 of 15 , May 4, 2008
                  • 0 Attachment
                    oabroad: a schematic and parts list would be great.
                    I've been fiddling with other ways; if I don't have the parts to make
                    a switching regulator, I'll probably use a 2N3055 with a 7805.

                    --- In nslu2-general@yahoogroups.com, "oabroad" <oliverb@...> wrote:
                    >
                    > One option worth considering is a switching regulator. These have the
                    > huge advantage that they are efficient so don't create all that waste
                    > heat and could halve the current drain from the battery.
                    >
                    > If you can get hold of one you could do worse than get the Texas
                    > instruments TPS5430EVM-173 evaluation module, I've seen it priced at
                    > £7.99 and is supplied configured as a 5v 3A regulator. Failing that
                    > I've got a design for a 5V 1A switch reg that can be built on
                    > stripboard for a BOM cost of about £2.50 last time I costed it.
                    >
                    >
                    > --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@>
                    > wrote:
                    > >
                    > > Thanks for all your responses.
                    > >
                    > > I'm using a 12V battery because it's what I happened to have on
                    > hand.
                    > > The NSLU2, three Arduinos, and a few various ICs and LEDs need the 5
                    > > volts, while the wifi router needs 12, and all the motors use 9 (the
                    > > actual robot itself is made with LEGO).
                    > >
                    > > As for solving this problem, I googled around a bit and found a
                    > > solution for connecting 78xx's in parallel; it involves diodes on
                    > the
                    > > outputs to isolate them, and one between their ground pins and the
                    > > real ground to cancel out the voltage drop.
                    > >
                    > > The other solution I am considering is from the datasheet that
                    > > bullfrog528 linked me to; on page 23, adding a PNP power transistor
                    > > and 3 ohm resistor.
                    > >
                    > > I'll try both of these later tonight once I get myself to
                    > RadioShack.
                    > > I neglected to mention before that this project is already about one
                    > > day late and I don't have the time to wait for orders to ship.
                    > >
                    > > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@> wrote:
                    > > >
                    > > > Is there any particular reason your trying to run this off a
                    > 12Volt
                    > > > battery?
                    > > >
                    > > > If you need 12V to run the rest of the project.You could have two
                    > > > 6Volt batteries in series use the the 12V to run whatever it is
                    > and
                    > > > tap 6V out from the link between the two and regulate that down
                    > to
                    > > > 5Volts. The lower battery will discharge quicker mind.
                    > > >
                    > > >
                    > > > |------ 12v ---> to rest of project
                    > > > []6volt batt
                    > > > |------6V ----> to 5volt reg and onto nslu2
                    > > > []6volt batt
                    > > > |______ov
                    > > >
                    > > >
                    > > > As they say there is always more than one way to string a cat.
                    > > >
                    > > > Bullfrog
                    > > >
                    > > > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@>
                    > > > wrote:
                    > > > >
                    > > > > Hi
                    > > > >
                    > > > > Must admit I'm somewhat rusty on my electronics theory.
                    > Regulators
                    > > > > are rated with suitable heatsinks fitted.They are very derated
                    > > > > without heatsinks. Various problems here - the regulator has to
                    > > > > disapate a 7V drop as well as the actual current drawn. There
                    > is a
                    > > > > way to use a 78xx regulator with an external transistor to
                    > boost
                    > > > > current.
                    > > > >
                    > > > > See page 22 of the datasheet below for a 7805 which shows a
                    > > > typical
                    > > > > cct.
                    > > > >
                    > > > > http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf
                    > > > >
                    > > > > A large Watt rated resistor between the 12V and the input to
                    > the
                    > > > > regulator may also help, but regulation might become an issue
                    > as
                    > > > the
                    > > > > volt drop across the resistor would increase as current
                    > increased.
                    > > > >
                    > > > > Jeremy (Bullfrog528)
                    > > > >
                    > > > >
                    > > > >
                    > > > >
                    > > > > --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@>
                    > > > > wrote:
                    > > > > >
                    > > > > >
                    > > > > > I'm trying to run my NSLU2 (with a 1GB flash drive, connected
                    > to
                    > > > > an old wifi
                    > > > > > router) from a 12 volt SLA rechargeable battery (5Ah) using
                    > 7805
                    > > > > voltage
                    > > > > > regulators.
                    > > > > > So far, I've tried a few different regulators (rated 1 or 1.5
                    > > > > amps), and
                    > > > > > when I turn the NSLU2 on, after about 30 seconds, the
                    > regulators
                    > > > > are too hot
                    > > > > > to touch and soon shut themselves down.
                    > > > > > I'm not sure what the problem is.
                    > > > > > Just to try, I connected it with a single 7805 (1 amp), which
                    > > > > immediately
                    > > > > > shut itself off.
                    > > > > >
                    > > > > > I connected the regulators in parallel with each other to
                    > > > provide
                    > > > > up to 3
                    > > > > > amps (more than the NSLU2 power supply), so I figured that I
                    > > > > wouldn't need
                    > > > > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
                    > > > > strangely?
                    > > > > > How many people out there have tried this?
                    > > > > >
                    > > > > > (For those wondering, this is for a robotics project for
                    > school,
                    > > > > and the
                    > > > > > NSLU2 is running Debian)
                    > > > > > --
                    > > > > > View this message in context: http://www.nabble.com/NSLU2-
                    > using-
                    > > > > 7805s-and-a-12V-battery-tp17030363p17030363.html
                    > > > > > Sent from the Nslu2 - General mailing list archive at
                    > Nabble.com.
                    > > > > >
                    > > > >
                    > > >
                    > >
                    >
                  • Philip Pemberton
                    ... Take a look at this: It s a two-transistor (plus three resistors, three capacitors and a Zener diode) switching
                    Message 9 of 15 , May 4, 2008
                    • 0 Attachment
                      efilvasers wrote:
                      > oabroad: a schematic and parts list would be great.
                      > I've been fiddling with other ways; if I don't have the parts to make
                      > a switching regulator, I'll probably use a 2N3055 with a 7805.

                      Take a look at this:
                      <http://www.romanblack.com/smps/smps.htm>

                      It's a two-transistor (plus three resistors, three capacitors and a Zener
                      diode) switching regulator based on parts you can get from most electronics
                      parts dealers. You might need to wind the inductor yourself, or steal one from
                      a broken electronic device of some kind (or even a PC power supply if you have
                      a broken one lying around).

                      The beauty of it is that it'll work with most small inductors and is
                      incredibly easy to build. It's also a nice, easy introduction to the workings
                      of an SMPSU (moreso with Roman's explanation of how it all works).

                      If you want more info on SMPSUs, Microchip's website has an appnote on "buck"
                      switch-mode converter design -- the so-called buck topology is a voltage
                      step-down type SMPSU variant (Boost is one of the other topologies, there are
                      a ton of others - see
                      <http://en.wikipedia.org/wiki/Switched-mode_power_supply> for a bit more info).

                      --
                      Phil. | (\_/) This is Bunny. Copy and paste Bunny
                      ygroups@... | (='.'=) into your signature to help him gain
                      http://www.philpem.me.uk/ | (")_(") world domination.
                    • Peter Serbe
                      Hi there guys, take a tip from an old H/W engineer: surf to the National website (www.national.com) and then go on the webench design software. Fill in Your
                      Message 10 of 15 , May 4, 2008
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                        Hi there guys,

                        take a tip from an old H/W engineer:
                        surf to the National website (www.national.com) and then go on
                        the webench design software. Fill in Your specs - it will
                        propose You an LM25576. You may have to register though.

                        It's not worth to try to learn the intricacies of switching
                        regulator design for such a simple task.

                        Best regards
                        Peter

                        Philip Pemberton wrote:
                        > efilvasers wrote:
                        >> oabroad: a schematic and parts list would be great.
                        >> I've been fiddling with other ways; if I don't have the parts to make
                        >> a switching regulator, I'll probably use a 2N3055 with a 7805.
                        >
                        > Take a look at this:
                        > <http://www.romanblack.com/smps/smps.htm>
                        >
                        > It's a two-transistor (plus three resistors, three capacitors and a Zener
                        > diode) switching regulator based on parts you can get from most electronics
                        > parts dealers. You might need to wind the inductor yourself, or steal one from
                        > a broken electronic device of some kind (or even a PC power supply if you have
                        > a broken one lying around).
                        >
                        > The beauty of it is that it'll work with most small inductors and is
                        > incredibly easy to build. It's also a nice, easy introduction to the workings
                        > of an SMPSU (moreso with Roman's explanation of how it all works).
                        >
                        > If you want more info on SMPSUs, Microchip's website has an appnote on "buck"
                        > switch-mode converter design -- the so-called buck topology is a voltage
                        > step-down type SMPSU variant (Boost is one of the other topologies, there are
                        > a ton of others - see
                        > <http://en.wikipedia.org/wiki/Switched-mode_power_supply> for a bit more info).
                        >
                      • efilvasers
                        First off, I d like to thank you all again for your help. I should have done a bit more research before jumping head first into this project. Next time around,
                        Message 11 of 15 , May 5, 2008
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                          First off, I'd like to thank you all again for your help.
                          I should have done a bit more research before jumping head first into
                          this project.
                          Next time around, I'm definitely going with a switching regulator.
                          My quick solution is this:
                          A 2N3055, bolted to an old CPU heatsink (which still had some thermal
                          compound on it), with the base connected to a 7805 (with a small heat
                          sink), collector to the battery, and emitter to the NSLU2 (and other
                          electronics).
                          Also, the ground pin of the 7805 is connected to the real ground
                          through a 1A diode; when I measured the emitter voltage without this,
                          it read about 4.4 volts, went up to about 5.2 after adding it (runs
                          about 4.9 with the NSLU2 on).
                          The 7805 heatsink doesn't even warm up, while the 2N3055 heatsink
                          warms up after a couple of minutes, but went back down to near room
                          temperature when I placed an extra 80mm fan next to it.
                          I'm using the same solution for the 9 volt regulator (both sharing the
                          same fan).

                          --- In nslu2-general@yahoogroups.com, Philip Pemberton <ygroups@...>
                          wrote:
                          >
                          > efil vasers wrote:
                          > > So far, I've tried a few different regulators (rated 1 or 1.5
                          amps), and
                          > > when I turn the NSLU2 on, after about 30 seconds, the regulators
                          are too hot
                          > > to touch and soon shut themselves down.
                          >
                          > OK, this is going to be a long post, mainly because I don't like
                          saying that
                          > something is going wrong, I also like saying exactly *why* it's
                          going wrong
                          > and how I came to the conclusion. If you've seen Big Bang Theory, think
                          > 'Sheldon with slightly better social skills' :)
                          >
                          > Two things that could cause this:
                          >
                          > You're trying to drop too much power over the 7805s.
                          > ----------------------------------------------------
                          > 7805s are linear regulators (and horribly inefficient ones at that,
                          but
                          > they're cheap and pretty much the 'jellybean standard' so everyone
                          uses them).
                          > That means that any voltage drop has to be dissipated in the form of
                          heat...
                          > So let's do the math:
                          >
                          > Your input voltage is 13.8V (assuming a fully charged SLA battery).
                          You're
                          > using 7805s, so your output is 5V. That means a voltage drop of 8.8V
                          by virtue of:
                          > 13.8V - 5.0V = 8.8V
                          >
                          > You're also dumping a peak of 2A over the the regulators (though ~1A
                          typical;
                          > the USB ports are rated for 500mA each for a total of 1A). That's
                          17.6 Watts:
                          > 8.8V * 2A = 17.6W
                          >
                          > Or with the USBs 'open' (nothing connected), we assume 1A because:
                          > 2A - (500mA * 2) = 1A
                          >
                          > Thus:
                          > 8.8V * 1A = 8.8W
                          >
                          > So your regulators have to dissipate between 8.8 and 17.6 Watts of
                          energy as
                          > heat. And probably more than that because of internal
                          inefficiencies. That's a
                          > lot of heat!
                          >
                          > Your heatsink isn't big enough
                          > ------------------------------
                          > You need to get rid of 17.6W of heat, and keep the temperature of
                          the chip die
                          > itself below the thermal cutoff point (70 Celsius if I remember
                          correctly). I
                          > honestly can't remember the calculations for heatsinks off the top
                          of my head,
                          > but you can probably find them in 'The Art of Electronics' by
                          Horowitz and
                          > Hill. Or on the internet.
                          >
                          > OK, so your possible solutions would be:
                          > - A switching regulator. These are pretty much turn-key these
                          days, but you
                          > have to be careful with them. Good PCB layout is essential,
                          heatsinking less
                          > so. Also, because you're not wasting as much energy as heat, your
                          battery will
                          > last longer.
                          > - A bigger heatsink. Probably something about the size of a PC
                          processor
                          > heatsink, with a fan, and drilled to take your regulator. You'll
                          need some
                          > thermal grease and an insulator pad too.
                          > - A pre-regulator. Add another regulator in front of the 7805 to
                          > pre-regulate the 12V down to 8V, then feed the 8V to the 7805. Still
                          horribly
                          > inefficient, but you're distributing the load over two separate
                          chips, which
                          > reduces the heat output per chip.
                          >
                          > > I connected the regulators in parallel with each other to provide
                          up to 3
                          > > amps (more than the NSLU2 power supply), so I figured that I
                          wouldn't need
                          > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
                          strangely?
                          > > How many people out there have tried this?
                          >
                          > You shouldn't parallel 7805s. One chip will end up with a lower
                          voltage than
                          > the others (due to internal tolerances), and that'll take most of
                          the load.
                          > Result being that it ends up getting roasted, then when it
                          eventually blows
                          > you get a cascading failure of all the other 7805s. Lots of fun,
                          involving
                          > burned plastic, melted silicon and smoke that really isn't good for
                          your
                          > health or the chips'.
                          >
                          > You can add an external pass transistor though -- though it's been
                          ages since
                          > I've done it. I do recall it involves a 10-ohm resistor and a beefy PNP
                          > transistor though. Cost is likely to be more than a switcher, though.
                          >
                          > Thanks,
                          > --
                          > Phil. | (\_/) This is Bunny. Copy and
                          paste Bunny
                          > ygroups@... | (='.'=) into your signature to help him gain
                          > http://www.philpem.me.uk/ | (")_(") world domination.
                          >
                        • Phil Reed
                          Take a look at the products from Dimension Engineering. They have a number of small, easily integrated switching power supplies you could use.
                          Message 12 of 15 , May 6, 2008
                          • 0 Attachment
                            Take a look at the products from Dimension Engineering. They have a
                            number of small, easily integrated switching power supplies you could use.

                            http://www.dimensionengineering.com/

                            (just a happy customer...)

                            ...phil

                            --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@...> wrote:
                            >
                            >
                            > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to an
                            old wifi
                            > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805 voltage
                            > regulators.
                            > So far, I've tried a few different regulators (rated 1 or 1.5 amps), and
                            > when I turn the NSLU2 on, after about 30 seconds, the regulators are
                            too hot
                            > to touch and soon shut themselves down.
                            > I'm not sure what the problem is.
                            > Just to try, I connected it with a single 7805 (1 amp), which
                            immediately
                            > shut itself off.
                            >
                            > I connected the regulators in parallel with each other to provide up
                            to 3
                            > amps (more than the NSLU2 power supply), so I figured that I
                            wouldn't need
                            > heatsinks for them. Am I wrong, or is my NSLU2 just behaving strangely?
                            > How many people out there have tried this?
                            >
                            > (For those wondering, this is for a robotics project for school, and the
                            > NSLU2 is running Debian)
                            > --
                            > View this message in context:
                            http://www.nabble.com/NSLU2-using-7805s-and-a-12V-battery-tp17030363p17030363.html
                            > Sent from the Nslu2 - General mailing list archive at Nabble.com.
                            >
                          • oabroad
                            I just remembered a design trick for boosting a regulator: one circuit I ve seen used a PNP power transistor with the base connected to the INPUT of the
                            Message 13 of 15 , May 6, 2008
                            • 0 Attachment
                              I just remembered a design trick for boosting a regulator: one
                              circuit I've seen used a PNP power transistor with the base
                              connected to the INPUT of the regulator (with a bypass resistor,
                              probably 22ohms). By putting the junction on the input side the
                              output regulation isn't compromised by Vbe drop.

                              --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@...>
                              wrote:
                              >
                              > First off, I'd like to thank you all again for your help.
                              > I should have done a bit more research before jumping head first
                              into
                              > this project.
                              > Next time around, I'm definitely going with a switching regulator.
                              > My quick solution is this:
                              > A 2N3055, bolted to an old CPU heatsink (which still had some
                              thermal
                              > compound on it), with the base connected to a 7805 (with a small
                              heat
                              > sink), collector to the battery, and emitter to the NSLU2 (and
                              other
                              > electronics).
                              > Also, the ground pin of the 7805 is connected to the real ground
                              > through a 1A diode; when I measured the emitter voltage without
                              this,
                              > it read about 4.4 volts, went up to about 5.2 after adding it (runs
                              > about 4.9 with the NSLU2 on).
                              > The 7805 heatsink doesn't even warm up, while the 2N3055 heatsink
                              > warms up after a couple of minutes, but went back down to near room
                              > temperature when I placed an extra 80mm fan next to it.
                              > I'm using the same solution for the 9 volt regulator (both sharing
                              the
                              > same fan).
                              >
                            • tbering2002
                              In nslu2-general@yahoogroups.com, efilvasers ... You might want to take a look at www.national.com and use one of their simple switching
                              Message 14 of 15 , May 8, 2008
                              • 0 Attachment
                                In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@
                                ...>
                                wrote:
                                > Next time around, I'm definitely going with a switching regulator.

                                You might want to take a look at www.national.com and use one of their
                                simple switching regulator circuits. Your battery would last longer,
                                and digikey can supply almost all the parts you need to build the design.

                                National Semiconductor even has a nice tool
                                http://www.national.com/appinfo/power/webench.html to automatically
                                design your application.

                                Additionally, digikey has some pre-made switching regulator modules.
                                If you use those, you only need to add capacitors, and thus they are
                                more prototype friendly. Some of the DC-DC modules will be even
                                easier to connect than your power boosted 7805. Look at the 78HCT205
                                or the 78ST305.

                                --- In nslu2-general@yahoogroups.com, "oabroad" <oliverb@...> wrote:
                                >
                                > I just remembered a design trick for boosting a regulator: one
                                > circuit I've seen used a PNP power transistor with the base
                                > connected to the INPUT of the regulator (with a bypass resistor,
                                > probably 22ohms). By putting the junction on the input side the
                                > output regulation isn't compromised by Vbe drop.
                                >
                                > --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@>
                                > wrote:
                                > >
                                > > First off, I'd like to thank you all again for your help.
                                > > I should have done a bit more research before jumping head first
                                > into
                                > > this project.
                                > > Next time around, I'm definitely going with a switching regulator.
                                > > My quick solution is this:
                                > > A 2N3055, bolted to an old CPU heatsink (which still had some
                                > thermal
                                > > compound on it), with the base connected to a 7805 (with a small
                                > heat
                                > > sink), collector to the battery, and emitter to the NSLU2 (and
                                > other
                                > > electronics).
                                > > Also, the ground pin of the 7805 is connected to the real ground
                                > > through a 1A diode; when I measured the emitter voltage without
                                > this,
                                > > it read about 4.4 volts, went up to about 5.2 after adding it (runs
                                > > about 4.9 with the NSLU2 on).
                                > > The 7805 heatsink doesn't even warm up, while the 2N3055 heatsink
                                > > warms up after a couple of minutes, but went back down to near room
                                > > temperature when I placed an extra 80mm fan next to it.
                                > > I'm using the same solution for the 9 volt regulator (both sharing
                                > the
                                > > same fan).
                                > >
                                >
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