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Re: I need to know what to put between a PIC and a Solenoid....

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  • rtstofer
    More on the kickback diode across the coil. If the diode is omitted and the reverse breakdown diodes in the MOSFET or ULN conduct, the entire reverse voltage
    Message 1 of 14 , Aug 31 9:35 PM
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      More on the kickback diode across the coil.

      If the diode is omitted and the reverse breakdown diodes in the MOSFET
      or ULN conduct, the entire reverse voltage generated by the coil is
      imposed on the power supply, spiking everything that is connected.

      If the diode is included, the kickback voltage is clamped by the diode.
    • Stefan Trethan
      On Wed, 31 Aug 2005 23:08:48 +0200, lcdpublishing ... Yes Sir! I m switching on the bubbler in the etch tank this instant ;-) ST
      Message 2 of 14 , Sep 1, 2005
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        On Wed, 31 Aug 2005 23:08:48 +0200, lcdpublishing
        <lcdpublishing@...> wrote:

        > So, instead of
        > servos, I will be running it with steppers (hint Stefan :-))


        Yes Sir!

        I'm switching on the bubbler in the etch tank this instant ;-)

        ST
      • margucl
        ... Try a high side switch, e.g. http://www.ortodoxism.ro/datasheets/siemens/BTS442D2.pdf martin
        Message 3 of 14 , Sep 1, 2005
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          --- In Electronics_101@yahoogroups.com, "lcdpublishing"
          <lcdpublishing@y...> wrote:
          > Hi all,
          >
          > Seeing as I got in on the group purchase of the SLA chips, I decided
          > to convert my lathe to CNC sooner rather than later. So, instead of
          > servos, I will be running it with steppers (hint Stefan :-))
          >
          > This is a small machine and the first thing I need to construct is a
          > transmission for it. It will be three speeds and I have the
          > mechanicals pretty well designed now. I mentioned this a few weeks
          > back, but now am getting very close to the final electronics design
          > too.
          >
          > To shift gears, I will be using a PIC for logic, which in turn sends
          > the outputs to a ULN2803 darlington. I have learned by now that
          > this chip isn't going to drive the Solenoid by itself, so I know I
          > need something between it and the solenoid.
          >
          > The solenoid's specs are:
          >
          > 24 volts
          > 10 watts
          > 60 ohms coil resistance
          >
          > This is a continuous pull solenoid and I will be needing to drive it
          > coninuous. From the little that I know, I think I could use either
          > of the following, but not sure which is the right way to go.
          >
          > Mosfet
          > Relay

          Try a high side switch, e.g.
          http://www.ortodoxism.ro/datasheets/siemens/BTS442D2.pdf

          \martin
        • lcdpublishing
          Actually, I am still in no hurry, I was just kidding! I really won t be ready for the stepper drives for at least a month, probably longer. Chris
          Message 4 of 14 , Sep 1, 2005
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            Actually, I am still in no hurry, I was just kidding! I really won't
            be ready for the stepper drives for at least a month, probably longer.

            Chris




            --- In Electronics_101@yahoogroups.com, "Stefan Trethan"
            <stefan_trethan@g...> wrote:
            > On Wed, 31 Aug 2005 23:08:48 +0200, lcdpublishing
            > <lcdpublishing@y...> wrote:
            >
            > > So, instead of
            > > servos, I will be running it with steppers (hint Stefan :-))
            >
            >
            > Yes Sir!
            >
            > I'm switching on the bubbler in the etch tank this instant ;-)
            >
            > ST
          • lcdpublishing
            WOW! Thanks everyone. Hopefully today I can spend an hour or so going over each of the suggestions trying to learn the differences between them. At least
            Message 5 of 14 , Sep 1, 2005
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              WOW! Thanks everyone. Hopefully today I can spend an hour or so
              going over each of the suggestions trying to learn the differences
              between them. At least the good news is that I was pretty close with
              my original thoughts! I am learning!

              Chris
            • Daniel Nicoson
              I ve been using a RFP50N06, an N-Channel power mosfet for several of my solenoid related projects. It will handle up to 50 amps, purely overkill for your app
              Message 6 of 14 , Sep 1, 2005
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                I've been using a RFP50N06, an N-Channel power mosfet for several of my solenoid related projects.  It will handle up to 50 amps, purely overkill for your app but robust.  These can be purchased for $1.29 each at Digi-Key.  I do use a 1N4003 diode ($.04 each) with this to keep the inductive spike form cooking it (I proved the need).
                 
                Another advantage to this one, you can drive it right from an IC.  I simply use a comparator with a pull-up resistor to run the gate with 12 volts.  Pull the data sheet down from Digi-Key.
                 
                I ran 8 fuel injectors (14 ohms each) in parallel at 20Hz with 40ms PW for 1/2 hour, no significant heat with my heat sink (heat sink is the die-cast aluminum enclosure), the injectors however were sizzling hot!
                 
                My $.02,
                 
                Dan Nicoson
                 
                -----Original Message-----
                From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com]On Behalf Of Tony Smith
                Sent: Wednesday, August 31, 2005 10:59 PM
                To: Electronics_101@yahoogroups.com
                Subject: Re: [Electronics_101] I need to know what to put between a PIC and a Solenoid....

                >  To shift gears, I will be using a PIC for logic, which in turn sends
                >  the outputs to a ULN2803 darlington.  I have learned by now that
                >  this chip isn't going to drive the Solenoid by itself, so I know I
                >  need something between it and the solenoid.
                >
                >  The solenoid's specs are:
                >
                >  24 volts
                >  10 watts
                >  60 ohms coil resistance
                >
                >  This is a continuous pull solenoid and I will be needing to drive it
                >  coninuous.  From the little that I know, I think I could use either
                >  of the following, but not sure which is the right way to go.
                >
                >  Mosfet
                >  Relay
                >


                Not too many amps, use the mosfet.

                For more amps (or if you're keen), use both.  Hook them up in parallel,
                turn both on at the same time, wait a bit, and turn the mosfet off.

                The idea is the relay can handle the current better than the mosfet (won't
                get hot).  Downside for a relay is you get arcing as the contacts close,
                that's where the mosfet comes in.  By the time the contacts close, current
                is already flowing thru the mosfet, so no arcing.  Since the mosfet is on
                for only a short time, it doesn't get the chance to heat up, so it won't
                even need a heatsink.

                This setup lasts forever, apparently!

                Tony

              • lcdpublishing
                Cool application, thanks Dan. It sure seems as though the Mosfets can replace Relays in many different applications. Perhaps I shoudl study them buggers a
                Message 7 of 14 , Sep 1, 2005
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                  Cool application, thanks Dan.

                  It sure seems as though the Mosfets can replace Relays in many
                  different applications. Perhaps I shoudl study them buggers a
                  little more.

                  Chris



                  --- In Electronics_101@yahoogroups.com, "Daniel Nicoson"
                  <A6intruder@a...> wrote:
                  > I've been using a RFP50N06, an N-Channel power mosfet for several
                  of my
                  > solenoid related projects. It will handle up to 50 amps, purely
                  overkill
                  > for your app but robust. These can be purchased for $1.29 each at
                  Digi-Key.
                  > I do use a 1N4003 diode ($.04 each) with this to keep the
                  inductive spike
                  > form cooking it (I proved the need).
                  >
                  > Another advantage to this one, you can drive it right from an IC.
                  I simply
                  > use a comparator with a pull-up resistor to run the gate with 12
                  volts.
                  > Pull the data sheet down from Digi-Key.
                  >
                  > I ran 8 fuel injectors (14 ohms each) in parallel at 20Hz with
                  40ms PW for
                  > 1/2 hour, no significant heat with my heat sink (heat sink is the
                  die-cast
                  > aluminum enclosure), the injectors however were sizzling hot!
                  >
                  > My $.02,
                  >
                  > Dan Nicoson
                  >
                  > -----Original Message-----
                  > From: Electronics_101@yahoogroups.com
                  > [mailto:Electronics_101@yahoogroups.com]On Behalf Of Tony Smith
                  > Sent: Wednesday, August 31, 2005 10:59 PM
                  > To: Electronics_101@yahoogroups.com
                  > Subject: Re: [Electronics_101] I need to know what to put
                  between a PIC
                  > and a Solenoid....
                  >
                  >
                  > > To shift gears, I will be using a PIC for logic, which in
                  turn sends
                  > > the outputs to a ULN2803 darlington. I have learned by now
                  that
                  > > this chip isn't going to drive the Solenoid by itself, so I
                  know I
                  > > need something between it and the solenoid.
                  > >
                  > > The solenoid's specs are:
                  > >
                  > > 24 volts
                  > > 10 watts
                  > > 60 ohms coil resistance
                  > >
                  > > This is a continuous pull solenoid and I will be needing to
                  drive it
                  > > coninuous. From the little that I know, I think I could use
                  either
                  > > of the following, but not sure which is the right way to go.
                  > >
                  > > Mosfet
                  > > Relay
                  > >
                  >
                  >
                  > Not too many amps, use the mosfet.
                  >
                  > For more amps (or if you're keen), use both. Hook them up in
                  parallel,
                  > turn both on at the same time, wait a bit, and turn the mosfet
                  off.
                  >
                  > The idea is the relay can handle the current better than the
                  mosfet (won't
                  > get hot). Downside for a relay is you get arcing as the
                  contacts close,
                  > that's where the mosfet comes in. By the time the contacts
                  close, current
                  > is already flowing thru the mosfet, so no arcing. Since the
                  mosfet is on
                  > for only a short time, it doesn't get the chance to heat up, so
                  it won't
                  > even need a heatsink.
                  >
                  > This setup lasts forever, apparently!
                  >
                  > Tony
                  >
                  >
                  >
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                  >
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                • Dave Mucha
                  ... overkill ... Digi-Key. ... spike ... simply ... PW for ... die-cast ... One MAJOR difference in the uses is that the MOSFET can only run DV loads. another
                  Message 8 of 14 , Sep 1, 2005
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                    --- In Electronics_101@yahoogroups.com, "Daniel Nicoson"
                    <A6intruder@a...> wrote:
                    > I've been using a RFP50N06, an N-Channel power mosfet for several of my
                    > solenoid related projects. It will handle up to 50 amps, purely
                    overkill
                    > for your app but robust. These can be purchased for $1.29 each at
                    Digi-Key.
                    > I do use a 1N4003 diode ($.04 each) with this to keep the inductive
                    spike
                    > form cooking it (I proved the need).
                    >
                    > Another advantage to this one, you can drive it right from an IC. I
                    simply
                    > use a comparator with a pull-up resistor to run the gate with 12 volts.
                    > Pull the data sheet down from Digi-Key.
                    >
                    > I ran 8 fuel injectors (14 ohms each) in parallel at 20Hz with 40ms
                    PW for
                    > 1/2 hour, no significant heat with my heat sink (heat sink is the
                    die-cast
                    > aluminum enclosure), the injectors however were sizzling hot!
                    >
                    > My $.02,
                    >
                    > Dan Nicoson


                    One MAJOR difference in the uses is that the MOSFET can only run DV loads.

                    another is that you can cycle a MOSFET at much as you like and as fast
                    as you can signal it ( I know Chris uses a Basic inturpedted PIC so it
                    is inherently slower than some others )

                    A relay, being mechanical will fail if switched too often, and too fast.

                    Dave





                    >
                    > -----Original Message-----
                    > From: Electronics_101@yahoogroups.com
                    > [mailto:Electronics_101@yahoogroups.com]On Behalf Of Tony Smith
                    > Sent: Wednesday, August 31, 2005 10:59 PM
                    > To: Electronics_101@yahoogroups.com
                    > Subject: Re: [Electronics_101] I need to know what to put between
                    a PIC
                    > and a Solenoid....
                    >
                    >
                    > > To shift gears, I will be using a PIC for logic, which in turn
                    sends
                    > > the outputs to a ULN2803 darlington. I have learned by now that
                    > > this chip isn't going to drive the Solenoid by itself, so I know I
                    > > need something between it and the solenoid.
                    > >
                    > > The solenoid's specs are:
                    > >
                    > > 24 volts
                    > > 10 watts
                    > > 60 ohms coil resistance
                    > >
                    > > This is a continuous pull solenoid and I will be needing to
                    drive it
                    > > coninuous. From the little that I know, I think I could use either
                    > > of the following, but not sure which is the right way to go.
                    > >
                    > > Mosfet
                    > > Relay
                    > >
                    >
                    >
                    > Not too many amps, use the mosfet.
                    >
                    > For more amps (or if you're keen), use both. Hook them up in
                    parallel,
                    > turn both on at the same time, wait a bit, and turn the mosfet off.
                    >
                    > The idea is the relay can handle the current better than the
                    mosfet (won't
                    > get hot). Downside for a relay is you get arcing as the contacts
                    close,
                    > that's where the mosfet comes in. By the time the contacts close,
                    current
                    > is already flowing thru the mosfet, so no arcing. Since the
                    mosfet is on
                    > for only a short time, it doesn't get the chance to heat up, so it
                    won't
                    > even need a heatsink.
                    >
                    > This setup lasts forever, apparently!
                    >
                    > Tony
                    >
                    >
                    >
                    >
                    ----------------------------------------------------------------------------
                    > --
                    > YAHOO! GROUPS LINKS
                    >
                    > a.. Visit your group "Electronics_101" on the web.
                    >
                    > b.. To unsubscribe from this group, send an email to:
                    > Electronics_101-unsubscribe@yahoogroups.com
                    >
                    > c.. Your use of Yahoo! Groups is subject to the Yahoo! Terms of
                    > Service.
                    >
                    >
                    >
                    ----------------------------------------------------------------------------
                    > --
                  • Roy J. Tellason
                    On Wednesday 31 August 2005 05:08 pm, lcdpublishing wrote: ... Not if that part isn t switching the load... ... There are 24V three-terminal regulators
                    Message 9 of 14 , Sep 1, 2005
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                      On Wednesday 31 August 2005 05:08 pm, lcdpublishing wrote:

                      <...>

                      > Also, the ULN2803 has diodes built-in (if I remember correctly).
                      > Would these built-in diodes be adequate to deal with the back EMF?

                      Not if that part isn't switching the load...

                      > There will be another aspect of this I need to deal with too, though
                      > at a later date. The machine will have 40 volts from the main power
                      > supply (Home made), 5 volts from a computer power supply, and 12
                      > volts from a computer power supply (as per the suggestions here).
                      > To get 24 volts out of this, I am guessing I would be best making
                      > another "Home made" power supply for just the 24 volt appliances on
                      > the machine. Would that make sense, or would there be a way
                      > to "Step down" the 40 volts to 24?

                      There are 24V three-terminal regulators out there. You need to look at how
                      much current you require to decide whether this is going to be a good choice
                      or not, and how much power you'll be wasting as heat.

                      > Based on a discussion about a week or so ago, I realized that the 5
                      > and 12 volt regulators (7805 7812) will generate a lot of heat and
                      > essentially waste energy. So, I don't think that is the path to go
                      > either for the 24 volt supply.

                      Depends on your current needs, if it's not much, then you should be okay
                      with it.
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