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Re: [SeattleRobotics] Circuit advice

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  • tbrenke@verizon.net
    good thinking. I will keep this in mind also. ... From: Larry Barello To: SeattleRobotics@yahoogroups.com Sent: Saturday, July 31, 2004 4:17 PM Subject: RE:
    Message 1 of 13 , Jul 31, 2004
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      good thinking.
      I will keep this in mind also.

      ----- Original Message -----
      From: Larry Barello
      To: SeattleRobotics@yahoogroups.com
      Sent: Saturday, July 31, 2004 4:17 PM
      Subject: RE: [SeattleRobotics] Circuit advice


      The power dissipation rating of a MOSFET is meaningless without knowing what
      the heat sink is capable of. It makes NO sense to try to calculate the
      current capacity of the device based upon the rated power dissipation!

      It is probably best to design for free-air dissipation. A 4 milli-ohm part
      will have roughly 6 mohm resistance at max temp of 175C. The TO220 package
      has about 2 watts dissipation capacity in free air (room temp, device at max
      temp). Watts = current * voltage. Voltage = resistance * current. So max
      current/device is square root of watts (2)/resistance (.006) or about
      18A/device. All this information is on the typical MOSFET data sheet.

      I suspect the solenoid being used to modulate the NO is not variable, but
      rather ON/OFF and the ratio of ON vs OFF at a particular supply pressure,
      will inject a variable amount of NO into the manifold. There should be no
      need for a table of PWM to flow. The PWM rate is low enough that the valve
      follows the PWM, just like the current follows the PWM in a MOSFET.

      Since the solenoid is on for something less than 100% of the time, it is
      likely that the AVERAGE current could be used to design the capacity. In
      any case two 1404's should be plenty. If you are worried, bolt them to a
      small amount of metal to buffer the temperature rise for the few seconds
      that the NO is flowing.

      You are not planning on letting it flow for a long time, right? Even at 35A
      (stated current rating of the solenoid), James could probably get away with
      one FET for 10-20 seconds at a time with no or little metal bolted to the
      device.

      I helped design a dual 80A combat robot controller (www.robot-solutions.com
      RS80D) which uses 2x1404's in each leg and has a small aluminum block for
      heat-sink. It handles 80A just fine for a 4-5 minute match, but, of course,
      overheats if you run 30A through it continuously. Actually, it doesn't
      overheat since I fold back the drive as the temperature rises and cut it off
      completely by 130C. Anyway, the point being that even at 40A/device not
      much heat sinking is needed for short periods of time.

      Cheers!

      -----Original Message-----
      From: tbrenke@...
      ..
      mosfet:
      the IRF3709Z has an on restance of .0078 at 5V 30V max power disapation
      of 79W
      TO262 1.87 each at digikey
      2+ are needed because of the 79W rating
      the IRF1404 has an on restance of .004 at 5V 40V max power dissipation of
      200W
      TO220 2.52 each at digikey
      1 is needed because of the 200W rating can run 5A with heat sink.
      36V / 200W = 5A



      Visit the SRS Website at http://www.seattlerobotics.org
      Yahoo! Groups Links






      [Non-text portions of this message have been removed]
    • James Fitzsimons
      Hi Larry, Kip, tbrenke, Chuck, and list Sorry for my late reply, I was laid up in hospital for a few days last week with food poisoning and haven t had a
      Message 2 of 13 , Aug 9, 2004
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        Hi Larry, Kip, tbrenke, Chuck, and list

        Sorry for my late reply, I was laid up in hospital for a few days last
        week with food poisoning and haven't had a chance to get back to this.

        New version at
        http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif

        This (hopefully) is an extraction of the appropriate part of the OSMC
        circuit for driving a solenoid. Do I have the solenoid part hooked into
        the OSMC circuit correctly?

        Also, I just re-read Larry's last email, and will probably just use two
        fets although the diagram above shows three.

        Cheers,
        James Fitzsimons

        On Sun, 2004-08-01 at 07:00, tbrenke@... wrote:
        > good thinking.
        > I will keep this in mind also.
        >
        > ----- Original Message -----
        > From: Larry Barello
        > To: SeattleRobotics@yahoogroups.com
        > Sent: Saturday, July 31, 2004 4:17 PM
        > Subject: RE: [SeattleRobotics] Circuit advice
        >
        >
        > The power dissipation rating of a MOSFET is meaningless without knowing what
        > the heat sink is capable of. It makes NO sense to try to calculate the
        > current capacity of the device based upon the rated power dissipation!
        >
        > It is probably best to design for free-air dissipation. A 4 milli-ohm part
        > will have roughly 6 mohm resistance at max temp of 175C. The TO220 package
        > has about 2 watts dissipation capacity in free air (room temp, device at max
        > temp). Watts = current * voltage. Voltage = resistance * current. So max
        > current/device is square root of watts (2)/resistance (.006) or about
        > 18A/device. All this information is on the typical MOSFET data sheet.
        >
        > I suspect the solenoid being used to modulate the NO is not variable, but
        > rather ON/OFF and the ratio of ON vs OFF at a particular supply pressure,
        > will inject a variable amount of NO into the manifold. There should be no
        > need for a table of PWM to flow. The PWM rate is low enough that the valve
        > follows the PWM, just like the current follows the PWM in a MOSFET.
        >
        > Since the solenoid is on for something less than 100% of the time, it is
        > likely that the AVERAGE current could be used to design the capacity. In
        > any case two 1404's should be plenty. If you are worried, bolt them to a
        > small amount of metal to buffer the temperature rise for the few seconds
        > that the NO is flowing.
        >
        > You are not planning on letting it flow for a long time, right? Even at 35A
        > (stated current rating of the solenoid), James could probably get away with
        > one FET for 10-20 seconds at a time with no or little metal bolted to the
        > device.
        >
        > I helped design a dual 80A combat robot controller (www.robot-solutions.com
        > RS80D) which uses 2x1404's in each leg and has a small aluminum block for
        > heat-sink. It handles 80A just fine for a 4-5 minute match, but, of course,
        > overheats if you run 30A through it continuously. Actually, it doesn't
        > overheat since I fold back the drive as the temperature rises and cut it off
        > completely by 130C. Anyway, the point being that even at 40A/device not
        > much heat sinking is needed for short periods of time.
        >
        > Cheers!
        >
        > -----Original Message-----
        > From: tbrenke@...
        > ..
        > mosfet:
        > the IRF3709Z has an on restance of .0078 at 5V 30V max power disapation
        > of 79W
        > TO262 1.87 each at digikey
        > 2+ are needed because of the 79W rating
        > the IRF1404 has an on restance of .004 at 5V 40V max power dissipation of
        > 200W
        > TO220 2.52 each at digikey
        > 1 is needed because of the 200W rating can run 5A with heat sink.
        > 36V / 200W = 5A
        >
        >
        >
        > Visit the SRS Website at http://www.seattlerobotics.org
        > Yahoo! Groups Links
        >
        >
        >
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >
        >
        >
        > Visit the SRS Website at http://www.seattlerobotics.org
        > Yahoo! Groups Links
        >
        >
        >
        >
        --
        It's 5.50 a.m.... Do you know where your stack pointer is ?
      • Kipton Moravec
        The snubber is missing, I am not certain you need it, but it is an extra margin of safety. For DC it is across the coil. I would use a 1 W 100 Ohm and a
        Message 3 of 13 , Aug 9, 2004
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          The snubber is missing, I am not certain you need it, but it is an extra
          margin of safety. For DC it is across the coil. I would use a 1 W 100
          Ohm and a 200V or 400V 0.1 MFD poly capacitor.

          I am not sure of the 1.5KE51CA. In the OSMB it goes between the drain and
          ground. I prefer it where you have it. I will have to think about it.

          Kip



          At 01:57 PM 8/9/04, you wrote:
          >Hi Larry, Kip, tbrenke, Chuck, and list
          >
          >Sorry for my late reply, I was laid up in hospital for a few days last
          >week with food poisoning and haven't had a chance to get back to this.
          >
          >New version at
          >http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif
          >
          >This (hopefully) is an extraction of the appropriate part of the OSMC
          >circuit for driving a solenoid. Do I have the solenoid part hooked into
          >the OSMC circuit correctly?
          >
          >Also, I just re-read Larry's last email, and will probably just use two
          >fets although the diagram above shows three.
          >
          >Cheers,
          >James Fitzsimons
          >
          >On Sun, 2004-08-01 at 07:00, tbrenke@... wrote:
          > > good thinking.
          > > I will keep this in mind also.
          > >
          > > ----- Original Message -----
          > > From: Larry Barello
          > > To: SeattleRobotics@yahoogroups.com
          > > Sent: Saturday, July 31, 2004 4:17 PM
          > > Subject: RE: [SeattleRobotics] Circuit advice
          > >
          > >
          > > The power dissipation rating of a MOSFET is meaningless without
          > knowing what
          > > the heat sink is capable of. It makes NO sense to try to calculate the
          > > current capacity of the device based upon the rated power dissipation!
          > >
          > > It is probably best to design for free-air dissipation. A 4
          > milli-ohm part
          > > will have roughly 6 mohm resistance at max temp of 175C. The TO220
          > package
          > > has about 2 watts dissipation capacity in free air (room temp, device
          > at max
          > > temp). Watts = current * voltage. Voltage = resistance *
          > current. So max
          > > current/device is square root of watts (2)/resistance (.006) or about
          > > 18A/device. All this information is on the typical MOSFET data sheet.
          > >
          > > I suspect the solenoid being used to modulate the NO is not variable, but
          > > rather ON/OFF and the ratio of ON vs OFF at a particular supply pressure,
          > > will inject a variable amount of NO into the manifold. There should
          > be no
          > > need for a table of PWM to flow. The PWM rate is low enough that the
          > valve
          > > follows the PWM, just like the current follows the PWM in a MOSFET.
          > >
          > > Since the solenoid is on for something less than 100% of the time, it is
          > > likely that the AVERAGE current could be used to design the capacity. In
          > > any case two 1404's should be plenty. If you are worried, bolt them to a
          > > small amount of metal to buffer the temperature rise for the few seconds
          > > that the NO is flowing.
          > >
          > > You are not planning on letting it flow for a long time, right? Even
          > at 35A
          > > (stated current rating of the solenoid), James could probably get
          > away with
          > > one FET for 10-20 seconds at a time with no or little metal bolted to the
          > > device.
          > >
          > > I helped design a dual 80A combat robot controller
          > (www.robot-solutions.com
          > > RS80D) which uses 2x1404's in each leg and has a small aluminum block for
          > > heat-sink. It handles 80A just fine for a 4-5 minute match, but, of
          > course,
          > > overheats if you run 30A through it continuously. Actually, it doesn't
          > > overheat since I fold back the drive as the temperature rises and cut
          > it off
          > > completely by 130C. Anyway, the point being that even at 40A/device not
          > > much heat sinking is needed for short periods of time.
          > >
          > > Cheers!
          > >
          > > -----Original Message-----
          > > From: tbrenke@...
          > > ..
          > > mosfet:
          > > the IRF3709Z has an on restance of .0078 at 5V 30V max power
          > disapation
          > > of 79W
          > > TO262 1.87 each at digikey
          > > 2+ are needed because of the 79W rating
          > > the IRF1404 has an on restance of .004 at 5V 40V max power
          > dissipation of
          > > 200W
          > > TO220 2.52 each at digikey
          > > 1 is needed because of the 200W rating can run 5A with heat sink.
          > > 36V / 200W = 5A
          > >
          > >
          > >
          > > Visit the SRS Website at http://www.seattlerobotics.org
          > > Yahoo! Groups Links
          > >
          > >
          > >
          > >
          > >
          > >
          > > [Non-text portions of this message have been removed]
          > >
          > >
          > >
          > > Visit the SRS Website at http://www.seattlerobotics.org
          > > Yahoo! Groups Links
          > >
          > >
          > >
          > >
          >--
          >It's 5.50 a.m.... Do you know where your stack pointer is ?
          >
          >
          >
          >
          >Visit the SRS Website at http://www.seattlerobotics.org
          >Yahoo! Groups Links
          >
          >
          >
          >
        • James Fitzsimons
          Hi Kip, ... Does this look right? http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif ... I have read you need the flywheel diode across the
          Message 4 of 13 , Aug 9, 2004
          • 0 Attachment
            Hi Kip,

            On Mon, 2004-08-09 at 21:12, Kipton Moravec wrote:
            > The snubber is missing, I am not certain you need it, but it is an extra
            > margin of safety. For DC it is across the coil. I would use a 1 W 100
            > Ohm and a 200V or 400V 0.1 MFD poly capacitor.

            Does this look right?
            http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif

            > I am not sure of the 1.5KE51CA. In the OSMB it goes between the drain and
            > ground. I prefer it where you have it. I will have to think about it.

            I have read you need the flywheel diode across the coil of the solenoid
            to allow the current flowing through the coil to dissipate once the
            circuit is "off".

            I really appreciate your help.

            Cheers,
            James Fitzsimons

            --
            It's 5.50 a.m.... Do you know where your stack pointer is ?
          • Andrew Plumb
            On Mon, 09 Aug 2004 23:06:56 +0100, James Fitzsimons ... [deletia] For a fun little variation on this circuit, replace the single flywheel diode with a circuit
            Message 5 of 13 , Aug 9, 2004
            • 0 Attachment
              On Mon, 09 Aug 2004 23:06:56 +0100, James Fitzsimons
              <jamesfit@...> wrote:
              > Hi Kip,
              >
              > On Mon, 2004-08-09 at 21:12, Kipton Moravec wrote:
              > > The snubber is missing, I am not certain you need it, but it is an extra
              > > margin of safety. For DC it is across the coil. I would use a 1 W 100
              > > Ohm and a 200V or 400V 0.1 MFD poly capacitor.
              >
              > Does this look right?
              > http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif
              >
              > > I am not sure of the 1.5KE51CA. In the OSMB it goes between the drain and
              > > ground. I prefer it where you have it. I will have to think about it.
              >
              > I have read you need the flywheel diode across the coil of the solenoid
              > to allow the current flowing through the coil to dissipate once the
              > circuit is "off".
              [deletia]

              For a fun little variation on this circuit, replace the single
              flywheel diode with a circuit to put the back-emf to use. For some
              really simple ideas, have a look at this SunSwinger Solarbotics kit:

              http://www.solarbotics.com/products/index.php?scdfa-250100084-viewDetail-productzq3884zq4categoryzq31=true

              ...specifically pg. 4 of the PDF (pg 6 of the PDf file) linked from
              the kit page:

              http://downloads.solarbotics.net/PDF/SunSwinger_1.0-Apr01-2004.pdf

              Enjoy!

              Andrew.

              --

              If you don't know what to do, do something.
            • tbrenke@verizon.net
              this looks good to me. I guess a build and a smoke test are in order now. keep in mind what was stated by another. about 18A per device for a total of 36A with
              Message 6 of 13 , Aug 9, 2004
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                this looks good to me.
                I guess a build and a smoke test are in order now.

                keep in mind what was stated by another.
                about 18A per device for a total of 36A with fan.

                with what you stated before (low pwm duty cycles) this should not be a problem.



                ----- Original Message -----
                From: James Fitzsimons
                To: srs
                Sent: Monday, August 09, 2004 3:06 PM
                Subject: Re: [SeattleRobotics] Circuit advice


                Hi Kip,

                On Mon, 2004-08-09 at 21:12, Kipton Moravec wrote:
                > The snubber is missing, I am not certain you need it, but it is an extra
                > margin of safety. For DC it is across the coil. I would use a 1 W 100
                > Ohm and a 200V or 400V 0.1 MFD poly capacitor.

                Does this look right?
                http://www.jamesfitzsimons.com/images/ami/temp/solenoid-driver.gif

                > I am not sure of the 1.5KE51CA. In the OSMB it goes between the drain and
                > ground. I prefer it where you have it. I will have to think about it.

                I have read you need the flywheel diode across the coil of the solenoid
                to allow the current flowing through the coil to dissipate once the
                circuit is "off".

                I really appreciate your help.

                Cheers,
                James Fitzsimons

                --
                It's 5.50 a.m.... Do you know where your stack pointer is ?




                Visit the SRS Website at http://www.seattlerobotics.org
                Yahoo! Groups Links






                [Non-text portions of this message have been removed]
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