Loading ...
Sorry, an error occurred while loading the content.

What are people doing for a high current disconnector?

Expand Messages
  • Lee McLaren
    I am currently rebuilding my controller and have a 80v 40A power supply. I have had problems in the past using large AC contractors to perform the safety
    Message 1 of 14 , Mar 23, 2013
    • 0 Attachment
      I am currently rebuilding my controller and have a 80v 40A power supply.

      I have had problems in the past using large AC contractors to perform the
      safety shut-off, the DC current causes the contractor to stick shut until
      the load drops. It is not the contacts welding but the magnetic field by
      the looks of things.

      Any suggestions? I am looking at automotive starter relays but are
      concerned that with 80v it will arc.

      regards

      Lee


      [Non-text portions of this message have been removed]
    • Tony Smith
      ... safety ... load drops. ... things. ... concerned ... Easiest solution is to add a snubber. It s basically a capacitor & resistor in series with the relay
      Message 2 of 14 , Mar 23, 2013
      • 0 Attachment
        > I am currently rebuilding my controller and have a 80v 40A power supply.
        >
        > I have had problems in the past using large AC contractors to perform the
        safety
        > shut-off, the DC current causes the contractor to stick shut until the
        load drops.
        > It is not the contacts welding but the magnetic field by the looks of
        things.
        >
        > Any suggestions? I am looking at automotive starter relays but are
        concerned
        > that with 80v it will arc.
        >
        > regards
        >
        > Lee


        Easiest solution is to add a snubber.

        It's basically a capacitor & resistor in series with the relay contacts.
        You know in old cars the condensor on the points? Same thing. There are
        formulas to work out the values you need, though they're not all that
        critical in your case.

        Otherwise you can get a contactor, which is essentially a heavy duty relay.

        Tony
      • Tony Smith
        Sorry about the use a contactor brain fade. But anyway relay + snubber may work. Tony ... safety ... load drops. ... things. ... concerned ... Easiest
        Message 3 of 14 , Mar 23, 2013
        • 0 Attachment
          Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
          may work.

          Tony


          > I am currently rebuilding my controller and have a 80v 40A power supply.
          >
          > I have had problems in the past using large AC contractors to perform the
          safety
          > shut-off, the DC current causes the contractor to stick shut until the
          load drops.
          > It is not the contacts welding but the magnetic field by the looks of
          things.
          >
          > Any suggestions? I am looking at automotive starter relays but are
          concerned
          > that with 80v it will arc.
          >
          > regards
          >
          > Lee


          Easiest solution is to add a snubber.

          It's basically a capacitor & resistor in series with the relay contacts.
          You know in old cars the condensor on the points? Same thing. There are
          formulas to work out the values you need, though they're not all that
          critical in your case.

          Otherwise you can get a contactor, which is essentially a heavy duty relay.

          Tony
        • morerust
          Interrupting a high current DC circuit is not a simple job. Arc quenching is the major problem. The currents involved are generally beyond the scale where any
          Message 4 of 14 , Mar 23, 2013
          • 0 Attachment
            Interrupting a high current DC circuit is not a simple job.
            Arc quenching is the major problem. The currents involved
            are generally beyond the scale where any sort of snubber
            is useful. For AC circuits the problem is less because
            the voltage will cross through zero twice for every cycle.
            For DC this does not happen. There are special purpose
            contactors for high current DC but they are expensive.

            Interrupting the primary of the power supply should be
            considered. If the power supply has large filter capacitors
            the output will be sustained for a short time, but if the
            supply is loaded this time delay may be acceptable.

            If you are trying to interrupt the circuit between the
            output of a servo amplifier and DC servo motors, you have
            little choice but to use a proper DC contactor.

            Regards,
            Steve Stallings
            www.PMDX.com


            --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@...> wrote:
            >
            > Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
            > may work.
            >
            > Tony
            >
            >
            > > I am currently rebuilding my controller and have a 80v 40A power supply.
            > >
            > > I have had problems in the past using large AC contractors to perform the
            > safety
            > > shut-off, the DC current causes the contractor to stick shut until the
            > load drops.
            > > It is not the contacts welding but the magnetic field by the looks of
            > things.
            > >
            > > Any suggestions? I am looking at automotive starter relays but are
            > concerned
            > > that with 80v it will arc.
            > >
            > > regards
            > >
            > > Lee
            >
            >
            > Easiest solution is to add a snubber.
            >
            > It's basically a capacitor & resistor in series with the relay contacts.
            > You know in old cars the condensor on the points? Same thing. There are
            > formulas to work out the values you need, though they're not all that
            > critical in your case.
            >
            > Otherwise you can get a contactor, which is essentially a heavy duty relay.
            >
            > Tony
            >
          • Les Newell
            If this contactor is in your power supply you can interrupt the supply before the rectifier or before the transformer. Les
            Message 5 of 14 , Mar 23, 2013
            • 0 Attachment
              If this contactor is in your power supply you can interrupt the supply
              before the rectifier or before the transformer.

              Les

              On 23/03/2013 09:43, Lee McLaren wrote:
              > I am currently rebuilding my controller and have a 80v 40A power supply.
              >
              > I have had problems in the past using large AC contractors to perform the
              > safety shut-off, the DC current causes the contractor to stick shut until
              > the load drops. It is not the contacts welding but the magnetic field by
              > the looks of things.
              >
              > Any suggestions? I am looking at automotive starter relays but are
              > concerned that with 80v it will arc.
              >
              > regards
              >
              > Lee
              >
            • chuck
              Steve, I have always read that you never want to break the connection between the servo amp and motor as it will destroy the Amp but should break the DC power
              Message 6 of 14 , Mar 23, 2013
              • 0 Attachment
                Steve,
                I have always read that you never want to break the connection between the servo amp and motor as it will destroy the Amp but should break the DC power to the amp.
                am I misinformed?
                Chuck

                ----- Original Message -----
                From: morerust
                To: mach1mach2cnc@yahoogroups.com
                Sent: Saturday, March 23, 2013 8:07 AM
                Subject: [mach1mach2cnc] Re: What are people doing for a high current disconnector?





                Interrupting a high current DC circuit is not a simple job.
                Arc quenching is the major problem. The currents involved
                are generally beyond the scale where any sort of snubber
                is useful. For AC circuits the problem is less because
                the voltage will cross through zero twice for every cycle.
                For DC this does not happen. There are special purpose
                contactors for high current DC but they are expensive.

                Interrupting the primary of the power supply should be
                considered. If the power supply has large filter capacitors
                the output will be sustained for a short time, but if the
                supply is loaded this time delay may be acceptable.

                If you are trying to interrupt the circuit between the
                output of a servo amplifier and DC servo motors, you have
                little choice but to use a proper DC contactor.

                Regards,
                Steve Stallings
                www.PMDX.com

                --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@...> wrote:
                >
                > Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
                > may work.
                >
                > Tony
                >
                >
                > > I am currently rebuilding my controller and have a 80v 40A power supply.
                > >
                > > I have had problems in the past using large AC contractors to perform the
                > safety
                > > shut-off, the DC current causes the contractor to stick shut until the
                > load drops.
                > > It is not the contacts welding but the magnetic field by the looks of
                > things.
                > >
                > > Any suggestions? I am looking at automotive starter relays but are
                > concerned
                > > that with 80v it will arc.
                > >
                > > regards
                > >
                > > Lee
                >
                >
                > Easiest solution is to add a snubber.
                >
                > It's basically a capacitor & resistor in series with the relay contacts.
                > You know in old cars the condensor on the points? Same thing. There are
                > formulas to work out the values you need, though they're not all that
                > critical in your case.
                >
                > Otherwise you can get a contactor, which is essentially a heavy duty relay.
                >
                > Tony
                >





                [Non-text portions of this message have been removed]
              • ptegler
                ...something I don t see anyone mentioning is many of the driver modules cannot handle a sudden power removal as the back EMF can over shoot the breakdown
                Message 7 of 14 , Mar 23, 2013
                • 0 Attachment
                  ...something I don't see anyone mentioning is many of the driver modules
                  cannot handle a sudden power removal as the back EMF can over shoot the
                  breakdown voltage of the output drivers. Many have warning right in the
                  literature to NOT place switches between the power supply output and the
                  driver modules.
                  Better to simply relay disconnect the pulse drive to freeze frame any
                  motion, then after, remove power as needed.

                  Paul Tegler
                  ptegler@...
                  www.teglerizer.com
                  ----- Original Message -----
                  From: "morerust" <stevesng@...>
                  To: <mach1mach2cnc@yahoogroups.com>
                  Sent: Saturday, March 23, 2013 8:07 AM
                  Subject: [mach1mach2cnc] Re: What are people doing for a high current
                  disconnector?


                  >
                  >
                  >
                  >
                  >
                  >
                  > Interrupting a high current DC circuit is not a simple job.
                  > Arc quenching is the major problem. The currents involved
                  > are generally beyond the scale where any sort of snubber
                  > is useful. For AC circuits the problem is less because
                  > the voltage will cross through zero twice for every cycle.
                  > For DC this does not happen. There are special purpose
                  > contactors for high current DC but they are expensive.
                  >
                  > Interrupting the primary of the power supply should be
                  > considered. If the power supply has large filter capacitors
                  > the output will be sustained for a short time, but if the
                  > supply is loaded this time delay may be acceptable.
                  >
                  > If you are trying to interrupt the circuit between the
                  > output of a servo amplifier and DC servo motors, you have
                  > little choice but to use a proper DC contactor.
                  >
                  > Regards,
                  > Steve Stallings
                  > www.PMDX.com
                  >
                  >
                  > --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@...>
                  > wrote:
                  >>
                  >> Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
                  >> may work.
                  >>
                  >> Tony
                  >>
                  >>
                  >> > I am currently rebuilding my controller and have a 80v 40A power
                  >> > supply.
                  >> >
                  >> > I have had problems in the past using large AC contractors to perform
                  >> > the
                  >> safety
                  >> > shut-off, the DC current causes the contractor to stick shut until the
                  >> load drops.
                  >> > It is not the contacts welding but the magnetic field by the looks of
                  >> things.
                  >> >
                  >> > Any suggestions? I am looking at automotive starter relays but are
                  >> concerned
                  >> > that with 80v it will arc.
                  >> >
                  >> > regards
                  >> >
                  >> > Lee
                  >>
                  >>
                  >> Easiest solution is to add a snubber.
                  >>
                  >> It's basically a capacitor & resistor in series with the relay contacts.
                  >> You know in old cars the condensor on the points? Same thing. There are
                  >> formulas to work out the values you need, though they're not all that
                  >> critical in your case.
                  >>
                  >> Otherwise you can get a contactor, which is essentially a heavy duty
                  >> relay.
                  >>
                  >> Tony
                  >>
                  >
                  >
                  >
                  >
                  > ------------------------------------
                  >
                  > www.machsupport.com - Web site AccessYahoo! Groups Links
                  >
                  >
                  >
                • morerust
                  It varies and unfortunately you need reliable information from the maker of the servo amplifiers. If you are using amplifiers with unknown requirements, your
                  Message 8 of 14 , Mar 23, 2013
                  • 0 Attachment
                    It varies and unfortunately you need reliable information
                    from the maker of the servo amplifiers. If you are using
                    amplifiers with unknown requirements, your caution is
                    well advised. Industrial servo drivers that are intended
                    for use with external disconnects have internal protection
                    against the high voltage back EMF caused as the contactor
                    opens the circuit.

                    For large (read dangerous) DC brush type servo systems,
                    safety requirements may dictate that there be a backup
                    safety system to stop the servo motor if the driver
                    fails. This is typically a special purpose contactor
                    that disconnects the servo motor from the drive and
                    instead connects it to a high power, low resistance
                    braking resistor. These safety systems are based entirely
                    on electro-mechanical elements because solid state
                    devices were not trusted. Typically they are activated
                    by the "hard" limit switches on the machine travel and
                    by all safety interlocks and emergency stop buttons.

                    Regards,
                    Steve Stallings
                    www.PMDX.com


                    --- In mach1mach2cnc@yahoogroups.com, "chuck" <chuckels@...> wrote:
                    >
                    > Steve,
                    > I have always read that you never want to break the connection between the servo amp and motor as it will destroy the Amp but should break the DC power to the amp.
                    > am I misinformed?
                    > Chuck
                    >
                    > ----- Original Message -----
                    > From: morerust
                    > To: mach1mach2cnc@yahoogroups.com
                    > Sent: Saturday, March 23, 2013 8:07 AM
                    > Subject: [mach1mach2cnc] Re: What are people doing for a high current disconnector?
                    >
                    >
                    >
                    >
                    >
                    > Interrupting a high current DC circuit is not a simple job.
                    > Arc quenching is the major problem. The currents involved
                    > are generally beyond the scale where any sort of snubber
                    > is useful. For AC circuits the problem is less because
                    > the voltage will cross through zero twice for every cycle.
                    > For DC this does not happen. There are special purpose
                    > contactors for high current DC but they are expensive.
                    >
                    > Interrupting the primary of the power supply should be
                    > considered. If the power supply has large filter capacitors
                    > the output will be sustained for a short time, but if the
                    > supply is loaded this time delay may be acceptable.
                    >
                    > If you are trying to interrupt the circuit between the
                    > output of a servo amplifier and DC servo motors, you have
                    > little choice but to use a proper DC contactor.
                    >
                    > Regards,
                    > Steve Stallings
                    > www.PMDX.com
                    >
                    > --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@> wrote:
                    > >
                    > > Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
                    > > may work.
                    > >
                    > > Tony
                    > >
                    > >
                    > > > I am currently rebuilding my controller and have a 80v 40A power supply.
                    > > >
                    > > > I have had problems in the past using large AC contractors to perform the
                    > > safety
                    > > > shut-off, the DC current causes the contractor to stick shut until the
                    > > load drops.
                    > > > It is not the contacts welding but the magnetic field by the looks of
                    > > things.
                    > > >
                    > > > Any suggestions? I am looking at automotive starter relays but are
                    > > concerned
                    > > > that with 80v it will arc.
                    > > >
                    > > > regards
                    > > >
                    > > > Lee
                    > >
                    > >
                    > > Easiest solution is to add a snubber.
                    > >
                    > > It's basically a capacitor & resistor in series with the relay contacts.
                    > > You know in old cars the condensor on the points? Same thing. There are
                    > > formulas to work out the values you need, though they're not all that
                    > > critical in your case.
                    > >
                    > > Otherwise you can get a contactor, which is essentially a heavy duty relay.
                    > >
                    > > Tony
                    > >
                    >
                    >
                    >
                    >
                    >
                    > [Non-text portions of this message have been removed]
                    >
                  • morerust
                    It is worthwhile to note that stepper motor drivers and brushless DC servo motor drivers differ from brush type DC servo motor drivers in that failure of the
                    Message 9 of 14 , Mar 23, 2013
                    • 0 Attachment
                      It is worthwhile to note that stepper motor drivers and
                      brushless DC servo motor drivers differ from brush type
                      DC servo motor drivers in that failure of the output
                      semiconductors will not cause the motor to "run away" in
                      stepper and brushless DC servo systems.


                      For this reason removing the source of the motion
                      commands (step signals or other motion command) is
                      usually considered sufficient for safely stopping
                      a stepper motor or brushless DC servo motor system.

                      Please note that this is about preventing motion, not
                      making the machine safe for playing around with the
                      electrical components. Only a full mains power
                      disconnect switch provides that safety.

                      Regards,
                      Steve Stallings
                      www.PMDX.com


                      --- In mach1mach2cnc@yahoogroups.com, "ptegler" <ptegler@...> wrote:
                      >
                      > ...something I don't see anyone mentioning is many of the driver modules
                      > cannot handle a sudden power removal as the back EMF can over shoot the
                      > breakdown voltage of the output drivers. Many have warning right in the
                      > literature to NOT place switches between the power supply output and the
                      > driver modules.
                      > Better to simply relay disconnect the pulse drive to freeze frame any
                      > motion, then after, remove power as needed.
                      >
                      > Paul Tegler
                      > ptegler@...
                      > www.teglerizer.com
                      > ----- Original Message -----
                      > From: "morerust" <stevesng@...>
                      > To: <mach1mach2cnc@yahoogroups.com>
                      > Sent: Saturday, March 23, 2013 8:07 AM
                      > Subject: [mach1mach2cnc] Re: What are people doing for a high current
                      > disconnector?
                      >
                      >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > > Interrupting a high current DC circuit is not a simple job.
                      > > Arc quenching is the major problem. The currents involved
                      > > are generally beyond the scale where any sort of snubber
                      > > is useful. For AC circuits the problem is less because
                      > > the voltage will cross through zero twice for every cycle.
                      > > For DC this does not happen. There are special purpose
                      > > contactors for high current DC but they are expensive.
                      > >
                      > > Interrupting the primary of the power supply should be
                      > > considered. If the power supply has large filter capacitors
                      > > the output will be sustained for a short time, but if the
                      > > supply is loaded this time delay may be acceptable.
                      > >
                      > > If you are trying to interrupt the circuit between the
                      > > output of a servo amplifier and DC servo motors, you have
                      > > little choice but to use a proper DC contactor.
                      > >
                      > > Regards,
                      > > Steve Stallings
                      > > www.PMDX.com
                      > >
                      > >
                      > > --- In mach1mach2cnc@yahoogroups.com, "Tony Smith" <ajsmith1968@>
                      > > wrote:
                      > >>
                      > >> Sorry about the 'use a contactor' brain fade. But anyway relay + snubber
                      > >> may work.
                      > >>
                      > >> Tony
                      > >>
                      > >>
                      > >> > I am currently rebuilding my controller and have a 80v 40A power
                      > >> > supply.
                      > >> >
                      > >> > I have had problems in the past using large AC contractors to perform
                      > >> > the
                      > >> safety
                      > >> > shut-off, the DC current causes the contractor to stick shut until the
                      > >> load drops.
                      > >> > It is not the contacts welding but the magnetic field by the looks of
                      > >> things.
                      > >> >
                      > >> > Any suggestions? I am looking at automotive starter relays but are
                      > >> concerned
                      > >> > that with 80v it will arc.
                      > >> >
                      > >> > regards
                      > >> >
                      > >> > Lee
                      > >>
                      > >>
                      > >> Easiest solution is to add a snubber.
                      > >>
                      > >> It's basically a capacitor & resistor in series with the relay contacts.
                      > >> You know in old cars the condensor on the points? Same thing. There are
                      > >> formulas to work out the values you need, though they're not all that
                      > >> critical in your case.
                      > >>
                      > >> Otherwise you can get a contactor, which is essentially a heavy duty
                      > >> relay.
                      > >>
                      > >> Tony
                      > >>
                      > >
                      > >
                      > >
                      > >
                      > > ------------------------------------
                      > >
                      > > www.machsupport.com - Web site AccessYahoo! Groups Links
                      > >
                      > >
                      > >
                      >
                    • cnc sales
                      Excellent point. It is also one reason I am using AC brushless drives and motors in my ongoing build of a T&C cutter grinder/surface grinder. The other reason
                      Message 10 of 14 , Mar 23, 2013
                      • 0 Attachment
                        Excellent point.
                        It is also one reason I am using AC brushless drives and motors in my
                        ongoing build of a T&C cutter grinder/surface grinder.
                        The other reason is cost (the AC brushless drives and motors are cheap,
                        relatively)/reliability/noise/value.

                        Its a 7-9 axes fully automatic T&C design, hopefully.
                        About 1/3 of the stuff is here, some of the drives, and the 32 mm
                        ballscrews (11 of) are on the way.
                        I got the 60x30x10 cm surface plate already.

                        I see stopping of signals as sufficient for a safe stop.
                        I plan to have 2 separate systems, the grinder and a parts loader robot.
                        This is how I hope to get the required nr of axes.

                        -hanermo

                        >
                        >
                        > It is worthwhile to note that stepper motor drivers and
                        > brushless DC servo motor drivers differ from brush type
                        > DC servo motor drivers in that failure of the output
                        > semiconductors will not cause the motor to "run away" in
                        > stepper and brushless DC servo systems.
                        >
                        > For this reason removing the source of the motion
                        > commands (step signals or other motion command) is
                        > usually considered sufficient for safely stopping
                        > a stepper motor or brushless DC servo motor system.
                        >
                        >
                        > Regards,
                        > Steve Stallings
                        > www.PMDX.com
                        >

                        --
                        -hanermo



                        [Non-text portions of this message have been removed]
                      • Tony Smith
                        ... beyond ... is less ... I ve seen snubbers in the range he s switching, they re not cheap or easily found though. A better contactor would be the simplest
                        Message 11 of 14 , Mar 23, 2013
                        • 0 Attachment
                          > Interrupting a high current DC circuit is not a simple job.
                          > Arc quenching is the major problem. The currents involved are generally
                          beyond
                          > the scale where any sort of snubber is useful. For AC circuits the problem
                          is less
                          > because the voltage will cross through zero twice for every cycle.
                          > For DC this does not happen. There are special purpose contactors for high
                          > current DC but they are expensive.


                          I've seen snubbers in the range he's switching, they're not cheap or easily
                          found though. A better contactor would be the simplest solution (but still
                          not cheap as you say).

                          Tony
                        • Dave
                          Siemens, ABB, and Allen Bradley make them. Do a search on Ebay for Siemens 3TC which is a popular series of DC power contactors made by Siemens. The trick
                          Message 12 of 14 , Mar 23, 2013
                          • 0 Attachment
                            Siemens, ABB, and Allen Bradley make them.

                            Do a search on Ebay for "Siemens 3TC" which is a popular series of DC
                            power contactors made by Siemens.

                            The trick will be to find one that is small enough for what you want!

                            I got 57 hits.

                            Dave



                            On 3/23/2013 8:56 AM, cnc sales wrote:
                            >
                            > Excellent point.
                            > It is also one reason I am using AC brushless drives and motors in my
                            > ongoing build of a T&C cutter grinder/surface grinder.
                            > The other reason is cost (the AC brushless drives and motors are cheap,
                            > relatively)/reliability/noise/value.
                            >
                            > Its a 7-9 axes fully automatic T&C design, hopefully.
                            > About 1/3 of the stuff is here, some of the drives, and the 32 mm
                            > ballscrews (11 of) are on the way.
                            > I got the 60x30x10 cm surface plate already.
                            >
                            > I see stopping of signals as sufficient for a safe stop.
                            > I plan to have 2 separate systems, the grinder and a parts loader robot.
                            > This is how I hope to get the required nr of axes.
                            >
                            > -hanermo
                            >
                            > >
                            > >
                            > > It is worthwhile to note that stepper motor drivers and
                            > > brushless DC servo motor drivers differ from brush type
                            > > DC servo motor drivers in that failure of the output
                            > > semiconductors will not cause the motor to "run away" in
                            > > stepper and brushless DC servo systems.
                            > >
                            > > For this reason removing the source of the motion
                            > > commands (step signals or other motion command) is
                            > > usually considered sufficient for safely stopping
                            > > a stepper motor or brushless DC servo motor system.
                            > >
                            > >
                            > > Regards,
                            > > Steve Stallings
                            > > www.PMDX.com
                            > >
                            >
                            > --
                            > -hanermo
                            >
                            > [Non-text portions of this message have been removed]
                            >
                            >



                            [Non-text portions of this message have been removed]
                          • John Dammeyer
                            We re using DC Solenoids from the marine industry to shut down our 100A battery charging current at 32V. It s a Blue Sea Systems L-Series PN: 9012 12/24
                            Message 13 of 14 , Mar 23, 2013
                            • 0 Attachment
                              We're using DC Solenoids from the marine industry to shut down our 100A
                              battery charging current at 32V. It's a Blue Sea Systems L-Series PN: 9012
                              12/24 Solenoid switch good for 300A. But looking at the back of the package
                              it says max voltage 60V. It may still work well enough for 80V and only
                              40A.

                              www.bluesea.com

                              Interestingly the web site doesn't list max voltage at all.

                              John Dammeyer



                              -----Original Message-----
                              From: mach1mach2cnc@yahoogroups.com [mailto:mach1mach2cnc@yahoogroups.com]
                              On Behalf Of Lee McLaren
                              Sent: March-23-13 2:43 AM
                              To: mach1mach2cnc@yahoogroups.com
                              Subject: [mach1mach2cnc] What are people doing for a high current
                              disconnector?

                              I am currently rebuilding my controller and have a 80v 40A power supply.

                              I have had problems in the past using large AC contractors to perform the
                              safety shut-off, the DC current causes the contractor to stick shut until
                              the load drops. It is not the contacts welding but the magnetic field by the
                              looks of things.

                              Any suggestions? I am looking at automotive starter relays but are concerned
                              that with 80v it will arc.

                              regards

                              Lee


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



                              ------------------------------------

                              www.machsupport.com - Web site AccessYahoo! Groups Links
                            • Dave Halliday
                              Coming in late to this thread but why don t you use a crowbar instead of a contactor? Put a 40Amp fuse in the circuit and then wire your contactor to place a
                              Message 14 of 14 , Mar 23, 2013
                              • 0 Attachment
                                Coming in late to this thread but why don't you use a crowbar instead of a
                                contactor?

                                Put a 40Amp fuse in the circuit and then wire your contactor to place a
                                direct short across the power supply. The fuse will then blow, stopping the
                                flow of electricity.

                                Dead reliable -- your only problem is replacing the fuses but this is
                                something that shouldn't be tripped that often.

                                Dave

                                > -----Original Message-----
                                > From: mach1mach2cnc@yahoogroups.com
                                > [mailto:mach1mach2cnc@yahoogroups.com] On Behalf Of Lee McLaren
                                > Sent: Saturday, March 23, 2013 02:43
                                > To: mach1mach2cnc@yahoogroups.com
                                > Subject: [mach1mach2cnc] What are people doing for a high
                                > current disconnector?
                                >
                                > I am currently rebuilding my controller and have a 80v 40A
                                > power supply.
                                >
                                > I have had problems in the past using large AC contractors to
                                > perform the
                                > safety shut-off, the DC current causes the contractor to
                                > stick shut until
                                > the load drops. It is not the contacts welding but the
                                > magnetic field by
                                > the looks of things.
                                >
                                > Any suggestions? I am looking at automotive starter relays but are
                                > concerned that with 80v it will arc.
                                >
                                > regards
                                >
                                > Lee
                                >
                                >
                                > [Non-text portions of this message have been removed]
                                >
                                >
                                >
                                > ------------------------------------
                                >
                                > www.machsupport.com - Web site AccessYahoo! Groups Links
                                >
                                >
                                >
                              Your message has been successfully submitted and would be delivered to recipients shortly.