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Force Battery Pack Supposed to be Isolated from Chassis Ground?

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  • Quin Garcia
    Hi, I have a 2001 Force with a 156V PbA pack. Today I noticed something alarming: I am able to measure 60VDC across Battery Pack positive and the chassis
    Message 1 of 4 , Nov 1, 2009
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      Hi,

      I have a 2001 Force with a 156V PbA pack.

      Today I noticed something alarming: I am able to measure 60VDC across
      Battery Pack positive and the chassis ground of the vehicle!

      I saw 0VDC across Battery pack negative and chassis ground of the vehicle.
      I saw 4.8Mohm of resistance across Battery pack negative and chassis ground
      of the vehicle.
      I saw infinite resistance across Battery Pack positive and chassis ground of
      the vehicle.

      These findings imply that there is not isolation between Battery Pack
      negative and the vehicle chassis ground.

      Is there supposed to be infinite resistance between the battery pack
      negative and chassis ground?

      If so, any ideas on how this short between battery pack negative and chassis
      ground may be occurring?

      Thanks,
      Quin


      [Non-text portions of this message have been removed]
    • Collin Kidder
      Y-Caps. The motor controller(s) should have y caps in them that are tied to ground. These will make it a shocking experience if you get yourself between them
      Message 2 of 4 , Nov 2, 2009
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        Y-Caps. The motor controller(s) should have y caps in them that are tied
        to ground. These will make it a shocking experience if you get yourself
        between them and the chassis ground. So I suppose the answer is that you
        *sort of* have chassis isolation. I'm sure you don't have a dead short
        or anything.

        On 11/1/2009 11:20 PM, Quin Garcia wrote:
        >
        > Hi,
        >
        > I have a 2001 Force with a 156V PbA pack.
        >
        > Today I noticed something alarming: I am able to measure 60VDC across
        > Battery Pack positive and the chassis ground of the vehicle!
        >
        > I saw 0VDC across Battery pack negative and chassis ground of the vehicle.
        > I saw 4.8Mohm of resistance across Battery pack negative and chassis
        > ground
        > of the vehicle.
        > I saw infinite resistance across Battery Pack positive and chassis
        > ground of
        > the vehicle.
        >
        > These findings imply that there is not isolation between Battery Pack
        > negative and the vehicle chassis ground.
        >
        > Is there supposed to be infinite resistance between the battery pack
        > negative and chassis ground?
        >
        > If so, any ideas on how this short between battery pack negative and
        > chassis
        > ground may be occurring?
        >
        > Thanks,
        > Quin
        >
        > [Non-text portions of this message have been removed]
        >
        >


        --
        -Collin Kidder
        K& K Mfg Inc
        951 9 Mile Rd NW
        Sparta, MI 49345
        616-389-6043 (direct)
        800-876-4286



        [Non-text portions of this message have been removed]
      • Ken Olum
        Quin, you can check very easily if your controller is the problem by unplugging it. You can also distinguish resistive and capacitative leaks by disconnecting
        Message 3 of 4 , Nov 2, 2009
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          Quin, you can check very easily if your controller is the problem by
          unplugging it. You can also distinguish resistive and capacitative
          leaks by disconnecting battery positive from everything else (if your
          car is like my 1998, it's sufficient to disconnect the service
          disconnect, the controller, and the charger output.) Then measure the
          voltage between battery negative and the frame. If there is a
          capacitor, it will slowly decline as the capacitor discharges.

          Then short battery negative to the frame temporarily to discharge any
          capacitors. Then measure the resistance between the frame and battery
          negative. If there is a capacitor, the reading on your ohmmeter will
          slowly go up as the current from the meter charges the capacitor. The
          final value (if not infinity) is the magnitude of the resistive leak.

          Of course you also need to test the equipment you unplugged for leaks
          between the terminals that you disconnected and the frame.

          You can isolate leaks by unplugging things. In my case, the problems
          were the DC/DC converter (capacitative) and the air conditioner motor
          (a resistive leak of several megaohms), and the controller. I fixed
          my DC/DC by removing the filtering circuit connected to the frame.
          See http://autos.groups.yahoo.com/group/solectria_ev/message/5538.
          Perhaps this was unwise: see the subsequent discussion.

          Nevertheless I'm inclined to disconnect my controller capacitors from
          the frame as well. My personal opinion is that the high-voltage
          system should be entirely isolated to decrease the chance of getting a
          shock. People have different philosophies on this. Mine is that a
          dangerous voltage requires 2 connection to hurt you, and so it's
          safest to start with none. Connecting electrical components to the
          case of a device seems to me essentially to be saying that you would
          like the operator, who might be touching the case, to act as part of
          the filtering system.

          To be honest, I have a non-isolated charger (PFC20), so on the one
          hand I'm not living up to my principles, but on the other hand I have
          an even stronger reason not to have ground faults.

          Ken
        • dnqfrommp
          Hi, I forgot to mention that when I took the measurements my controller was unplugged, all the fuses had been removed from the EV fusebox, the charger was
          Message 4 of 4 , Nov 2, 2009
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            Hi,

            I forgot to mention that when I took the measurements my controller was unplugged, all the fuses had been removed from the EV fusebox, the charger was unplugged, the service disconnect was unplugged, and the charger negative wire was unplugged.

            I also did notice some capacitive behavior when I checked across chassis ground and Battery pack main negative.

            Does that change your guys assessment?

            Thanks for the input,
            Quin

            --- In solectria_ev@yahoogroups.com, Ken Olum <kdo@...> wrote:
            >
            > Quin, you can check very easily if your controller is the problem by
            > unplugging it. You can also distinguish resistive and capacitative
            > leaks by disconnecting battery positive from everything else (if your
            > car is like my 1998, it's sufficient to disconnect the service
            > disconnect, the controller, and the charger output.) Then measure the
            > voltage between battery negative and the frame. If there is a
            > capacitor, it will slowly decline as the capacitor discharges.
            >
            > Then short battery negative to the frame temporarily to discharge any
            > capacitors. Then measure the resistance between the frame and battery
            > negative. If there is a capacitor, the reading on your ohmmeter will
            > slowly go up as the current from the meter charges the capacitor. The
            > final value (if not infinity) is the magnitude of the resistive leak.
            >
            > Of course you also need to test the equipment you unplugged for leaks
            > between the terminals that you disconnected and the frame.
            >
            > You can isolate leaks by unplugging things. In my case, the problems
            > were the DC/DC converter (capacitative) and the air conditioner motor
            > (a resistive leak of several megaohms), and the controller. I fixed
            > my DC/DC by removing the filtering circuit connected to the frame.
            > See http://autos.groups.yahoo.com/group/solectria_ev/message/5538.
            > Perhaps this was unwise: see the subsequent discussion.
            >
            > Nevertheless I'm inclined to disconnect my controller capacitors from
            > the frame as well. My personal opinion is that the high-voltage
            > system should be entirely isolated to decrease the chance of getting a
            > shock. People have different philosophies on this. Mine is that a
            > dangerous voltage requires 2 connection to hurt you, and so it's
            > safest to start with none. Connecting electrical components to the
            > case of a device seems to me essentially to be saying that you would
            > like the operator, who might be touching the case, to act as part of
            > the filtering system.
            >
            > To be honest, I have a non-isolated charger (PFC20), so on the one
            > hand I'm not living up to my principles, but on the other hand I have
            > an even stronger reason not to have ground faults.
            >
            > Ken
            >
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