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5913Re: [solectria_ev] Force Battery Pack Supposed to be Isolated from Chassis Ground?

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  • Ken Olum
    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.

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