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HV voltage when service plug is removed

Discussion in 'Gen 2 Prius Technical Discussion' started by cgates30, Nov 12, 2013.

  1. cgates30

    cgates30 Junior Member

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    I apparently have a dead HV battery on a 2006 with 151k miles. Don't have the code right now but it corresponded to unbalanced hv battery pack, had the red triangle, check engine light, etc.

    I pulled the service plug and the cover off of the hv pack and measured voltage. I was under the impression that when the plug is pulled that there will be no voltage across the battery side leads, but I measured 177 volts. The car side was 0 volts. I then put the service plug back in and measured voltage again and it was 216 volts (battery side) and 0 volts on the car side.

    Does this sound fishy? Why would I measure something above 0 volts with the service plug removed? I thought its purpose was to isolate anything on the outside of pack from high voltage? Is there a clue here that maybe something other than the hv battery is not working?

    Thanks
     
    #1 cgates30, Nov 12, 2013
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    That is a clue that the traction battery has a high voltage ground fault. Probably at least one module has an electrolyte leak to the battery case, which results in your being able to measure voltage even when the orange safety interlock is removed.
     
    #2 Patrick Wong, Nov 12, 2013
  3. cgates30

    cgates30 Junior Member

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    Okay, that's something to look for. If the orange interlock is removed, does the potential for high current to flow exist in this situation?
     
    #3 cgates30, Nov 12, 2013
  4. vincent1449p

    vincent1449p Active Member

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    Hi cgates30,

    Pulling out the service plug merely separate the pack into 2 portions:
    HV Battery Assembly.jpg

    High voltages are still present depending on where you take the measurements. I assume your car side refers to (B) and battery side refers to (A). Your measurement of 177V is not a valid value since the other end is not grounded. If you measure (A) to the service plug connector, you should get about 216/14 * 5 = 77V. If there are leakages to the ground on any of the 5 blocks, 10 ~ 14, you should get some voltage lower than 77V, not 177V.

    To isolate anything on the outside of pack from high voltage is the job of SMR (System Main Relay).

    Until you removed 1 side of the busbar, be sure to wear high voltage insulation gloves at all time when working on the HV system.

    Vincent
     
    #4 vincent1449p, Nov 12, 2013
  5. cgates30

    cgates30 Junior Member

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    I've measured cell voltage on all 28 cells (1-28, 1 being closed to the ECU/service safety plug):
    7.51 *
    7.64
    7.67
    7.66
    7.67
    7.69
    7.66
    7.66
    6.79 **
    7.67
    7.66
    7.67
    7.67
    7.65
    7.67
    7.67
    7.68
    7.67
    7.66
    7.67
    7.67
    7.67
    7.66
    7.67
    7.66
    7.68
    6.38 **
    7.58 *

    Obviously numbers 9 and 27 have strayed from the flock. It looks like 1 and 28 are falling, but should they recover if I discharge/charge cycle 3 times?

    Regarding a previous post, when I pull the service plug and measure voltage on the terminals I am still seeing 166 V on the battery side of the contactor. (between the green circles in the photo below, sorry I borrowed this photo from someone else). I may be misunderstanding, but I was under the impression the service plug interrupts this circuit. I have not measured from either post (green circles) to the service plug. contactor.jpg
     
    #5 cgates30, Nov 14, 2013
  6. Britprius

    Britprius Senior Member

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    The problem with using most digital volt meters is that the draw so little current any leakage "particularly on high voltages" will give readings. A 10k ohm resistor between the measuring probes will give a more realistic measurement. Or measure with a old style analog meter.

    John (Britprius)
     
    #6 Britprius, Nov 14, 2013
    Ken Klimkowski and usnavystgc like this.
  7. cgates30

    cgates30 Junior Member

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    I put a 10K (brown, black, orange, gold) resistor between one lead of the meter and one post on the contactor and connected directly from meter to the other post. I'm still getting a high voltage (144V. originally it was 177, then 166, now 144...). Meter is an HP E2378A multimeter. I guess it is a little old, but has compared well to other meters in the past.
     
    #7 cgates30, Nov 14, 2013
  8. Britprius

    Britprius Senior Member

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    Sorry I did not make it clearer in my post. The resistor does not go in series with the meter but across or between the two meter probes in parallel with the meter. This act as a very small load on the voltage being measured.

    John (Britprius)
     
    #8 Britprius, Nov 15, 2013
    cgates30 likes this.
  9. cgates30

    cgates30 Junior Member

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    Yeah, that did it. Thanks for the suggestion.
     
    #9 cgates30, Nov 15, 2013
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