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Measuring windings

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by DaveWave, Jan 20, 2014.

  1. DaveWave

    DaveWave New Member

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    I'm all un-bolted and I'm getting continuity from the main motor terminal lugs at the back of the motor controller to ground. I'm even getting continuity from the lugs to the aluminum bracket/piece holding the lugs to the back of the controller when the aluminim piece is un-bolted and not touching anything!
    Any technical folks out there that can help/share on the procedure to take motor winding measurements?
     
    #1 DaveWave, Jan 20, 2014
  2. Britprius

    Britprius Senior Member

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    Hi Dave, welcome to PC.
    If you have any conductivity from the three motor connections to ground, the motor is faulty. The cables are screened and the screen is in contact with the end brackets.
    Any ground fault on the HV side will give fault codes. The HV battery on the gen1 is prone to this via battery leakage.
    OP Usnavystg will no doubt come in on this as he has extensive experience with the gen1 Prius.

    John (Britprius)
     
    #2 Britprius, Jan 20, 2014
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I agree, assuming the OP is talking about either MG1 or MG2 within the transaxle.
     
    #3 Patrick Wong, Jan 20, 2014
  4. DaveWave

    DaveWave New Member

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    Brittprius, do you mean shielded? If so, I was guessing that, but you sure as heck don't connect the shield to the conductor! I got continuity from the lugs of the conductor to their aluminum brackets for all three phases which made me think im missing something.
    The car drives, and I'm getting cell mismatch and MG over temp (P0036 or around there), but if it were shorted to ground, I would think the overcurrent protection would have popped/blown or I'd smell something, no?
     
    #4 DaveWave, Jan 20, 2014
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Normally, no part of the high voltage circuit is connected to ground. If a component has a high voltage ground fault, then some part of the component has a path to ground.

    However that would not cause a short unless at least two different components, or different parts of the same component, have a path to ground. In that case you would expect overheating or overcurrent to occur.
     
    #5 Patrick Wong, Jan 20, 2014
  6. DaveWave

    DaveWave New Member

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    Thanks.
    So any ideas about all 3 phases having continuity from the lug to the aluminum piece? (Aluminum piece un-bolted & not touching anything)
     
    #6 DaveWave, Jan 21, 2014
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes. Each phase is connected to the other, so if one phase develops a short to ground, the other phases will also show some resistance to ground (the resistance from one phase to the next is not that large because the wire gauge is fairly thick. If you have an accurate ohmmeter you may be able to measure some small differences as you measure resistance of each of the three MG terminals, to ground.

    The following provides a generic description of an AC three-phase motor. Note how the stator windings are connected together so that if one winding develops a short to ground, the other windings will also show some resistance to ground.
    http://www.nfphampden.com/3phmotor.pdf

    This will give you an idea about how MG1 and MG2 in the transaxle work (as they also are specialized AC three-phase motors.)
     
    #7 Patrick Wong, Jan 21, 2014
  8. DaveWave

    DaveWave New Member

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    Figured it out. The shields are tied in AT the aluminum brackets. (terminals at the controller end to motor, then motor to ground {by short}, then ground to shield at the motor end, then shield to aluminum bracket at the controller end).
     
    #8 DaveWave, Jan 31, 2014
  9. Britprius

    Britprius Senior Member

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    The complete high voltage system in the Prius is what is known as floating. No part of it is grounded. So if you do get a ground fault there is no extra current flow "no burning".
    On the gen2 there is a sensing circuit that prevents use of the car, but I believe on the gen1 this was not fitted. I could be wrong about the gen1 not having this, but no doubt OP Usnavystgc will confirm this.
    Burnt windings on one of the MG's through shorted turns will often ground them.

    John (Britprius)
     
    #9 Britprius, Jan 31, 2014
  10. edthefox5

    edthefox5 Senior Member

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    What did you figure out? Are any of the 3 phase connections shorted to shield or ground which is same thing?
     
    #10 edthefox5, Feb 1, 2014
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