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megohmmeter help

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by flyboy09, Apr 24, 2015.

  1. flyboy09

    flyboy09 Junior Member

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    Instructions for meter say

    2) Test connecting cable

    Connecting cable of E terminal socket of the meter is earthing cable;

    Connecting cable of L terminal socket of the meter is circuit cable;

    Connecting cable of G terminal socket of the meter is shielding cable and connected to surface of the to-be-tested object to prevent surface leakage and affect impedance test.

    Toyota manual says

    1. d) Using a megohmmeter set to 500 V, measure the

      insulation resistance between the positive terminal on the HV battery side of the system main relay and the body ground.
    My question is how do I hook up the 3 leads to do this test when it sounds like the measurement is done with only 2 leads?
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    E to body ground.
    L to the circuit where you are trying to assess insulation resistance to body ground.
    G floating (per Chap's provided link below)
     
    #2 Patrick Wong, Apr 24, 2015
    Last edited: Apr 24, 2015
  3. ChapmanF

    ChapmanF Senior Member

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    A megohmmeter is pretty specialized gear - if you have come into possession of one without training, you'll probably want to read this intro, which does cover when you would want to use the guard terminal and how, along with a bunch of other stuff you'll want to know.

    -Chap
     
  4. ChapmanF

    ChapmanF Senior Member

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    ... btw, after you've read what the guard terminal is for, you'll probably realize that if you connect it and E to the same thing, you leave the instrument with nothing to measure.

    -Chap
     
  5. flyboy09

    flyboy09 Junior Member

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    Not sure i am using the megger right...directions say
    1. (a) Turn the power switch OFF.

    2. (b) Remove the service plug grip (see page 21−116).
    NOTICE:
    Turning the power switch ON (READY) with the service plug grip removed could cause malfunction. Therefore, never turn the power switch ON (READY) in this state

    (c) Disconnect the B12 and B13 battery ECU connectors.

    1. (d) Disconnect the main battery cables from the system main relays.

    2. (e) Using a megohmmeter set to 500 V, measure the insulation resistance between the positive terminal on the HV battery side of the system main relay and the body ground /////test shows nothing on meter.... L to Positive terminal, G and E to body ground...
    (f) Using a megohmmeter set to 500 V, measure the

    insulation resistance between the negative terminal on the HV battery side of the system main relay and the body ground.

    NOTICE:
    Be sure to set the megohmmeter to 500 V when performing this test. Using a setting higher than 500 V can result in damage to the component being inspected.

    Standard resistance: 10 MΩ or higher

    Test on negative terminal shows greater than 10Mohm.....L lead to negative terminal G and E to body ground.
     
  6. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Be very careful.

    We used to use 'meggers' a lot in the canoe club.
    Sometimes even for their intended purpose..... :D

    Used improperly, they can easily damage electronics.

    Good Luck!
     
  7. ChapmanF

    ChapmanF Senior Member

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    Did you read about the purpose and use of the G terminal in the reference I linked?

    If you connect it to the same point as the E terminal, magically you will never find any problem with anything. :)

    -Chap
     
  8. ChapmanF

    ChapmanF Senior Member

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    What do you use a megger for on a canoe?

    -Chap
     
  9. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Wakeup incentive for a tardy watch relief.....
     
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  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Let G float unused, and see if there is any difference in the results. Chap provided an excellent reference.

    Since you are measuring resistance of the system main relays, hopefully you will find a very high resistance value.

    Remember that the traction battery must be disconnected from the relays prior to doing this measurement on the relays.

    Perhaps we should step back for a minute and ask, what is prompting you to measure resistance of the system main relays? If there is a problem with those components, it should be visible via visual inspection - for example, if there are burn marks showing high voltage arcing.

    The megger test would be very useful on the transaxle and inverter, to assess whether those components have high voltage ground faults.
     
    #10 Patrick Wong, Apr 24, 2015
    Last edited: Apr 24, 2015
  11. flyboy09

    flyboy09 Junior Member

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    i was just trying to follow the checks for a poaa6, 526, 612 code with mini vci...there is some corrosion underneath the hv batteries...unable to determine the source of the acid. not sure what to do next. IMG_3309.JPG
     
  12. SageBrush

    SageBrush Senior Member

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    IIRC, "Canoe" is ETc's slang for a naval submarine.
     
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The most likely source of the corrosion is the electrolyte from one or more battery modules. Your photo shows a stain below one of the modules - what does that module look like?

    The electrolyte may not be easy to see but should cause corrosion of the metal parts of the leaking module. The electrolyte is potassium hydroxide which is alkaline, not acid.

    By now you probably know that P0AA6 points to a high voltage ground fault. 526 is a general info code and can be ignored. 612 is the info code of significance, and points to one or more of the following:

    HV battery assembly
    Battery ECU
    System main relay
    System main resistor
    Main battery cable
    Main battery cable No. 2
    Battery plug
    Frame wire No. 2
    Junction block assembly

    Since you have obvious corrosion in the traction battery case which most likely came from a leaking module, that is also the most likely source of the high voltage ground fault. If you jump to step 14 (Inspect HV Battery Assembly) in the factory repair manual troubleshooting tree, that step has you measuring resistance from each module's positive and negative battery terminals to the traction battery case, after the busbars have been removed. That is the step which is most likely to yield a failure, which of course is what you are seeking.

    I recommend you identify the failed module(s) and replace them at minimum, removing all 28 modules so that you can clean out the traction battery case bottom. Make sure the modules you reinstall are totally clean and have no electrolyte leaks, prior to reinstallation. The least amount of voltage leakage from a module to the sheet metal case will result in the P0AA6 code being triggered.

    Ideally, replace the entire traction battery case and 28 modules, if you can afford that move.

    Since you have the megger available to you, please report the measurements that you take at the system main relays, using just the L and E test leads.

    I guess this means you are using the megger to measure the skin resistance of the tardy person in question? 500V (although at very low amperage) probably would get that person's attention.
     
    #13 Patrick Wong, Apr 25, 2015
    Last edited: Apr 25, 2015
  14. flyboy09

    flyboy09 Junior Member

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    with the 2 batteries in question positioned on the frame...a volt meter registers voltage from the plus and minus sides to the battery frame. all the other batteries register zero voltage to the battery frame...The Megger won... i don't think i can make it work.
     
  15. Patrick Wong

    Patrick Wong DIY Enthusiast

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    What happens if you use just the megger's L and E test leads to measure resistance? It seems like you were able to measure a reasonable value back in your post #5, when measuring the negative terminal.
     
  16. flyboy09

    flyboy09 Junior Member

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    most of the time it registers nothing but a 1...the last time i tried it sort of ran away with values then went back to 1. should i paint the battery frame after i scotch bright the corrosion off?
     
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Regarding painting the bottom of the battery case - isn't it just bare metal right now? I would leave it as-is after removing as much of the corrosion as you can. The Toyota repair manual recommends use of saturated boric acid to neutralize the alkaline electrolyte.

    So if the megger is not working for you, replace the leaking modules, make sure the adjacent modules are totally free of electrolyte from the leaking modules, clean up the battery case, reassemble the battery, and reinstall in the car to see what DTC if any are logged. Hopefully that will take care of the problem.

    If you note any corrosion problems with the orange bus bars or the battery cables that connect to the system main relays, this is the time to replace any questionable parts. Those parts need to be perfect. The voltage sense wires that connect module pairs to the traction battery ECU tend to be fragile and can easily break if exposed to electrolyte.
     
    #17 Patrick Wong, Apr 25, 2015
    Last edited: Apr 25, 2015
  18. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    I have repaired dozens of batteries. Your case is the most corroded I have seen. As Patrick said, the electrolyte is alkaline, not acid. Vinegar might be a good idea for cleaning. A weak acid will help neutralize the alkaline electrolyte.

    You really need to clean all of your battery modules. Like kitchen dishes clean:). Spotless:cautious:. A little electrolyte and a little dirt is all it takes. I mean stuff so small you can hardly see it. Did your battery look like the inside of a vacuum cleaner the first time you took it apart? I have used a bucket full of soapy water and a rag. Submersing the separate modules will not hurt them. Let them dry in the sun. Before washing use a standard ohm meter with a 200M ohm setting. Measure between each terminal and several places on the plastic battery module case. Any continuity reading is too much.

    It is possible that your suspected modules got electrolyte on them from the modules you already replaced. If you have more time than money then clean everything and put it back together. See if the codes come back. I think you used dielectric grease on the buss bars. Clean that off to. Dielectric grease is not conductive but dirty dielectric grease could be.

    Remove the one 10mm nut holding the white plastic end piece of the compression fixture. Unplug the temp sensors from the ECU. Unplug the line to the inductive amp counter. Then you can remove the entire compression fixture from the battery case. It will be much easier to clean up the case with that out of the way. The easy way to reassemble is to put the modules in the compression tubes without the case. Then flip the modules upside down, install the temp sensors, and then set the bottom of the case on top of the modules. Install the module mounting bolts and then flip the whole thing right side up.

    Good Luck,
    Brad
     
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  19. flyboy09

    flyboy09 Junior Member

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    Question Brad, Won't the soapy water get inside the battery vents?... i suspect the the grid charger had something to do with this...i must be doing something wrong with the charge/discharge sequence.
     
  20. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    Water can not get inside the batteries through the vents. It can puddle up in the vent hole. Shake the water off the batteries and let them dry in the sun.