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Re-hydrating the battery modules.

Discussion in 'Gen 2 Prius Technical Discussion' started by Britprius, May 6, 2015.

  1. tracy ing

    tracy ing Active Member

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    sounds good keep us posted.

    I previously years ago had success in getting h20 into a dead battery using my harbor freight vacuum pump through the relief valve, i only inserted water knowing it would do little and i was right lol
     
  2. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    My research into the NiMH failure modes as it relates to hydration specifically has led evidence that use of NaOH as an augment/replacement to the KOH electrolyte has benefits to the cell electrochemistry in a significant way.
    Have a look at this electrolyte refinement data for NiMH cells:
    upload_2022-6-18_17-29-28.png
     

    Attached Files:

    alftoy likes this.
  3. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Further, I will be employing ultrasonic pulse charging with custom made gear to distribute the NaOH homogeneously and assist the electrode repair as per this analysis:
    upload_2022-6-18_17-36-19.png
     
    T1 Terry and alftoy like this.
  4. T1 Terry

    T1 Terry Active Member

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    Wow, very high tech way to get the cells back into a usable condition, but I'm not knocking it at all.
    How do you plan to flush out the detritus from each cell so it doesn't simply build up in the cavity at the bottom of the cell and end up recirculating through the plates?

    As long as there is an escape for excess electrolyte and a circulation system employed and the return to the storage reservoir was piped to the bottom of the module, it would flush out the detritus .... I just need to double check if the bottom of all the cells is linked, but from memory it is ..... but I'm getting old and memory isn't something I tend to rely on these days :lol: A filter system and an electrolyte cooling system could replace the need for the fan/air cooling or even utilise this area for a liquid to air heat exchanger.

    I like the idea of the plastic fittings replacing the plastic plug screws, easy enough to slip a piece of hose down through a barb fitting at one end of the module to reach the sump and the electrolyte fed in at the other end, the flow would gradually move and detritus to the drain end and be removed from the cell.

    Are you sure the pulse charging would really be needed? The original charge/discharge current the pack suffers during normal operation is quite high, surely that would dislodge any build up if there was a method to wash that build up out of the cell. The problem is dispensing the clean cooled electrolyte across the top of each cell to flush the rubbish out and cool the plates .....

    T1 Terry
     
  5. Rmay635703

    Rmay635703 Senior Member

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    AC pulsation can recombine some dendrite material into the electrolyte
     
  6. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    The cells are like AGM cells, they are not really awash in liquid. Thus the 'detritus' cannot be flushed. If the detritus is very significant then the cell is at end of life anyway and will fail shorted from the build up at the bottom or would have low capacity and not be suitable for re use.
    My understanding is the crystalline KOH forms due to loss of H2O via venting, resulting in increased cell impedance, increased heating and more venting etc. Thus once sufficent H2O is reintroduced and the electrolyte is homogenized via the ultrasonic pulsing and cavitation, the module is cycled 3 times and rerated for decent AH capacity and an internal resistance of sub 10mΩ.

    I am designing for commercial sustainability so once I have ascertained the optimum parameters for module renewal I will document it.
     
  7. tracy ing

    tracy ing Active Member

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    All 6 cells in a module share a common atmosphere channel, if they didn't, they couldn't vent.

    They vent through a pressure relief valve, leaking and disposing of valuable contents that lead to cell damage.

    Why does this vent process even exist

    There is no reason that I can see that all 168 cells cant share a common atmosphere, with one single vent. If 6 can, then why cant 168 ?

    Perhaps the risk of conductivity at a high voltage between modules from one end of the hv pack to another ?

    If there is no conductive issue, a single atmosphere would have stopped many of these issues with the cells. IMO

    Even if there is a HV risk, a common atmosphere between a number of banks could have proven helpful and reduced any conductive issues ?
     
    #367 tracy ing, Jun 21, 2022
    Last edited: Jun 21, 2022
  8. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    I imagine it's safer to handle low voltages cells with a removable circuit breaker stacked in series for serviceability and assembly. So low voltage cells with local vents.
     
  9. tracy ing

    tracy ing Active Member

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    Here is my thinking, using good cells, we will pretend we can get nice new cells
    We drill out the pop off valve
    connect all of them to each other for a common atmosphere
    Place a low pressure relief valve (cause we now have a lot of places for excess pressure to run to in those other cells).
     
  10. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Why go thru all that ?
     
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    This is exactly what crossed my mind a long time ago...

    On a side note, Gen 4 NiMH modules do not have the relief valve/vent. The round fitting is still on the top of the module, but there is no valve inside. Good, fully tested modules are available all day long for $30. How much effort is worth saving 30 bucks..
     
  12. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Well...just swapping out a few modules is not enough to rebuild the HV battery. In fact placing very good modules among mediocre modules will cause the ECU to throw a code. So it is best to rebuild aged packs with modules of reasonably similar capacity and impedance. Thus not only the weakest link causes failure, the strongest link also causes a different failure.
     
  13. tracy ing

    tracy ing Active Member

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    1- to prevent the escape of the gases from the battery system
    2- allow all the cells in all the modules to stay more chemically balanced with the hv pack
     
  14. tracy ing

    tracy ing Active Member

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    correct, i can fill a pack with mediocre cells and run it all day long
     
  15. tracy ing

    tracy ing Active Member

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    quote
    I tested the amount of pressure the modules are likely to operate at. It was found with the modules clamped in a vice the pressure relief valves stick somewhat after a period of non use. The pressure required to open them was 120 psi + or - 5 psi measured with both a mechanical, and an electronic digital gauge. After the initial opening this fell to a constant retest figure of 80 psi. This gives a module sidewall load of 1.7 tons imperial at the lower pressure.

    OK, THERE IS NO WAY THIS ANYWHERE NEAR ACCURATE.

    When I charge the module goes to delta end voltage, it swells, it gases
    To prevent loss of gas I take a Q TIP, place saran wrap around it, place it in the vent hole seated fully down.

    THERE IS NO WAY A Q TIP IS STAYING IN THAT HOLE AT 80 PSI LOL

    If I remove the Q Tip 30 seconds after end of charge, it can gas out for 5 seconds, a LOT OF GASSSING.
    You have to wait for the pack to unswell, 15 minutes or so, to allow the pressure to drop and the vent to close.

    THERE IS NOT ENOUGH VOLUME IN THAT MODULE TO SUPPORT A 5 SECOND GAS AT 80 PSI MUCH LESS 120, NOT TO MENTION THE QTIP WOULD BLOW OUT LIKE A 223 ROUND LOL
     
  16. dolj

    dolj Senior Member

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    It would be great if you could use the quote function correctly so we can see who it is you're quoting.
     
  17. TMR-JWAP

    TMR-JWAP Senior Member

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    Hmmm. Never thought about that. I'll have to look into it. Not sure if I 100% believe it. :rolleyes:
     
    #377 TMR-JWAP, Jun 22, 2022
    Last edited: Jun 22, 2022
  18. tracy ing

    tracy ing Active Member

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    THANKS, NEXT YOU CAN CORRECT MY GRAMMER AND SPELING
     
  19. TMR-JWAP

    TMR-JWAP Senior Member

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    I don't understand why you believe this "swelling" and "unswelling" is acceptable, and you use these in customer's cars?
     
  20. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    So the latest NiMH modules lack a pressure vent?
    That makes for a dangerous situation if an overcharge happens.