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Re-hydrating the battery modules.

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

  1. dolj

    dolj Senior Member

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    That makes sense, I was just about to edit my post to add that's what I'd do if I had the capability. I manually do that starting at 7 V down to 1.75 A (from 2.1 A) and end up at 0.25 A by the 6.7 V mark.
     
  2. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Concerning the sonification and cavitation. I am applying peak charge pulses in excess of 500A over milliseconds to average down to the few amps average charge currents. This creates the cavitation shock wave for bubble formation and collapse as well as decimates incipient dendrites when combined with hot electrolyte & sonic agitation.
     
  3. Ancel Bhagwandeen

    Ancel Bhagwandeen Junior Member

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    Small refinement today:
    Having permitted the cavitation to be observable via the hydration ports, it create a bit of a clean up exercise post regeneration via the sputtering.

    4-40 nylon 'plug' screws have been loosely fitted (no thread tapping) as caps to reduce the out gassing/vapour of the electrolyte. for the current blade process. This won't seal tight.
    Now when nylon is exposed to heat/moisture it will naturally expand, so i expect the process to be self sealing at near end of charge. This is just an operation precaution to limit exposure to hot electrolyte when going commercial.
    After completion/re rating, plastic welding with PP will complete the job.
     
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  4. pasadena_commut

    pasadena_commut Senior Member

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    (pictures removed)
    Anybody have a cross sectional drawing of this valve installed in the module plastic? The pictures don't label which is the inside and which is the outside face, and I'm not familiar enough with this device to know.

    What happens if a needle is pushed straight through the valve from the outside? Will the "X" part close up enough to seal, or will it just leak afterwards? Does that X represent precut flaps which go all the way through, or are they just weak points where the rubber is designed to tear? This assumes that there is not some stiff piece in the way which would thwart the needle entirely.

    Even if injecting water this way does muck up the valve some, perhaps it would be easier to seal a small hole in the valve rubber than a hole in the plastic case? A tiny blob of RTV at the right point might do it, for instance.
     
  5. Panicos

    Panicos Junior Member

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    I remember my teacher many years ago said to add only distilled water in lead acid batteries. No acid needed. I think this would work on nimh batteries as well. Im Trying this after reading these posts.
     
  6. tracy ing

    tracy ing Active Member

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    use de-ionized water











    in the last video the resistance is 9mu should be 6.5 to 7 on a good used module
     
    #426 tracy ing, Aug 29, 2022
    Last edited: Aug 29, 2022
  7. T1 Terry

    T1 Terry Active Member

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    I charged mine to 9v per module, but at a very slow rate, 0.5a which is a little less than 0.1CA. After reading this https://en.globtek.com/nimh-battery-safety-notes#:~:text=As%20a%20fully%20charged%20battery,the%20battery%20begins%20to%20deplete. I believe I should add a 35* thermostat to sense the temp of the discharge electrolyte or simply attached to the outside of the module close to the discharge tube.
    By venting both ends of the cell and attaching small diam tubes to the plastic garden irrigation barb fitting from the local hardware store, a container of electrolyte dribble feeds into the module and the return hose goes partway up the electrolyte container.
    The head pressure of the feed side electrolyte is greater than the return side, so air and gassing will flow out of the return tube and be replaced by the feed tube.

    Determining if the gassing is hydrogen or oxygen being liberated from the electrolyte, or the electrolyte actually reaching boiling point at spots within the cell and turning into steam .... is hard to determine, except by feeling if the module is just warm or actually feels hot.
    A fully charge NiMh cell will hold 1.5v, so 9v across 6 cells in series, it actually requires more than 1.5v per cell to achieve the 1.5v fully charged due to internal resistance within each cell, but averaging out the 1.5v per cell and the electrolyte flow to shift and heat build up, and now adding a temp sense, should help reduce the risk of cell damage, yet fully charge the cell for each load cycle.
     
  8. tracy ing

    tracy ing Active Member

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    determining gas is easy, put it in a balloon, take outside and light a match, if it explodes, its not oxygen

    panasonic, their nimh require at least 1/3 C end of charge to balance the cells
     
  9. OBJUAN

    OBJUAN Member

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    I cored a valve out of a blade yesterday(pics) and milled off the remaining case on one side. I took it out to see if there was visible evidence of why it fails and causes electrolyte to come out the negative post(overpressure). Which spreads across the bus bars, down the sense wires and possibly reaching the ECU connector to short it out... I can try a band saw to cut a cross section if you like.
     

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  10. TMR-JWAP

    TMR-JWAP Senior Member

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    Nice job!
     
  11. ChapmanF

    ChapmanF Senior Member

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    I'm still skeptical about that being what causes issues at the ECU connector ... that's a long way for stuff to wick along an insulated wire.

    If I remember right, from when Bob Wilson was working on batteries, the question wasn't so much "what makes the relief valves fail?" as "did they ever open in the first place?" (except at some pressure above what makes the terminals leak).
     
  12. pasadena_commut

    pasadena_commut Senior Member

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    Nice pics. What is holding these valves in place? From the second picture it sort of looks like there may be a cylindrical rubber sleeve between it and the case. Maybe they just press them in? I was expecting a rigid bottom flange extending beyond the hole, but don't see one.

    If these are just pressed in, perhaps then can be pried out, the battery serviced, and a new valve pressed in. (Probably with some fraction of the cases cracking during the process.)

    Has anybody ever grabbed one of these from the top and pulled or twisted it out? Of course with a face shield, gloves and an apron, as doing this seems very likely to spray electrolyte towards the person doing the extraction.
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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    A new challenge for me!!
     
  14. OBJUAN

    OBJUAN Member

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    I cut the remains of the blade from the valve. Didn't see any glue, might be an ultrasonic welding process.
    If a compressors meter is reasonable, valve didn't open below ~100psi.

    I think I'll just cut the bottom cylinder cup off even with the bottom of the shoulder, band saw cross section might be too destructive.
     

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  15. OBJUAN

    OBJUAN Member

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    If you've stripped the wires coming off the battery terminals, the copper is black all the way back.
    The other is traveling down the outside of the nearer sense wires. If humidity is able to condense and spread the electrolyte on the bus bars, leaking down or through the sense wires is not a big strech...
     
  16. TMR-JWAP

    TMR-JWAP Senior Member

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    If I were to get into rehydrating (but I'm not), I would just drill out the relief, add what I want to add, fill the upper "tube" portion with epoxy and then call it a day....
    The gen 4 modules have the upper "tube" part, but there is no opening (small hole) on the inside like the earlier generations. I've always just gone with the assumption the relief has been eliminated on the Gen 4 modules.
     
  17. OBJUAN

    OBJUAN Member

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    Probably work, tilt the bottom up after filling and level. That will allow the fluid to get through the gas ducting. Might have to vibrate the cell to get the bubbles out of the way so the fluid can travel and level. Then put it upright, worth a shot. Still need to allow these old gens to vent.
     
  18. TMR-JWAP

    TMR-JWAP Senior Member

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    This is an actual question I think about. The Gen 4, 3, 2 modules are effectively identical. If the venting has been "obsoleted" in the Gen 4, do we really need it on the others? Aren't the relief vents mostly stuck shut anyway?
     
  19. pasadena_commut

    pasadena_commut Senior Member

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    Perhaps venting is not entirely absent, just more subtle, in the gen 4? I don't see how they could avoid putting in some form of vent since any NiMH battery overcharged at more than 0.1C is going to make more hydrogen gas than it can catalytically convert back into water. The pressure will build and if it does not vent the cell will deform, crack open, or explode.

    I always thought that NiMH batteries dry out, other than through venting, due to a tiny leakage of water gas through the case or valve. A molecule or two at a time, not as a macroscopic gas or liquid flow. Another possibility though is that in the time that the H2 gas exists inside the cell, before it hits the catalyst, it might instead diffuse into, and then through, the plastic case. Hydrogen gas is notoriously difficult to contain because of the molecule's small size. The O2 could similarly diffuse out, but probably not faster than the H2O molecules since it is heavier and slightly larger in diameter. Also since there is plenty of O2 on the other side to diffuse in the "atmosphere" inside a cell probably has about as much oxygen as the air outside of it. Neither loss process is going to show up in days or even months, but after 15 years these slow losses could be substantial.

    This "slow leakage of gas molecules" is not a new idea, see for instance: https://buffalomanufacturingworks.com/barrier-properties-in-plastics-does-your-product-pass-gas/
     
  20. OBJUAN

    OBJUAN Member

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    They seem to be stuck, over pressure pushes electrolyte out the negative post seam and then corrode the bus bars.
    Does the battery need the pressure to reabsorb what is in the gas under normal conditions?