Re-hydrating the battery modules.

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

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  1. a_triant

    a_triant Member

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    But during the first few cycles with holes open to heat up the modules that may also will boil off some of water and then it will have even less left?

    Maybe better should i fill with John's method and then every cycle i can weight them, that may also will be useful info, first i will weight them before re-hydration, then i will fill them and weight again and again after every input of charge 9200mAh?

    And we still don't know that if with John's method the vent will open quicker
    also we don't know maybe when they are new the plates are covered above with the gel electrolyte

    Also i think after a filing with John's method even if it will vent the half of injected water with some KOH that would be still fine, the member Jeff K that drove 20k miles he injected to he's dried modules only a water without KOH and he did not has any issue, and time by time i can monitor the internal resistance in techstream so if it will vent out a lot of KOH then maybe the resistance will increase.


    Brad, thanks for warning about KOH safety (y)

    Alex.
     
    #161 a_triant, May 29, 2015
    Last edited: May 29, 2015
  2. SageBrush

    SageBrush Senior Member

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    Wonderful thread guys.

    I have only one (perhaps useless) thought to throw out: if KOH deposits are seen in dead cells, it sort of implies that the venting was of water. So perhaps all that is needed is to replace distilled water and let the dry deposits return to solution. On the flip side, if a fairly concentrated KOH solution is used, the concentration may continue to rise as the deposits return to solution.
     
    #162 SageBrush, May 29, 2015
  3. Britprius

    Britprius Senior Member

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    No well intended thoughts are useless. The KOH in a NiMH battery is mainly used as an electrical conductor. If to week a solution is used the resistance of the cell rises, but unlike a lead acid battery if the concentration is increased no harm is done.

    The reason I added some KOH to the water is that under venting conditions particularly near the end of the cells dried out capacity it is possible that some may have been vented. I chose a 20% solution realizing that some water would be used to re-hydrate the existing dry KOH, and so strengthening my 20% solution. However this needs to go to near 80% solution at operating temperatures to begin crystallizing out, and even then there should be no deterioration of the operation of the cell.

    Only adding water risks weakening the electrolyte, and thus increasing cell resistance (not capacity). We may also be adding more fluid than was originally in the cell, and by adding just water again we weaken the mixture.
    Brad is working at one end of the scale (just water in small amounts), and I am perhaps working the other end of the scale. Working on the principle of more is more to dry out taking longer.
    We have a good friendly helpful discussion going with lots of input from others like Alex, and I believe we are all open minded about the best way to go.

    Again I say any constructive input is welcome.

    John
     
    #163 Britprius, May 29, 2015
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  4. royfrontenac

    royfrontenac Active Member

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    Hi John - Roy from Canada reporting on my progress with re-hydrating a complete 38 module battery.

    I have just finished reinstalling the re-hydrated battery after replacing a module that had a reversed cell. I made the mistake of not sealing the cells while charging the battery installed in the car and some solution boiled out of some cells and caused a ground on the battery. Had to remove battery from car again and remove all modules and clean and repaint the metal as the solution ate the painted surface of the enclosure. One last thing I added was to cover all the screw heads that plugged the 6 filling holes in each module with a dab of liquid electrical tape, this made sure there was a good seal, electrically isolated the screws and will stop the screws from working out over time . I did a test run up and down my test hill and found the battery was much stronger in that the voltage drop on going up the hill was less then before re-hydration and the current draw going up the hill went from 60 amps to 69 amps (peddle to the floor in both cases). I am going to repeat and record the test again with techstream as I then will have a before and after re-hydrating comparison. For those that have techstream I may be able to post the before and after recording files that they could run in their techstream software.

    I also bench tested 2 more modules before and after re-hydration. With a 9000mah charge I got 6500mah discharge capacity (round figures) on both modules. Before rehydration I could only get around 5400mah on each module. I will take pictures later showing the re-hydrated battery, the screws and the liquid tape can I used for the final seal.

    Roy
     
    #164 royfrontenac, May 30, 2015
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  5. Britprius

    Britprius Senior Member

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    Thanks for the update Roy. Great to hear of success on a 14 year old battery regaining not only capacity, but a reduction in internal resistance shown by the increase in current able to be drawn. This along with other results proves that modules with low capacity can be restored to near new performance.
    As said in previous post it will not work on reverse charged,open circuit, or shorted cells,but the system gives more chance of a good recovery than balance charging alone.

    It is a pity you had to dismantle and clean the modules after charging with them open installed in the frame. This is something I had envisaged, and commented on in an earlier post even with a battery stood on end. It is also why I recommended washing the module before returning them to the battery. However this is now something people that follow will be more aware of. KOH is a good conductor of electricity, and is partly why it is use in these cells.

    The KOH attacks the plating on the steel frame removing it. It does not damage the steel frame, but leaves it exposed for rust to take hold. This is why I warned against plated screw or any materials other than steel or plastic to seal the holes. Some grades of stainless are ok some are not, (needs more research) but it is often difficult or impossible to find what grade stainless screws are from your local hardware store. My suggestion here is to soak some screws intended for use in KOH solution to see if they react.
    Thank you again for taking the time to give your results.

    John.
     
    #165 Britprius, May 30, 2015
    Last edited: May 30, 2015
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  6. a_triant

    a_triant Member

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    That's a good idea, i can try this right now on one of my screws, since the screws are very small will be enough to add few flakes of KOH(of size like the screw) and some drops of water?
     
    #166 a_triant, May 30, 2015
  7. Britprius

    Britprius Senior Member

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    Yes you can try, but the screws you have should be fine. Be careful you have a reasonable amount of water when adding the KOH. To much KOH in to little water will make it boil violently throwing strong solution out. Add the KOH slowly.

    John
     
    #167 Britprius, May 30, 2015
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  8. a_triant

    a_triant Member

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    Hope that's enough KOH i added, tomorrow will check and update if something changed :)
    the screws i bought through eBay and the material was described as 12.9 grade steel

    IMG_1227.jpg IMG_1229.jpg

    Update:

    a day after, nothing happened to the screw.

    Alex.
     
    #168 a_triant, May 30, 2015
    Last edited: May 31, 2015
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  9. Britprius

    Britprius Senior Member

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    That's enough to check the screws. Did the water get warm when you added the KOH?
    12.9 is the tensile strength of the material, and that is very high.

    John
     
    #169 Britprius, May 30, 2015
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  10. royfrontenac

    royfrontenac Active Member

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    John - these batteries are generation 2 not generation 1 - they came from my friend who rebuilds batteries and were ones that he determined were not good enough for his rebuilding process. I have no idea what the ages of these batteries are as they came from many different gen 2 batteries. I still have 3 - 2001 prius cars with generation one modules that have not been re-hydrated that are running well I will convert them to gen 2 modules as they fail. I have purchased a spare Gen 1 battery box complete with the computer and relay box that I am now going to rebuild with generation 2 modules, this will allow a quick swap so my daughter and my wife will only have a short time without their cars.
     
    #170 royfrontenac, May 30, 2015
  11. a_triant

    a_triant Member

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    #171 a_triant, May 30, 2015
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  12. Britprius

    Britprius Senior Member

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    You can add more KOH, but a little at a time. You should feel the plastic container get warm.

    Johm

    If you tell him you have revived the modules you will not be getting any more.

    John
     
    #172 Britprius, May 30, 2015
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  13. a_triant

    a_triant Member

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    #173 a_triant, May 30, 2015
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  14. royfrontenac

    royfrontenac Active Member

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    I wont probably need anymore - I have 230 Gen 2 modules to work with as well as the the Gen 1 modules (3 x 38) that are in the cars. He is not wanting to re-hydrate at this time but he may try it at a later date.
     
    #174 royfrontenac, May 30, 2015
  15. Britprius

    Britprius Senior Member

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    My mixture was 20% so 400ml would take 80grams of KOH.

    John
     
    #175 Britprius, May 30, 2015
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  16. a_triant

    a_triant Member

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    #176 a_triant, May 30, 2015
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  17. Britprius

    Britprius Senior Member

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    Leave some room in the container for adding the KOH and possible boiling.

    John
     
    #177 Britprius, May 30, 2015
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  18. a_triant

    a_triant Member

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    #178 a_triant, May 30, 2015
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  19. Britprius

    Britprius Senior Member

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    Divide the amount of water by 5. So 350 divided by 5 = 70grams.
    20% is 1/5th

    John
     
    #179 Britprius, May 30, 2015
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  20. a_triant

    a_triant Member

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    #180 a_triant, May 30, 2015
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