Re-hydrating the battery modules.

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

  1. Britprius

    Britprius Senior Member

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    I have been experimenting with re-hydrating Toyota hybrid battery modules after reading earlier posts by Bob Wilson. The results on 15 year old gen1 modules kindly donated by UK member "Hybridbatt" are remarkable. These modules have recovered capacity from under 2000 mah to 7175 mah with an internal resistance falling from 0.022 down to 0.013 ohms.

    First a word or two on safety the chemicals used to re-hydrate the cells are very corrosive so suitable protection should be worn, and at minimum a large bucket of clean water is at hand to dilute any possible spillage or contact with skin or eyes. It is advised that mixing the chemicals produces lots of heat possibly with fumes dangerous to breath so this should be done outside. The chemicals should be added to water not the other way round. Plastic or steel containers should be used for mixing. Other metals will react with the chemicals, and the chemicals etch glass so this also should be avoided. I used disposable plastic milk containers
    There is plenty of information on the web for handling the chemicals KOH or NaOH so I will not fill this thread further with information.

    The modules were checked for capacity, and internal resistance. They had already been cycled previously at leased 3 times.
    Module 1:- 1950 mah resistance 0.022 ohms.
    Module 2;- 1825 mah resistance 0.022 ohms.

    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.

    The chemicals should be mixed at this point (see the safety paragraph) to allow time to completely dissolve, and also to cool after mixing as this produces plenty of heat.
    I used 2 different chemicals to see what if any difference it made, and partly because in my research more than one article implied a mixture was used in the modules.
    The first chemical is KOH (Potassium hydroxide) mixed by weight 20% KOH to 80% distilled water adding the chemical to the water!!!!
    If KOH cannot be obtained use NaOH (Sodium Hydroxide also know as Caustic Soda or drain cleaner)
    This is mixed in the same proportions, and in the same way as KOH. Again produces lots of heat.
    In my final results no measurable difference was found using either chemical.

    The amount to mix guide:-
    Each module takes about 60 ml depending on how dried out it is. Imperial pints of water (20 fluid ozs) takes
    4 ozs of chemical, and a total of 3 pints will be needed with 12 ozs of chemical to refill 28 modules.
    2 ltrs (3.5 imperial pints) would need 14 ozs of chemical.

    Method.
    Each module will need to be drilled on the top surface near each end with as small a hole as you can inject into. I used a 1 mm drill. The hole will be tapped for a 1.4 mm screw. Any small size can be used that can be tapped using a fine thread such as BSF. Small holes seal more easily. The drill should be fitted in the chuck so that no more than 3/8 of an inch of the drill protrudes from the chuck (see picture).This is so that when you drill through the top of the module the drill does not come into contact with the cell plates shorting them out.

    The positions of the holes are marked on the plan below by the crosses in the circles. You will notice the hole in the left hand end is about 2/3 the way across the module while the one on the right is on the center line. This plan is for gen2 modules. Gen1 are slightly different but the principle is the same. The process exploits the fact that all the cells are joined by a manifold to the pressure relief valve

    Bat1.JPG IMG_20150506_165521[1].jpg

    Lay the module to be filled on it's side preferably on a plastic tray with the offset hole uppermost. Raise the end with the offset hole with a small block about 2 inches off the tray (not critical). With a hypodermic syringe (I used a 20ml version) draw in your mixed chemical and inject steadily into the raised offset hole making sure you do not push the needle to far into the module and touch the cell plates. I found this took about 60 ml before the liquid begins to run out of the hole at the other end. Stop at this point and draw up any spillage with the syringe. Stand the module upright and leave for a few minutes.
    At this point I was going to put the module in a home made vacuum chamber, but found it totally unnecessary.
    You can now fill the next module. After filling that go back to the first one and lay it on it's side again without raising it on a block. Add more chemical through the same hole as before until it appears from the other hole. repeat the mop up with the syringe then stand the module back up.

    At this point I discharged the module down to 6 volts. I then charged the module at 3 amps regulated for
    3 hours at which point it was warm (about 100F). This was then discharged down to 5.4 volts (0.9 volts per cell) at a 5 amp rate. The module was then recharged as before and discharged to 7.2 volts at 5 amps for an internal resistance check then continuing down to 5.4 volts at 5 amps then further discharged down to 3 volts (0.5 volts per cell) at 300 ma. These settings are not critical, but when discharging down to 3 volts keep the current low, and it does take some time. Also charge the module till it gets evenly warm about 100F.
    The module was charged again and checked for capacity being discharged at a 10.5 amp regulated rate and timed down to 6 volts. This gave a capacity of 7175 mah.
    All this can be done without clamping the modules as pressure cannot build with the holes open. A very small amount of fluid may appear at the holes ( about the size of a rain drop) this can be removed with the syringe.

    (Edit) With cell capacity information supplied by member "Royfrontenec in a later post" another 1ml of electrolyte per cell has been added to the modules.This is to bring the fluid between 1 and 2mm above the cell plates. This should be added after the refresh charging to avoid the possibility of fluid being ejected while on charge with the modules open. The method is as follows:-

    Lay the module on it's side on the plastic tray. Lift the edge with the holes drilled in about 1/2 inch. Inject 6ml of electrolyte into the fill hole (the offset hole). lower the raised edge a small amount at a time until fluid appears at the drain hole. Immediately stand the module up. Job done. Seal the holes as below.

    I have sealed the hole with 1.4 mm steel screws as steel is not affected by KOH or NaOH. I have pressure tested the steel screws at 160 psi, and have no leaks. This is double the release pressure of the safety valve on the module, and as high as I was prepared to go with the modules clamped at the sides but no protection around the edges.

    IMG_20150506_184653[1].jpg

    I may replace the steel screws with resin screws bonded in with plumbers plastic pipe weld, but really see no reason to do this.
    Once the work is completed clean the module thoroughly to remove traces of electrolyte.

    I used KOH on one module and NaOH on the other. No measurable difference could be found between them. In some articles researched before starting the work it was said the modules contain a mixture of both chemicals. In theory KOH should have a slightly lower internal resistance because it is more conductive, but it is possible that only the water content of the electrolyte is lost anyway in the ageing process.

    There are bound to be things I have inadvertently left out of this post so if you have questions please ask.

    John (Britprius)
     
    #1 Britprius, May 6, 2015
    Last edited: May 17, 2015
  2. royfrontenac

    royfrontenac Member

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    Hi John - Roy here - read your post and they are very good instructions - do you think the cells could be filled in place in the battery (if someone did not want to remove the battery out of the car)?
     
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi John,

    Thanks very much for providing this excellent write-up of your experiments.

    1. Have you tried just injecting distilled water into a module to see whether that is sufficient?
    2. What is your method to pressurize the module to 120 psi and 160 psi when testing the pressure relief valve and the ability of the screws to seal the two holes drilled per module? How are you able to pressurize at 160 psi if the pressure relief valve opens at 80 psi subsequent to the initial opening?
     
  4. Britprius

    Britprius Senior Member

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    You could refill all the cells with the battery in place but you would have to drill above every cell one hole, and put say 10ml in each.

    John (Britprius)
     
  5. royfrontenac

    royfrontenac Member

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    I understand the problem of filling now. could the vent cannot be used to fill the cells as it is connected to each cell as is it damaged when removed? The vents seem to not do their job as the module gets older. I had a module blow the top of a module. I had just changed a G1 battery to G2 cells and installed it back in the car. I was testing the battery by going up and going up and down a steep hill and observing the battery modules with techstream (my wife was driving I was reading techstream). The battery was delivering 60 amps going up the hill when Iheard a load bang like a gunshot - we drove home (the battery was still working) and when I looked at the battery one of the middle modules had blown its top off. The valve was still in place.
     
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  6. Britprius

    Britprius Senior Member

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    I only had two modules to work with donated by PC member "hybridbatt" so I did not have enough modules to try just using water.
    To pressure test the module after drilling the holes I plugged one hole with a steel screw and used a mini tyre compressor fitted in a jump start pack complete with pressure gauge. The pack came with a needle type adapter for blowing up foot balls (see picture below). This was a tight fit in the hole drilled in the module. It was then just a matter of turning on the compressor and watching the pressure rise. This was only a few seconds perhaps 15 because of the small area above the cell plates.

    IMG_20150506_213324[1].jpg

    John (Britprius)
     
  7. Mendel Leisk

    Mendel Leisk Underfoot

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    Has anyone done this before? Seems a quantum leap in battery maintenance.
     
  8. royfrontenac

    royfrontenac Member

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    Could you rem
    By top of the module I mean the whole top cover of the module came off exposing the top of the plates.
     
  9. Britprius

    Britprius Senior Member

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    The safety valve had obviously stuck closed on that module. This is why in my experiment I only took the pressure up to 160 psi just in case the same happened. You will note in my test the valves did not open initially till 120 psi. Repeatedly after that the pressure released at 80 psi.

    You cannot top up via the safety valve as this sits above only one cell, and only lets pressure out and will not let air or liquid in. The method in my post uses a waterfall principle. When the first cell reaches a level of about half full the liquid flows to the next cell as you keep topping up the first cell. This is why I drilled the fill hole at a slightly higher level, and why I finish with the module horizontal all the cells get to the level of the lower drain hole.

    John (Britprius)
     
  10. royfrontenac

    royfrontenac Member

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    I now understand why you could not do it with the module in place, I have old modules that I may try your method on and see how they work under load. I now have four 2001 prius cars, one for my daughter, one for my wife and one for me plus a spare. The spare car has the back seat out and the battery is exposed so I can remove and replace it to test my conversions from G1 to G2 batteries. Because the batteries are heavy and awkward to get in and out of the trunk I will wait till I do another conversion to try some rehydrated modules under load.( My 75 year old back is going to be 76 in a few days so I have to take care I dont over use it).
     
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  11. Britprius

    Britprius Senior Member

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    To get the pressure up to 160 psi I just plugged the safety release hole.

    John (Britprius)
     
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  12. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Bob Wilson tried to rehydrate the battery modules several years ago but was unsuccessful in resealing the holes that he made. John's breakthrough was to drill very tiny holes, tap the holes, and use fine-threaded screws so that the screws could provide an effective seal.
     
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  13. ChapmanF

    ChapmanF Senior Member

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    I really like these results, thanks! A few things occur to me....
    1. Maybe as a routine step in rehydrating modules, one ought to pressurize every one until the relief valve unsticks and returns to operating at 80 psi (or, if it can't be unstuck, replace that module).
    2. If doing this to Gen 1 modules, they will probably be taken out of batteries that had the terminal-sealing service done. After disassembly and cleaning, they'll have leak-prone terminals again (and the sealant used in the SSC is discontinued). It might be worth some more experimentation to find at what pressure stuff starts to ooze around the terminals, compared the vent relief pressure. (Maybe if the terminals only leak below 120 psi but above 80, making sure the vents work will forestall leaky-terminal problems).
    3. ... does it then become a preventive maintenance item every n years to unscrew all your refill screws, poke in the football inflator and burp the relief valves? :)
    4. Or maybe, all told, are Gen 1 owners still better off to obtain old Gen 2+ modules, and rehydrate those?
    5. I still wonder whether there is some aging-related process that may deteriorate the voltage-sense harness, eventually presenting a fire hazard, so that it might be wise for anyone rehydrating an old battery to at least carefully inspect, or just preemptively replace, that wiring harness at the same time.
    6. Is it possible to rehydrate without removal from the pack, by standing the whole pack at some funky angle? One might then avoid disturbing the terminal seal work on an old Gen 1 pack. (But I guess then you'd miss the chance for thorough cleaning, and might be called back for a P3009 before long.)
    -Chap
     
  14. Britprius

    Britprius Senior Member

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    Yes it would be possible to do rehydrating on a complete battery by standing it on end. The problem is that some electrolyte will spill out when topping up the modules, and it would be difficult to clean the modules to stop leakage currents. If washing with a mild acid would overcome that problem there is no reason why this could not be done.

    John (Britprius)
     
  15. royfrontenac

    royfrontenac Member

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    Roy from canada - John - I just cut off the top of 2 modules, one a Gen1 the other Gen2. Both had tested in the 2000 to 2500 range so I considered them junk or defective. They both looked the same inside - very dry yellow white powder coated the sides of the modules. As John said there is ventilation that connect the cells - there is about a 1/2 in gap between the top of the cover and the battery itself, so short screws are needed 3/8 in would be OK. Both modules seemed identical with the tops off, their is the vent in the 3 rd cell and beside it is the temperature pot in the next cell.
     
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  16. royfrontenac

    royfrontenac Member

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    The vent channel is really the space between the top of the cell and the battery below it is about 1/2 in deep by 1 and 1/4 in long by 1/2 in wide - a very big channel. the vents between the cells are 2 verysmall holes about 1/16 by 1/8 each. This would limit the flow of fluid from one cell to the other as the fluid has to rise in the cell to get to the next cell as the holes from cell to cell are right tight to the top of each cell.
     
  17. royfrontenac

    royfrontenac Member

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    To help you imagine it ---- it is like 6 match boxes glued together with match diameter holes at the very to top of the boxes on each side - fluid has to fill the box to get through the small holes to the next box. Fluid could be added with the module standing up but the small holes limit the rate of flow from cell to cell - when john places the cells on a slant it still takes time for the fluid to pass from cell to cell due to the small holes between cells but the cell does not have to fill up to move to the next cell - if you laid the match boxes on their sides with a slight rise at one end fluid would flow like he says like a waterfall.
     
    #17 royfrontenac, May 6, 2015
    Last edited: May 6, 2015
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  18. royfrontenac

    royfrontenac Member

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    Hi John- drilling 6 holes instead of 2 does not sound like a bad way to go if you wanted to do the work with the battery in the car - make your mixture, inject each cell to the top, let it set for a while - start the car and let it charge. The difference in module voltages at the start would likely give the triangle of death to come up but just keep clearing the code until the module recovers. This would save a lot of work removing the battery from the car and removing the modules. Module would look funny with 6 screws but you could cover them with the black liquid rubber that is sold in department stores as liquid electrical tape.
    Real caution would be required as the connections would be still left on the modules and high voltage would be present while you are doing this even though the orange plug is out. If you disconnected the bus on each end of the module to isolate the module while doing the operation would make it a bit safer. What do you think?


    Roy
     
    #18 royfrontenac, May 6, 2015
    Last edited: May 6, 2015
  19. ChapmanF

    ChapmanF Senior Member

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  20. royfrontenac

    royfrontenac Member

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    I read the article - just like doing the cars air conditioning system - pull a vaccume wait to see if their is a leak - then fill with freon.
    I use a hand operated pump to purge my brake lines when working alone to pull the brake fluid through the lines instead of pumping the brake peddle. Maybe this could be used. I also have a large vaccume pump I use to evacuate my cars air conditioning system after a repair.
    Only 2 holes would be needed if you did it that way.
     
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