Re-hydrating the battery modules.

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

  1. Mendel Leisk

    Mendel Leisk Sand Pounder

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    The above are potassium hydroxide and sodium hydroxide respectively? Excuse me, swear I didn't google it, just wanna test my battered old brain cells.

    Also, what would happen if the cells could vent freely, say via a pin hole, they'd quickly dry out?
     
  2. Britprius

    Britprius Senior Member

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    The 10 to 30% range is a bit wide or vague. I based my solution on a 20% solution in 80% water. In theory the mix listed could be a minimum of 20% chemical to a maximum of 60% chemical.
    Looking at the data sheet (click on data sheet then click on COSSH sheet) brings up the detail. I can find no mention of potassium hydroxide (KOH) or sodium hydroxide NaOH.
    Where did you see these mentioned.

    Check Boots Chemists (Drain cleaner)

    John
     
    #102 Britprius, May 13, 2015
    Last edited: May 13, 2015
  3. royfrontenac

    royfrontenac Member

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    John the red pads are very thin O,13 mm thick and appear to be a type of plastic tape that runs around the battery - I pulled a piece off to measure it.

    Roy
     
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  4. nh7o

    nh7o Off grid since 1980

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    I drilled and filled a couple of 2004 GenII modules, which had 200K miles on them. They were low in capacity, based on Techstream, but I don't have the charger to accurately check them. Once one gets setup, it take less than 10 minutes to do one module. It went much as John describes in the first post, with each module taking close to 60ml, maybe a bit less. I used a 1/16" (1.6mm) drill. Both were bone dry initially.

    I popped the relief valves without issue. I found that they released around 110psi (7.6 bar), or maybe a little less, using my shop air compressor with a not terribly accurate gauge. I clamped the modules in a vice with wood blocks which completely covered the faces.

    My level checking setup is shown in the picture. I used a high value resistor (1Meg ohm seems to work, less is OK) across the DVM leads. The negative voltmeter lead goes to the negative of the module. The positive lead goes to a small gauge solid wire, whatever can fit in the holes. The insulation is left on the wire, so that only the cut end of the copper comes in contact with the electrolyte. The wire is pushed into the hole and the voltmeter will show a sudden increase in reading as the fluid is contacted. It seems that I ended up with just a few millimeters of fluid above the plates. However, I am thinking that level will change as the battery charges and rehydrates completely. So I will keep checking as I go. They are charging, with the drill holes open for now.

    I was thinking, as I mixed the KOH, that John's suggested concentration seemed high. Over time, if a large amount of KOH was actually expelled from the module, there would be evidence of white powder in the vent tubes, and rather more corrosion than what is seen. Surely some electrolyte is expelled, judging by the green interconnects that are typically seen in older batteries, and we can only guess at this point, but I think that it is mainly water that is lost. I ended up using half of the concentration of KOH that John suggested, just to see what happens. I got my KOH from Essential Depot: Sodium Hydroxide, Lye, Potassium Hydroxide, Argan Oil, Shea Butter, Essential Oil, Fragrance Oil, Vegetable Oils, Food Grade

    Question: is there a possible problem with excess KOH concentration?
     

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    #104 nh7o, May 14, 2015
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  5. Britprius

    Britprius Senior Member

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    Thank you Roy. I cold see it in your pictures but could not see it's purpose or thickness.

    John

    The concentration of KOH to water by weight to achieve a fully saturated solution at 20C is 83 grms KOH to 100 grms water or 83%
    The concentration I am suggesting is well below this figure.
    There are pro's and con's to different strengths as the electrolyte is basically used as a conductor in NiMH cells. This means to weak a solution will raise internal resistance, and to strong a solution crystals forming as the water dries out. In my opinion at some point crystals are going to form anyway as the cells dry. This is confirmed by the white powdery deposits found in opened modules. My concentration will have to loose more than 75% of it's water before it becomes saturated at 20C. However once drilled and sealed with screws the module can have it's level checked at any time, and water added if needed. Adding water would require at minimum the battery being removed and stood on end.
    It would be reasonable to assume checking the levels of the modules near the middle of the battery "the warmest in use" would give a good indication of the need to top up or not say initially after the first year to get a base line then perhaps every two years.
    I base my concentration on a number of things, but primarily on the basis of keeping down the internal resistance. This reduces voltage drop within the cells, and also reduces heating within the cells "one of the reasons why cells dry out".
    I am totally aware I could be wrong on this, but this seems in my opinion to be the better of the two evils. I am totally open to being proved wrong.
    After "popping" the relief valves at what pressure did they then open? I like the level checking system.:)

    John
     
    #105 Britprius, May 14, 2015
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  6. nh7o

    nh7o Off grid since 1980

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    I will recheck but it was definitely less than the initial, much as you found. First time there was a "psshhhh" sound, second time was just "ssshhhh" without the percussive start.

    OK on your reasoning about the KOH concentration. I would be curious to know what the factory fill level and concentration is, but I doubt anyone is going to drill a new module to find out. Do new modules make a sloshing sound when shaken?
     
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  7. 2009Prius

    2009Prius A Wimpy DIYer

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    If water is evaporated slowly off the battery and KOH or whatever solute deposits on the inside wall in powder form, then I would just add pure water to re-dissolve the powder.
     
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  8. a_triant

    a_triant Member

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    I remember when i charged/discharged all my modules to measure the capacity, the last one was about 4Ah i inputed charge to it over 9Ah(like in all other modules) at low rate charge 0.7Ah, then almost immediately started disassembling the modules from battery pack and that last module started little swelling and making little sound like "shhshhshh" :).

    At assembly process i shaken some modules and like i heard some sounds, but i did not pay much attention to it, now when will start the re-hydration process i will try again, i have 40 modules at different capacity, from 5Ah to 1Ah.

    I wonder if the "valve unstick" procedure is necessarily during re-hydration process? i think maybe when the water will be injected it will wet the dried valve and will soften it and then it will open normally during operation in the car?
     
  9. Britprius

    Britprius Senior Member

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    Releasing the safety valve is not required to get the module back to capacity. It is desirable from a safety point of view. A cheap 12 volt tyre compressor is the easy way but even a foot pump would do the job as the amount of air space in a module is very small.

    John
    While in principle I agree with your statement. If the cells were originally filled in the same way as AGM batteries are "for wan't of a better analogy" the so called starved method filling with water to the top of the plates or slightly over would be more than double the original content seriously weakening or diluting the contents lowering the internal resistance.
    If someone tries this, and the results show high resistance "this wold limit the current output causing battery heating" the mixture content could be increased later. This would require removal of the battery from the car again.

    John.
     
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  10. royfrontenac

    royfrontenac Member

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    Roy from Canada here :


    Thanks to strawbrad who referred us to a this post by Jeff K - this man did his experiment with boiling water and reported 2 years and 20000miles later, it reads as follows -----


    "Hi Forumites! Recently I acquired a 2001 Prius for $1200. I own a 2008 and a couple of EV's so I figured I could bring this Prius back to being a usable daily driver. I was told by the previous owner that the car got a new battery not long ago. Be that as it may, I was soon finding out through codes that I had a few HV battery issues. First, there was one block giving code 3028. This means they are weak or some such. Armed with info from here, I tore into the pack.

    I found it to be a 2007 replacement! I got a couple "good" modules from the Bay of E and installed them. The symptoms of fan blower coming on, brake light and racing engine occasionally went away and I was happy. But still the error lights came up! So I had the car scanned by a competent individual. The pack showed low capacity and to make matters worse, the block of two modules I replaced were WORSE than mine! But now I was really mad.

    Why would the pack from 2007 (well after all the leaking KOH nonsense was sorted out) still fail in just a few years? My theory was heat because the car lived near Death Valley! What more brutal test of a battery, huh? So basically the moisture in the cells simply dries up. It happens in many battery chemistries.

    Now I should say not only am I cheap--I am creative. I thought about putting in Gen 2 modules but thought matching the two from different cars would be a pain. I certainly did not want to spend actual money on a new pack or even a Re-Involt. My mileage was telling the story. The car could barely do 29MPG in the city!

    I decided with nothing to lose, I would try reviving my pack. I looked over Bob and other's great info here and other places on the web and came up with my own approach which I now share here...

    Because each module has 6 cells, I wanted to be able to attack them individually and not have to take the modules out or be baking them and stuff like that. Here is the basic method:

    Small holes are drilled above each well. Boiling distilled water is injected via syringe--30ml each. The boiling water makes the grids or plates more likely to wick up some water. Panasonic used a gel originally but "re-gelling" them would be impossible...

    Stainless steel screws are "self-threaded" right into the case after the water is insjected. I wanted to use some o-rings but got lazy. The screws can be opened in the future should you go to Death Valley once more. As Bob notes, The dissimilar plastic screw interface may leak vapors. But between the main vent opening and the fact that these batteries should not vent under normal conditions, I did not make any big deal over it. I did test melting chunks of a junk case into the holes with a simple soldering iron and it works great but is time consuming. May be the way to go if you are worried about leaks.

    Now the real-world data: I have a battery analyzer and used it to come up with the water amount and test a few loose modules. As Bob notes, you need to do several charge discharge cycles to get capacity back. I started by seeing 2.5AH and in the end around 6AH before I decided things were going well and I started drilling holes in the modules of the car.
    After the pack was rehydrated and I had been driving it around a bunch I found the mileage going back up to the normal Prius expected range. Today, I drove it about 10 miles city driving and it stayed at about 42.5MPG. I will update here with the ongoing results...

    I invited the competent individual to scan the car again and repeat the battery tests. The HV battery now tests within usable range as far as capacity. ...For how long? That I don't know but things look great so far for my $4 screw investment and the gobs of time drilling and filling. Sadly, I still have an HV leak (not in the battery) that may be the dreaded MG2. I am resolved to grinning and driving with much better mileage and not looking at the error lights. I doubt I can stand that very long and soon will be drilling holes in the MG 2!

    Jeff K."

    He posted again 2 years later

    "Thought someone would want to know... Car is still working fine, no codes, no issues (other than people like to crash into it!). Approximately 20,000 miles on rehydrated pack as of today! I'd say it worked. Jeff"


    What do you think - he used 30 ml of water???

    Gen 1 Battery Rehydrating Experiment Results | PriusChat
     
    #110 royfrontenac, May 15, 2015
    Last edited: May 15, 2015
  11. Britprius

    Britprius Senior Member

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    Hi Roy.
    To add 30 ml of water per cell seems a lot. I added 60 ml or just under for the module in the initial experiment, and after reading your findings on levels checked and adjusted the quantity added to bring the level about 2 mm above the plates. This only took another 6 ml so 66 ml in total for 6 modules. This works out at 11 ml per cell
    This is in line with your findings.
    I am sure there wold not be enough room to add another 19 ml or if there was the cells would be full to the top. Filling the cells with water would not affect there electrical capacity, but would increase there resistance.
    However all the modules being treated in the same way would have within reason the same resistance, and voltage drop characteristics. All higher. This may be enough to keep the ECU happy particularly as the battery current in the gen1 at 273.6 volts would be lower than in a gen2 at 201.6 volts for the same power output.
    Gen1 at 273.6 volts = 3.65 amps per kw.
    Gen2 at 201.6 volts = 4.96 amps per kw.
    The fact that the system seems to work bodes well.

    John

    In the light shed on the module liquid capacity kindly supplied by Roy I am editing my first post to update the quantity of fluid added. An extra (1ml per cell) and the method to maintain equal amounts in the cells.

    John
     
    #111 Britprius, May 15, 2015
    Last edited by a moderator: May 18, 2015
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  12. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    I suggest that what Jeff K meant was he used 30 ml per module. A careful reading of his post shows he did not specify 30 ml per cell or module.

    I had some time today for experimenting and cut the top off a Gen I module. Then I used a digital scale to weigh the module dry, with the plates covered, cells full, and finally with the water shaken back out after the plates had 30 minutes to absorb what they could. The weight gain with the plates covered was 53 grams, full 75 grams, and just the plates absorbing what they could hold 9 grams. It is interesting that the absorbed weight gain matches the number mentioned in the patent. Even a dumb Merican can convert grams of water to ml.:sneaky: So I came up with 53 ml to cover the plates, 75 ml of total free air space, and the plates can absorb 9 ml. These numbers are in agreement with what you and others have measured.

    I cut just the very top of the module off. I had to clean up and finish the cut with a file to reveal the inside of the module. I could not find the vent holes between the cells. I might have cut through them if they are at the very top of the cells. I can fill one cell full and it does not drain to the others. The module I opened had one bad cell that measured .06 volts. On a 6.5 amp charge it took just 27 seconds for that cell to reach 1.5 volts. So I learned something today. Watch for a rapid voltage rise in the first half minute of charging. That would be an indication of a dead cell with little capacity. I charged the module at 6.5 amps with just the 9 ml of water the plates held on to. The dead cell started to gas right away so added enough water to cover its plates. The bad cell bubbled away like a slow boil. The other cells started to gas at about 1.45 volts. It is cool to see inside a module charging. I stopped the charge at 3000 mAh. On discharge the bad cell had just 85 mAh before going in to reversal. I continued the discharge on the other 5 cells for about 2500 mAh. The 5 cells are now on a cycle charge and discharge for the night.

    Brad DSC00067.JPG DSC00070.JPG DSC00065.JPG DSC00074.JPG DSC00077.JPG
     
  13. Britprius

    Britprius Senior Member

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    In the post it clearly states
    "Quote" Small holes are drilled above each well. (possible typo perhaps should read cell, but could be referring to cell area above plates) Boiling distilled water is injectedvia syringe--30ml each.
    You could read that as each well, cell, or hole, but not module.

    John
     
  14. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    John,
    I just measured the free air space capacity of a module at 53 ml to cover the plates and 75 ml to the top of the cells. Per cell this is 8.8 ml to cover the plates and 12.5 ml to the top. Roy measured 7.5 ml to cover the plates and 10.5 to close to the top. His last measurements where done after the plates had already absorbed what they could. Our results are close enough to be in agreement. John K did not put 30 ml of water into a cell with a capacity of 12.5 ml. He could have put 30 ml into a module or 5 ml per cell.

    Brad

    So I managed to NOT burn my garage down overnight. I always worry about leaving chargers unattended. I set the charger for nine cycles with a 6.5 amp charge, 1 mv delta peak per cell, 20 amp discharge to .9v per cell :eek:. This was done to just the 5 good cells. The dead cell I bypassed. The five good cells had just the tap water that the plates could absorb, 1.5 ml each. The dead cell was filled with tap water to the top and did not drain into the other cells(n). The last discharge shows 6091 mAh at a 20 amp discharge rate. Not too bad for a junk module.

    I doubt the dead cell can be revived. Does anyone have any ideas of how to try to revive it?

    Brad DSC00078.JPG DSC00079.JPG
     
    #114 strawbrad, May 18, 2015
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  15. Britprius

    Britprius Senior Member

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    Brad.
    I agree with what you are saying, and is why Roy put a series of question marks in his post. Also why I said "I'm sure there would not be enough room to add another 19ml". Obviously the statement was wrong, but this could easily confuse the uninitiated into trying to put to much into a cell.
    Putting 5ml in a cell would probably have good results "possibly in a shorter term" because the concentration of KOH would be high. The water would possibly through capillary action wet most of the plate surface giving low resistance along with good capacity.
    I think adding 10 or 11ml per cell with added KOH will help to keep the cells hydrated for longer staving off the day when the process will need to be repeated or the modules/battery need to be replaced.
    I must admit it is easy to accidentally get the terminology wrong writing module instead of cell or the other way round, but feel it important we do en devour to get it correct to stop those with less knowledge reading the posts getting confused.

    John

    Brad allowing for the "Peukert" effect discharging the cells at 20 amps is in line with the figures I recorded. The actual capacity could be higher if you stopped charging at an input of 6.5 AH or was that 6.5 amps the charge rate? If so what was the input charge time.

    John

    Is the dud cell open circuit between it and it's neighbor? Possibly the reason for lack of capacity, but more likely it got reverse charged. You could try adding some KOH to that cell, but the chances are the composite plates are destroyed.

    John

    It is good to see independent verification that re-hydration would be likely to give more capacity gains before cycling the modules than cycling on it's own.

    John
     
    #115 Britprius, May 18, 2015
    Last edited: May 18, 2015
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  16. strawbrad

    strawbrad http://minnesotahybridbatteries.com

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    The 6.5 amps was the charge rate. I did not monitor the cycles. Since the last charge was 6658 mAh at 6.5 amp rate the charge would have taken just over an hour. Slamming charge in at 6.5 amps and then immediately discharging at 20 amps 9 times is almost as abusive as cutting the top off the module:confused:. A high charge rate with the delta V set at 1mv per cell will tend to end the charge early.

    The dud cell is not open circuit. I put the first 3000 mAh charge through all six cells. The dud just bubbled away most of the water over the plates.

    When adding water to the dry cells I could see the plates quickly absorb and spread the water. Given a five minute soak completely covered the plates absorbed 7 grams of water. Then after a thirty minute soak they had absorbed 9 grams of water. I could also see the plates start to slowly bubble at about 1.45 volts. Durring the 3000 mAh charge the dud cell boiled off 3 to 4 ml of water. Someone smarter than me could calculate how much pressure that could build up.

    Why can I leave just one cell full of water overnight and you can pour water through the module from one cell to the next?

    Brad
     
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  17. Britprius

    Britprius Senior Member

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    Brad although the results are very good on the cut open module I feel the charge input in AH is not enough to give full capacity output.
    An input of 6658 mah allowing for the inefficiency of charge take up by the module will give an output of less than the input. Even at 90% efficiency that input would give just short of 6000 mah output. The modules being rated at 6500 mah, but many including myself have found they are capable of well over 7000 mah. Basically the charging is being cut off to early as you suggest.
    Did you measure the internal resistance of the 5 cells so we can compare by extrapolation to a 6 cell module?

    With the dud cell it is possible the KOH has been burnt off by reverse charging thus leaving only water in the cell and why it just gasses. This would be the normal reaction of 2 electrodes put in water and supplied with current. Oxygen off one electrode. Hydrogen off the other, and why I suggested adding some KOH.

    I do not understand the last question in your post about water from one cell to the next.

    John
     
    #117 Britprius, May 18, 2015
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  18. iduncan

    iduncan Junior Member

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    Just a quick question John @Britprius,

    Would you recommend rotating module positions from near the center of the pack to the ends and vice versa if one has refilled the electrolyte in all of the modules?
     
  19. a_triant

    a_triant Member

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    #119 a_triant, May 19, 2015
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  20. Britprius

    Britprius Senior Member

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    It would do no harm to rotate them, but I think with re-hydration it will become unnecessary. My reasoning being that in the past without re-hydration the modules from the center of the pack were moved out because they were more likely to be dried out being in the warmest positions. With hydration they will all be equal again.

    John

    Part of the reason for charging to that capacity is to get all the cells in the module warm. This will help any dry KOH on, and between the plates to dissolve bringing it back into use. As the temperature goes up so does the ability of the amount of KOH that can be absorbed, and the rate of absorption. It also helps balance the cells within the module.
    As the capacity of the module/cells rises so does the requirement to put in more charge.
    The modules I used had capacity of 7175 mah at a discharge rate of over 10 amps, and may improve further. At a discharge rate of most hobby chargers 0.7 amps this would equate to over 7500 mah due to the "Peukert" effect.
    For those that like mathematics here is an explanation of Peukert's law applied to some different battery chemistry's.
    Peukert's law - Wikipedia, the free encyclopedia
    There would be little point in only charging to 7000 or 7500 mah and expecting the same amount back in discharge. These modules are no where near 100% efficient.

    John
     
    #120 Britprius, May 19, 2015
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