Re-hydrating the battery modules.

I tried one more charge and discharge cycle on my topless module today. I used a different charger that had a delta V lower limit of 3mv per cell . The charger never found the delta V and I stopped it at 9400 mAh. It was charging at 6.5 amps. On discharge this charger is set for .8 V per cell, but I set it for six cells even though my poor module has only five cells now. All that works out to a cutoff of 4.8 V or .96 V per cell. At a 5 amp discharge the 5 cell module delivered 6637mAh. Before this module was re-hydrated its capacity was 600 mAh. This was as a full six cell module with the dead cell most likely having a big effect on capacity.

This module has now been through 11 hard recharge cycles since re-hydration. I can see gas bubble out of the plates on charge. After I cut the top off and before any water was added the module weighed 1019 grams. The plates were then covered in water for thirty minutes and then all excess water was shaken out of the module. It then weighed 1028 grams. The plates absorbed and held onto 9 grams or ml of water. After the last charge and discharge cycle I decided to weigh it again to see how much water had been boiled off in the abusive charge cycles. It now weighs 1003 grams. That is 16 grams lighter than before re-hydration. And the darn thing can still put out over 6 Ah at a high discharge rate. Such odd results deserve confirmation.

Next I will try taking the top off a module with low capacity but holding at 7 volts or better. That should be a good candidate for re-hydration. I will measure the capacity before re-hydration. It's also time to move up to distilled water instead of tap water. For this round I will carefully measure and place 1.5 ml of water on the plates of each cell. It's time to try some slow charging also.

Brad

 

I haven't read this whole thread (as it's a bit too technical for me), but you guys seems to be getting some great results from your experiments - keep up the good work!

 

Since re-hydration is starting to spread to other threads I would like to add to The Electric Me's concerns.

First is that re-hydration is an experiment. Anyone attempting to re-hydrate modules is part of the experiment. If you need step by step instructions you are not ready to re-hydrate modules. There are no set standards or procedures. We are testing to find what works. My tests are done with junk modules that could never be used in a car again. Do not try this on a whole pack that you need to run your car. Try one module. Test it. Improve your procedure. Test it again. We have a long way to go before this should be considered mainstream. We have a long way to go before we know the best way to re-hydrate a module.

Very few have tried to re-hydrate modules. Most of the information we have is old and incomplete. Britprius has re-hydrated a total of two modules, I have now done two modules also. None of those modules have made it into a car. There is lots of work to be done. If you can contribute to advance the art that would be great. If you need a recipe spelled out it would be best to wait.

Most important is that this is dangerous. KOH electrolyte is nasty stuff. We never hear reports of venting of the tens of thousands of modules cycle charged to rebuild packs. Out of thousands of modules I have worked with the one and only one that vented I had re-hydrated and overfilled. It sprayed KOH electrolyte like an aerosol can. I got lucky. I was in an open air garage and not next the module. Just a wiff of the KOH was enough to cause me to abandon more testing.

Test, share, and be careful.

Brad

 

This is very good advice Brad - I was testing a battery that I had converted from G! to G2 cells - the battery was not rehydrated and I was testing the battery without the metal top on the battery ( all the module tops were exposed) and no back seat installed. I took the car for a test by running it up a steep hill and back down again 2 times. I used my techstream to monitor and record and found I was hitting 60 amps going up and 40 amp recharging going back down the hill - on the second run down the hill I heard an sound that sounded like a gunshot at the back of my head. I drove the car home a couple of miles to my garage and went back to look at the battery - a module had one cell with the top of the cell completely blown off and the cell was still supplying voltage with the top blown off. The car did not have dry KOH sprayed around it and I found the blown off top had blown into the trunk area ( remember I did not have the metal top on or the fan system installed).

It was a cold day here in Canada, just above freezing so I felt the battery would stay cool without the fan coming on, techstream showed the temperature of the battery was under 80 deg F at the time of the explosion ( the temperature probe was not on that module that exploded, but may have been quite hot- I did not touch the module till a day later when I removed the battery from the car). If that module had been filled with liquid, when it exploded ,I could have been sprayed with the acid in the battery.

Please (I was foolish) do not test without the battery top on after re-hydration - the top will contain any liquid to the inside of the battery.

I have four (4) 2001 prius cars and they all are in good shape and running. One of the four is used as a test car. I have a spare battery that I clamp my test modules in to do my charge and discharge cycles. I have made a high voltage charger/dis-charger that I use to cycle the complete pack of 38 modules with a 1 amp charge and a 2 amp discharge (after I have tested each module individually for discharge capacity).

Having worked around high voltage and the rewinding of electric motors and generators for many years, as well as installing high and low voltage electrical equipment in industrial plants, I feel qualified to help in this experiment and will continue to contribute.

Brad I appreciate your and John's words of caution. This is the second time a have posted about the explosion of the cell in the hope it may prevent others from having a similar accident.

Roy from Canada

 

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This is what is left of the Gen II module that I had peeled back the side of the case. This module had blown off part of its top while in a car. That is why there are not six cells. This module has been open to the atmosphere for at least six months. The plates are still wet with a black goo.


It is really hard to get a good shot inside a module top. There are too many shadows. This is a close up of the inter cell passages that Roy has described. I could not find any evidence of them on my other topless module because I had sawed right through them.


This is a Gen II top. It might help for hole placement to know what you are drilling into.

I have been cycle charging my next two victims to get a good measurement of there initial capacity. I am going to try a variation of John's two hole method. I did not think six holes per module was a big deal but the difference does add up to 152 holes in a Gen I pack. For now I am going to stick with adding just water. It will be good to have some more data on water vs KOH. My theory is that only oxygen and hydrogen gas escape from the modules so only water needs to be put back.

Brad

 

All very good data. Thanks to all for the continued efforts.

My rehydrated junk modules, 11 years old with 200K miles, initially looked like there would be some life left. But my simple manual discharging method ended up being neglected, and I discharged the modules to 0 volts, for most of a day. They have been rendered real junk now, sadly.

Just a note for the tinkerers out there. These modules take so much heavy current cycling in use, but this particular fault is definitely game over.

 

Please! Share more info on your attempt to re-hydrate modules. Even failures, or maybe mostly failures are valuable learning experiences.

Brad

I wanted to know how much pressure normally builds up in a non re-hydrated module.

My first attempt leaked and did not build up any pressure. The screws are there to measure the voltages of individual cells.

At 65 psi this module was quite swollen. It was not clamped on purpose. Charging at 6.5 amps with a 1mv delta per cell had terminated at this point.

I then clamped the module. I had to reseal the pressure gauge because the module flexed while clamping. It took another 2 amp hours of charge to about 9.4 volts to bring the pressure up to 80 psi. At that point the value opened and started blowing bubbles. The charging it took to reach this pressure was abusive.

Brad

 

Hi John - after reading all the posts from the beginning I would like to make a comment on the charge and discharge capacity of these modules - in the past you have mentioned at figure of 70 % efficiency for the metal-hydroxide battery thus requiring a 9000 mah charge for a 6500 mah discharge.. In a previous post by Brad he posted a picture of a charge discharge close to 91 % for a re-hydrated module ( discharge 6091/ charge 6658) with only 5 good cells. See the attached picture from his post. Any thoughts on the higher efficiency?

These prius cells are truly remarkable.


" 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 . 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. The last discharge shows 6091 mAh at a 20 amp discharge rate. Not too bad for a junk module.

Hi Brad - how did you attach or mount the pressure gauge to the module - could you show a picture of that attachment.

Rot

I have some observations but no pictures of my latest test on a gen 1 battery converted to Gen 2 cells ( 38 modules). This battery had all of its Gen 1 modules changed over to Gen 2 modules (there age I do not know) - all the modules were cycled at least 3 times (dry) with RC chargers and each module had over 5000 mah discharge. I had been running them about a month in my test car when battery codes appeared and one module showed a 1.5 volt lower reading then the rest. It should be noted the internal resistance of all 38 batteries was 0.020 internal ohms by techstream before and after the failed cell appeared.

(Side note However ---- In my other 3 cars I still have the dry G1 cells installed - there internal resistance readings are a mixture of 0.018 and 0.019 ohms for battery module groups as measured by my toyota techstream software.).


Yesterday I re-hydrated all 38 modules in the G2 conversion hv battery by drilling 228 holes with a 1/2 inch long #6 self tapping screw and filled each cell in all the modules with 11 ml of near boiling distilled water (with the hv battery still in the car and the red safety disconnect removed, using gloves and the low voltage battery disconnected from ground ). Connected my techstream for before and after readings of the modules after a 30 minute soak and again 20 hours later. The voltage readings of each module group came a little closer to the same voltage except for the bad module group which reads 1.5 v lower then the rest.

The significant thing I noted was that all the 19 module groups remained at 0.020 internal ohms before and after re-hydration. John any thoughts on this?

Note techstream says internal --- meaning ( I think) it is measuring the wiring and connections as well as the module group resistance. Even the failed module group still showed 0.020 internal ohms????

I have plugged all the water filling holes with (larger) 1/2 inch # 8 stainless steel screws and removed the battery from the car to replace the bad module. The bad group was # 6 (modules 12 and 13) and 12 read 7 volts and 13 was 8.5 volts. Tomorrow I will remove the defective module and replace it with a good one and reinstall the battery in the test car.

This note added later - I covered all the stainless steel screw heads with a coating of liquid electrical tape that comes in a can with a brush enclosed and can be bought red or black - it has the benefit of assuring a good seal, electrically isolates the screws and will stop the screws from backing out over time due to vibration.

Roy from Canada

 

Hi Roy

I remember on my car after a disconnect of the 12v battery the techstream always shows 0.019 ohms on all pair modules

after some driving the numbers are changing, so later my battery pack shows about 0.023 to 0.026
maybe it needs some load to show the actual numbers.

Alex.

 

Hi Alex - In a few days after I have re-installed the battery I will record the resistances after running the car up and down hills to load the newly re-hydrated battery and see what I get. Will post results.

Thanks for the suggestion.

Roy

 

The pressure gauge has a 3/8" brass pipe fitting. A hole was drilled in the module. I screwed the gauge in without tapping threads. After compressing the module I had to add some teflon tape to get a good seal. Here is a shot of testing it on the bare module top.
Brad

 

Thanks brad - it looks like the module could not be used after the testing.
So each re-hydrated module should not be tested ??

 

Thanks for the explanation I want see if my screws will hold pressure without a sealant.



Roy

 

Roy, way to jump in and participate. You have made a big investment in re-hydrating a whole pack at once. We now have John adding KOH, me adding as little water as possible, and you are in the middle with a moderate amount of water added. That will give us good data to compare. Did you use machine screws or sheet metal screws? In the US a #8 screw is larger than a #6.

Do not worry too much about the internal resistance that Techstream measures. It seems to lag behind what is really going on.

I recommend getting some bubble soap on those 228 screws. There is no way I would have noticed the leaks in my test modules without it. Soaping up a whole pack will be a mess. And you would probably have to take the darn thing apart again to clean it all up.

This is what I use for installing batteries. The Gen I packs are just too heavy. It is called a Hoyer lift and was designed for patient transfer. In the US used medical equipment is almost worthless.
Brad


Brad