Re-hydrating the battery modules.

Hi John,
Can I apply this method on prius hybrid nimh battery for 2010 and up or it is different electrolyte

 

Hi Alex, what is the KOH ratio for the rehydration. Is 20% in water is good to rehydrate battery for prius 2010?

 

I noticed someone didn’t bother drilling holes and instead “pressure filled” their cells by submersing in distilled and pressuring above the relief valve pressure and had similar results

I am wondering how someone would do this at home, I don’t know of any cheap pressure vessels I can stick battery cells in and seal up to pressurize

 

To what pressure? You could rig up an old pressure cooker if the pressure isn’t crazy high.

 

160psi+

 

This idea fills me with questions, not least about the assumption that a pressure vent valve also will open inward under some external pressure ... it's easy to picture valves that would not ....

 

That’s too high for a pressure cooker. Is that the blowout pressure? If it’s a check valve type assembly the inbound pressure might be less. Especially if the battery is at a cooler temperature.

 

Even if they opened how could you be sure they closed properly?

 

Many failing cells have blown the relief to vent,
on these cells a release out can break the relief (once and done) so no guarantee there either

 

Pictures? Good idea.

This module self removed it's top for testing.




Valve removed.



I used a bicycle pump to test the valve. In the reverse direction the valve did not open at up to 140 PSI. In the forward direction the valve first opened at 120 psi. After that it would open at 80 psi.




Inside the valve is a simple rubber plug. It is held tight to the smooth bottom of the valve. When pressure builds up inside the rubber plug distorts and gas is vented through the "X" pattern on the inside of the top of the valve.

The bottom of the valve does not have any passages to allow gas to enter the valve.

I consider the valve to be one way only.

 

Hmm, so I take it the difference between gas venting and top self-removal ought to be somewhere between 80 and 120 psi?

 

I completed reconditioning my Gen 2 Prius battery. I put 5800-6300mAh modules in it, so it should be fine for quite awhile. But I want to experiment with my old modules and try to rehydrate them.

What is the best internal resistance meter under $200?

 

Just did this and I have some tips. On the Gen 2, drill in the center of the depression on the battery lid. You'll see small indications in the plastic where the supports on the inside of the cover are. Drilling in the center ensures you don't drill into one of those supports. The depth is shallow to drill, only 2.2mm of plastic, so be careful not to go too far in. Earlier ITT, saw there was ~13mm down to the top of the battery. I tried both a 1mm drill bit and 1.4mm x 3mm screw and also 0.8mm drill bit and 1.2mm x 3mm screw. I did not notice a difference other than the smaller screw was quite a bit easier to strip out. You'll want a good screwdriver or two. I put in 9ml of 20% KOH to start. I filled the cells from both ends (giving an hour in between fills to ensure it would soak up). Then drained them down to 7.6v, then applied a 0.4amp charge and watched how quickly they rose in voltage. The better cells rose in voltage slower and accepted more mAH when getting to the same voltages. If a cell rose quicker than the other ones, I put in another mL and tested it again. I repeated until I found the cell improved or for 1 module it never improved. There was maybe 5 modules that were marginal afterwards, rose quicker in voltage and couldn't get to improve beyond a point. But I put them back in because I don't have many extra modules. We'll see how they do. I think the key here is observing how they take charges, they all seem to have decent supply (even under load). And make sure your temperatures are ok, not too cold as NiMH is somewhat sensitive to temperature when charging.
I've put one drive under my belt on this new setup, and the battery indicator on my '05 does go up and down, and quickly hits the full charge, so I'm thinking it hasn't "broken in" yet, the cells aren't rejuvenated very well, or the computer is having a hard time with the slightly mismatched voltages (I didn't balance the cells before reinstalling, in a bit of a hurry). They were all 7.80-7.92 tho, so not too far off.
Good luck guys.

 

With enough dead modules in the world, I wonder if somebody will start grinding their plastic cases to make a replacement powder of the same resin. I could see molding it into little taper plugs that could be coated with the right solvent and driven into holes, letting them solvent-weld.

I wonder what the right solvent is....

 

I don't think that's necessary. The small self tapping screws I used seem to hold well. Earlier ITT they were pressure tested as high as folks dared go.

How much fluid to add is a big deal. Too much and it overpressure. Too little and its still dry and subpar. I'm thinking start with a small amount and test the cell to determine how it responded. Keep adding and testing until diminshed returns. Make sure to leave enough time for absorption

 

I didn't see this question at the time, but I'm thinking "whatever decent multimeter you already have, a load resistor whose resistance you know, and your calculator" will come in at under $200 and do a swell job. Measure the open circuit voltage, measure the voltage across the resistor, calculate the current through the resistor at that voltage, calculate the module internal resistance from the voltage drop at that current.

 

I use the B6AC hobby charger. It has modes for nimh, lipo, lead acid, and a resistance meter. Does discharging and charging. Though the discharge is limited to 0.6amps for the nimh. It counts how many mah it has discharged or charged. Also not very expensive, I have 4 to make the process quicker.

 

just wanted to share some paper i came across about upcycling of spent NiMH battery Material.
interesting reading. i dont pretend to understand half of it. but maybe some of you will.
props to the owners.

 

Do I have this right (in simplified terms), a layer of crud builds up on the plate surfaces, and physically removing it actually makes it better than new? With the reactions that cause this crud are irreversible, doesn't bode well for trying to rejuvenate bad cells with just distilled + KOH?