Discharging questions.

I don't remember seeing anything about NiMH chemistry that ever recommended a cutoff lower than 1 V per cell, or maybe 0.9 V at the outside. 1 volt per six-cell module sounds bogus to me.

 

Make sure to note if voltage is per module or cell. 4.5 amps charging? I'm charging at .45 amp, I'm in no hurry.

 

It's a spare pack, 4 channel charger, charging modules wired in series = 14 blocks.

Colorado Springs guy looking for Prolong reconditioning help | PriusChat

 

Originally Prolong suggested to take each module down to the equivalent of 0.6v in the third round... But they've twice boosted that number because of module failures.

I can atest that negative voltage / switched polarity is hard to happen even when a module is down to 0.0v when I've fallen asleep. Those mistakes tested out fine, likely because light bulbs don't draw amps much at 0.0v.

Negative voltage is something I've seen in old packs that have sat for years though... And as I've said before, all these techniques are needed due to lack of high quality equipment that's very expensive. If you have lab-grade battery maintenance gear you don't have to go below 6v.

And I can assure you that packs I've very slowly taken down to 0.6v usually test better than packs that didn't get as thorough of a treatment.

 

Majority of the modules. For pack storage.

 

Up to you, I'm sticking to 7500mAH, no time limit, I let the charger and module determine voltage, 6cell or 12cell.

 

yes

 

This is my first attempt at reconditioning modules. I’m not the best for suggestions, just bumbling my way through, just like you.

 

If that works, then great. How are you cooling the modules? Heat is the enemy here. Especially since you're using "high" amperage.

I went discharge to 6V, (then 5V or less next cycles if capacity didn't improve) maybe 2A charging to 7500mAh, no deltaV. Yes, with chargers to do 5 modules at a time it took like 5 weeks to do 5-6 cycles on all the modules and the replacements.

All modules were clamped in the HV pack frame and I had air from a small box fan blowing the whole time through the (car's) exhaust duct that was fitted to the bottom slot of the pack. So airflow was up from the bottom through the modules.

There are other ways to do it but this worked for me- 2 years and 30k later my HV pack operates fine.

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I have been cycling at 6.5 amps for a decade. I recently decided to go to 0.75 C (6.5 amps * 0.75) 4.875 amps, make that 5 amps cause that's what I really set it at, merely to reduce heat on charge and minimize any swelling and pressure.

I place a qtip wrapped in saran wrap with a few ounces on top of it in the valve, because the valves are old and they can go off at radically different pressures leaking your precious gasses.

I used to use a 12 volt lead acid car battery charger at 6 amps for YEARS to do these modules, and a meter, and a watch.
Using the meter (and visible inspection for radical swelling) one can easily charge these batteries safely to delta end of charge. The meter will go FLAT for an extended period (1 , 2, 3 minutes, followed by a drop). You dont have to wait for the drop just a long extended failure to rise in voltage MAY indicated end of charge or close enough. The only reason to wait for the actual drop is to hopefully get CLOSE to BALANCING the internal cells with each other assuming any are out of wack.

As for going below 1 volt, there is ZERO reason to be taking these below that, there is no benefit at all. I tested three different modules and in two there was no difference in on it lost capacity, as it should might will.

I do not like your clamping method and would never use it on my battery.

 

I never work on modules unless the are bolted into the rack that keeps them from swelling. Not sure why that concept is so hard for people to understand? Also don't take a pack out of it's rack until it's cooled down or you'll have a giant accordion mess to deal with...