Cell #1 I discharged to 5 volts. Let it rest 30 minutes then started charging at 2.5A. I'm not sure if the charger didn't detect the delta peak or what, but 3 hours later I came back to the basement to see it had swollen rather badly. When I unhooked it, the charger showed 6850MAh capacity, and using my voltmeter, the voltage is at 8.93 volts. Somehow the deeper discharge seems to have made it swell easier, as I used this charger to charge all 28 modules and none swelled like this one did now.
If you are going to discharge below 7.2 V (per module), you shouldn't really charge at a high current until you are back to 7.2 V. I wouldn't charge at more than 325 mA when the voltage is below 7.2 V personally.
Oversight on my part, I meant wouldn't. Good spotting. I have edited the original post to correct that.
Lol, the blind leading the blind. Glad I'm experimenting/learning on a salvage yard HV battery. In total I've probably spent close to $750usd with gadgets, chargers, meanwell power supplies to be able to learn to maintain my 2008 Prius HV battery. I would have been better to spend $1800usd to just get a new Toyota battery from my local dealer. Since I don't think I'll be buying another used Gen2 Prius its been a learning experience. The Gen 2 are getting up in age, noting all the threads on what can go wrong with an 14 year old Prius.
I doubt you are getting a new battery for $1,800. Every dealer I looked at online is a minimum of $3,000. They were around $1,600 a month or so ago..not sure why they have skyrocketed in price.
I tried connecting a lightbulb to a module while it was discharging, but since the hobby charger can't see the load applied, the capacity it showed when it alerted to 6v cut off was not anywhere near what it should of been. I noticed while my charger lists a discharge current of 5A, while it's discharging it only hits about 2-2.5A, and it also sweeps up and down, which adds to the time. The other module just finished discharging...it took 13 hours and 30 minutes. From my researching on NIMH cell reconditioning, the capacity displaced while discharging is much more relevant than the capacity displayed while charging. I might have to look into ordering a discharger.
Ordered this one. Shows discharge capacity mAH. Best price $89, AmainHobbies price $129, everywhere else backordered. SkyRC BD250 Battery Discharger & Analyzer RC LiPo Battery 250W 35A BD200 688977150524 | eBay Or this discharger. West Mountain Radio - CBA V - Computerized Battery Analyzer
This is not a job for the impatient. If you want to do it faster, get more chargers and dischargers. In actual fact taking a long time to discharge is a good thing. What is more important though, is following exactly the same process for each module so you can compare them relatively. It is not actually important what the numbers are, but how the modules compare to each other.
Not impatient, I just don't want to be down to one car for 2-4 weeks. As I said in another post, the more money you spend on chargers and other tech, the more you start getting into "sunk cost" territory. If I could do this all over again, I probably would of bought a $600 HV pack from a wrecked 2015 Prius with under 100k miles, as I assume a pack with nearly 1/2 the miles and 7 years newer would be in far better shape. The reason discharge is taking so long, is because even though my hobby charger is supposed to discharge at 5amps, turns out this is distributed on both channels, so in reality 2.5A is the max it can discharge per module. It also doesn't apply the load constantly, I imagine because it doesn't have the "guts" to do so without overheating. It sweeps from 0 to 2.5A with about a 10 second pause in between, this is what is adding to the enormous discharge time. So I ordered this: https://www.ebay.com/itm/184266440118 Which means hopefully I don't have to wait upwards of half a day to discharge 2 modules. At that rate, it would take 3 weeks just to complete the 3 discharge cycles on all 28 modules, plus around 3 hours per module to recharge..you'd be looking at about a MONTH. That discharger doesn't sit there and wait 10 or so seconds and then ramp up and down the current, it's a constant load.
Hindsight is a wonderful thing. if you are only discharging to 6 V per module, there is very little benefit to doing multiple charge/discharge cycles. You are in effect only doing top cycling and one discharge and one charge is going to accomplish much the same as two or three. What you do is really determined by what it is you're trying to achieve.
Yes that discharger can slam 10 amps into the module, but below 6 volts better to discharge at .325 as suggested by dolj and others. At least the BD250 has a shutoff when the set voltage is reached, instead of babysitting lightbulbs.
Not an expert but I have successfully installed a NPB system and lurking on battery posts here for years. Most important thing is if your charging a module and not concentrating cooling on it and walk away it could distend. Almost guaranteed based on all the swollen modules poorly charged we see here. That's why you must charge a module all bolted up tight as a total pack. If the factory module pack was not bolted up tight as a pack so as not to distend it wouldn't last 2 months.
I am using the hybrid fan which is very high CFM to blow air on the modules while charging. I can't really sit in the basement and babysit them. Of course I don't charge when sleeping in case any issues errupt.
I might of discovered something. When doing a charge>discharge cycle, it takes a much longer time to discharge than doing a single charge cycle, waiting an hour or so for the voltage to "stabilize" and then doing a discharge cycle. With 2.5A discharge current, using my crappy charger than doesn't apply constant current (sweeps up and down and pauses), it's only taking 4-6 hours to discharge a module to 6v rather than 8-13. I am wondering how flawed the capacity reading is when people are cycling with hobby chargers and only giving the cell 10 minutes of rest, as the voltage read out when finished charging is somewhere around 8.4v-8.6v, and giving it time to self-stabilize seems to bring it down to 7.8v-8.1v. I am also not sure how long this self stabilization takes, but it seems to be about an hour. I wonder when batteries are tested at factories, how much of a pause is given between a charge and discharge when they test for capacity. What exactly is occurring in this process for the initial voltage reading upon charge completion to stabilize to a reading that stays constant for a few days or more? Is the heat produced during charging affecting the chemistry of the battery leading to a higher voltage that stabilizes when the battery reaches room temp?
