Quote:
Originally Posted by Mike Dabrowski 2000
A single cell charger is also on the list. Maybe if I can cycle only the cells that are behind the others,I can achieve a better balance than trying to do the whole subpack.
I als need some cooling if I will be testing at 100A. Dont want to cook any more cells. The first 100A test got the subpack to 150F.
A close look at subpack 2 trace, shows that the white #1 cell reaches a plateau and starts to get hot while the rest continue to rise and are running cooler, I am assuming that this means that cell 1 is fully charged and the rest are still charging?
MIMA Honda Insight Modified Integrated Motor Assist - Subpacks 1-8
If anyone wants a copy of the actual excel spreadsheet datalog file to look at, just send me an e-mail and I will send them to you. |
Normally I see a dip that goes along with the temperature rise, I've never seen the voltage hang that steady when I've played with them, so I couldn't tell you if they were done, I'd probably keep charging until that cell reached 120 degrees or I see voltage drop to be sure, unless the drop was missed already. It's hard to tell when you can't see the full picture from discharged to charged at the same amperage throughout.
I played with the idea in my head about single cell charging and then realized that it might not help much. The reason being is that usually we charge these when cycling with slight overcharge, which I've verified by measuring temperature. I played with charging them and measuring temperature with an infrared thermometer and watching the lowest cells to make sure that by the time they terminated the charge(which the lowest temperature cells always did later) that they had the voltage drop to indicate that their charge was complete. Since the cells that have the least capacity are the ones to drop to the .9 volt level first, they will already be getting the full cycle, so charging separately might not help much. Although taking the lowest capacity cell and discharging at a very low amperage(say .6 amps or something) to .9 volts to ensure they are really getting a full cycle might help, but I'm not sure to what extent, I have a feeling that it won't progress things too far, but it's worth a shot. I've read in some places that the actual cell reversal is at 0.6 volts if done at a very low amperage, I can't find this information anymore, so I wouldn't do it unless it was for experimentation on a stick that is already deemed bad in case it makes things worse.
As far as cooling goes, I tried putting a few sticks in the refrigerator for an hour and then charging them at 7 amps(max of my charger) and the voltage was much higher as they can't absorb it as well but at the end of charge I noticed the same stick had a much wider final temperature range when before they ended at a difference of less than 5 degrees C and I'm not sure if what I was doing was a bad idea or not. I've been avoiding getting them hotter than 45 degrees C (113 degrees F), but have noticed that at 7 amps when stopping the charge at 45 degrees C that they have climbed to 50 degrees C in about 5 minutes, even with that relatively low amperage. Most commercially sold chargers that I've come across terminate between 45 degrees C if based solely on temperature and ones based on -dV use 50 degrees C as the 'failsafe cutoff' in case standard end of charge detection fails.
