So when I put everything back together last, I failed to mention a dummy moment I had. I managed to short out a cell for a couple of seconds. I really wasn't sure if I had done any damaged so thought I'd figure it out one way or the other before posting the results.
The cell was directly shorted out for a good two seconds, maybe a bit more, although it seemed liked a minute as I was jumping around trying to stop it. :)
I gave the cell a separate charge knowing I had discharged it quite a bit and definitely exceeded the maximum discharge amperage. Somewhere during the first or second week of driving to work the cell didn't have enough capacity to make it here and dropped to zero volts. I knew I had done some damage to it now, not from the zero volt, but the fact that it reached zero volts. If you recall, I've taken another cell to zero volts and it's still alive and kicking so no final verdict there yet.
I manually charged this cell up again for about a day at 5 amps, AFTER the pack itself had reached full charge. This one cell, however, would never fully charge. It seemed it internally had a self discharge of a couple amps maybe.
However, it continued to get me to work...until today. The cell reached zero volts again on the way to work and I knew it was time to replace it. This time, the cell would not charge...at all. I could not get the voltage above 0.7v and the cell got very warm when charging.
So although this is the extreme case of discharging at high rates, it may speak slightly to what happens to a cell when exceeding the maximum continuous ratings, just to a lesser degree. In short, it's bad :)
So, I've now lost my first cell. Luckily it was due to my own ignorance and not a failure for general use.
On a side note, I have noticed much greater voltage sag with the colder weather under load. This may be because the cells don't charge as much in this weather as well as the temperature it self during operation. It's about 45-50F when I leave in the morning and the car charges outside. We'll see how bad it gets when winter really kicks in here.
Friday, October 16, 2009
I realized I hadn't posted on in here in a couple months now! I'm just having too much fun driving and not working on the car.
I did tear it down just a couple weeks ago to look things over, make sure no welds had broke, check the motor brushes, etc. Everything looks great!
Since I had it all apart, I took the time to FINALLY install my version 2.0 of the LiFePO4 Volt Blocher.
I'm normally parked outside the garage these days as my truck sits here, but thought it was a nice shot charging with the solar inverters in the background.
You can definitely tell this is MY kid, just look at that EV GRIN?!?