I have what seems to be an unusual situation, well at least to me but maybe not to others with more experience. I have been discharging and recharging various modules which I bought from my local used Prius dealer, as one of my Gen 2 blocks was weak. I only have one dual charger, an HTRC C240 Duo. Originally, I had set the discharge capacity at 7500mA, 4.8V (6S) and started the 3 times cycle, starting with discharge. They were clamped up as a full set of 28, using a Gen 3 frame to provide cooling. I had left it running overnight and in the morning found that both displays showed 'Over Capacity Cutoff'. Unfortunately, I could not get it to give me a report to see if it had cutoff during a Discharge or Charge cycle. So last night, I turned off the Capacity limit and ran the cycles again. The first picture shows the display first thing this morning, the top one is charging and the bottom one is discharging. I decided to end the cycle and assumed that at least one was on the final charge cycle as it had been running for almost 9 hours. When I pulled the report, the second module shows the charge 1 capacity of 15,930mA, as seen in the second picture. It didn't get to fully discharge as the 3rd picture shows that Charge 2 had not started. My question is, is this normal and is it likely that the module has been damaged by overcharging. I would appreciate any comments and/or advice. Thanks, Al
Why are you talking about 4.8V and 6S, does it automatically discharge to 0.8V per cell? Is that a setting? I often stop at 1V I think. Although the cycling sometimes adviced on here on the full pack goes very very low for a Gen2 pack (I keep forgetting, 34V for a full pack?). I know that my 80W B6 chargers (clones of the original Imax) fail to recognise the deltaV that signals that the cells are full. So you should always set a charging maximum as well. My 50W version is better at this, but I will never fully trust them without setting this maximum. This deltaV is inherent to NiMH (and NiCd) cells: when they are full, there is a slight dip in their voltage (so a charger will suddenly see an increase in current I think, not too sure how that works exactly). This is the signal to stop charging and go to trickle charge, or in case of cycling, go to the discharge phase (probably after a few minute pause). At what rate did you charge? NiMH's can be 'abused' with a trickle charge of about 1/20C, so for the 6.5Ah NiMH's of the Prius, with about 325mA indefinitely. That should in normal conditions get the cells warm, but not so warm to damage them. If you charged at a much higher rate while they were full for a prolonged period of time, they may have overheated (or have been damaged in another way, but I think heat is the main cause).
