EV 6

Author	Message
Trev Guru Joined: 15/07/2006 Location: Australia Posts: 676	Posted: 10:21am 01 Aug 2011       Equalizing stuff up. I have 1 cell in particular (cell 23) requiring a top up every week end to maintain comfortably the range I need. I have these 2 equalizer samples on cell 23 (centre of the pack, & always the hottest) and cell 5 (which isn’t really bad). Cell 5 did not have the resister and therefore was not charging (no problem anyway), but cell 23 did have the resister. Cell 23 was low so I switched it on, without the main charger on, holding pack voltage, and thought I would come back later and switch it off before it got higher than the other cells. I forgot. That in itself is not a problem because the equalizer charger will only go to 3.75v. The problem occurred the next morning after I had charged the pack with main charger. Cell 23 was higher than the others and so became over charged, by 0.7v. As pictured. This would not happen if a complete system was in place. These are samples in test. The complete system requires all cells have their own equalizer charger and they are only switched on with main pack charger holding full pack voltage. As a result I noted a huge internal resistance in cell 23. With a full pack voltage, at 300A, temperature at 18C the terminal voltage drops to 1.7v. Remove the load and terminal voltage comes back to 3.3v. As the cells warm up, the terminal voltage under load drop is less, but even at 40-50C the terminal voltage of cell 23 drops below 2.5v with load. I see the same pattern when charging. The load of the charger pushes the terminal voltage of cell 23 higher, but as the charger cuts back at the end of charge, the terminal voltage comes back to normal. I also note that heat generation is now higher in cell 23 than it used to be. On a positive note, I have not noticed any drop in capacity in cell 23. Trev @ drivebynature.com