Milwaukee Brewers or batteries anyone?

[pengyou]

The Milwaukee battery packs are coming down a bit in price now. They are 28 volt, I believe 3 amp. Does anyone have any experience with them? How about putting 3 of them together (74 volts) to power a 72 volt motor? I sent an email to a vendor that does custom Lixx packs and he recommended not putting his packs together in series like that. I am not sure if he was just being overly cautious or is there really a reason for not doing this?

Are these packs durable? Easy to mod?

[BroadwayJoe]

I think they're Emoli cells which have a good reputation - endlesshpere is the place to ask specifics. I understand Milwaukee BMS is easier to deal with than Dewalt.

As with any series string, the more cells in series the more possibility of cell imbalance either during charging or discharge. Unless you have provision to monitor individual cell voltages I wouldn't be going for series wiring these packs together.

For example my A123 Systems pack has 8 cells. Nominal voltage for each fully charged cell is around 3.6V. The other day, I noticed one cell was now only getting up to 3.2V, next charge cycle it was barely 3V. During discharge that cell was getting really close to 2V while the other cells were barely hitting 2.5V once the pack was consumed. That weak cell never quite fully charged up, so every time it's cycled it settles a little lower and lower until finally the entire pack is seriously compromised by that one weak cell.

Fixing it was easy enough - just charged that one cell up to where I guessed it was close to the others and the pack is back to normal capacity for now. Of course, it will change again and with constant monitoring I will know when it does and take steps to correct the imbalance.

If you don't monitor cell balance in a lithium/NiMh/NiCd pack you will eventually wind up with a serious condition that could create safety issues. I wouldn't call that overly cautious - prudent guy at Lixx it would seem.