Battery charging help requested! (E-moli LiMn)

[lazarus2405]

So, roughly three years ago I wrote up my build, a 5303, Kelly controller, and a 84v 9ah (21s3p) battery built from Milwaukee 28v power tool battery packs (These ones, they're 7s1p 3ah E-moli LiMn cells). I bypassed the BMS for discharging and used the BMS and the Milwaukee chargers for charging. Over time, the flimsy little BMS's have died out, and I've kept the batteries juiced by putting the cells in parallel and allowing the BMS/charger to (slowly) charge and balance increasingly-large packs. Well, this spring, I've come to find that my last BMS won't work. I need another way to charge and balance my cells.

So, what are my options? I'm on a budget, and I really want to completely ditch the finnickey Milwaukee charger/BMS technology. Does anyone sell a good LiMn charger? I'm not averse to building something myself, but I'm a chem e, not an EE, so I'd need schemata to go off.

Thanks

 

[Ypedal]

I would say it's time to invest in a lipo charger !!!

LiMn is the same voltage range as Lipo ( cobalt .. )

 

[lazarus2405]

I would say it's time to invest in a lipo charger !!!

LiMn is the same voltage range as Lipo ( cobalt .. )

Charge termination would work correctly? That's really my biggest fear.

 

[auraslip]

If you're comfortable enough, bulk charging seems to be the method the experienced guys are doing. Basically using a modified meanwell powersupply to charge the whole pack to the voltage desired. Cheap, powerful, and reliable.

I've read that LiMn cells do some self balancing or aren't as easy to overcharge making them very easy to use in this sort of setup.

Basically, adjust the power supply to 4.1 * x number of cells.(21s in your case - 86.1v) If everything is balanced (get cell-logs and battery medics to make sure everything IS balanced), the voltage in the pack will rise until it hits 86.1v and the current will drop to zero. The power supply doesn't terminate per se, but effectively no more current is flowing into the pack because they have matching potentials.
You may need to put more than one power supply in series to get the desired voltage.

People do this all the time with lipo. The trick is to making sure everything is balanced. With LiMn it's even easier.