Looking for a balancing BMS, no charge/discharge control

[Zeropointbug]

http://www.rcgroups.com/forums/showthread.php?t=1863221

See this, this is a simple balancing board for RC batteries, I have one, works awesome, but you must manually turn it on as it has auto off when balanced. I am looking for a nice little board that can balance a motorcycle starter battery (4s A123). Thanks.

 

[dmwahl]

Without charge control, the only way it can balance is if the balance current is greater than or equal to the charge current, otherwise you'll still overcharge cells while leaving others undercharged. Dnmun may chime in here, he has a lot of experience with the various analog BMS boards out there and can probably give you a good suggestion.

 

[Ykick]

I've ordered 2 MOQ (minimum order quantity) BMS/PCM from this factory before and it might be worth an email to see if they'll quote this balancer board for your chemistry?

http://bestechpower.com/balanceboard/D172.html

But as noted, not sure if this will control charge shut-off? You can always use a BMS/PCM for charge only and discharge unprotected, so to speak.

 

[dnmun]

i don't know of a BMS that does auto shut off of the charging. chargers can have a latching output but never seen a BMS with that feature.

 

[dmwahl]

It would certainly complicate analog BMS boards to latch the charger off, I was thinking more of the charge control FETs to stop charging when any shunts turn on. I haven't used an off the shelf BMS in a while though, just used my own boards which interrupt charging when the voltage on any cell gets to a specific point.

 

[dnmun]

this is one of the really big advantages i see in your aurdiuno based controls over balancing.

you can create a look up table of the previous cell voltages at balance and be able to refer the current cell voltages to that table to see if the battery is balancing the cells to the same voltage as previous.

with analog type there are always some cells that lag under the full charge voltage while some will be floating above full charge and shunting while hoping for the others to catch up to full charge.

if the arduino could flag a sudden change in the order or dimension of the imbalanced cells that would be a good signal to generate to warn of some unexpected variation in the balancing, imo.

for 4S this is kinda like a wasted effort. maybe if it was 48S it would be worthwhile to investigate.

 

[dmwahl]

That's actually part of what I've been playing around with, "smart" algorithms to do more than just turn on a shunt above 3.5V (or whatever). Not much point to a digital BMS if all it does is the same thing an analog one does. I've got a bunch of log data I've collected with various cell capacities, manufacturers, charge rates, balance current levels, etc, and at some point I'll make a post comparing them and explaining (with real data) what the advantages of digital over analog are and why some of the systems that can't/don't control the charger as well fall short or cause actual damage.

 

[Zeropointbug]

Everyone is missing the point here. I HAVE used this for this exact purpose and it works great for A123 cells as they balance so well to begin with. I guess I will just make an extension balance lead out the side of the bike to balance the pack every so often.