Connecting new BMS to salvaged Bionix 13s battery

[bikezen]

Hi all,

I've got two battery packs salvaged out of Bionix battery housings, 13s, 8.8AH charged to 52V. They appear to be sound once the BMS is removed.

I want to replace the Bionix BMS with a load balancing BMS from eBay (https://www.ebay.com/itm/254285645186) but found the female JST block containing the 14 balance wires from the battery and the male port on the BMS are not compatible. Wishful thinking on my part that they would be direct plug n play.

Images: https://www.evernote.com/l/AA7rgg52FupH8KluLFm1fRIqBqMuSytpMh8/

The BMS comes with a bare female plug and wire harness. I know I can trim each balance wire from the battery and solder it to the new harness. Is there some other way to do this? Perhaps an adapter or some technique other than soldering? Thanks. I want to make sure before I warm up the soldering rig.

 

[BlueSeas]

The board you purchased isn't a BMS really, only an active balancer. It will attempt to balance the pack, but will not provide any protection from cell undervoltage or overvoltage events. It would normally be used in addition to a regular BMS to provide more advanced balancing than there was on the stock BMS.

There isn't a "rule" you have to have cell level protection. Your cycle analyst can be programmed to cut off on low voltage, but remember the CA is only looking at pack voltage, not individual cells. Should an individual group of paralleled cells (ie. Cell 3) get out of sync with the rest of the bank, it might not detect that soon enough and push the bad cell way to low, perhaps even into a negative voltage. The same thing could happen charging, if the charging current is high enough that the balance board can't keep up, overcharging the high cell before the charger reaches the termination voltage.

I'm new to 3.7V 18650 lithium chemistry, but know enough that it's a lot more dangerous than the lithium iron phosphate I know well. You really don't want to push these cells out of their normal operating range or really bad things are possible. If the original BMS's are serviceable, I'd leave them in addition to the balance board.

Looks like there are more than 14 cell tap wires emerging from the pack. Don't know what the extra wires are, perhaps thermistors for temp monitoring. But you probably can't find a premade conversion harness. So you probably need to cut and splice. You can just add the balance board to the system if the BMS works. I'd do one wire at a time, starting with C0- working up to C13+. Then double check the harness before plugging it into the board.

You could splice using crimped butt connectors or better use Wagos see:

https://www.wago.com/us/products/datasheets/Data_Sheet222-413_.pdf?product=222-413&lang=en

Or

https://www.wago.com/us/products/datasheets/Data_Sheet221-613_.pdf?product=221-613&lang=en

Both better than soldering in a vibration prone environment. But I'm a bit biased here, we never soldered anything in the marine electrical world. Only the electronics guys did that and my engineer/boss cringed every time.

 

[bikezen]

Thanks for the reply, that's really helpful. I knew the card was a balancer but didn't really think that through in terms of over and under voltage protection like a BMS provides. Doesn't seem really practical to have two cards balancing the cells in a pack. I don't have the original BMS for the packs as they failed and were removed.