The BMS connector of a LiPo stack

H folks,
just interested in the collective experience here: I have 4 off 5Ah lipo bricks in parallel on my bike. Each brick has the internal cell voltages brought out on a 0.1" socket connected via small wires, this is for a BMS connection. The wires look like they would be OK for 2 or 3A - the connector for 2A or less.
Now it would be most convenient to parallel all these up on the 4 parallel stacks - that way I can BMS the whole shebang in one go, but I'm not confident it's the right thing to do - I figure if a cell starts to drop off you'll get a LOT more than 2A in that internal connection & things will fry. What have others done?
cheers
Bob

I'm starting to think it will be OK with a wee bit of resistance in between; I will only see a few 10s of mV there so a few milliohms will suffice. The charger/BMS will still work through that. And the resistors will fuse to protect PCB tracks if the worst does happen....

I wouldn't put any extra resistance in there, but rather just connect them to "balance connector" boards, either ones with LVC/HVC on them like the ones Methods has for sale, or like the ones HK has. Then if you have a BMS just connect that to the board when needed.

If you do have a cell fail shorted internally, you'd need a high enough resistance in a big enough wattage to drop all the voltage of the paralleled cell(s) and not cook the resistor, at either low currents or high ones, depending on how it shorts. Well, unelss you want the resistor to be the fuse.

Having any resistance in there is going to make it tough for the BMS to determine charge state correctly, until there is no current flowing thru the resistors, if you have parallel cells that are at different SOCs.


Also, it's worth noting that if you were using individual cell group chargers rather than bulk charge, it'll see the full charge voltage on there all the time, even when the cells are totally discharged, because the resistor will drop the rest of it. That may even make the chargers or BMS cut off immediately, if it's designed to do it when the cell voltages = the charge input voltage.

Thanks for the reply AW, I'm surprised no-one else has tried to run their paralleled batteries as a single pack; I will start with the resistor'ed version but just put the R's on the internal nodes (the max + and min - connections are hard wired anyway)- fact is I'm not using a conventional BMS, instead I have a bunch of independent isolated single cell chargers. Note the resistance value will be very small, ~ 0.1ohm
Cheers
Bob

I paralleled my balance leads on my packs. I made the first "Y" connectors myself, which was a bit fiddly, but then I found some ready-made ones on Ebay. Here's some, but I think if you search a bit more, you can get a pack of 10 cheaper.
http://www.ebay.co.uk/itm/JST-XH-6S-Parallel-Balance-Adapter-Balance-2-Once-/330583397471?pt=Radio_Control_Parts_Accessories&hash=item4cf84e545f

bobc said:

Thanks for the reply AW, I'm surprised no-one else has tried to run their paralleled batteries as a single pack;

Click to expand...

I'm not sure what you mean--it's quite common for people to parallel LiPo packs (or other types) including at the balance leads. Icecube57 even makes and sells custom harnesses for that, among other things. Also, Methods' LVC/HVC boards automaticaly parallel any packs plugged into them/ :?

Thanks again to respondents, it's becoming clear that my worries about hard paralleling through the balance leads seem to be unfounded - which is a relief. AW I just meant no-one had replied with "don't be soft - just wire 'em up" so I concluded (wrongly) that nobody had ;^)
Cheers me dears

I have always had my balance taps P'ed ( using home made P adaptors ) it has never been a issue , the packs stay balanced much better.