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BMS
#1
hello all,
Just got 10 24v 3kw battery packs. They will be parallel, so 24v 30kw. The packs have a balance/temp pigtail already.
My question is, is there a BMS that is multi channel and used for parallel wiring. Or is the pigtail purely for monitoring?
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#2
Pigtail is more or less for monitoring... really should not be used as a current path.

With this type of configuration you really should have a BMS monitoring each module.
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#3
which 24v pack?
Most BMS's can handle packs in parallel
later floyd
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#4
You could probably connect the balancing wires in parallel with a custom board & use a single BMS (better quality, with higher bypass current) across them all.
The temp wires you would have to figure out that separately eg depends on type of sensor, etc.
Running off solar, DIY & electronics fan :-)
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#5
(09-11-2020, 11:47 PM)Redpacket Wrote: You could probably connect the balancing wires in parallel with a custom board & use a single BMS (better quality, with higher bypass current) across them all.
The temp wires you would have to figure out that separately eg depends on type of sensor, etc.

Depending on the setup, the load, and how good/bad the modules stay in balance, I have found this to not always be a sustainable move.

I tried doing this with some modules that had some 300-400mV balance issues and its near impossible to report to the BMS that some cells were in distress.

Eventually is would equalize, but with heavy loads it had too much current moving thru the balance leads. 

So it can work, but it depends.  I ultimately put one Bluetooth BMS per module that was in parallel to keep tabs on each cell.
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#6
(09-12-2020, 01:20 AM)Crimp Daddy Wrote:
(09-11-2020, 11:47 PM)Redpacket Wrote: You could probably connect the balancing wires in parallel with a custom board & use a single BMS (better quality, with higher bypass current) across them all.
The temp wires you would have to figure out that separately eg depends on type of sensor, etc.

Depending on the setup, the load, and how good/bad the modules stay in balance, I have found this to not always be a sustainable move.

I tried doing this with some modules that had some 300-400mV balance issues and its near impossible to report to the BMS that some cells were in distress.

Eventually is would equalize, but with heavy loads it had too much current moving thru the balance leads. 

So it can work, but it depends.  I ultimately put one Bluetooth BMS per module that was in parallel to keep tabs on each cell.

Agree if your packs differ, are DIY or have balance issues.
Good point about issues being "hidden".
I was thinking since the OPs packs are all identical, this might not be so much of an issue?
Running off solar, DIY & electronics fan :-)
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#7
(09-12-2020, 11:25 AM)Redpacket Wrote:
(09-12-2020, 01:20 AM)Crimp Daddy Wrote:
(09-11-2020, 11:47 PM)Redpacket Wrote: You could probably connect the balancing wires in parallel with a custom board & use a single BMS (better quality, with higher bypass current) across them all.
The temp wires you would have to figure out that separately eg depends on type of sensor, etc.

Depending on the setup, the load, and how good/bad the modules stay in balance, I have found this to not always be a sustainable move.

I tried doing this with some modules that had some 300-400mV balance issues and its near impossible to report to the BMS that some cells were in distress.

Eventually is would equalize, but with heavy loads it had too much current moving thru the balance leads. 

So it can work, but it depends.  I ultimately put one Bluetooth BMS per module that was in parallel to keep tabs on each cell.

Agree if your packs differ, are DIY or have balance issues.
Good point about issues being "hidden".
I was thinking since the OPs packs are all identical, this might not be so much of an issue?

It depends right... Unless each module is cycled and tested ahead of time for problems, then maybe, maybe not.  Really just depends on the batteries and the likelihood of it developing a problem after the fact.

I am working with EV modules that put me in a similar position... and on paper it seems fine, but in real life execution you find things that make you question what you are doing is really the right thing.

I've tried both ways and at the end of the day, decided that spending an extra $50-60 for a BMS setup for each string of series cells (or one per pack/module) was just the right move.  In fact it simplified the wiring and made the system less fragile.
Redpacket likes this post
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#8
OK, so I'll give more info on my scenario.
I am building a skoolie. I have solar panels (7 x 400w), 24v 6000w inverter, 100a solar charge controller, 10 24v 3kw batteries.
the batteries came from a solar field, with tap for temp/volt monitoring.
since the batteries will be parallel on a bus, I am thinking that i will need a bms on each pack.
i saw that there is a 8s 24v bms, but no way of monitoring all 10 packs.
any ideas or suggestions ?
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#9
As mentioned above, sounds like you will need 10 BMS units, ie one per pack.
Probably best to look for mid range one.
At the better end, a batrium system would need 240 (+spares) cellmons & the one controller + shunt, that'll add up!
Running off solar, DIY & electronics fan :-)
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#10
It would be 80 Mons and not 240 though Wink
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