Multiple battery packs in parallel. How does BMS hook up?

How-Tos & Esk8 mechanics Esk8 Mechanics
#1

Back story:

  • My electric unicycle consists of two battery packs. (One on each side of the wheel)

  • Each pack has their own BMS. (proprietary gotway bms)

  • The discharge ports to the ESC is hooked up in parallel. The charge ports is hooked up in parallel

  • There is a BMS “signal cable” that joins the two BMS’s together in case one battery pack goes wrong

  • One pack goes wrong… :frowning: Had a dead group in one of the packs

  • Both the packs stopped charging at 23s (24s normally). The BMS overcharge circuitry behaved as expected.

  • I did a test by disconnecting the “signal cable”, and both packs started to charge over 23s. (overcharging the dead pack slightly to 4.25v) I ended the test immediately and discharged until they were 4.2v.

  • I ended up replacing the 2 cells in the dead group and all is well and both battery packs are healthy and working as expected

Conclusion:

  • had there not been this “signal wire”, the bad battery pack would have charged to 24s full! (4.38v/cell which is dangerous)

Question:
I am adding a 3rd battery pack because there is space in the enclosure, and I am putting one of these regular BMS’s in there (this) or with (bluetooth).

But these ones don’t have the proprietary “signal cable” that lets other BMS’s know to stop charging in case i get another dead group

If this same scenario happens to some of the guys on here that are paralleling packs, would they charge to dangerous levels? :frowning: Since all of our BMSs are cannot communicate with each other (guys over here)

Is anyone here a BMS expert that can chime in and shine a light on this topic?
Thanks :slight_smile:

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#2

Yeah. I have a skate w/ separate packs that are wired in parallel, and had to give this a bit of a thought. Each has their own BMS and they are charged independently (separated w/ a loop key). If I’d had room and didn’t mind the weight, I’d put a bluetooth BMS on each pack and charge them all together.

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#3

Would the Bluetooth BMSs have the capability to talk to each other? Or will you be monitoring them via an app every time you charge them up?

#4

Yeah, I keep an pretty close eye on my packs when I’m charging them.

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#5

I feel like if there is nothing in the app about this than it wouldn’t have this capability.

Having two separate bluetooth connections for each battery would be a pain too, if they could communicate to a single BT transmitter that would be dope af.

#6

Maybe Metr can now that it can connect to one

@rpasichnyk

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#7

WHAT I missed that :blush: :upside_down_face: :kissing_smiling_eyes:

News like that deserves it’s own thread nearly!

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