is it possible to “stack” BMSs? in my case i have 3 packs of either 10s7p or 12s6p. one would be in the bottom enclosure while 2 in a top enclosure. i made the top into 2 packs so i can evenly draw power from all 3 packs. but i would also like the option to take the top packs off if i need more portability so id have 2 bms, 1 for bottom pack and one for the two top packs. but if i were to parallel from the 2 bms, the bottom pack would draw double the amount as one of the top pack. so would it be possible to wire the bottom bms’s output into the input of the top bms so i can draw evenly? i have a diagram for better clarity. i dont see any problems with this but id like outside feedback from more knowledgeable people. Thanks!
I would say use a separate bms for each pack and don’t connect BMSs, only put the packs in parallel. But if you don’t know how this is supposed to work I would say leave it alone, connecting batteries in weird ways is how you get into trouble
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+1 i smell fire hazard.
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Besides the potential to fuck this up easily, this is compounding failure points and could be very dangerous.
I’m not certain about what you’re describing, but i think your describing a parallel series parallel pack. You don’t need to do this, and it’s better to keep it simple. Three packs three bmses.
12s6p is a large battery. You don’t need to run them in parallel. You could just have 3 separate packs and use exposed xt90s with water tight covers to switch between the packs. The benefit of an auxiliary pack run in parallel is typically drawing less current per cell, which will improve cycle life. Unless you’re drawing a huge amount of current at 12s6p you probably won’t see a significant enough benefit from running your packs in parallel.
If you do decide you do want to wire the packs in parallel you have to make sure that they are all charged to the exact same amount before connecting them. You should fuse the parallel connections between each of your exhilarate for packs and your primary pack. I’d even consider not bypassing each of the auxiliary pack’s bms. So that you get fused protection and software protection from overcurrent on your auxiliary packs. With both of those protections your chance of fire from accidentally connecting packs different voltages is reduced.
Never run your ESC with settings above your primary pack’s rating. That way even if the your auxiliary packs are disconnected by software, or a fuse breaking, you will still be fine.
Thanks. I think ill just get 3 bms to make it simple.
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IHMO the safest way to deal with 3 batteries, is to have one male XT90 (yes, only one) on a short “pigtail” and each battery has a female XT90s on it, and you can physically only have one plugged in at a time.
This would be instead of a loopkey. These would serve as the loopkey, but also make sure that only one battery could be connected at a time,
genders:
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