BMS Hunting No More

[scepterr]

Hold onto your brain buckets folks. So here’s the thing, if you have a dumb BMS(no IC,nothing fancy) like the D122, D140, D190 etc, you can use for instance a 12S BMS on lower S counts. They work on a per series basis, the actual total voltage is irrelevant for it to function. So if you take a 12S BMS and wire an 11S battery and charge to 11S voltage. IT WORKS

I’ve tested this on the 12S D122 on my 11S I’ll be testing the 12S D140 tomorrow on a 10S battery

I wanna buy up as many BMS as I can find to test this functionality on, if you wanna contribute to the effort, my PayPal [email protected]

[barajabali]

Works for supower bms too

[scepterr]

Technically this should work on any that are just discrete component based logic

[isqueromeroderviz]

I already wanted to know about this from the 12s bms to 11s

[Deckoz]

Yep…I’ve done this a few times before… Even wired dumb 3s & 4s BMS together to make a 12s just share some balance leads that need to be shared between the bms and you can. Have a multi part pack… That takes up far less BMS space…

[scepterr]

I’ve always assumed this was possible just didn’t wanna say anything till I did it and everything was fine.

[ZackoryCramer]

But how exactly does it work? Wouldn’t this mean the bms would output even if one of the cells disconnected resulting in a “type 2” error?

[scepterr]

I have no idea what you just said lol

[Deckoz]

@ZackoryCramer

But how exactly does it work? Wouldn’t this mean the bms would output even if one of the cells disconnected resulting in a “type 2” error?

Forget all you just wrote… Two words

Charge only.

Also @scepterr 11s5p?

[scepterr]

Lol yeah 12S fit but with no room for all the extra bits I wanted, 12/5V stepdown, Arduino. 10S left too much room, 11 was the magic number

[Deckoz]

Still… You have 14 more cells then it was designed for. Gonna be awesome.

Where’s the build thread?

[scepterr]

Once it’s rolling I’ll put a build thread up Got 4 build threads incoming, easier to post when done

[pat.speed]

@Deckoz do you think you could give a little more of an explanation to how you wired multiple small bms together? Pm maybe as not to go off topic

[Hummie]

sounds like a squeeze job. want to see.

[scepterr]

@Hummie I’ll be mocking up the battery for your deck tomorrow, let’s see what happens The 11S5P is 18.5"x6.5"

[ZackoryCramer]

I meant to ask technically why it works. Shouldn’t the bms block all current flow if one of the cells is faulty/disconnected?

[scepterr]

If it’s in the middle yes, if it’s at the end no

[Deckoz]

Well every balance lead except B- and B+ is really a ±

Let’s take 3s bms’s. Cell 3 balance lead needs to share b- balance lead of the next group. Which technically happens because of the series connection. B- of each group must be connected. Ie cells 1-3 group cell 1 connected to b- of BMS 1. Cell 4-6 cell 4 connected to b- of bms2. Etc. B- is the ground and no balance functions will work without it connected on most dumb BMS

To charge -ch on BMS one to charger negative. Charger positive to end of pack b+(not group b+)

[b264]

@scepterr do you have a schematic for exactly how you’ve hooked up the 11SxP to the 12S BMS?

[scepterr]

11 wires instead of 12, last one skipped There’s really nothing to it other than pretending it’s for whatever S count you have