# 10s BMS help - 11 balance leads?

So I just received this 10s BMS in the mail from used parts sale on here. Just confused as to why there are 11 balance leads? What’s the extra one for?

That is for the negative lead, aka B-

Awesome thanks!

If you have ten cells in series, there are 11 connections. Lay them all out on a desk and look. If you connect on the negative side of each cell, then on the one end there will be a positive-end connection for B10

All relative to battery negative:

B-: 0V B+: 42V

balance wires: B0: 0V B1: 4.2V B2: 8.4V B3: 12.6V B4: 16.8V B5: 21V B6: 25.2V B7: 29.4V B8: 33.6V B9: 37.8V B10: 42V

So 0 through 10 is eleven wires

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Connect battery minus before you plug that in

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Still learning, so thanks for the more detailed explanation. Hoping to eventually use it to wire up a battery similar to this

Notice how that wiring diagram only shows a balance port with 10 wires

Yeah, if your BMS has the extra wire (B0) you can wire it this way and you can charge through the balance leads and just run the big fat wires to the ESC only. (Leave B- unhooked, but first verify with a multimeter that it’s connected to B0)

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Those last two diagrams really clear that up! Thanks yo

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@ryansinatra I edited the bypassed diagram a tad, check it again. It’s slightly more clear now. You need to verify that internal connection exists before leaving B- unconnected on the BMS.

@b264 is it standard that if the bms has a “B- or B0” Balance lead, it is intearnally connected to B-? How can you be sure they are connected. Genuine question.

Before charging through the balance leads, you should make sure the wires are rated for the charge current. For example, if you have 24 AWG balance leads, you shouldn’t use more than 3.5 amps for charging or you should connect the big black wire to the B-.

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You can use a multimeter and check reisstance between the two. Very low resistance means it’s connected.

There also shouldn’t be any kind of circuitry between them, as it likely connects to a common ground.

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Yes, what @TowerCrisis said and also why you should check to be sure. Sometimes you don’t even need a multimeter, you can see the copper traces connecting them if you look. But you should use a multimeter anyway and verify zero ohms between them.

Also some BMS don’t have B0 at all.

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thnaks for the info! im guessing a continuity test would also work?

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Still kind of new to all this, so I need to ask, what is this cable for? E switch install?

That’s the temperature sensor

If you use this BMS for discharge, too (what I recommend) then you should connect B- in any case. Discharge (-) and charge (-) goes to C- on the BMS, no connection at P-.

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Why do you recommend using it for discharge to rather than charge only? Just wondering

Because of all the safety features like over-charge, over-discharge, over-temperature, short circuit protection for battery and charge port…

This BMS is for 60A cont. and can handle up to 110 or 120A for a short period of time. I use this BMS for discharge, too without any problems. And on my MTB I use a Bestech 50A BMS up to 100A. In the past I had a tiny BMS for charge only but I like the added safety.

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Where you found the max characteristics? I mean if a bms is rated for 60a, where I can find the peak current they can handle for which time? In the specs from bestech for example it’s nowhere mentioned. Always wanted to know that. As i was never sure I also never used a bms for discharge, only a fuse where I knew which current I can draw for which time.