Did I buy the right bms?


I got tired of opening my enclosure to charge lipos and ordered a bms I intend to use for charging only. I started looking at some wiring diagrams and got kind of confused. I bought the following cheap BMS without much information: https://www.ebay.com/itm/222272460111.

The only pads I am seeing are B+, B- and P-. I see most other BMS diagrams feature a C or CH port. Is this bms good for discharging only or should I connect the battery ground to p-?


The battery negative always connects to B-

If there is no C- port then the charge jack negative connects to P-


Thanks, I understand. I’m only charging with 2A, so shouldnt matter if I use the last balance lead of the second lipo (2*4s) or the large/main ground wire right?

If you’re charging at 2A there shouldn’t be a problem using only the balance leads. As long as you’re only using the BMS for charging and not for discharging. That specific BMS isn’t even one that could be used for discharging, so you’re okay. You should put a 5A automotive fuse on the charge jack though, if you can.

why would you only use a bms for charging?

So your brakes can never cut-out. Or because your BMS is rated for 5A and you are drawing 80A peak. Or because you want to remove a possible failure point in your drivetrain.

I’d rather slightly overcharge my battery and reduce its lifespan SLIGHTLY than have my brakes cut out because I hit the brakes on a big hill with a fully-charged battery and when the battery got full, the BMS cuts off charging.

And then of course the #1 reason: cost


I buy this bms, the description say is a normal bms, safe for charging and discharge. but i’m suspicious with circuit, because i don’t have -P port


It would appear C- is the P- port on this specific one.

Beware that running the ESC from C- will POSSIBLY cut-out the brakes on full battery conditions. It really depends a lot on the internal design of the BMS.

Edit: this one does cut off brakes if the battery hits 42.8 ± 0.5 V


Using a magsafe instead of jack actually, but I’ll keep it in mind, thanks!

As @b264 said. It will cut off your brakes even if you charge the battery to 41V instead of 42. In the first kilometers if you brake hard it will cut your brakes. I learnt it in the wrong way :tired_face: Use it charging only!

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Maybe. It depends on a lot of things. It most certainly CAN though. Envision the scenario where the total pack voltage is 41V but a few cells got unbalanced because the pack is old – and once one single cell hits 4.2V the BMS can cut off charging to the whole pack, effectively killing your brakes. Not that I want to damage my battery, but if the alternative is cutting the brakes at high speed, I’ll take slight battery damage in that rare scenario.


The overvoltage to the battery is gonna be for few sec so not a big deal to me. On the other hand don’t have brakes will 100% damage you in few sec :laughing:


so, im fuck…prefer be safe, what BMS you guys have?

The Bestech D190 is a good one. You will be fine, I just would not route the ESC negative wire through the BMS.

just to make clear! this BMS can balance the cells on charging! and (can/cant) balance the cells on discharging? for brake i can´t trust! And how works the break sistem, i thought if you not accelerate, the longboard automatically braake because the motor work like a resistance. if I, move back with the remote controle, will probrably brake?

10A!! if the battery are 36 volts, you just have 10A*36V=360Watts, what is the power of your motor? and the speed you can get

If you aren’t discharging through the BMS (and also charging the regenerative power through the BMS) then the 10A only applies to charging with the charger and not discharging

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true, so you have a bypass. i dont know if i go to this way, because the battery, probably will be unbalanced

It won’t be unbalanced if you charge through the BMS but don’t discharge through the BMS.

i don’t remember which topic was, but i remember to read, the bms stop charging after the first cell reach 3.6 V, so the others will be lower, is this right?