Tiniest 12s bms with balancing

I use this @dickyho BMS for balancing only. Pretty sure he has a 12s version too. Works great!


on his ebays store he only states 10s. but i’l pm him and se what he says.
i have also reached out to 5 different factories in china. i’l let you guys know if I find a gem.

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I remember I have 12S 3.7V one before, but not sure now…

there’s a lot of 12S 3.2V BMS, very few 12S 3.7V one, need to custom made. if many people need it, I can arrange that. How many Amp is popular using?

i would say 80% of all DIYers are bypassing their BMSes. so we care about very few things:
one 10s version and one 12s version (very few go 13s) made for Li-ion / 18650 batteries
size: as small as possible
it has to have a balancing function
charging current limit of at least 4-5A
and they have to prove reliable (but only time will tell that)

and if possible customize: lengthen the balancing wires to 45 cm or something and if possible use high quality fine strand silicone wires made for 200C° temperatures. (so you dont have to lengthen the wires yourself and so they doesn’t vibrate and break)


So, if only for charging, then I will make some 20A one first, it can take 10A when charging. and size is small, with silicone wires. have balance.


Just to clarify:
at the moment the majority of people are using the “D140 bms” originally made by besttech. It is however fairly hard to get hold of sometimes and the size is of" L75mm * W65mm * H8mm" is not super large but if you could save some space that is always a big bonus.

most people charge at 2 or 4 amps. (some crazy people go as high as 8-12 amps) so that parameter is fairly important. but yeah

we solder on the thicker/ main wires ourselves so that should not be included. the 10 or 12 tiny wires that does to each P group however if they could be of higher quality and long enough to reach all over the battery that is a huge time saver. because having to crimp or solder 10-12 new wires is a pain in the ass. so 45-50cm should be enough for most peoples batteries I think.

the “discharge current” parameter is completely useless so go for the lowest possible.

some people like to have high “Balance current for single cell” values of 80mA or higher. But personally I think most people including myself just leave the board connected to the charge at all times when im not actually riding the board so the bms has more than plenty of time to balance the battery . so im fine with 30mA and even lower.

(but yeah there are people like me who just cant fit a larger bms, and by having a smaller bms who knows you might have space for more batteries or something else.)

okay so I have contacted a few different companies/factories most of them have either not answered, or could not fulfill my requirements. I have however gotten in contact with:
Wuxi Bellhope Technology. they said they could adjust one of their 13s BMSes and have it made for 12s batteries. (there are plenty of tiny ie 35 x 60 mm small 10s bmses around but 12s is harder to get hold of)

anyways dickyho you might wanna contact them through alibaba regarding the 12s BMSes. I also invited them to the forum and this thread.

would be sweet if someone with more knowledge regarding bmses to chime in.

picture and data sheet (the data sheet is made fore the 13s version but should be the same):



if you’re getting a custom batch made, Jst xh if possible, and doesn’t make it huge.

Jst ph is so delicat especially if crimping your own custom cable.

Does your 10s version work with lower voltages like 8s?

This really isn’t good for the batteries.

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I know I’m just lazy,

Just measured the 12s one I have it’s the 20A version (I’m not sure if they make the 12s in 15A) and it’s 2 inches by 2.5 inches.

yeah it seems like there arn’t really any easy accessible 12s versions of the smallest bms module.

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the 15A or 20A one I am going to make will be pretty much the same size and look like this on the picture.
is about 60X35X9mm. the balance wire normally is 40cm.


@dickyho can you post a link to your eBay listing

you can find it under his profile

This discharge is only too small for 35A, 30Q HG2 C6 40T group 10-12 string 4-5 and all are 100-150A, isn’t it?

not if you “bypass” the bms and only use it to balance each P-group, and then we rely on the vesc to handle the rest of the safety features.
and like you said the alternative is something that can handle alot of amps and that usually also means a very large and expensive bms.
so that is why a large majority of us like to bypass our bmses and therefore also be able to use super tiny models.

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