Choosing a BMS and charger

This is the second post I’m making about this subject because I am confused. So I’m upgrading my board and I want an easier charging solution, I read about BMS’s and it seemed like the best (and only?) option. I figured out how to connect a BMS to a board, where to solder and stuff, but what I still don’t understand is the difference between a 3$ 6s BMS and a 50$ 6s BMS. The only difference I can spot is the difference in Amps, does that mean the speed it’s charging at? How many amps will not go too slow for two 3s 8000mAh batteries in series? And am I supposed to use one of those cheap eBay chargers? When I thought I had it figured it I was thinking of getting these two: But the shipping to my country alone is 110$, thats too much. If anyone knows where to get these parts on another site that would be great too. Any help aprecciated Thanks

Usually the amps highlighted on the BMS ads are the discharge amps, meaning that you can put that much current through to electronics until the overcurrent protection kicks in.

Quality is also an factor when you compare them.

If you want cheap, then Aliexpress and eBay.

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You have any specific BMS’s to recommend?

So your setup is 6s right are you using a vesc or what? if you are you can choose to buy one of the cheaper ones since you can then bypass the discarge. Beacuse the cheap ones are rated to 10A depending on which one. Chargeing dosent require that many amps i think my charger is 2 Amps. But if you are using a bms for dischare it needs to be alot higher since the motors is taking alot. The pros with the expensive one: -Safe charge and discharge, meaning your cells is being messured when chargeing and discharging.

The pros with the cheap one: -Its cheap, and many people finds that this is enough. With a vesc you can set voltage cut off limits.

Im not sure how much your motors is drawing at its high. But could probalby find a cheaper charger.

Thats the one i’ve got, but mine is for 12S meaning a 52V or so. The voltage doesnt really matter aslong as it is more than your batteries max.

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Alright, yeah I just bought a vesc, it’s on its way, and I really only need a BMS for charging and not discharging. Do you have any BMS’s you recommend? I can’t seem to find any just randomly searching online And about that charger, isn’t it too slow for 16000mAh? Thanks for the response

Do you have a recommendation for a good BMS for a 10S4P with the samsung 30Q batteries? The price isnt that much of an issue, i’d choose quality over price.

Hi ShakeNBake

I’m actually sort of in the same situation as you and looking for a BMS/charger solution.

But i can give you some insight into how capacity and charge time works:

  • You have a 8000 mAh battery, even though you are using two 8000 mAh batteries. This is because you have them in series, if you put them in parallell it will make a 16000 mAh or 16 Ah battery.
  • To figure out a rough charge time, take your battery capacity(8000 mAh/8 Ah) and divide by the charger current(2 A): 8 / 2 = 4 hours.

In reality there is some powerlosses to heat when charging, say 10%. But you also will not be using the stated 8000 mAh, doing so will destroy your battery. Most likely you will only use 6000 mAh or maybe 6500 when the battery is completly flat, so this will put you charge time at 3-3.5 hours.

So now it’s up to you to decide if that is a good or bad charge time, personally I’d say it’s quite alright. if not then get a stronger charger, at 4A you will cut the time in half. Though i’d recommend that you don’t exceed 6A, slower charging is better for the batteries.

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The problem with the charger is that what i understand that its safer, but you could go for a 4amp charger. Like petter said.

For you @RazzleDazzle you need to find one that suits you i bought mine at The only problem that you need to buy atleast 2 units at once. Mine was lipo so dont know about diy li-ion packs. And again you can choose to get one with low amps continues or a higher one that suits your motor draw. So that it protects the cells when chargeing and dischargeing. :slight_smile:

Thank you! that makes more sense, 4 hours is a little too long so maybe the 4A charger that will be around 1.5 hours? I’ve been looking around on and i cant find a non-discharge bms, do they not have them or am i missing something?

You need to look for the ones with a low continues current. And then find at topic in here on how to charge only. :slight_smile:

Yeah, what i think Migro means is that you buy a normal BMS, connect it but still leave your ESC and motors etc connected just as they are now.

image This picture for example is wired for a BMS with a high discharge rating, say a 60A BMS for a 50A load? Should work fine.

If you instead have a low discharge BMS and still need to pull high amps you can bypass the BMS with the discharge wire. That is, in this picture you would move the black discharge cable from P- to B-.

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Thanks for the responses, So in that picture, where does the xt90 connect to? the battery or the vesc?

The xt90 connects to the vesc :slight_smile:

The stack of red and white circles on the are supposed to represent the battery

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Oh lol, how didn’t I figure that out haha The diagram shows a discharge+charge connection? So if I want a “charge only” BMS, I need to put both the + and - of the battery on the b-? so the current won’t go “through” the BMS? Another thing, BMS’s capable of high discharge are more expensive, and I don’t need/want to have another protection because I already have a vesc to control the voltage, so I need to look for a bms with a higher charge rate (30-50A?) and the lowest possible discharge rate? (just to drop the price considering I’m not going to use the discharge function at all) don’t know if that logic is stupid or fine. Thanks

Um… No.

It’s actually quite simple but a bit confusing.

  • You connect the vesc to the battery. Just like you probably already have.

  • connect charge cable to bms and bms to the battery.

That is all. This is also why its charge only, since the vesc is not connected to the bms at all.

Oh, thanks for explaining Only thing I still don’t get, is how I choose my bms. I see so many models in here and I cant tell the difference: How much continues current do i need?

Here you see both charging and discharge. Of these it’s only charging that you are interested in.

But even with a 4A charger, pretty much any bms will be good enough so i’d say pick one you feel will fit in your enclosure.

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I cant explain how much youve helped me, thank you. One last thing, i looked on amazon, ebay and aliexpress and couldnt find 1 4A charger, only 2As Am I just not looking right or an i supposed to buy them somewhere else? Edit: talking about a 22.2V-25.2V charger for 6s

Glad i could help :slight_smile: Also since i’m pretty much looking for the same thing it’s nice to see all the options

You are right though they were not very common, there seems to more of this style:

Just remember to tell us what you decide to get in the end!

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The 4A one looks good, thanks! ill look at all the bms’s and choose one, problem is i cant see the pricing so it makes it harder to pick one