Need some BMS Advice Please

[NovaOx]

Hello, My E-bike's BMS has died, I think I know the proper BMS I need for my E-bike (Moscow plus), but I am not 100% sure so I thought I would ask and see if I was right. The battery is a Dehawk I5 48V 16ah 768wh, there is no AMP rating that I can see at all on the board, but on the positive output wire I have a 30A fuse, so I assume the BMS should not exceed 30A? If I get a 13S 48V 30A BMS will this be suitable? I had seen on some info for the battery its constant discharge is 18A, and the motor on my bike I believe is 500W, The 30A BMS's often state suitable for a 1000W motor, will this hurt my motor using it? I assume the controller on the bike itself governs the amount of amps/watts used but I am not sure as I am new at this stuff.

 

[harryS]

The motor controller determines the max amps. They don't stop working when you hit the limit. You just won't get any more current. You can use the biggest 48V battery you want, but the controller will just use what it was designed to use.
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I believe a 20A BMS means it uses transistors rated for 20A. It doesn't hold the max current to 20A. If the controller asks for 30A, you may get it if the cells are string enough, but you may melt the BMS transistors. Nothing wrong with using a larger BMS if that's all you have, but you don't put in a smaller one because it may overheat.
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The problem I have seen with hard case batteries is that there is often no space available for a larger BMS. Check the space you have and the dimensions of the one you're going to buy,.
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When you choose a BMS, make sure it has balance capability, Look for the balance current specifications, usually 40-70 ma. If this is missing, it won't balance. If the cells are off by .15 volt, you could lose 20% of the available AH easi;y.
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[NovaOx]

The motor controller determines the max amps. They don't stop working when you hit the limit. You just won't get any more current. You can use the biggest 48V battery you want, but the controller will just use what it was designed to use.
.
I believe a 20A BMS means it uses transistors rated for 20A. It doesn't hold the max current to 20A. If the controller asks for 30A, you may get it if the cells are string enough, but you may melt the BMS transistors. Nothing wrong with using a larger BMS if that's all you have, but you don't put in a smaller one because it may overheat.
.
The problem I have seen with hard case batteries is that there is often no space available for a larger BMS. Check the space you have and the dimensions of the one you're going to buy,.
.
When you choose a BMS, make sure it has balance capability, Look for the balance current specifications, usually 40-70 ma. If this is missing, it won't balance. If the cells are off by .15 volt, you could lose 20% of the available AH easi;y.
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Thank you for your reply, You are correct when it comes to limited space for the BMS, I need to find one that is no wider than 55mm, length isn't as bad with about 100mm of space. My main concern is not destroying my batteries, there is zero help from the manufacture as they wish you to spend another 600-1000$ on a new battery rather than fix the one you have with a 30$ part. I guess I was sort of right about the controller being the part that governs the current. I have a 30A fuse on the main power output line, I wonder if it may be wise to get a 35A BMS, my thought is, if the BMS is rated higher than the fuse, than the fuse should pop before the BMS does, do you think this is ok? I have been triple checking any potential BMS has a separate port (connection for B-/C-/P-, Balance, a Temperature probe, and an on/off switch, the latter being the hardest thing to find on a BMS it seems most are common port, and many lack a temperature probe and seems very few even offer an on/off function. The Battery specs stated a constant discharge of 18a max, does this number represent the max draw of the controller? It would have been nice had the manufacturer actually labeled the battery with relevant info, or even the BMS as neither have any real info on them, The BMS does have a 13S on it, but nothing else, and the battery simply has the type I5 and volt/ah 48V/16ah, but nothing regarding max output, I had to discover that through digging. this is one BMS I was considering Do you think it would be an ok one to use? (They also offer a 30A if 35A is too much) https://www.aliexpress.com/item/1005004820133678.html?gatewayAdapt=4itemAdapt









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