Bypassing a BMS for only charging

Making my first board and looking into BMSs, could I buy an BMS with a lower Current rating and only use it for charging?

Yes. This is very common.

And recommended for user safety.

You should add a fuse from your battery pack in case of ESC failure to avoid fire.

How would I add a fuse/what does that mean? Not familiar with electronics

A fuse protects the system (and wires) in case of touching the red and black together, this can happen in a failure of component, or because of an accident or mis-use.

Here is a typical circuit:

Here’s a 150A auto fuse.

You can also get a normal 15A auto fuse in holder for your charging port.

Where are you getting your battery from, as these things are dangerous, and it is advised to understand basic electronics and read up well on best practice and tips if you plan to play with lithium cells. Many battery builders will wire in fuses and BMS units for you, so you may not need to worry about any of this if you buy the right parts.

I bought cells from the 18650 Battery store. I understand the basics and am getting help from someone who is majoring in electrical engineering (I’m a college student)

Great, always good to have someone watching your back.

Did you buy a BMS yet?

I recommend a DeliGreen or Daly BMS, as they are small and in a neat case. Their smallest model 20A (10A charge) is enough for most boards.

There is a smart bluetooth one sometimes called LTT, it’s a bit larger, but you can view the cell voltage on your phone.

I haven’t bought the BMS yet, for those 2 brands is there an 8s configuration? Or a 10s that I can use if not?

Thanks for all the help btw

They will do you one like this:

I cannot find an 8s listed, you have to make sure it is for Li-ion (3.7v), as there are other types of batteries BMS are used for.

Basically this listing shows you all the sizes, the charging current is half the actual rating, you contact them and tell them that you want an 8S Li-Ion BMS in whatever current rating, and they will sort you out.

Cool thanks for the help, I think there’s a Daly one on Amazon that I’ll probably get.

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I would not fuse the main ESC power wire but whether you do that or not, definitely fuse the charge port.

Would an 10s bms work for an 8s battery pack?

No. It won’t you need the correct S and cell type.

Otherwise it will prevent charging.