4s 21700 Battery Pack

[travo]

Basically, I want to build a battery pack for a speaker that I wish to create. I have 4 LG M50 21700 batteries and wanted to connect them to this bms. https://www.aliexpress.com/item/New...04e4-4411-a16f-a09e107b9125&priceBeautifyAB=0 I was wondering what I could use to charge the pack. I have a usb C female port and was wondering if I could just charge it with 5v 1a?

 

[amberwolf]

If it's not a 5v battery pack, then you can't charge it with 5v.

You have to charge it with the voltage it will be full at.

Since you have a 4s pack, then you would need to multiply the fully-charged cell voltage listed on the spec sheet for that particular cell by 4, to find out what the full pack voltage will need to be for the charger.

 

[travo]

Okay so basically the cells max voltage is 4.2 volts. So 4.2 x 4, because it would be in series, would make it 16.8 volts. So I would use a 16.8-volt charger. Then I need a BMS which I assume the one in the post above would work. Also would the amperage of the batteries affect the amp board? Did I miss anything?

 

[amberwolf]

Then I need a BMS which I assume the one in the post above would work.

Can it supply the current your speaker will draw?

Is it meant for the cell chemistry (voltage range per cell) you're using?

If both are true, then it should work, otherwise, it wont'.

Also would the amperage of the batteries affect the amp board?

Not sure what you mean by that, but if the batteries can supply the current the speaker will draw, without dropping in voltage (sagging) significantly, then they'll work. Otherwise, you need more parallel cells, or different cells that can supply more current.

 

[travo]

Okay, that makes sense. This is the bms I will be using - https://www.aliexpress.com/item/4S-...tion-board-with-equalization/32859593497.html It is a 40amp (Perfect for my project) with 4s formation (also perfect). Here is the charging cable I was going to get. I believe that it should work just fine. I'll plug it into a 12v female jack I have lying around. Thanks for the answer!!!