I took it out of a solar power bank. I just happen to need a 2s charger.

 

What is a "2s" charger?

 

2s is probably two Lithium Ion or Li-PO cells in series. Conventional Lithium cells charge to 4.2V each.
The pcb is marked 7.2V for two fairly discharged cells and 10.8V for three fairly discharged cells. But the unknown pcb might be set at the low 3.6V per cell charging for newer LiFePO cells.

The charging current for the battery and the charging current limited by the pcb are unknown so they might not match.

 

But I guess I could try right?

I mean if I wired up 2 batteries in series and connect a solar panel to it (9-10V/2A).

 

It's a 3S cell BMS

 

Please make and post a video of your battery exploding. But the charging pcb might do nothing since the voltage from your solar panel is much too low.
Why didn't you say what is the voltage and mAh ratings of the original battery and your battery to see if they match? What was the voltage and current of the original solar panel?

 

At least this one I probably won't be doing chest compressions on. I'll have to brush up on my treatment of burns training though.

 

Since you did not post the voltage and mAh rating of the original battery and your new battery, are they the same chemistry and sizes?

 

ok so my questions should be, how do i design a battery charger for 2S 18650s.

Im using the same batteries that came with the BMS board, I just ripped them out.

How do I calculate the V/A required for the solar panel?

And since this is a 3S then I cant use it for 2 batteries.

 

ok so my questions should be, how do i design a battery charger for 2S 18650s.

Grab any number of battery charge control ICs for Lithium Ion chemistry and start with the Typical Application circuit. Digikey search of "Battery Management System" will work.

Im using the same batteries that came with the BMS board, I just ripped them out.

Were the batteries welded to the wires, soldered, mechanically connected. Ripping might not have been a good way to do it.

How do I calculate the V/A required for the solar panel?

If you want V/A.... use a multimeter using the resistance setting. If you want open circuit voltage and short circuit current use the part number on the solar panel and look at the datasheet. Otherwise, you need a "perfectly" sunny day, at 25C temp and measure the voltage at the terminals for open circuit voltage. Then, short the terminals together and measure the current that is going through the wire for short circuit current. The real operation of the panel is somewhere between there.... and it's a non-linear curve for both voltage and current. Good luck.

And since this is a 3S then I cant use it for 2 batteries.

Depends on how they implemented the BMS. If it were me and I saw that the 3rd battery was "open circuit" I'd shut down the system. That's me and I'm kind of a wimp like that.

 

That pcb and the power supply voltage that feeds it were designed for 3S and probably will not work with 2S.
It might not even be a charger circuit that is inside the computer. The pcb is probably the "protection circuit" that was inside the battery case.

 

A 2S Lithium battery charger circuit feeds 3 wires to the 2 cells in series so that the cells are balanced charged. My RC airplanes came with the chargers. you can buy a suitable charger from a hobby store. Get one that charges at about 1A or 2A. My chargers are powered from a 12DC wall-wart but might work with your solar panel.