# How to control current to charge batteries?

I have an Arduino project that is powered with a 1s battery pack (multiple 18650 in parallel).

I use following module to protect against overcharge/overdischarge : https://aliexpress.com/item/32982853134.html Let's call it my "BMS", eventhough this does not balance anything since my battery pack is 1s1p right now (and will become a 1s6p pack later once tests are ok)

The reason I chose this module over the famous TP4056 is because I also use my project to charge some peripherals (earbuds, etc) which draw more than 1A (the TP4056 has overcurrent protection that kicks in at 1A maximum). I have a DC boost that converts the 2.5V/4.2V of my battery pack to constant 5V output (and can output up to 3A, which is sufficient).

Here is my problem : my BMS does not limit INPUT current. I choosed this BMS specifically because it has big OUTPUT current (about 15A).

The datasheet of my 18650 cell says I can charge it at 1.7A max. So I need a way to limit the INPUT current to 1.7A today, but 10.2A later (6*1.7A, because of 1s6p). How can I do this?

For now, I am using my bench PSU to charge the battery pack, where I set it at 4.2V output and current controlled at 1.5A max. This is not very convenient. I later want to use my phone's usb charger, that can output up to 60W. But right now that would probably not end very well since it will output 12A (5V*12A=60W) into my 18650 cell (1s1p).

What I tried so far:

I tried to put this module between my PSU and my battery pack : https://aliexpress.com/item/1128315250.html It has 2 potentiometers : 1 to set the output voltage, and 1 to set the max current. I set my PSU to output 12V and 5A max. I set this module to output 4.2V and turned the amp potentiometer at max. I put an ampmeter in my circuit to mesure what would happen and noticed my battery was drawing about 0.75A and it was slowly decreasing to 0.74A, 0.73A, 0.72A, etc as it was charging I believe. I was not able to make this module output 1.5A...

I will provide a hand drawn schematic if necessary.

TL;DR : How to charge 18650 Li-ion with controlled current?

• Purpose-built battery charger.
– user16324
Commented May 18, 2022 at 21:39
• I want to charge it with a phone's usb charger and not carry a chunky "Purpose-built battery charger" (which I do have already).
– Musa
Commented May 18, 2022 at 22:13
• "I put an ampmeter in my circuit to mesure what would happen and noticed my battery was drawing about 0.75A and it was slowly decreasing to 0.74A, 0.73A, 0.72A, etc as it was charging I believe. I was not able to make this module output 1.5A..." - The meter was in line with the battery, not the power supply - right? Ammeters have shunt resistance which causes voltage drop. What voltage did the battery have on it while you were doing this? (you will need another meter to measure voltage and current simultaneously). Commented May 18, 2022 at 22:38
• The ampmeter was in line with the PSU. It looks like this : bench PSU -> Buck converter -> ampmeter --> "bms" -> battery. I will draw and post a schematic at daylight.
– Musa
Commented May 18, 2022 at 23:02
• The battery defense should be on the device, if not on the battery. Don't use Aliexpress crud when safety is at hand, meaning anything with AC power or anything with lithium BMS. UR-Recognized at the least. Commented May 19, 2022 at 2:40