Parallel charge and series use with two TP4056?

I just do not know if this will work, but here is my scenario:

I want to charge 2x 18650 batteries in parallel with two TP4056 charge controllers with just one charge input. I know i can that. BUT.... i want the 18650 batteries to output 8.4V to my project.

My project is not important here, but i need to know if i can do this charge circuit i any way?

I know i can use an 2S Charge controller and connect the batteries in series, but i do not trust the balancing function on the BMS boards so i want to charge them i n parallel.

It is a language barriere here, but i'm understand english a lot better than i write :slight_smile:

This is the picture of the module. *t's the module with protection etc.

Unfortunately no, you can't charge two batteries from the same source at the same time as getting output from the two batteries in series. The only way that you could do it would be to use two isolated power supplies.

If you are not too bothered about the charge speed, you could use a couple of 1W isolated dc-dc converters... that would supply about 200mA charge current, so 10 hours to charge a 2000mAH 18650.

I see. But what if i separate the circuits wth an switch or something when charging?

Maybe i just can use an powerbank in stead?

I see. But what if i separate the circuits wth an switch or something when charging?

If it's ok to charge just one battery at a time, that would be possible. You would need to use a double pole double throw switch, as you would need to switch both 5V and GND lines between the inputs of the two TP4056 modules.

Why...? There are gazillions of applications that do it successfully every day.

Here's a video showing the use of parallel TP4056s to charge parallel batteries:

If that works, you could use 2 TP4056 modules connected in parallel charging 2 18650 cells in parallel, then use a boost converter to get the voltage up to 5V, or whatever other voltage you need. My understanding is that cells in parallel are self-balancing. It's not clear from the video how battery protection would work. Maybe you would use protected cells.

I have seen some Youtube videos that claims that these balancing boards do not work properly. Maybe it's wrong, but i just do not know...

What is the final regulated voltage you need to produce from the 8.4V? Is it 5V? If so, you could use the batteries in parallel and use a boost converter to produce the 5V. Then there would be no balancing issue, and battery life should be as good as with batteries in series.

Yes, i think 5V is good enough. I'm planning to power arduinos and 8266 etc. so i think a TP4056 (or two for encrease charge current) for charging 3-4 18650 is the way to go.