Hello everyone,
I am new to electronic and I am working on a project, for this project I am using 2 Li ion batteries of 3.6V 2600mAh (this one actually
https://www.tinytronics.nl/shop/nl/...650-li-ion-batterij-2600mah-5.2a-icr18650-26j) and I use them in series because I need more than 3.6V but the amp is the good one, the thing is I use them in series for the use in the circuit, but I also need to recharge them, and I Don't want to recharge them separatly because it is a pain and it is for a product that should be sell one day to some people.
The thing is I don't know how I can use them in series in my circuit and in parralel to recharge them (I was doing some researches and found that if i want to recharge them together I have to put them in parallel), also I can't use them in series to recharge because I would need a stronger charger and it needs to be charged by usb, it would be better if it has to be sale one day.
At the moment I have a TP4056 to charge them, this board was nice for only one battery but I Don't think it is ok for two of them.

If you have some question it would be a pleasure to reply, and if you can help me you would really made my day!
Thanks.

 

You won't need a different charger , the one you have can be used to charge any size (capacity) of 3.7V ... So with two cells in parallel it will just take twice as long to charge ..

If the cells are removable (not soldered in place) it might be easier to get a cheap dual charger ,

If you don't want to remove them each time you charge , you will need a balancing circuit ...

https://www.ebay.co.uk/itm/2X-2S-Li...h=item1c9d0b7968:g:H9oAAOSw0RpXlkfH:rk:2:pf:0

this is connected to the two cells in series and it makes sure the cells are balanced and not over charged . the cells don't have to be removed from your device to charge them, but you will need a higher voltage (9 to 12V) source to charge

 

Thank you so much for your reply, this is exactly what I need!

 

You won't need a different charger , the one you have can be used to charge any size (capacity) of 3.7V ... So with two cells in parallel it will just take twice as long to charge ..

If the cells are removable (not soldered in place) it might be easier to get a cheap dual charger ,

If you don't want to remove them each time you charge , you will need a balancing circuit ...

https://www.ebay.co.uk/itm/2X-2S-Li...h=item1c9d0b7968:g:H9oAAOSw0RpXlkfH:rk:2:pf:0

this is connected to the two cells in series and it makes sure the cells are balanced and not over charged . the cells don't have to be removed from your device to charge them, but you will need a higher voltage (9 to 12V) source to charge

One more thing, I found a tutorial where the guy shows how to use this dual charger, but I Don't understand it, because he use this schema :


But then when he mounts it :

He plugs the positive side on B+ and B- and the 2 negative sides on BM, whereas it is not what is on the schema, so I am affraid to do Something wrong and I Don't know which one I have to respect.

Also which charger is better, 9V or 12V, how can I know this?

Thanks for your help.​

 

The positive B+ gives "2 x battery voltage", the middle pin keeps the voltage stable for the second battery, the B- is the "0VDC" or "GND".
He plugs Battery2+ to B+, Battery2- to middle pin, middle pin to Battery1+, Battery1- to "GND".

In your case the "9VDC" should be better, but normally it does not matters if you setup the circuit correctly.

 

A relay to switch between parallel and serial connection will also do the job.

 

A relay to switch between parallel and serial connection will also do the job.

​

Which one di you think is the best and cheapest solution?

 

that photo is correct he must have the batteries both with +ve terminal to the left , so the black wire connects +ve of one battery to -ve of the other going to BM on the board ...

As for charging voltage , the manufacturer of the board should say , often they don't , and it's assumed any reasonable DC voltage will be OK even up to 24V (1A) .... I would imagine 9V (3A). would be enough ... the circuit will adjust things so it makes no difference to charging speed.

 

​

Which one di you think is the best and cheapest solution?

The charger IC that you were given is better. Otherwise it will be hard and with additional costs to setup the relay.

 

that photo is correct he must have the batteries both with +ve terminal to the left , so the black wire connects +ve of one battery to -ve of the other going to BM on the board ...

As for charging voltage , the manufacturer of the board should say , often they don't , and it's assumed any reasonable DC voltage will be OK even up to 24V (1A) .... I would imagine 9V (3A). would be enough ... the circuit will adjust things so it makes no difference to charging speed.

Do you think this charger could be what I need? because I Don't know if it will stop to charge until it the battery is full.
https://www.cheaptech.nl/ac-110-240...tm_medium=6888600&utm_source=Channable.Google

 

you must have a protection circuit as pictured in post 2 ... this prevents charging at too high current , and balances the voltage in the two cells .

I think 8.4 V is too low to feed into this circuit , I would choose 12V at 2A.max