Solar charging multiple 18650 Li-on cells with TP4056?

Thread Starter

Theo_KVA

Joined Dec 6, 2019
10
Hi everyone,

I plan to build a high capacity 3.7V/5V solar charging powerbank (something like 10-15ah).
I’m going to use modules of TP4056 breakout board each coupled with two 18650 cells in parrallel.
But I was wondering what would it need to charge two or three of these TP4056 modules with a medium solar pannel.
I aim to use this 10W solar panel. It is rated to output steady 5v with up to 2A. I understood that the TP4056 tend to draw 1A each. But then I don’t get why a lot of other’s setup (like his) are only using small 1-3W PV and that seem to work fine.

Capture d’écran 2020-02-16 à 16.05.18.jpg

The 10ohm resistors are to prevent a too high voltage difference between the cells pack. The OUT- and IN- are bridged on the TP4056 boards, so black wires are good. What do you think about this setup? I'm confused for the charging. Is the 10W going to charge them all? can I upscale it to 5 modules?

Thanks a lot :)
Theo
 

Dodgydave

Joined Jun 22, 2012
8,807
If the TP boards draw 1Amp each , then you need a 15W solar panel min. (3Ax 5V) , otherwise the tp boards are not drawing 1A as stated...
 

Thread Starter

Theo_KVA

Joined Dec 6, 2019
10
But I don't get what is going to happen if there is only 500mA available. Is it charging anyway but slower? Because this chip is also quite used with low power solar panels (less than 3W). What about a cloudy day, even a solid 15W solar panel won't output 3A
 

oz93666

Joined Sep 7, 2010
736
I don't see the need for the fuses .....or the 10 Ohm resistors ... the cells will presumably remain charging until the light indicates they're done....

It depends how urgently you need the cells charged what size panel you use.... 3W panel will never deliver 3W ... perhaps about half that on average in normal use , so it would take a day to charge one 18650 ( 10WHrs capacity, 3400mA) ...

I'm not sure what 5V panel means ... if open circuit voltage then under optimum load voltage will be 3.75 too low for your circuit ... check the voltage with just a meter and no load , under strong light it should be just over 6V to get the maximum possible power for your charging ....

I would stock up on panels , they're very cheap....
 
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Thread Starter

Theo_KVA

Joined Dec 6, 2019
10
Thanks for the reply :)

Fuses are to prevent a too quick discharge. To prevent a too high voltage difference between the packs when used in parallel I added resistors to let them equalize (never too much caution).

I guess 5V means there is some kind of a regulator to make sure the voltage is fixed. I was hoping someone would know haha. They also state that the open circuit is 6V. I don't really understand how solar charging behave.
I saw a lot of these small panels which are design to be able to directly charge your phone (so fixed 5V). If so, it could probably be used with TP4056 boards.

Anyway I guess I'll have to buy these to make sure :)

I will post the evolution if the project see through. Maybe it could help
 
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