Solar Panels for greater charging capacity

Thread Starter

quique123

Joined May 15, 2015
404
I have a solar panel I took out of a solar charger for mobile devices that i bought online. I believe the packaging says it's output is 5V & 2.1A.

I have a setup with 1 of those panels which charges 2x18650 batteries (3.7V) in series, which powers an arduino. I have tested the setup to be autonomous and it works for about 1 week or so. Id like to increase the charging power to the batteries by connecting the 2nd solar panel in parallel in order to get 5V, 4A. But I noticed my battery charging module is this one:

https://www.aliexpress.com/item/32715523217.html?spm=a2g0o.productlist.0.0.5bf34f5bLX6G0M&algo_pvid=d3cffb51-bd16-4303-a465-3692745666ce&algo_expid=d3cffb51-bd16-4303-a465-3692745666ce-1&btsid=0ab6f82415927615157901893e0b5f&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

Which states 5V/1A. So Im guessing this means no matter how powerful a panel, the charging module will only let 1A thru, correct?
 

KeithWalker

Joined Jul 10, 2017
1,019
The charger shown in the attachment is for charging a single LiPo cell from a 5 volts,1 amp USB outlet. What it does not tell you is that it only supplies a charging current of 100 mA. The charging voltage cutoff is approximately 4.2 volts so it certainly will not charge two 18650 cells connected in series and will not charge a single cell at 1 amp.
Regards,
Keith
 

Thread Starter

quique123

Joined May 15, 2015
404
no wonder. ok maybe this one: 2S 20A 7.4V 8.4V Li-ion Lithium Battery 18650 Charger PCB BMS? I forgot, this is actually what I have:
IMG_7183.jpgIMG_7184.jpg
 
Last edited:

KeithWalker

Joined Jul 10, 2017
1,019
That one will do the job but be aware that if you charge 18650 batteries at more than one amp, you may damage them and reduce their capacity. That charger is for the fast charge LiPo batteries that are used in radio controlled drones and planes.
The one you showed in the first posting could be used if the programming resistor, R3 is changed to 1.2 Kohms. It will be perfect for charging one cell at 1 amp. With two of them, each one connected to a separate solar panel and battery, you could charge both cells at the same time at 1A each. The spec on the solar panels is 5V/2.1A. That is 5 volts with the panel open circuit and 1.2 amps short circuit when the panel is in bright sunlight. You may have to reduce the charging current to get enough voltage to run the chargers from them.
Keith.
 

Thread Starter

quique123

Joined May 15, 2015
404
Ok wait, those specs on that panel don't seem right. Those panels are usually rated at 3W [ali]. The 5V/2.1A spec is for the mobile charger itself, which really depends on the internal circuitry. Ive been testing the panel and it does output between 7-9V in the sun. For a 3W panel thats only 333mA which sounds more reasonable to me.

So if i put 2 of these in parallel I get about 600mA which is still under 1A. I have a charger like the second one i posted, sorry I confused everything up with the first charger. So I should be good then.

Here is my panel. I get 7-9V from the panel and into the BMS charger. The BMS charger has 3 terminals for the 2 batteries (0V, 3.7V and 7.4V) and then 2 terminals for incoming from the solar panel. So I would wire the new panel in parallel without modifying any connection to the BMS.
 

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KeithWalker

Joined Jul 10, 2017
1,019
That may not work if the panels can not supply enough current for the BMS to operate correctly. That charger is not designed to run on a limited current supply. You can try it. It should not damage anything as long as the voltage across each cell never exceeds 4.2 volts. Keep a close eye on it.
 
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