Solar powered 5V-device charger

Thread Starter

nickbuhling

Joined Oct 27, 2017
28
Hello everyone, thanks for reading this thread.

For a few days now, I am struggling with getting my solar powered, 5V charger to work.
I am using 2 of these panels from which I removed the dc-dc converter, so the data on the image is correct. Not the data in the description.

Based on a previous thread I posted, I wire them in series. The open circuit voltage easily reaches say 8-10V in the sun. Which made me decide to hook that up to a dc-dc buck converter with a min input of 6V and a USB output of 5.1V with a max of 2A. Seems fine to charge a powerbank.
Now while this sounded nice to me, in reality when a load (powerbank) is connected. The voltage from the solar cells across the input of the dc-dc converter decreases to only 4.1V which hardly charges anything. The current seems reasonable.

So why this massive drop in voltage that causes it to drop below the minimum rating of the converter? I am probably missing a basic insight here. Is there anybody that can explain me this solar panel behavior and maybe come up with a nice solution? Would be highly appreciated! Thanks in advance.

PS I have some different dc-dc converters at hand, and don't mind 1 extra solar panel if it is needed.
 

Yaakov

Joined Jan 27, 2019
1,612
I found this only is the case with one of my powerbanks. The rest does nicely charge at 5V. How can this be?
The load on the cells will drop the voltage. Apparently one of the devices is drawing too much current. A third cell might be enough to deal with the load.
 

sghioto

Joined Dec 31, 2017
1,314
The open circuit voltage easily reaches say 8-10V in the sun
Seems rather low. According to the specs each panel should deliver 7.2 volts with no load in full sun.
You should be reading at least 14 volts with two panels in series.
Panels are rated 6 volts at 1 amp in full sun.
So either the panels are defective or not getting enough sunlight.
SG
 

Wolframore

Joined Jan 21, 2019
1,748
Those panels were designed for 5V output... do you have them wired in parallel? Doesn't look like you need regulator for it if you go parallel. Nevermind you wires in series and removed the converter.... Why not just wire two in parallel with the built in converters?

upload_2019-3-27_10-48-40.png
 

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Thread Starter

nickbuhling

Joined Oct 27, 2017
28
Those panels were designed for 5V output... do you have them wired in parallel? Doesn't look like you need regulator for it if you go parallel. Nevermind you wires in series and removed the converter.... Why not just wire two in parallel with the built in converters?

View attachment 173444
You are correct. After all I should have done that haha. But "after all" doesn't get me anywhere now...
 

Thread Starter

nickbuhling

Joined Oct 27, 2017
28
Seems rather low. According to the specs each panel should deliver 7.2 volts with no load in full sun.
You should be reading at least 14 volts with two panels in series.
Panels are rated 6 volts at 1 amp in full sun.
So either the panels are defective or not getting enough sunlight.
SG
Yes that's right. As there is no sun in the Netherlands at the moment I couldn't test it. But I am 100% sure the panels are working. Easily reached 12.5V in semi-sun.
 
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