I took apart a solar charge controller for mobiles which didnt work anymore. The panel works fine and i salvaged some of the 18650s which were still in good condition. The solar panel itself has a few terminals and I noticed that at a couple of terminals I get 1.7V - 2V in low sun, which I think provide 3V in max sun ( ill check tomorrow) and then i found 2 other terminals that product 7.9-9V in the same low sun.

So Im guessing the low V tap has a higher current throughput than the high V tap?

 

Without a schematic you cannot be certain that the lower V has higher current.

Regards, Dana.

 

Examine the face of the panel , It should be apparent which parts supply what .... Are all the solar cells the same size ??? count the cells which make up the two strings of the panel , these small cells are cut by laser from broken large cells ..

Can you supply pictures?

 

Examine the face of the panel , It should be apparent which parts supply what .... Are all the solar cells the same size ??? count the cells which make up the two strings of the panel , these small cells are cut by laser from broken large cells ..

Can you supply pictures?

Sure here they are:

 

What we have there is a total of 4x15= 60 cells ... If you look carefully you can see some cells have 4 silver horizontal wires and some have 5 , the manufacturer would have tried to match all cells so they had the same amount of active , (black) area , the cells with 5 wires often won't have any black area on one side of the silver wire (as we look at it) ... these were all cut by laser from reject broken 100mm square cells....

Each cell produces a maximum of about 0.5V if wired in series they could develop 30V open circuit(max V) .... but they are wired in strings and then put in parallel to make two separate outputs , no way of knowing by looking how they are wired ... measuring open circuit voltage in full sunlight will give the answer ..... however wired the total output from both voltages should be about 2W in full sunlight ... A good quality 18650 can hold 10W Hrs , so it might take a day of strong sunlight to fully charge it ....

If you measure voltage and short circuit current in strong light for both outputs we can figure out the wiring and hence the best way to charge the 18650's ... For current measurement just put a multi meter set to Amps across the outputs ... it's impossible to damage the solar cells by shorting .