Solar Modules & DIY USB charger

Discussion in 'The Projects Forum' started by St.Elmo, Mar 23, 2010.

1. St.Elmo Thread Starter New Member

Mar 23, 2010
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Good afternoon,

I am substitute teaching a class in which a student is building a solar usb charger for a science fair project. The circuit diagram the student is using can be found here

http://www.reuk.co.uk/OtherImages/ipod-battery-charger-circuit.JPG

I helped him build the circuit on a breadboard and it seemed to be in working order. The output voltage was just over 5V but the current was only getting up to around 50mA. He was using two Radioshack 6V 50mA solar modules in parallel.

After realizing this wasn't going to work with just the two modules I dug around in the science closet at the school and found what I believe to be electric fencing solar panels mounted on some foamboard. I tested the panels, which put out about 3.5V and have a much higher current (over 200mA). We have tried various configurations with the additional panel(s) (3.5 V cells only, series/parallel with radioshack cells, and just parallel with radioshack cells) and the output voltage drops to 1.6V in the circuit whenever these other panels are used. My questions are: What could be the reason for this? Do we need 500mA to charge his ipod or will a lower current suffice? Would the best thing to do at this point be to find a couple of higher amperage cells?

Thanks for the help!

-Steve

2. Bernard AAC Fanatic!

Aug 7, 2008
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414
How many of the electric fence panels do you have? I would put two 3.5 V panels in series. If there are more, parallel groups of two with one blocking diode for tho group. With the RS panels, put them in parallel with one blocking diode. Connect the diode outputs together. Need to know battery type and amp-hour rating. Assumed panel V is open circuit. Peak power will be achieved when panel is loaded to about 5V.

3. St.Elmo Thread Starter New Member

Mar 23, 2010
3
0
I have two of the fence panels.

Thanks for the idea, but I've tried a series connection with the fence panels and the voltage output was 1.6 with a current of at least 200mA (lit with a 100 watt light bulb).

4. Bernard AAC Fanatic!

Aug 7, 2008
4,232
414
Sounds like panels were in series oposing, ie, + to +, or - to -. Were these measured with out a load? Can you supply a sketch?

5. St.Elmo Thread Starter New Member

Mar 23, 2010
3
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Thanks for your help. I went back today and wired the circuit with the fence panels in series and it worked as it should have. Perhaps I did put them in series opposing (though I'm pretty sure I didn't). Anyway, the ipod still wouldn't charge. I suspect the current was still too low.

6. Bernard AAC Fanatic!

Aug 7, 2008
4,232
414
What is ipod battery voltage? What type battery? Meybe not high enough V, try without V regulator and measure I.