howdy all, ive never played around with solar panels before. i looking to solder about 50ish solar panels that output 4v @ 50ma each. i going to series/ parallel them to 8volts, and connect the outputs to a lm7805 to usb so i charge my phone. i have a few questins i hope yall can help with.

1) will the above plan work as described?

2) will the lm7805 reg act as a diode if the panel goes dark? I have some 1n4007, but i dont want the .7v drop across it. Phone might not recognize 4.3v
Edit: just realized i could put diode between panel and 7805, but dont think i would want the voltage drop there either if a cloudy day is present

3)Any potential danger to my phone using this?

Any tips or suggestion to do to this circuit?
http://uploads.im/NhsU1.jpg


Edit: i know that most modern phones charge at 2 amps. I realize the max potential of the design i 1 amp, unless i used a 78S05, but i dont have the cells, or room for them.

Thanks!

 

Are the 4V & 50 mA open circuit & short circuit measurements or rated operating measurements ? If true operating conditions & using a buck converter you could be close to 5V @ 2 A before losses. If you are charging in bright sun & removing when charged, then a blocking diode is not required.
I don't have a cell phone to play with so these are untested opinions.

 

1) will the above plan work as described?

Not so well. The 7805 requires a few volts higher input to regulate to 5V at the output. With any significant current draw from your 8V panel, you'll no longer have enough voltage and the output will sag below 5V. The good news is that there are much more efficient regulators available that can use a range of voltages below and above your target of 5V. These are purpose-built for solar applications.

2) will the reg act as a diode if the panel goes dark?

No, these regulators can be damaged by an output voltage in excess of the input voltage. The data sheets recommend a diode from output to input to prevent this by shunting current around the regulator if the output exceeds the input.

3)Any potential danger to my phone using this?

Your phone should be safe as long as the voltage supplied does not much exceed 5V. It has smarts inside and may not like charging with your arrangement (phones vary in this regard), but again it should be safe from damage as long as it never sees an over voltage. My hunch is that 6V would probably be fine, but I'd get very nervous above that.

 

Thank you for the responses and help.

Ill look into a solar purposed regulator and see what questions i have from there!

 

Are the 4V & 50 mA open circuit & short circuit measurements.

Not sure, i got a bunch of these from here
https://www.fasttech.com/products/0...00ma-polycrystalline-photovoltaic-solar-power

i did measure 4v unloaded cell just in room lighting. i read they were only 50ma instead of the 100ma advertised

 

The good news is that there are much more efficient regulators available that can use a range of voltages below and above your target of 5V. These are purpose-built for solar applications.

quickly took a gander at digikey, not sure what im looking for though.. should i be looking under linear, or switching?

Hoping im not pushing my luck, but any recommendations??

thanks again!

 

You could try one of there..
https://www.ebay.com.au/itm/Voltage...885311?hash=item1ed219317f:g:RfMAAOSwke9Z6quW
Adjust the output to 5V. But definitely go switch mode. A Buck/Boost one may be better. This one is just buck.

 

quickly took a gander at digikey, not sure what im looking for though.. should i be looking under linear, or switching?

Hoping im not pushing my luck, but any recommendations??

thanks again!

I don’t have a specific recommendation but take a look at this as an example of what’s out there.
http://www.ti.com/lit/ds/symlink/lm25118.pdf
I believe there are pre-built DC-DC converters you can buy (look on eBay) that use chips like that. 5V is a popular choice so there should be a lot of them. You shouldn’t have to build your own. You could probably get away with just a buck converter. You won’t get charging in low light but that’s true anyway even if you use a boost converter. Those can increase the voltage up to 5V but there’s hardly any power available so it’s not worth the trouble.

 

I think that I would put 3 cells in series, 16 strings in parallel & use a buck DC-DC converter. Might allow for wider sun conditions. My buck converter came from eBay.

 

I think that I would put 3 cells in series, 16 strings in parallel & use a buck DC-DC converter. Might allow for wider sun conditions. My buck converter came from eBay.

 

i appreciate the help everyone! thank you all for helping me work this out and realize potential problems!