Solar Cell Phone Charger

Thread Starter

RodneyB

Joined Apr 28, 2012
697
I am trying to make a solar cell phone charger. So far I have been relatively successful using a 6 volt 0.3 Watt solar panel. Through a 7805 positive voltage regulator to a USB socket which connects to the phone I have a solar cell phone charger.

This has limitations as the panel is small 75mm x 50mm so the smallest amount of cloud cover and the charge stops.

I want to find if using this configuration it would be possible for the solar panel to charge 4 x 1.5 volt AA batteries which then feed the USB socket, when the phone is plugged into the socket the batteries charge the phone.

Is this possible if so do I have to have a separate charging circuit for the batteries and then the regulator to the USB socket.

Any advice and assistance will be appreciated
 

ronv

Joined Nov 12, 2008
3,770
Your solar panel is kind of underpowered. But you could improve things some by using a shunt regulator instead of a series regulator like the 7805. The 7805 needs a couple of volts to regulate so you will loose power whenever the panel goes below ~7 volts. If you put a 5.1 volt zener diode across the output of the panel it will "short it out" if it's voltage goes above 5.1 volts. In this way all the power is available to the charger until the panel goes below 5 volts instead of 7.
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Thank you for the replies, I was hoping to charge the 4 batteries in series.

I have never built a shunt regulator what would you suggest I use or could you point me in the direction of a circuit.
 

wayneh

Joined Sep 9, 2010
17,495
Take a look at the circuit in posts #11 and 12 here, specifically everything to the right of Q2. That's a shunt regulator that uses a zener to control the "dump" voltage, where the excess current is dumped thru the shunt.
 

wayneh

Joined Sep 9, 2010
17,495
Agreed. And you probably don't need a blocking diode either. Ronv has not shown one, and I'm not sure that was intentional. I don't think a phone would allow power to be drawn from its USB port but I admit I'm not sure of that.
 

wayneh

Joined Sep 9, 2010
17,495
Nope. And it potentially could deliver a high voltage (the panel's unloaded, open circuit voltage) to whatever you hook it up to. I'd leave it out.
 
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