Solar Cell Phone Charger

Discussion in 'The Projects Forum' started by RodneyB, Jul 1, 2014.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    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
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Were you hoping to charge the 4 batteries (1.25V perhaps?) in series?
     
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  3. ronv

    AAC Fanatic!

    Nov 12, 2008
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    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.
     
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  4. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    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.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    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.
     
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  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Since your cell puts out only a little current just a zener would work.
     
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  7. wayneh

    Expert

    Sep 9, 2010
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    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.
     
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  8. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Would there be any advantage to putting a capacitor across the output?
     
  9. wayneh

    Expert

    Sep 9, 2010
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    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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