Solar Mobile Phone Charger

Discussion in 'The Projects Forum' started by BryanFury, Jul 22, 2010.

  1. BryanFury

    Thread Starter New Member

    Jul 22, 2010
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    Hi there.

    I want to build this mobile phone charger, but I have a higher wattage (7.5V, 80mA) solar panel. At first I thought it will be okay as it will charge my mobile faster, but the author gives a warning if using a higher-powered solar panel.

    Can anyone modify the circuit so I can use my solar panel? I suggest no power is wasted from my panel just to get the approximate 3V as described.

    http://www.techlib.com/electronics/battery_chargers.html

    OR
    If someone has a different circuit, I would be thankful.
    Thanks.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    My cell phone has a 5V, 350mA adapter that charges it overnight.
    Your tiny little solar panel has such a low current (only at noon, pointing directly at the sun) that it might take weeks to fully charge your cell phone.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
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    If you want to charge 5 nicad cells (6V) then you could probably safely enough just connect the solar through a diode to the battery pack. 80mA for only part of the day is probably low enough to trickle charge the battery without damage.
    Don't use NiMH batteries, I don't think they would like it as much.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    A little AAA size Ni-MH cell has a capacity of 850mAh. It normally charges overnight at 85mA.

    Cell phones use Lithium-ion or Lithium-Polymer cells today. They haven't used Ni-Cad or Ni-MH cells for many years (remember carrying a heavy cell phone in a huge case?).
     
  5. Markd77

    Senior Member

    Sep 7, 2009
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    The circuit the OP linked to uses the solar cell to charge a battery pack, which can later be used to charge the mobile phone. A lot of the circuit is to increase the 3V to enough to charge the battery, but with a 7.5V solar cell is fairly redundant.
     
  6. BryanFury

    Thread Starter New Member

    Jul 22, 2010
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    Actually, my main purpose is to trickle charge my phone (or the spare battery) while I am biking, as the GPS on my phone drains the battery fast. I do not really expect the charger to fully charge my battery. I am still on search of an alternative circuit.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    An old-fashioned battery (lead-acid) drains away all by itself so it needs to be trickle-charged or charged frequently even if it is not used.
    But a modern Lithium battery in a cell phone has a charge that lasts for years. It is destroyed and might catch on fire if it is trickle charged. Its charging circuit disconnects the charger when it is fully charged.

    Since your GPS drains the battery fast then you need a lot more current than a trickle.
     
  8. BryanFury

    Thread Starter New Member

    Jul 22, 2010
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    Maybe I will find a portable lead-acid and trickle charge it with a solar panel. Then, the lead-acid will be the one to charge my phone/spare battery. What do you think?
     
  9. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    Instead of trying to use solar (I am sure you don't just bike in the open, or when the sun is at its hottest during the day, maybe you do, maybe you like to get a good tan:rolleyes:...) why not come up with a permanent magnet DC motor generator to be driven off one of your wheels.... then even at night, you can still charge/power your phone... similar to those bike dynamos I used to see around where it powers the headlights and tail lights for nigh biking...

    You can find a small Permanent magnet dc motor, and drive it with a rubber wheel attached to the shaft, then come up with a bracket that would "push" the rubber wheel against your rear wheel to drive it.. hence, every time you are pedaling, you are generating power... and you can still use the solar panel as a redundant backup system, in case you want to rest for a while and then let the sun take over the charging....

    or, you can just get this, it has the battery charging circuit already for batteries.... plus, it has selectable power outputs...

    http://www.harborfreight.com/solar-panel-recharger-41427.html



    B. Morse
     
  10. BryanFury

    Thread Starter New Member

    Jul 22, 2010
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    Actually I already thought of using DC motor, but I already have the solar panel on-hand. Mostly on weekends we go biking most of the daytime, and I can leave my bike on the open at noon to charge it.
    If I cannot find a suitable solution, maybe then I will go the DC-motor way. Thanks.
     
  11. BryanFury

    Thread Starter New Member

    Jul 22, 2010
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