Need help rewiring multiple small solar panels conected to rechargeable battery

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I bought these small solar powered sidewalk light, but what i really wanna do is rewire them so i can use the solar panel for something more useful like say to charge my phone. here are the pics of the lights and itheir wiring.

http://i1090.photobucket.com/albums/i375/Chrisicus/IMG-20111127-00597.jpg
http://i1090.photobucket.com/albums/i375/Chrisicus/IMG-20111127-00600.jpg
http://i1090.photobucket.com/albums/i375/Chrisicus/IMG-20111127-00598.jpg

I really wanna make this happen and i mean i dont know balls but you guys seem like pros so i"d really appreciate some step by step help.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Need help rewiring multiple small solar panels conected to rechargeable battery

    You're going to have to figure out two things:

    1). How much power these panels produce.
    2). How much power you need to do what you want.

    Now for the first it isn't likely they'll have printing on them that says "1.5 V 100 mA" but that would be nice. You'll be able to test the open circuit Voltage (Voc) and short circuit current (Isc) and possibly extrapolate from that a good estimation of the Voltage at maximum power and current at maximum power (Vmp & Imp). It's going to be small as these were picked to recharge 1.2 Volt NiCads of probably 300 mA hours capacity.

    Once you know those specs you can do the math and figure out you need 'X' of the panels in series to get enough charge Voltage and possibly 'Y' in parallel to produce sufficient current for a reasonable charge rate.

    The trickiest bit is regulating the output so that whatever you charge doesn't over-charge.
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Need help rewiring multiple small solar panels conected to rechargeable battery

    Alright the battery from this solar powered light takes 8 hours to charge in a good sunny day. This Description of the battery says 1 x Ni - Mh 1.2V/60 mAH battery

    My phone charger says Input 100 - 240 V Output - 5V

    I'm sorry if Im putting useless information, I'm not really too knowledgeable about this. Maybe if I get multiple lights and hook em together?

    Also my phone shows how much its being charged, would that keep from over charging.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Need help rewiring multiple small solar panels conected to rechargeable battery
    Chrisicus wrote: »
    Alright the battery from this solar powered light takes 8 hours to charge in a good sunny day. This Description of the battery says 1 x Ni - Mh 1.2V/60 mAH battery

    My phone charger says Input 100 - 240 V Output - 5V

    I'm sorry if Im putting useless information, I'm not really too knowledgeable about this. Maybe if I get multiple lights and hook em together?

    Also my phone shows how much its being charged, would that keep from over charging.

    What we can extrapolate from that:

    1). These are really small panels. Their output is probably on the order of .75 Watts, possible less.
    2). Your phone charger is of the "USB" variety. The AC in we won't worry about because you're not going to be powering up an inverter just for this! The DC output is probably the same as mine: 5 Volts at .7 Amps.

    If you were to put four of those little panels in series you could expect to see about 6 Volts @ 0.5 Amps (perhaps less). It would be a good idea to measure them panel's output in full sun; both the "no load" Voltage and the short-circuit current. You would need a digital multimeter to do this.

    I'm not sure how tolerant the phone is of Voltage and current variants.
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