Voltage, USB, and an Android phone

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SUCCESSOR
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Voltage, USB, and an Android phone

Post by SUCCESSOR » Sun Jan 15, 2012 3:37 pm

I am working on a project, making a solar charger for my HTC EVO 4G. I am using panels from solar lawn lights that I have laying around my yard. There are 3 types. One group is a 3-3.15 volt in direct sun and one group is 2-2.15 volt both 20 mA. Then I have some that are around 3.5 volts that i'll talk about later. From what I understand the 2 type aren't compatible because of the voltage difference.

So the Evo charges via USB and most like has a 3.7-4.2v Li-Ion battery. If I wire the panels together to raise the voltage I end up with about a 6 volt and a 4 volt. I am wondering if the 6 volt is too high for the phone which is made to work with 5-5.2 volt USB. I am worried also that the 4 volt wont be strong enough to charge the Battery fully. I know the power from the panels vary by how much sun they catch.

Also I don't know if i have enough 3 volt panels to raise the amps high enough to charge a running android device which ideally is 500mA.

Should I go for 6v or 4v?

Separately:
The third type is a 3.5 volt panel that I don't intend to use(for this project). It confuses me. It has 3 different wires on it. A black, a yellow, and a blue. the black and yellow put out 3.5 volts but only 1.5mA while the black and blue puts out less than one mA and no voltage reading. yellow and blue show no reading. From the circuitry there is a black and red going to the batteries: there are 2 instead of the usual 1. It's just weird that the amperage would be so low.

tom61
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Re: Voltage, USB, and an Android phone

Post by tom61 » Mon Jan 16, 2012 12:00 pm

You need a fair number of those low-end solar cells in parallel to get enough amps to power a phone. Not knowing the specifics of that phone, I'd go with 6 volts or more and then using a high-efficiency regulator to give more steady 5 volts.

For the odd-ball solar cells with extra wires, my guess would be that a small bit of the cell is being used as a light detector to turn on/off the light.

whatchitfoool
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Re: Voltage, USB, and an Android phone

Post by whatchitfoool » Tue Jan 24, 2012 11:08 pm

you shouldn't (probably) be able to wire 2 panels in series, because you would be forcing energy through another panel. they are designed to be a photovoltaic cell, producing VOLTAGE when struck with light. that's why the amperage isn't vary high.
the single LED on the front of my computer uses more then 20ma. you would need a minimum of around 500ma to charge your phone. and that's at a regulated ,clean,steady 5 volts. it uses a li-po or similar battery, with a max charged voltage of 4.2 volts. all lithium battery needs a special charging circuit to charge it, which would be running off the 5 volts. i would say in standby, if you provided ~100ma (at 5 volts) you could have your phone on , but not loosing charge. but even having your back-light on would take you to needed a few hundred ma just to maintain your battery level. a standard USB port will put out 500ma, and that doesn't charge anything that's power hungry fast. most of these things like charging at at least 700ma, with the ipad and some other devices running around 1.15A if the port "says" it can out output high current.

if you where going to use your " 3-3.15 volt in direct sun at 20 mA" , i would think you would need 30-40 of them to get anywhere charging it. probably around 50-70 to be efficient in non-optimal light. of course these would need to be wired in parallel onto a buck converter, changing the 3.1volt into about 5.1v .

overall, the way i see it, totally not worth it.

armarares
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Re: Voltage, USB, and an Android phone

Post by armarares » Thu Jan 26, 2012 8:18 am

I have done something similar and you need an voltage regulator.
(helpful video about voltage regulators and how to make an USB power supply.)
http://www.youtube.com/watch?v=GSzVs7_aW-Y
And you have to charge RECHARGABLE batteries with the solar panels and from those you can charge the cellphone.Why? because the solar panels will stop charging when there is less sun (or even a cloud) and it will ruin your phone.

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