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# Cell phone solar charger voltage Answered

I am a newbie so sorry for such a basic question. I want to build a solar cell charger with a USB plug. My problem is finding a USB port with the appropriate voltage. Would I be able to take a car lighter USB charger and alter it or use resistors so that it would work for me? I'm not really sure how to go about obtaining or building a USB port for my charger. I appreciate any help!

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## 3 Replies

The car-lighter-USB-charger is probably a good choice, since its output is regulated, so as to keep its output voltage constant at roughly 5.0 volts, which is the voltage a USB port is supposed to have.

For this kind of power converter, if it is the kind I am thinking it is, the voltage of the input can vary widely, probably anything in the range of 6 to 24 volts is OK, provided the input side can supply enough power, for both the load on the output side, plus a little extra to run the converter.

So a natural question is, "How much power does your phone use when it is charging? Or equivalently how much current at 5 volts?"

It's probably not more than 500 mA. I mean, I think that was part of the power specification for USB,

http://en.wikipedia.org/wiki/USB#Power

that no single device would use more than that.

Regarding the PV (photovoltaic) panel, it is common to find PV panels intended for charging a 12-volt lead-acid battery, and a panel of this kind would probably be a good match to the input of the car-lighter-USB-charger.

You might also want some sort of energy storage on the input side, like a large capacitor, or a small 12-volt lead-acid battery. The reason for that is to sort of smooth out the power flow, so the darned thing does not just die every time the sun goes behind a cloud.

Also a gizmo like this:

http://dx.com/p/usb-av-usb-power-current-voltage-t...

might be a fun addition to the output side, so you could actually measure the power (as voltage and current) your phone is drawing as it charges. I'm not sure how much power that gizmo itself uses, in the act of measuring your power.

sailorondatea (author)2014-02-22

i have 3x 6V 2W solar panels just soldered them on usb port. it gives around 1A they can directly charge nokia phones if they need max 800mah. sometimes phones tell me voltage too high but that only happens under direct sunlight at noon. so i didnt put anything like a regulator. there are only 3 diodes between them to protect each cell from reverse current.

if you have something like 18V panels then 12-24V usb chargers for car lighters would be the best. 1A rated ones draw about 200-300mah @12.6V so a single 18V 6W panel may be enough to run them.

mpilchfamily (author)2014-01-19

The USB connectors can be purchased form parts supplies like Digikey and Mouser. As for the rest... What are the specs of the solar panels in question? They will need to offer at least 5V to charge a device through USB. I suggest you look at the projects list down the right side of this page.