solar pannels driving an LED

[davidbball13]

Hi i am new to the forums.Ok i had a great idea today in math. i saw at the shack the other day that they had some small solar panels each one driving .5 volts. If you are a makezine fan they make something called a joule theif. bacasly it is a small circuit that can drive an LED at 1.5volts and brings it up to about three volts. i made one last week. So i thought that if i had three of theses solar panels together in series i could make 1.5 volts.would it work????????

 

[audioguru]

It won't work if the solar panels don't make enough current. A 3V white or blue LED would not be very bright at 5ma and the solar panels are making 15mA. You wouldn't see the LED in the sunshine anyway.

My solar garden lights use a single AA Ni-cad battery cell that is charged all day by a 2V solar panel. Then a voltage stepup circuit drives the LED for a few hours at night.

 

[davidbball13]

yes i know but if u read about the jule thife it can make a 3V led run off of 1.5 volts (AA battery). so i will check the ma on the solar panels

 

[justDIY]

to get 3v from 1.5v you need a lot of current. the joule thief takes advantage of the generous current yet low voltage remaining in a "dead" alkaline cell.

depending on the type, a solar cell offers a generous open circuit voltage but a very low short circuit current. there are however cells offering a low OC voltage but a very high SC current. Often these cells put out 0.5v OC and upwards of 2A SC. A few of these in series would have no trouble running a puny led, but they're going to cost as much as a small case of alkaline batteries.