In the summer of 2001, I constructed a very useful camping light that may not produce as much light as a fluorescent lantern, but is much smaller, can operate for 55 hours before needing to be recharged, which can be done with nothing more than a solar panel and sunlight. I built it using parts from Radio Shack and the Electronics Goldmine for about $25. The solar panel I use to charge it cost an additional $15. Here's what it looks like:
The unit contains a solar controller board from the Electronics Goldmine that turns the light on at dusk and off at dawn. The batteries are two lithium 3.6 v cells in series, providing 7.2 v @ 1.1 amp hours. The two white LEDs are in series and draw 20ma. The only other parts used are a switch and power connector for the solar panel connection. I would have preferred a white box for the project since it is in the sun for charging. Now, let's take a look at what's inside the box.
At the left is the solar controller circuit board. Although the board has a power switch on it, I chose to use a separate switch to simplify mounting of the circuit board. The board contains a 358 dual op amp. One op amp is used to turn the light on at dusk and off at dawn and the second is used to turn off the light when the battery drops to about 5.5 volts. The CDS cell pokes through a hole drilled in the box. There are various ways to mount the LEDs. Not having any mounting hardware at the time, I mounted them to a circuit board which I bolted to the box.
Below is a picture of the unit being charged. The meter measures the current. I use a rate of about 100ma for 14 hours.
Below is a parts list I used to construct the unit
The batteries come in a plastic module that fits into a cell phone. This has to be broken apart and the batteries removed. After unsoldering the batteries from a circuit board that contains charging circuitry, I mounted them onto a perf board and mounted that to the box.
I made a variation of this unit that feeds an output connector rather
than the two LEDs, which I use to power an LED light chaser string, that
will flash 40 LEDs. You can buy a kit to build the light chaser circuit
from Electronic Rainbow.
The transistor on the solar controller board can supply up to about a 200ma
load. The light chaser circuit draws about 100ma at 7.2 volts, with a string
of 40 LEDs.
Copyright © 2002, Colin Pringle