You can now buy me cake and things to take apart at:- https://www.patreon.com/bigclive
Finally I get round to combining a couple of recent teardowns into something new. This is a project to make the common ebay meteor lights solar powered, using a common ebay solar panel, an old or generic phone battery (lithium cell) and a few components.
The circuit will also run strings of parallel LEDs or even a single high power LED.
It’s been mentioned that the reverse biased solar panel will leak some current as it is connected between the positive rail and base of the transistor. I’m not sure what current will flow when a 10 or 12 cell array has a reverse voltage of 4.2v – 0.6v = 3.6V across it. A test with 5V showed a current of 300uA which would flow into the transistor base. Is a slight reverse current likely to damage the array? I’ve never really considered anything other than battery discharge through a reverse biased solar cell. Can such a low reverse bias voltage damage the array of cells?
Comments and thoughts on that are welcome.
A solar panel capable of putting out 5 or 6V at around 100mA or more. (But not too high a current as it will be charging the cell directly.) If you live somewhere with dull winters a higher current (larger area) solar panel will be a good idea.
A typical cellphone battery (lithium) with built-in protection. Many of the generic Nokia type are commonly available on ebay.
A set of typical meteor lights that usually come with a slightly dodgy power supply.
A transistor, either a BC547, 2N3904 or anything general purpose.
A rectifier diode like a 1N4001 to 1N4007 (all 1A just different voltage ratings.)
A 10 ohm resistor to limit the maximum current through the transistor.
A 10K resistor (10,000 ohms) to limit current to the transistors base.
And a little bit of solder, wire and time.
Here’s the Jaycar (Australia) link to their resistor dial.
And another Australian supplier:-
An American supplier of a different type of resistor substitution box in kit form:-