My parents have solar lights in their driveway, recently the controllers on some of the lights broke and the lights stopped working.

This light has a proximity sensor that switches on and off the main ring of LEDs when triggered and normally when it’s dark only the center LED is on. I couldn’t fix the PCB so I decided to design a circuit to replace this PCB.

To make the project easier I decided to not use the proximity sensor. If I left the main ring of LEDs and the center LED on all the time it would drain the batteries too fast and the light wouldn’t stay on all night, so I decided not to use the main ring of LEDs either.

The light will have three main components a 1.37V LED, a set of 3.6V rechargeable batteries and a 5V solar panel.

The solar panel will be used to detect light levels as well as charge the batteries.

This is the circuit that I designed to replace the PCB. I loosely based this design on a circuit from galigear.com.au.

When it’s bright and the solar panel is creating a voltage the PNP transistor turns off which keeps the LED off and the battery gets charged. The two diodes are used to drop the 5V solar panel voltage to 3.6V (5V-0.7V-0.7V=3.6V) which is the voltage of the batteries and they also prevent current flowing back to the solar panel from the batteries, this charges the batteries during the day.

When it’s dark and the solar panel isn’t creating any voltage the transistor turns on which turns on the LED. The LED is powered by the batteries which were charged during the day.

The first step was to take out the three batteries.

I opened the light.

I removed the PCB and used hot glue to secure/seal the wires for the proximity sensor and LED ring that I wasn’t using.

I prepared the transistor with the resistors and wires.

I joined the diodes and added wires.

I added shrink wrap to the diode and transistor assemblies. When shrink wrapping the transistor assembly make sure to individually shrink wrap each of the three legs before doing the overall shrink wrap for the assembly. The colours of the wires should be noted before shrink wrapping, I printed the schematic and wrote the colour of the wires on each part of the schematic. Shrink wrapping is important for waterproofing and preventing shorts especially as this project will be used outside.

I soldered the LED, solar panel and battery holder onto the assemblies and shrink wrapped the connections.

I put the light back together and tested it with the batteries (The LED is on because the solar panel is against the desk so it is dark).

I fitted the light back outside.

This design should be better than the PCB as it is more rugged and simpler which means it is less likely to break or malfunction.

So it should last for several more years!

 

As always if you have any questions please don’t hesitate to ask,

Conor.