Revitalising a Sun Jar and the Joule Thief Revisited

Cleaning out a long-neglected cupboard recently I found a Sun Jar that I had forgotten I owned. If you have not come across a Sun Jar before, it is a Mason jar with a circuit inside that charges up when it is light and then lights an LED in the dark; the conceit is that during the hours of daylight it catches a little bit of the Sun and lets it out again in the dark.

Fig 1 Sun Jar

Well, this Sun Jar wasn’t capturing light anymore. So, I thought I should have a look and see if I could fix it.

Inside the mason jar is a plastic holder supporting a PCB. One side of the PCB holds a solar cell which is held pointing upwards just below the glass lid, the other side has the main electronics, including the rechargeable battery, and a connector to an LED that is suspended in a diffuser within the main body of the jar.

When I extracted the circuit there was an obvious problem; the AA battery in it had leaked and corroded a number of the circuit board tracks and connections (See Figure 2). However, cleaning up the corrosion and fitting a new rechargeable cell didn’t bring the circuit back to life. Further investigation showed that the LED was fine, the cleaned-up connections were connected and the battery voltage was getting to the parts of the circuit where it was supposed to. Clearly something deeper was wrong.