I wanted to run a medium-duration test of the electrically-complete blinker before going through all the trouble and expense of encasing it in aluminium and glass. I decided to cast the electronics in transparent resin. This would be reasonably mechanically and chemically robust, but it would degrade in sunlight over a few years, turning yellow and crumbling. This would give me a test good enough to check for any drastic short-term problems with the electronics.

I bought this resin from bunnings. It's a styrene/polyester resin with a MEK catalyst.

I cut out a cardboard box on the laser cutter and lined it with gladwrap.

Solar cell invested.

Not too bad!

I was reasonably happy with this result. There is some white discolouration on the solar cells visible in that photo. That discolouration did not exist when I took the panel out of the mould. It formed shortly after I put it in the sun for this test. It seems to have been formed by some combination of:

• UV radiation,
• Heat,
• Resin,
• Flux, and/or
• Solder.

In direct sunlight this panel generates 3.1V open circuit voltage, 190mA closed circuit current. That was about double the current I was anticipating. This caused me mild concern as the voltage limiting zener might not be able to keep the voltage down. I could add more in parallel to pass more overvoltage current, but that would increase the passive energy loss in the system considerably.

I soldered it to a blinker circuit and put it in the sun:

Awesome!

I was puzzling over why the voltage dropped off so quickly. I wanted to check whether it was panel degradation related to the discolouration or due to the panel heating up inside a pretty good thermal insulator. I put the whole shebang in the freezer for a while to see if that had any effect.

Dubious?