projects:blinker:work_logs:9_resin_casting
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projects:blinker:work_logs:9_resin_casting [2022/04/17 23:28] – tjhowse | projects:blinker:work_logs:9_resin_casting [2022/04/18 00:22] – tjhowse | ||
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===== The Plan ===== | ===== The Plan ===== | ||
- | 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. | + | 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. |
===== The Results ===== | ===== The Results ===== | ||
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Not too bad! | 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 | + | I was reasonably happy with this result. There is some white discolouration on the solar cells visible in that photo. That discolouration |
* UV radiation, | * UV radiation, | ||
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* Solder. | * Solder. | ||
- | In direct sunlight this panel generates 3.1V open circuit voltage, 190mA closed circuit current. | + | In direct sunlight this panel generates 3.1V open circuit voltage, 190mA closed circuit current. |
- | I soldered it to a blinker circuit | + | I soldered it to a blinker circuit |
+ | {{: | ||
+ | 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. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | This seemed to indicate that the voltage limit was related to the temperature of the panel. Part of the way through this test the panel fell into shade, probably at the inflection point at 2710 seconds. | ||
==== Failure ==== | ==== Failure ==== | ||
+ | Following from my success investing the solar cells in resin I decided to cast the electronics to the back of the cast panels. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | I used the same cardboard box as previous, however I smeared vaseline over the inside to prevent the resin soaking into the cardboard. That part worked great, aside from the thin layer of goo over the resulting casting. | ||
+ | |||
+ | I had previously sought advice from knowledgeable folk, like Zak Crow of [[https:// | ||
+ | |||
+ | {{: | ||
+ | |||
+ | The resin shrank and cracked as it set. I was able to chip off most of the prominent chunks. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | And I attempted to cast a new layer over the top to seal it all up. This new layer cracked off as it set, knocking off the backflow protection diode in the process. :( | ||
+ | |||
+ | ==== Dissolving cast polyester resin ==== | ||
+ | |||
+ | I wanted to try to salvage the electronics trapped in this failed casting. I had noticed that isopropyl alcohol made the surface of the cast solar cell a little tacky, so I submerged some chunks of solid resin in IPA overnight: | ||
+ | |||
+ | {{: | ||
+ | |||
+ | It had no effect. | ||
+ | |||
+ | I also tried Methyl Ethyl Ketone (MEK). Nothing happened after an hour or so, so I added a splash of IPA to see if their power combined would have any effect. I left it overnight and found this in the morning: | ||
+ | |||
+ | {{: | ||
+ | |||
+ | The resin had started to crumble away. I'm not sure if this was the effect of the MEK+time alone or a result of the MEK+IPA+time combo. | ||
+ | |||
+ | I was able to salvage the diode from this cast block, unfortunately I dropped it into the carpet in my office and it was gone forever. | ||
+ | |||
+ | ==== Better casting mould ==== | ||
+ | |||
+ | Getting good dimensional control with a cardboard mould was hard, so I cut one out of 3mm plywood. The pattern was generated by a great OpenSCAD [[https:// | ||
+ | |||
+ | I happened to be rendering some beeswax at the time, so I dipped the panels in wax before assembly. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | {{: | ||
+ | ==== Resin selection ==== | ||
==== Videos ==== | ==== Videos ==== |
projects/blinker/work_logs/9_resin_casting.txt · Last modified: 2022/04/18 05:02 by tjhowse