I have a basic understanding of electrical/electronics (please be gentle). This question is more electrical than electronics, but I hope it's close enough that it qualifies.
I have a friend that has a metal building with an exhaust fan near the ceiling. In the winter when it's cold outside and warm inside, condensation accumulates on the ceiling. The exhaust fan helps remove condensation, but it's currently on a light switch and he doesn't want to manually turn it on and off throughout the day. I offered to add a Raspberry Pi and solid state relay and program it to turn on the fan every hour for 15 mins.
The existing switch box has a 20 amp light switch connected to a red and blue wire (no neutral) so I'm guessing the light switch simply switches one side of the circuit. I should be able to swap in the Raspberry Pi and an SSR (3v - 32 v DC input, 24 v - 380 v AC output - 40A).
I have two questions:
1) I want him to be able to look at the switch box and know if the fan is on or not so I ordered an indicator light (LED but runs on 110 v). My initial thought was to just place this inline between one side of the SSR output and the wire going to the exhaust fan. After thinking about it, I believe this would send the entire circuit/motor amperage through the indicator light and blow it out. What is the easiest (fewest components) way to make this work?
I could add an LED to the Raspberry Pi side of it and that would tell me when the RPi was turning on the SSR, but I really would rather have the indicator show if the fan motor circuit is energized.
2) It would be nice to have a manual override switch in case the RPi/SSR stops working or if he just wants the fan on for an extended period of time. Can I safely wire the existing light switch in parallel with the outputs on the SSR so that either the RPi or the light switch can power the circuit? Will turning on the light switch cause any kind of damage on the SSR?
I didn't find the right solution
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