I'm trying to figure out what to use to PWM (≈50mHz) a ≈500W resistive heater on 240V:
· Relay? Would work, but will break after only a few hundred thousand cycles.
· SSR? Should be more reliable, but prices start at US$50?
· Triac+optoisolator/pulse transformer?
· MOSFET+opto?
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I figure that 100000 cycles is 500–600 hours at one PWM cycle per 20 seconds, and that seems really short. Are there higher-reliability relays out there?
The last two options seem like they might amount to building my own SSR, and I'm not sure it would be better or cheaper.
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20 seconds seems too fast. This should be in the same order of magnitude as the time constant of the room you're heating. more like 2-3 minutes, maybe even more.
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It's not a room; it's a container of food that needs fairly precise temperature control. You might be right that it will have fairly long lag.