What should you set your duty cycle length to be on your brewery controller, such as one based around StrangeBrew Elsinore software?
The short answer to this is 2-5 seconds. The lower end of this is especially preferred for boil kettles where visible pulsing can occur with cycles longer in duration, or with RIMS tubes where there is high importance on consistent heat output. The higher end of this is entirely adequate in most other uses, such as with a hot liquor tank.
Theoretically the heat input will become more consistent as cycle length decreases, so you may ask why is it not suggested that duty cycle length is less than 2 seconds. The first reason is that the life of an solid state relay is partially dependent on the number of switches it performs. I have also learned of a second reason – with duty cycles much less than 2 seconds in length, incremental changes in duty percentage (such as those that occur with PID control) may not result in the expected change in output due to synchrony of the duty cycle with the cross over frequency of alternating current electricity (50 or 60hz depending on where you’re reading this from).