Wiring a thermostat to switch off a light

[ban-all-sheds]

I'm trying to get the incubator stable at 38.5c

Not possible if you have a thermostat with 6° of hysterisis.

It doesn't matter what lamps you use, or fans etc - when the thermostat switches off it won't go on again until the temperature has fallen by 6°.

The best you'll get is it moving between 34° and 40° all the time.

It's the wrong sort of thermostat.

 

[slup]

Aquarium thermostat

The unit above is adjustable in 0.1 degree increments, has an external temperature probe, separate heat/cool outputs and adjustable time based hysteresis. About £20 including delivery.

It's the right tool for the job.