I have a (USA) NESCO FD-50 Food Dehydrator, rated at 120Vac 500W. It has a built-in thermostat, settable in degrees F. The nominal setting appears to be ~130deg F; that is where we set it for drying food.
I plugged it into my
Kill-aWatt. During initial warm up, the FD-50 draws 485W. After about 5 min, the thermostat began cycling, and after 40 min, it settled to a heater on/off duty cycle of about 9sec on, 19 sec off. The power input to run just the fan motor is 24W. The power input to run both the motor and the heater is 485W.
The calculated average power required to keep the exhaust air at 130degF (measured with an accurate lab thermometer) is (9s*485W + 19s*24W)/(9s+19s) = 172W. The inflow air was 65degF.
I did not have any food loaded in the FD-50. I'm guessing that if I did, the initial warm-up time would be longer (to heat up the mass of the food). However, since loading the trays would reduce the net air flow through the box, the power required to maintain the outflow air at 130degF would be less than I measured, say ~150W.
So, my conclusion is that simply adding the diode will not sufficiently reduce the power input. If you go back and look at my post #9, adding the diode reduces the initial heater power by only 40%, leaving a power input of over 280W with the diode in place.
Looks like you either fix the thermostat or add an outboard dimmer, like the
230Vac version of this one (the linked one is for 120Vac).
ps: The Kill-a-Watt reports 370Wh in 2h 5min, or 370Wh/2.083h = 177W average power input. This is the steady-state measurement, beyond the initial warm-up.