I was just thinking about electric ranges and wondering how the controls for the heating elements actually work. Does anyone know? They can't be variable resistors because they would dissipate too much power. They obviously aren't variable autotransformers. They can't be triac-dimmers because they pre-date that technology. So what are they? Some sort of duty-cycling switch? Thanks.
You got it, the higher you set it, the longer period of cycle time it keeps the circuit closed
What's the typical on-off cycling rate at say 1/2 power.
Jeff (Who is too lazy to stick a clamp on ammeter on an element lead.)
Do you mean how often does it cycle, or how much power is being cycled? If the former, just listen for the sounds! Mine clicks when the power cycles.
They contain a small heater, which is energized whenever the element is energized, and a bimetallic strip thermostat mechanism. When you first turn it on, the element and heater are energized. The heater warms up the innards of the control, which bends the bimetal strip and shuts off the element and heater. Then the control cools down, the switch closes again, and the whole process repeats over and over. The higher the contol setting, the larger the fraction of time the heater needs to be on to get the control to cycle, and the more heat you get from the stove element.
The idea is rather similar to triac dimmers, but because the element has so much thermal mass, it's OK for the on/off cycle to last 10 seconds or so instead of being 1/120 second. It doesn't distort the AC supply waveform by turning on in mid-cycle like a triac, but it does produce a load that cycles between zero and a couple of kW.
Dave
I haven't got a clue
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