An infinite switch, simmerstat, energy regulator or infinite controller is a type of switch that allows variable power output of a heating element of an electric stove. It is called "infinite" because its average output is infinitely variable rather than being limited to a few switched levels. It uses a bi-metallic strip conductive connection across terminals that disconnects with increased temperature. As current passes through the bimetal connection, it will heat and deform, breaking the connection and turning off the power. After a short time, the bimetal will cool and reconnect. Therefore, infinite switches vary the average power delivered to a device by oscillating quickly between on and off states. They may be used for situations that are not sensitive to such changes, such as the resistive heating elements in electric stoves and kilns.
Disadvantages of the high-speed mechanical switching include erosion of the switch contacts by arcing and generation of radio-frequency interference and a general unsuitability for handling high powers and inductive loads.
It can be considered as a very slow pulse-width modulation device. Although the device is similar in operation to a bimetallic switching thermostat, the device does not actually sense the temperature of the "burner" to be controlled, but uses the heating time of a very small electric heating element as an analog.
A rotary knob/cam arrangement is usually employed to switch-on the electric current to the "burner" and to also set the desired heating level.
Within the device, the very small electric heating element heats a bimetallic strip. After some time, the bimetallic strip bends to open a set of switch contacts, thus interrupting the electric current to the heating element. At the same time, another (more robust) set of spring-loaded switch contacts, mounted in parallel with the former, also open, cutting off the heavy current to the "burner". Both the small heating element and the "burner" now begin to cool off. At some point the bimetallic strip will be sufficiently straight to trigger both sets of switch contacts to close, thus causing both the small heating element and the "burner" to recommence the above heating cycle.
Rotating the rotary knob/cam arrangement further increases the pre-load on the trigger mechanism. Consequently, it takes longer for the bimetallic strip to warp sufficiently to trigger the electric "cut-out" described above. Thus the "burner" becomes hotter.
- FCS Electrical Workmanship L4, Pearson South Africa, 2009, ISBN 177025370X, page 96