Electronic – Choosing a rheostat

rheostat

I have a cartridge heater with the following specs: 50W and 220V AC.

I would like to control it with a rheostat, but I am not sure how to pick an appropriate rheostat. Could someone give me a hand?

Best Answer

As others have pointed out using a rheostat to control the heater is not the best way to solve this problem due these factors:

  1. It wastes a lot of power.
  2. The component is costly.
  3. There is a question of safety.

There is a better way to deal with the control of the heater. Even better than the AC phase control that is typically used for controlling lights. This better method takes advantage of the fact that heaters generally have a long time constant and so fairly low frequency control is feasible.

I would suggest that you get a SSR (solid state relay) that has optical isolated input control (this helps to address the safety factor) and implements zero crossing switching (this helps eliminate the electrical noise created by AC phase control switching). Use a simple microcontroller board to manage the SSR input such that you plan the ON / OFF control across a certain number of half cycles of the AC mains. Lets say you shoot for control period of 0.4 seconds. At a 50Hz line frequency this translates to a total control period of 40 half cycles of the AC line. With suitable input drive signal to the SSR you can have 40 steps of power control.

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