Controlling Etched Foil Heaters
 

I am trying to control the temperature of several etched foil heaters that are currently just on a ON/OFF switch (using solid state relays). I have spoken to several individuals and just would like to get more advice. I was recommended to use a rheostat (light dimmer) or a variable transformer. I would like to control each plate separately. Each plate runs on 120 VAC at 600 W (5 A), there are 6 total plates. I think if I would use a rheostat is may burn out quickly, but if I use a variable transformer, would the heater function properly. Any advice/recommendations would be great. Thanks in advance.

Use a line voltage thermostat.

I do not think this will work. This heaters are encased in aluminum and will be immersed in water. The thermostat will be varying the heater temperature based on the ambient temperature ( I believe that's correct?).

I probably should have clarified it better, the heater temperature is not what I really what to be controlled but the power of the heaters.

You really want to control heater power, not temperature? That's easy. Just use a light dimmer rated for at least 600W. Lights and heaters have almost identical electrical characteristics. If you need more power than a light dimmer can handle, then use an "infinite control" from a stove. They work exactly the same way but are rated for higher current.

If you actually want to control temperature, you'll need a somewhat more sophisticated solution. A PID controller and solid state relay could keep your liquid temperature within 2 degrees of the setpoint for about $50 in parts.

I guess you are trying to control the temperature of the water. Get a fish tank (aquarium) heater t-stat and use that to operate a control relay to the heaters.