Hi. I want to turn off a 3kw heater 240v , it makes distilled water into a tank, the tank has a float valve that closes two contacts when the tank is full and I want to turn off power to the heater when the tank is full. the float valve is rated at low voltage probably 12volts.

 

What electrical experience do you have

 

What electrical experience do you have

Physics technician in a college so have been learning electrical stuff for a few years. I have built circuits and did the electrics in my house. I am not sure if the float valve switch can be connected to one side of a relay without a seperate power supply?

 

You have correctly assess the problem, a separate voltage for the switch in the device specified, together with an interposing relay to switch the higher power circuit. Beyond that you must address the electrical codes and safety in your area.

 

Sounds to me like you might need an interposing relay and a contactor. The interposing relay would need a 12 volt coil and a normally closed contact that will open when the float switch closes. The contacts of the interposing relay need to be able to handle the voltage and current of the contactor coil. The contactor would need to be rated to handle the 3 kw / 240 volt heater. This scheme requires at least two voltage levels (12 volt and 240 volts) plus depending on the contactor coil maybe a third. If possible it might be cleaner if the float switch can be replaced with one which can handle the higher voltage and have a form C contacts (Com/NO/NC). This would allow the elimination on the interposing relay and its require low voltage source. In other words the float switch could de-energize the contactor directly when tank is full cutting off the heater. Good luck on the project.