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How do I wire a temperature sensor to operate a relay switch? What kind of relay do I need? Answered

There's a 2-wire thermostat sensor in my hot water storage tank that I want to signal a relay switch to turn on a circulating pump when it gets hot enough and off when it cools. An in-floor-heating relay might work, as the principle is the same (although reversed), but the temperature range is different. I want my pump to come on when the water in the tank is 50 degrees centigrade, and off when it's 45. Any suggestions?



7 months ago

A little schematic:

The thermal switch might cause problems regarding to accuracy,

It can probably be set for to switch off around 50 Degrees, but hysteresis is not adjustable, so, it will witch on again at something round 45 C if lucky, but it might be

40C or anything in that range.

I did made work this circuitry 25 Years ago, it worked with a solar heater and a Hot water tank.

If accuracy is needed,( witch i doubt) , then electronic thermostat will be needed.


pumps if hot.jpg

7 months ago

One mechanical relay is enough.

Wire the coil in place of the heating resistor.

Feed with correct voltage.

(For more appropriate answers,you could tell how your system is powered) .

Use the normally close (NC) circuit to power your pump.

Anti spark circuit is useful applied in parallel of the thermostatic switch.

But that one depends on power source and relay type.



Your suggestion won't work from the electrical side of things.


7 months ago

If the sensor applies power when the tank is cool 45 to heat, and turns off power when the tank hot 50.. A first SPDT normally closed relay goes closed at 50 and trips a DPDT hold relay. When the first relay closes at 45 it clears the hold relay..

The hold relay operates your pump