thermostat switch - where can I get one

[andycook]

I'm looking for a 12v thermostatic switch.
But not the type you would normally expect.

I want one that switches OFF when temperature meets a pre-defined temp e.g. 70 degC. I have looked on http://www.vehicle-wiring-products.co.uk
which is a useful site -
but they only have the normal type, where the switch activates, goes ON, at a set temp - e.g. to turn on a cooling fan.

basically i want the switch so it switches OFF a fuel line heater, when the coolant gets to a good temp, and heat exchanger takes over heating fuel.

[NiftyNev]

How about hooking up a relay to the fuel heater so its normally on and then have the temp switch activate the coil of the relay to cut power to the heater when it reaches the set temperature.

Neville

[andycook]

Neville

I thought of that, but couldnt figure out how you could have the relay on all time, and then switch it off??
how do you wire it up to do that? as i am being a bit thick
andy

[AndyLala]

Set the control signal across the coil... then when it reaches temperature the thermo switch powers off, this powers off the coil, relay opens...

[NiftyNev]

I was hoping you could figure it out.Relays tend to confuse me too.Have a look at this page.

http://www.bcae1.com/relays.htm

I'm sure it can be done.I'll let you know if I work it out.

Neville

[NiftyNev]

Set the control signal across the coil... then when it reaches temperature the thermo switch powers off, this powers off the coil, relay opens...

Thanks Andy.

Neville

[andycook]

AndyLala: Yes - Andy, that would work with a normal relay, and a thermostat switch that goes OFF at a set temp.
But i cant find a thermo swtich that does that. I can only find Thermo switches that go ON at a set temp e.g. a rad fan thermoswitch


Neville: Thanks for link, I need one of these types of relays~: and will work with a rad fan thermoswitch.


Single Pole Double Throw relay. Current will flow between the movable contact and one fixed contact when the coil is DEenergized and between the movable contact and the alternate fixed contact when the relay coil is energized. The most commonly used relay in car audio, the Bosch relay, is a SPDT relay

[AndyLala]

A couple of relays should handle this.

First relay powered on by the ignition.
Second relay uses the temperature sensor connecting at said temperature to switch the earth off for the heating relay...?

NiftyNev: nice site, good descriptions...

[NiftyNev]

I need one of these types of relays~: and will work with a rad fan thermoswitch.

Single Pole Double Throw relay. Current will flow between the movable contact and one fixed contact when the coil is DEenergized and between the movable contact and the alternate fixed contact when the relay coil is energized. The most commonly used relay in car audio, the Bosch relay, is a SPDT relay

I think you are right.Just make sure it is a SPDT relay which is marked with the 87 and 87A terminals.I have a relay here which has two 87 terminals and did some experimenting but it wont work because the two terminals are linked internally.The SPDT relay terminals marked 87 and 87A should be independant.

Neville