Temp sensor Circuit

[sideoiler]

i need a bit of advice in making a circuit up and the best way off doing it to run off 12v dc

i have a low voltage temperature sensor that needs to turn on a relay and off

the problem is the sensor is normal closed contact up to 150deg then over that temperature goes open circuit
i need it to switch a relay on when it goes over 150 deg ie open circuit so the relay can fire a solenoid

any idea,s ?

[Terry_VK5TM]

One idea off the top of my head assuming the sensor is a mechanical contact type.

[Buzby123]

Is the sensor some kind of bi-metal switch, like an over-temperature device ?.

If so, you can use it in a 12v circuit to directly drive a relay, then just use the normally-closed contact from the relay to fire your solenoid.

No electronics needed !.

[sideoiler]

hard to tell what type of sensor it is with out opening it up
it,s not thermistor so i guess some type of by metal sensor / switch
that switches open circuit any thing over 150 deg

[elanman99]

Can you post a picture of the sensor which (from your description) sounds like a thermostat

Ian

[duncanlowe]

An alternative solution is to buy one of the devices available in many places online. Adjustable temperature, hysteresis, and can be set to switch on over a temperature (for cooling) or off over a temperature (for heating). Run off 12v with volt free contacts on the relay on the board.

[sideoiler]

it,s a bit like this but with a brass screw on the end

[elanman99]

By screw, I take its for mounting rather than an adjusting screw. Either way its some sort of thermostat often used for thermal protection or maybe temperature control in a none (temperature critical) product.

Its going to be able to pass more than enough current to drive any relay you might need

Ian

[Bazz4CQJ]

That's not a sensor it's a bi-metalic switch, and I guess that it has normal closed contacts (NC) that go open at 150'C. They are usually used as safety cut off features. However, I'm sure somebody will suggest a way of using it.

B

[elanman99]

Referring to your first post and wanting to 'fire' a solenoid.

Over 150 degrees the solenoid is going to be powered continuously until the temperature drops, is that what you want?

Ian

[Bazz4CQJ]

It might be possible to do the whole job using a capillary thermostat like this https://www.ebay.co.uk/itm/353048429...iTpgR3enXBRnO5.

That particular one looks as if it might have contacts for both the normally open and the normally closed, so at the set T, it could be made to either switch on or switch off and may handle sufficient current to not need a relay.

Those types of thermostat have been extensively used in boilers and ovens for years and are very reliable, though not perhaps very precise.

B

[duncanlowe]

Yes that's a bimetal thermostat. Have a few rescued from various small appliances. Two terminal devices that open at a set temperature, loads of hysteresis and thermal lag. The temperature varies depending on application. IMO, most useful as a safety backup for more subtle controls.