Temp sensor to turn on relay to fan

[discostuee]

Im installing a thermo fan in my car but want to use the existing temp sensor to my temp gauge for the sensor. I can find out the resistance for it but something i can vary too would be good.
If anyone knows a simple circuit / diagram i would appreciate it.

thanks

 

[Vizier87]

I don't really understand your sentence. Anyway, temperature sensors are very cheap (like a thermistor, they're like 50 cents apiece),you can buy one, and control it using op-amps in comparator mode, if it goes to a certain temperature it turns on a fan, under that temperature it shuts off.

 

[discostuee]

Thanks Vizier87.
You have the right idea. i know the thermister is cheap but as my inlet manifold on the car already has a temp sensor to the gauge in the dash and thought i could use that so i dont have to try hook up and find somewhere to put the thermister.

any shematic that i can follow based on using the sensor i already have installed?

cheers

 

[Boncuk]

Hi discostuee,

I do not recommend a thermistor sharing two circuits. Car electronics normally work at low impedance which could cause erroneous readings of the circuit already in use if the thermistor is hooked to another circuit.

Better make a completely independent circuit.

Boncuk

 

[Dragon Tamer]

try this circuit TEMP

 

[MikeMl]

Hi discostuee,

I do not recommend a thermistor sharing two circuits. Car electronics normally work at low impedance which could cause erroneous readings of the circuit already in use if the thermistor is hooked to another circuit.

Better make a completely independent circuit.

Boncuk

Not if the added circuit is just monitoring the voltage (hiZ input to an OpAmp) across the existing thermistor sensor. I have done this and it works fine. Measure the voltage across the existing sensor cold and again at the temperature you want the fan to turn on, and write back...