Temperature control

[ady68]

Hi
Total noob here but very willing to learn.
I after some much needed help, I have searched and searched and have come close to what I am after but always seem to be not quite there.
So here I am after your help.
What I want is a simple and effective way of controlling a cooling fan on my car engine.
Thats quite simple, yes if you want the fan to swith on and off.
But I don't.
I want the fans speed to be controlled by a pwm.I already have the pwm.
Here is the tricky bit.
I want the fan to start at a low rpm and increse up to its full speed as the temperature of the engine rises.
ie at say 89'c the fan should start and at 97 the fan should be a full speed.It would be good to have a pot to enable me to trim the control.
The fan is 80 watt.
The pwm can have a input voltage of 0-5v dc
Is there already a circuit I can use or could someone point me in the right direction.
Many many thanks

 

[davenn]

hi welcome to EP

tell us more about the PWM unit you have
link to info ... circuit diagram etc

 

[ady68]

Hi
Thanks for the reply
Here is the link to the pwm I am using
http://www.ebay.co.uk/itm/390953900759?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

It states that the pot can be replaced with a 0-5v signal.
I need to find a simple and cheap way of doing this Ie I want the full 5v at say 95'C and 0v at 90'C
Help please ?

 

[duke37]

I suggest that you use a thermistor to detect the temperature and find the resistances at the temperatures that you want. Design an op-amp circuit to give the outputs that will give 0V at 95C or below and 5V at 90C and above. You will need a power supply for the amp, this could perhaps be stolen from the PWM circuit.

 

[Colin Mitchell]

Simply put the thermistor in place of the pot and see what RPM you get at the temperatures you are talking about.
Put the thermistor between the high-voltage end of the pot and the wiper. Put a 1k to 10k between the wiper and 0v.
Let us know what RPM you get and we will work out the next step.

 

[ady68]

Hi
sorry for the tardy reply
I have the thermistor now that I want to use.
At 99C it is showing 1k on my meter.
Time to start the experiments.
Thanks again for showing interest in this.
I know what I want but I am struggling to be able to convey this