# temperature controlled fan speed

#### markosillypig

Joined Jul 21, 2008
188
hi every one
my quest this month is to find a circuit for my winter heat exchanger.
basically i want the fan to spin slowley as the heat gets hotter i want the fan to spin faster as to cool it down quicker to a set temperature so the hotter it gets the faster it spins
thanks for any help
marko

#### wayneh

Joined Sep 9, 2010
16,102
I'd use LM35 to sense temperature, a voltage-to-duty cycle PWM control, and a MOSFET switch to take the PWM signal and control the fan(s). There are tons of examples all over the 'net since this is the same need that computer fans have - speed in proportion to temperature. A lot of those circuits, though, are not PWM. I'd focus on the ones that are.

Joined Jul 18, 2013
19,029
You could check out one of the $5-$10 PWM controllers on ebay and hook up a thermocouple to the analogue input, you may have to add a little bit of interfacing between T.C. & input.
Max.

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#### markosillypig

Joined Jul 21, 2008
188
I'd use LM35 to sense temperature, a voltage-to-duty cycle PWM control, and a MOSFET switch to take the PWM signal and control the fan(s). There are tons of examples all over the 'net since this is the same need that computer fans have - speed in proportion to temperature. A lot of those circuits, though, are not PWM. I'd focus on the ones that are.
any links or schematics would help thanks

Joined Jul 18, 2013
19,029
One for a start, ebay 271214914630
Just Google The LM35 data sheet.
Max.

You could check out one of the $5-$10 PWM controllers on ebay and hook up a thermocouple to the analogue input, you may have to add a little bit of interfacing between T.C. & input.