PC fans

[Fast Finger]

you're ignoring basic microelectronic principles, just apply Ohm's law. if you have something in the circuit that has a resistance which changes with temperature (aka thermistor) you will have automatic fan speed adjustment. an increase in resistance will reduce the voltage across the fans, which will reduce their speed. this means you need to use a negative temperature coefficient (NTC) thermistor. these cost about 25p at an electronics shop. knowing which one you need will require a bit of experimentation.

you need to see what effect a change in resistance will have on the fan speed, and what effect fan speed will have on temperature, do this at a variety of voltages. bascially you should use a pot (potentiometer- a volume knob) to allow the resistance in the circuit to be changed a lot, then you can see what amount of resistance is required at any given temperature and voltage, once you know that you can build the circuit to have this amount of resistance using a selection of resistors and thermistors (your reference voltage will be based on what thermistors are available) that will ensure the circuit always has the correct resistance. total cost will be very little.

Cheers jug.

I suppose its the way of modern society really, but i was that busy looking for something pre-made, i forgot to go back to basics.

Ill definatly look into this, maybe at the weekend. Ill let you lot know how it goes on if i do get time.

 

[alexGS]

Arctic Cooling (AC) make the best low-noise PC fans in my experience. They're carefully made with a rubber-mounted chassis etc. and look very little like normal fans, yet they're not that expensive and the difference is amazing.

-Alex

 

[hmallett]

how about a central heating thermastat, they go from about 13degres up

Central heating thermostats close (come on) when temperature falls below a certain point. You want something to come on when the temperature rises above a certain point.

 

[reaper1988]

If your using a PSU and not plugging the psu into a motherboard you will need to join 2 pins in the ATX socket otherwise it wont power on. Google will help you find what ones.

 

[Fast Finger]

Central heating thermostats close (come on) when temperature falls below a certain point. You want something to come on when the temperature rises above a certain point.

Not all .of them. Some are the opposite.
Some, like the Honeywells, have one set of contacts that closes, and one that opens at the same time.