DIY fan speed controller

[qazwsx]

I was planning on making a PC fan speed controller for a project at school to go along a large portfolio.

I was planning on making a simple temp controlled controller with a manual override. I've found a load of diagrams using an IC but does anyone know how to do it without one?
Thanks

[gvblake22]

If you want it to be temperature controlled, then I don't know an easy way of going about that. You could get one of those temperature controlled fans and take it apart and try to get something from that. when I made my own fan speed controller, I just used a small rheostat and had it adjust the voltage output on the 12V line to the fan(s); worked quite well actually. This is the guide I followed...

[Reloadron]

Originally Posted by qazwsx

I was planning on making a PC fan speed controller for a project at school to go along a large portfolio.

I was planning on making a simple temp controlled controller with a manual override. I've found a load of diagrams using an IC but does anyone know how to do it without one?
Thanks

Short of using an IC or a small handfull of semiconductor components I don't see an easy way.

The simplest method was mentioned by gvblake22 as to using a rheostat type circuit.

Now if you want to control a fan(s) as in cooling for temperature you have basic On/Off where the fan is on above a temp and off below a set temp (Setpoint) or proportional where the fan spins faster with increasing temp.

Using anything "automatic" you need some type of sensor to monitor the temp and drive some additional circuits. Really depends on exactly what you want to do and what you mean by control.

Ron

[Lead Head]

My friend just made a variable voltage PSU using LM317 voltage regulators. Output voltage is defined by two resistances. One remains constant, while the other can be connected to a variable resistor. At least thats how I gather it works. You could put the input side to the 12v of a PSU, find a resistor to suit your needs for the constant resistance part, then get one of those temperature resistors that increase/decrease resistance with heat. A switch to another constant resistor could be used for manual over ride.

Here is what my friend linked me.

LM317 Voltage Calculator

You may need to figure out a way how to raise the input voltage, according to this, the input voltage must be 1.5v higher then the output, on a normal PSU, that top you out at around 10.5v. It may be enough to demonstrate that it works though

[Reloadron]

Originally Posted by Lead Head

My friend just made a variable voltage PSU using LM317 voltage regulators. Output voltage is defined by two resistances. One remains constant, while the other can be connected to a variable resistor. At least thats how I gather it works. You could put the input side to the 12v of a PSU, find a resistor to suit your needs for the constant resistance part, then get one of those temperature resistors that increase/decrease resistance with heat. A switch to another constant resistor could be used for manual over ride.

Here is what my friend linked me.

LM317 Voltage Calculator

You may need to figure out a way how to raise the input voltage, according to this, the input voltage must be 1.5v higher then the output, on a normal PSU, that top you out at around 10.5v. It may be enough to demonstrate that it works though

Excellent thought, you would use a thermistor in a small circuit like this:



The thermistor would need to have a (-) Negative temperature coefficient meaning its resistance decreases with temperature increase. If you want to pursue this angle we can mess with a span of values.

Damn, I have to get to work.

Ron

[qazwsx]

Perfect, thats for the help everyone. I'll go with the temp based one using the LM317 as its a bit more complicated, but I doubt i'll ever use the controller or even if i'll even ever get it back.

Thanks again everyone

[Reloadron]

Originally Posted by qazwsx

Perfect, thats for the help everyone. I'll go with the temp based one using the LM317 as its a bit more complicated, but I doubt i'll ever use the controller or even if i'll even ever get it back.

Thanks again everyone

Just keep a few things in mind. It is a rough concept, not a final draft. There is a bit more to things. You will never get 12 Volts out with 12 Volts in so read no full speed. Typically a 12 Volt fan will turn on (start to turn) with about 7 to 8 volts applied.

I suggest you download a basic data sheet for an LM 317. There are also a few case designe for the 317 and you want the TO-220 case. This is not as simple as it looks. Should you run with this or another design ask questions.

Ron

[Lead Head]

One way to get 12v out of the LM317 would be to power it using the +12 and the -12v lines on the PSU, you may not want to do it on your rig, but just an extra PSU, but you'll have an effective 24 volts going into the regulator, which could then bring down to 12v, you might need to bolt it to a small piece of metal to keep it cool though. The downside is that it would allow for a potential over voltage if the temperature gets to hot.

[qazwsx]

as this is a school project, I won't be running this off a PC PSU but a power pack with ajustable voltage. I asked about the LM317 and all is good(for parts and all). I will download the data sheet. Thanks

[qazwsx]

Ok the time has come now to talk values. So as R2's resistance goes down the voltage also goes down, so I would need to place a thermistor with a positive temperature coefficient OR replace the R1 with a thermistor and put R2 as a normal resistor. As for values, if the voltage can go over 10.5v off a 12v source, does that mean that I can go for any as long as you can see a differnce in fan speed between 20*c and 50*c? (sorry for the poor grammer)
Thanks for the help guys.