how to change the speed of a fan with only 2 wires?

ExecutorKevin · 23 Aug 2011 at 18:34

my fan sounds like a hoover, its a 120mm one that I found in one of my old pentium II cases, and when plugged in to the motherboard header its really good, blows a gust of wind and managed to cool my graphics by 6 degrees, but I can't change the speed of it, there is no yellow wire, so I can't monitor the speed, but surely I can increase/decrease the voltage somehow, Speedfan is useless, and the bios has no options on it, and it would be a shame to throw away a perfectly good fan. So are there any programs that can do this or something, as I don't want to buy a controller, thanks!

Emphacy · 23 Aug 2011 at 18:45

It's not possible to do so unless you fancy getting a soldering iron out and ordering a potentiometer.

Tealc · 23 Aug 2011 at 18:49

Your prayers have been answered.

http://www.overclockers.co.uk/showproduct.php?prodid=OA-000-ZA&groupid=701&catid=57&subcat=189

Now all you need is for OcUK to have stock of the item.

or this 10v one, which to be honest wouldn't make it all that quieter.

http://www.overclockers.co.uk/showproduct.php?prodid=FG-006-GE&groupid=1929&catid=153&subcat=

There's also stuff like resistor cables or zener diode cables that will drop the 12v down to something less than 12v, although not in an adjustable way.

You can also plug the fan wires into a Molex extension and swap the red and black wires so that the fan get's it's power from the yellow 12v and the red 5v to make a 7v potential difference as detailed here and a million other places.

Again once you make the change it'll be stuck there until you switch the wires back.

Another ghetto solution might be to get some diodes and use the natural 0.7v drop across the silicon to reduce the voltage supplied to the fan. You could mount several diodes to a rotary switch to make a ghetto fan controller.

As for using software I think that might be a little tricky unless your motherboard can control the DC voltage supplied to the fan. 3 pin DC fans are only controlled by the red and black wires anyway, the yellow wire is just a tach output from a hall effect sensor and has no bearing on anything other than telling the fan controller how fast it's going.

Krony · 23 Aug 2011 at 18:52

Most fan controllers just pulse the 12v supply to change the speed therefore u only need the red and black wires.
Edit: jusat noticed u don't want a controller so as mentioned above u can get in line resisters like 5v and 7v but it will still be uncontrollable other than say 5v or 12v which would require adding in or taking it out.

Krony · 23 Aug 2011 at 18:57

I actually have a couple of thoes little controllers kicking about and i think i have one that fits into one of the expantion slots at the back of the case, ill have a look.

ExecutorKevin · 23 Aug 2011 at 18:58

Thanks Tealc for your information and time, but I'm hoping for a quick fix and don't want to buy anything, and that molex switch thing looks good, but I don't wan't to be fiddling with anything, and the pulse the 12v thing, I don't know what you mean, I'm sure the yellow wire is only for the speed sensor so could I still change the voltages somehow from the motherboard header?

Thanks

Krony · 23 Aug 2011 at 19:13

I actually have something similar to that little fan mate 2 but it fits in an empty expantion slot at the back of the pc so u could adjust it without opening the pc up each time, i'll have to have a look for it.

Krony · 23 Aug 2011 at 19:23

This is what i have, u can have it for nothing just pay the postage.

Tealc · 23 Aug 2011 at 21:17

Pulse the 12v thing refers to PWM or Pulse width modulation where the voltage is sent to the fan in a series of on/off pulses, usually at a high frequency. This requires a 4 pin fan connector and a motherboard with a Pwm circuit.

The only way you can control through software is having a motherboard that supports the feature. Some motherboards can have several fans controlled, some just the one, usually the CPU fan. Older boards should be able to regulate fans by DC and newer ones tend to be pwm or DC.

If speedfan doesn't work with your motherboard and cannot slow the fans down then maybe the motherboard manufacturer has its own software.

What motherboard is it? Might be tricky to find info on it if it is old though.

spleenharvester · 23 Aug 2011 at 22:26

Krony said:
This is what i have, u can have it for nothing just pay the postage.
http://img6.imageshack.us/img6/3131/dscf4984s.jpg[img][/QUOTE]

I have one of these, nice controller, given out with many Akasa CPU coolers. Go for it OP :p

I'm doing a mod to a Fanmate 2 at the moment for my GFX cooler. Have stripped the RPM wires, removed the ends of the connectors, and removed the wires from the Fan Mate 2 connector. Gonna solder them to the actual fan and heatshrink.