rheostat for the HSF?

[bhess]

OK I hit Radioshack and bought some rheostats. Now how do I hook them up to slow down the HSF? They have s posts on them, and 3 wires on the fan. How do I hook them up?

Thanks
Brian

[Graham]

Bhess,
I dont know if there is a "standard" way of doing it, but ....

From the fan there are three wires, red, black, yellow, and on the rheostat there are 3 terminals. Looking from the front (knob side) of the rheostat with the terminals downwards, connect the left hand and middle terminals together, break (cut) the red wire and put the end from the MB connector to the single remaining terminal and the red wire going to the fan to the two terminals previously joined together, the other two wires are not cut and go to where they did originally. Turning the knob clockwise will slow the fan, be carefull, depending on the value of the rheostat, you might be able to stop the fan alltogether.
What you are doing is introducing resistance into the power lead thereby reducing the voltage across the fan.
You can do it another way but the value of the pot (rheostat) is more critical.


PS if you want the fan to increase speed with clockwise rotation, then link the right hand and middle contacts instead.


G

[bhess]

Thanks. That will be my project tonight.

[Graham]

Hope you can understand my explanation.

G

[bhess]

It's working. Kind of.

I can't turn it down much. The rheo gets hot and the fan gets slower without me turning it anymore. I must need a bigger one.
It's at 6400 and 44C.

[bhess]

I think I'm overworking the rheo. I've heard about changing the volts to the fan. Anyone have any links?

[Xeroid]

Take a look @ 7volts.com. I have never tried it but it involves using the 12v as the positive and the 5v as the negative. The potential difference is 12 - 5 = 7 volts.

Mike

[Tachyon]

I'm using the 7 Volts mod in one of my computers and its works pretty nice. Be sure to check if your fan will start on 7 volts though. It wouldn't be good it you forget to put it on 12v before you start the computer and fry something.

Also, if your interested in picking up a higher wattage rheostat you can get 5 watt ones here. I'm using one on my 8K Delta which draws 0.80 amps and it works well.

-Tachyon

[Xeroid]

Originally posted by Tachyon
Be sure to check if your fan will start on 7 volts though. It wouldn't be good it you forget to put it on 12v before you start the computer and fry something.-Tachyon

Good point. You could get a single pole/double throw switch and start the fan at 12v then switch it to 7v after startup. The rheostat would also require some caution. You might want to start it at full RPM, then slow it down after you get it turning.

Mike

[bhess]

Nice link Xeroid. Good info there. I'm gonna get a better rheostat.