what is a rheostat?

[touser]

hi all, i was wondering what a rheostat was and how it works? if anyone can inform me it would be greatly appreciated.

[HaM]

A rheostat is a small device that can be used to control the speed of a fan in your computer. Sometimes when i fan is hooked to a readiator for water-cooling, people hook it up to a rheostat to turn the fan's speed down because it is quieter, yet produces the same temps. So its basically a fan speed controller.

I think i got that right...

matt

[Colin]

Variable resistor.

[touser]

ahh thank you HaM and Colin, i guess i will be buying one when my watercooling kit gets here :)

[Hoot]

HaM (Jul 19, 2001 12:26 a.m.):
A rheostat is a small device that can be used to control the speed of a fan in your computer. Sometimes when i fan is hooked to a readiator for water-cooling, people hook it up to a rheostat to turn the fan's speed down because it is quieter, yet produces the same temps. So its basically a fan speed controller.

I think i got that right...

matt

Well, almost Matt ;D
If you reduce the voltage to a DC fan, chances are good that you will reduce the speed of the motor.
If you reduce the speed, chances are good that you will reduce the airflow.
If you reduce the airflow, chances are good that it will not cool as well.

Hoot

[zoopa_man]

First off, when you use a rheostat to turn down the speed of your fan, your temps slowly go up because the fan isn't moving as much air across the radiator fins any more.

What a rheostat does is lover the voltage going to the device that is attached to it. You can put rheostats on lots of things. In fact I bet you have one in your car. The knob that controls your dashboard lights, try tuning that, if your dashboard lights dim...get brighter then that's a rheostat !

People use them on fans mainly to control noise levels. When you slow down a fan by giving it less voltage it gets quieter. I turn all my fans down to the lowest setting when surfing the net because I don't need that much cooling, but when I use intense programs like Quake3 I turn the fans up to full speed so I can get more cooling form them.

[Mord-Sith]

Hoot (Jul 19, 2001 07:53 a.m.):

Well, almost Matt ;D
If you reduce the voltage to a DC fan, chances are good that you will reduce the speed of the motor.
If you reduce the speed, chances are good that you will reduce the airflow.
If you reduce the airflow, chances are good that it will not cool as well.

Hoot


You need to add 1 more thing to your explination
If you reduce the voltage using a rheo it will heat up alot in some cases

[Hoot]

Very true. That's why it is good to locate it near an exhaust fan input.

Hoot

[zoopa_man]

Yes, I missed that too. Good call. You have to remember that when you turn the rehostat down that extra Energy has to go somewhere so it is disipated as heat energy, I'v seen some people put a small heatsink on the back of there rheostat to help with this. I had a rheostat on a large 120 mm fan that would get very hot to the touch when turned down all the way. It made me nervous so I put a heatsink on the back of it and it cooled down enough to where I was comfortable.

[Hoot]

The biggest challenge facing a rheostat is usually not exceeding its rated wattage. They also come with a maximum current rating because the wiper, that rides along the wound wire can only handle so much current in the surface area it has in contact with that wire. In higher wattage rheostats, the wiper is often a small cube of sintered copper, or carbon, much like the brushes on a DC motor.

Hoot

[zoopa_man]

Cool fact. I didn't know about the higher end rheostats having a different contact for better transfer. I might have to get my dremel tool out so I can say i'v seen one :)

[touser]

thank you so much for the help Hoot and zoopa_man, you cleared a lot of questions i had :)

[zoopa_man]

Your welcome.
Now go throw some circuit breakers ???
that's what happened to me the first time I ever tried messing with the wireing in my computer. Mom almost killed me. I know better know, pay attention and you'll be just fine.