Ridiculous Rheostats

[370forlife]

http://www.ocforums.com/showthread.php?t=312170

I followed the instructions there to calculate which rheostat I need to get to control my 92mm nidec's, I wound up needed a rheostat about 4 ohms, 6.42W.

After checking all the major websites, any that had some close enough were about $25-50. ridiculous.

Anyway, is there any other cheaper way to do this? Each fan is 12v, 1.1A. One will be controlled independently from the other 2.

[Krankshaft]

Re: Ridiculous Rheostats

Rheostat haven't heard that term in awhile. Gone the way of LPs and 8-Track tapes .

They used to use them (among other things) as dimmer switches before triacs. As you probably can guess they heated up ALOT and I'm sure caused a few fires.

This is quite simply the caveman way of reducing fan speed. Can't screw up installing a 2 terminal device .

2 ways to do this:

Voltage Regulation

Pulse Width Modulation

Voltage Regulation

With the VR route you set up a variable voltage regulator (with a suitable heatsink rated for the total current draw of the 2 fans) tie 1 resistor and a POT (in a voltage divider arrangement) to the control pin and ground and you have a speed controller.

The disadvantage of this is heat dissipated you also must make sure that the fan will start from a dead stop at your selected speed (voltage) and not stall. Since each fan model has a minimum voltage needed to overcome inertia. Once it's going it will continue this is a quick check and only needs to be done once.

Also the speed range adjustment of the fan will be limited for the reason described above.

Pulse Width Modulation

Building this yourself isn't practical and would probably cost more than buying a PWM fan controller premade. Basically it switches the fan rapidly on and off from 0V to 12V to regulate it's speed.

Check this link out about regulating DC fan speeds:

http://www.analog.com/library/analog...fan_speed.html

[370forlife]

Re: Ridiculous Rheostats

Can you draw a diagram or something of the VR method?

Any specific ratings I need to look for the voltage regulator, the resistor, and the pot?

[PlainBill]

Re: Ridiculous Rheostats

By searching on LM317 I found a number of circuits, and component calculators for it. This guy has a 12V to 9V regulator using an LM317. With a few modifications you can have a variable speed control for your fans. The most important one - attach a heat sink to the LM317. I recall there was an earlier thread, but I don't remember what you want to do. The big choice - do you want the fans to run at a fixed speed, or do you want to adjust the speed easily. If you want an easily adjustable speed, get a 1K pot with a shaft and put a knob on it. Otherwise use a simple trimmer pot.

PlainBill

[lucky13]

Re: Ridiculous Rheostats

http://www.ocforums.com/showthread.php?t=312170

I followed the instructions there to calculate which rheostat I need to get to control my 92mm nidec's, I wound up needed a rheostat about 4 ohms, 6.42W.

Is the 4ohm to be in series with the +12v line to reduce the voltage at the fan to something like 7v?

If so, and assuming you don't need to adjust the fan speed, you could buy a 3.9 or 4.3 ohm 10W resistor and just wired it up. There are some wirewound resistors that can be chassis mounted so use your computer case as heatsink.

[370forlife]

Re: Ridiculous Rheostats

I think I am just going to break down and get a lamptron fc-2 controller. Does PWM with 4 channels at 20w each. blue led lit dials and a black finish in a 5.25" bay.

Only 20 bucks too.

[PlainBill]

Re: Ridiculous Rheostats

I think I am just going to break down and get a lamptron fc-2 controller. Does PWM with 4 channels at 20w each. blue led lit dials and a black finish in a 5.25" bay.

Only 20 bucks too.

That would be gross overkill, but probably it would be cheaper than building one yourself. Even more so if you factor in the hassle of building it.

PlainBill

[370forlife]

Re: Ridiculous Rheostats

Each one of these fans are 13.2W (1.1A). 110cfm nidec screamers.

[PlainBill]

Re: Ridiculous Rheostats

Each one of these fans are 13.2W (1.1A). 110cfm nidec screamers.

I prefer quiet fans. If I want screaming I can always complain about my wife's housekeeping.

PlainBill

[Toasty]

Re: Ridiculous Rheostats

>>If I want screaming I can always complain about my wife's housekeeping.<<

OUCH !!!