Plain old resistors an alternative to fan controllers?

[MasamuneXGP]

Greetings all. I've been looking for a nice way of under-volt the multitude of fans in my system. I'm looking all all these pricey fan controllers, but the more I look at them the more I question how useful they would be to me. I not going to be constantly changing my fan speeds, I just want to find a good voltage and then leave it there. I'm aware of the yellow-wire-red-wire 7 volt trick, but I've heard that's a tad dangerous due to it cutting the actual ground wire out of the loop, and I'm looking for a little more precision anyway.

That's when inspiration struck. Unless my understanding of fan controllers is grossly mistaken (which is very possible! All I know is what I learned in Physics class about voltage and resistance!), a basic fan controller consists of a potentiometer in series along the voltage wire. If since I don't require the voltage to be changeable, it occurred to me that maybe all I really needed was to get a few 10-cent resistors from Radio Shack and spice them my fans' red wire.

Is my understanding of fan controllers massively off? Is there any reason why this wouldn't be a good idea? Would there be anything I needed to know when buying the resistors (other than how to translate those color bands into to ohms)?

 

[sodcha0s]

It will work just fine, you just need to figure out what ohm rating to use for the speed you'd like to achieve. You could also throw a SPDT toggle switch into the mix and switch from full to reduced speed at will.

 

[Navid]

Originally posted by: MasamuneXGP
Greetings all. I've been looking for a nice way of under-volt the multitude of fans in my system. I'm looking all all these pricey fan controllers, but the more I look at them the more I question how useful they would be to me. I not going to be constantly changing my fan speeds, I just want to find a good voltage and then leave it there. I'm aware of the yellow-wire-red-wire 7 volt trick, but I've heard that's a tad dangerous due to it cutting the actual ground wire out of the loop, and I'm looking for a little more precision anyway.

That's when inspiration struck. Unless my understanding of fan controllers is grossly mistaken (which is very possible! All I know is what I learned in Physics class about voltage and resistance!), a basic fan controller consists of a potentiometer in series along the voltage wire. If since I don't require the voltage to be changeable, it occurred to me that maybe all I really needed was to get a few 10-cent resistors from Radio Shack and spice them my fans' red wire.

Is my understanding of fan controllers massively off? Is there any reason why this wouldn't be a good idea? Would there be anything I needed to know when buying the resistors (other than how to translate those color bands into to ohms)?

A typical fan controller is not just a variable resistor. It is a variable voltage source (regulator). The difference is that when you set the output voltage of the regulator, it keeps it constant, to a reasonable degree, even if you change its load, temperature, source, etc.

Any reason using a resistor could be a problem?
In addition to the correct resistor value, you need to pick the correct power rating. If the resistor is too small (low power), it could burn and disconnect the fan completeley. It could also start a fire!

An advantage of a variable setup as opposed to a single setting (constant resistor) setup is that you may need to vary the RPM depending on the occasion. You can raise the RPM when you play a game when the sound of the game is so loud that you do not care about a little bit of fan hum but could benefit from better cooling for your overclocked GPU. Then, you can drop the RPM when you want to just work on a Word document and need peace of mind and silence.

If you are picky and want to find the absolute optimum setting between cooling and silence, you may want to use a fan controller, which gives you resolution.

If you are going to be happy with a resistor, go ahead. Just make sure to calculate the power rating in addition to the resistance you need.

 

[Zepper]

Welcome to the AT forums Masamune.

Yes resistors can be used but when a Sunbeam Rheobus can be had for so little money, why bother? Just be aware that the Sunbeam doesn't include fan extensions so order a few along with it. Oh and the Rheobus uses ordinary power transistors so that an inexpensive, low-power potentiometer can be used to control a higher current. Little if any load regulation is involved - a nearly constant resistance load (a fan) as well as a constant supply voltage are assumed. But a nearly constant output voltage will be maintained as long as the input is constant and the load is within the rating of the transistor.

.bh.

 

[GalvanizedYankee]

N-Joy! http://www.cpemma.co.uk/index.html

Look for bits 'n bobs at bgmicro.com or allelectronics.com

 

[soydios]

Yep, just make sure you get a resistor with the right number of ohms and a sufficient amperage rating.
To clarify, most 5.25"-bay fan controllers are variable voltage sources, not variable resistors.
If you want a variable resistor with cable extensions, get the Zalman FanMate 2. It's included with every new Zalman heatsink, and even allows RPM-sensor data to get back to the fan header if you need it. It's a variable resistor, so you can fine-tune the fan speed to get the right balance. I have one of them for my case fans (120mm) set at about 3/4 resistance, and one for my CPU fan (Zalman CNPS9500) set at max resistance.

 

[Zepper]

Wrong again soydios. The Zalman Fanmate 2 is a PWM (pulse width modulation) controller - it varies the output POWER by varying the pulse width of a constant voltage pulsed wave. The Rheobus and similar from, Vantec and Thermaltake (which also make PWM types) are linear variable voltage fan controllers.

.bh.

 

[Navid]

Originally posted by: Zepper
The Zalman Fanmate 2 is a PWM (pulse width modulation) controller - it varies the output POWER by varying the pulse width of a constant voltage pulsed wave.

If you connect a 12V DC to Fanmate 2, does it create a pulse, or does it not work at all?
Is there a reference for reading on this?

 

[Zepper]

wikipedia has good articles on most of these topics. You can also get a lot of info from the spec/application docs for the IC. And yes the Fanmate chops the 12V DC into an approx. 11V pulsed wave and controls the pulse width. All done by one little IC and a few passive components - that's why they can be so cheap. The Fanmate 1 was an early PWM with a very low freq pulse so it buzzed or whined almost every fan it was hooked to. The FM2 is much better. To avoid the side-effects, the freq has to be pretty high and/or variable and the pulses can't get too narrow.

.bh.

 

[VinDSL]

Originally posted by: MasamuneXGP
Greetings all. I've been looking for a nice way of under-volt the multitude of fans in my system. I'm looking all all these pricey fan controllers...

Huh?

Here you go -=- fully automatic fan controller -=- $5.95

 

[Zepper]

Ha, ha Vin... And when Sunbeam says bright LEDs, you'd better be wearing your shades! One channel for 6 bucks vs Rheobus's four channels for $12... The Rheo has bright LEDs too.

.bh.

 

[soydios]

Originally posted by: Zepper
Wrong again soydios. The Zalman Fanmate 2 is a PWM (pulse width modulation) controller - it varies the output POWER by varying the pulse width of a constant voltage pulsed wave. The Rheobus and similar from, Vantec and Thermaltake (which also make PWM types) are linear variable voltage fan controllers.

.bh.

Never mind then.
I thought it wasn't PWM because it uses 3-pin fan headers, but I guess you can still do that without Intel's 4-pin spec. Cool.

 

[Henny]

I prefer to use Zener diodes if the BIOS won't adjust fan speed.

 

[SparkyJJO]

Or skip the resistors altogether. Rewire the fan to 7V.

 

[Bluefront]

Humm....I really don't think a Fanmate uses PWM at all. It has little heatsinks inside, much like an Analog controller. And I've never heard it add any "clicking" noises to a fan, which is the down-side of PWM control. I must have installed a dozen of the things over the years on many different fans.

 

[Navid]

Originally posted by: Navid

Originally posted by: Zepper
The Zalman Fanmate 2 is a PWM (pulse width modulation) controller - it varies the output POWER by varying the pulse width of a constant voltage pulsed wave.

If you connect a 12V DC to Fanmate 2, does it create a pulse, or does it not work at all?
Is there a reference for reading on this?

I would like to try to clarify my question. I am not asking for reference on Pulse Width Modulation.
I am asking for reference confirming that Fanmate implements PWM.

 

[Zepper]

It's possible I'm wrong about the Fanmate - I just saw the insides of the FM1 and it is a power transistor on an aluminum heatsink that takes up almost all the space in the unit . What had me confused was that it only has a range of 5 to 11.xV - where most linear controllers can go down to zero and most PWM can't go below 5V equivalent or so because most would cause buzzing below that as the pulse width gets so narrow. I haven't seen the guts of the FM2 - still looking.
. Well, it looks like the FM2 is the same - haven't seen the insides fully exposed yet but it looks like there is still a big heatsink in there (seen thru the cooling holes in it) - a PWM unit wouldn't need near as much. Sorry about that - maybe my memory was faulty but I'm sure I read a review where the tester mentioned some side effects - but maybe he just didn't know the working voltage range of the fan he was using and had turned it down too low - fans will get kind of chuggy before they stop entirely....

.bh.

 

[Bluefront]

If you want to know for sure, hook up a small light to a fanmate. A PWM control turned down to the minimum, will cause the light to pulse (blink). This does not happen with a Fanmate. You can use one to dim computer lighting.

 

[God Mode]

for those with access to a bunch of 1/4 resistors and no 1-3watt ones, can you parallel a bunch together to handle more watts?

 

[Zepper]

Sure, but it will make a cumbersome final product as you'll need up to eight of them to make the proper value.

.bh.

 

[Navid]

Originally posted by: God Mode
for those with access to a bunch of 1/4 resistors and no 1-3watt ones, can you parallel a bunch together to handle more watts?

Let's say you have 4 10-Ohm resistors. But, each of them is 1/4W. Put 2 of them in parallel. That gives you a 5-Ohm 1/2W resistor. Do the same thing to the other 2. Now, you have 2 5-Ohm 1/2W resistors.
Put them in series. Now, you have one 10-Ohm 1W resistor.

 

[Clem]

Yes, you can just splice in a resistor.
In fact, that is exactly what Noctua does to make their 'U.L.N.A' device - it's a 3 pin fan
extension cable with a resistor spliced into the RED lead.
I just measured mine and it reads about 80 Ohms; you can figure out the wattage by using
your Physics class formulas, but the resistor is so small that it's about as thick as the RED
lead.

http://www.hardwarecanucks.com/hardware...65-noctua-nf-s12-120mm-fan-review.html

 

[Modelworks]

You could save yourself all the trouble and just buy a couple LM7808.
If you want a different voltage just buy a 7809,7810,7805.
The last two digits specify the output voltage.
They can handle 1A and its regulated.

You can even get them at radio shack at a premium , though online they are available at 50 cents each.

They have just three pins, voltage in, ground, voltage out.
Each is more than capable of running a fan or two without using a heatsink on the 7805.
Your normally supposed to put a capacitor on the input/ouput leads of the 7805, but with a fan I don't think you really need to worry about the ouput being stable within .1%.


with resistors, your actually wasting power as your converting it to heat.

Someone messaged me about using other voltages with the above regulators, for 6volt or 7.5 volt ,etc . Yes its easily doable.
In afact you can easily make it so its switchable with as many fans controlled, etc as you want.

Heres a very good site on it: http://www.cpemma.co.uk/index.html

 

[Navid]

Originally posted by: Modelworks
You could save yourself all the trouble and just buy a couple LM7808.
If you want a different voltage just buy a 7809,7810,7805.

with resistors, your actually wasting power as your converting it to heat.

With the voltage regulators you have named here, you will be wasting even more power than with resistors.

The advantage of a resistor, or any other variable control, over these regulators, is that you can change the RPM and find the RPM you want. You will not be stuck at one RPM for all the time.