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Simple Fan Quieting Circuit

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  • Heatsinks
  • Fan
  • Overclocking
Last response: in Overclocking
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February 27, 2003 7:13:42 AM

Here's a simple way to quiet down noisey fans...

The values given will only take a couple of hundred RPM off most fans, but that's usually enough to quiet them down considerably. As a plus, this circuit will give your fans a full power "kick start" to ensure they spin up every time.


<pre> 1) Cut the Red Wire on the fan and strip the wire ends...

2) Build this small circuit into the red wire...
____________
_______|10 ohm 2watt|______
To Fan | |____________| | To Motherboard
---------| ____________ |-----
|______|100uf 16volt|______|
|____________|+

3) Solder all connections.
4) Trim off excess part leads.
5) Cover with electrical tape.
</pre><p>Parts ...
1 - 10 Ohm 2 watt resistor,
1 - 100 Microfarad 16volt Capacitor
6" - Electrical tape.

You can vary the resistor if you like... 16 ohms will make it even quieter, but I don't suggest going beyond 20 ohms.

Increasing the value of the capacitor to 220 microfarads will give a bigger kick start to the fans, but 100 is adequate in most cases.

Total cost... less than a buck.

(sorry about the lousy graphics...)

More about : simple fan quieting circuit

Anonymous
a b K Overclocking
February 27, 2003 6:47:11 PM

Someone with a little ambition could probably make a killing selling a PWM fan control circuit to overclockers. Never worry about start up, choose any RPM you want...hmmm.
February 27, 2003 8:53:55 PM

I do indeed have more comprehensive circuits for this kind of work. Using a rather straightforward 2 transistor circuit I've spun fans down to as little as 120 rpm...

But these fans are not simple motors. They already have circuitry in them which requires something resembling a steady DC current to work. Pulse width modulation, as good as it sounds in theory simply confuses the hell out of the fan's internals.

There are lots of fan controllers already on the market:
<A HREF="http://www.directron.com/speedcontrol.html" target="_new">http://www.directron.com/speedcontrol.html&lt;/A>
but where else but here are you going to get one for under a buck? :smile:

<b>(</b>It ain't better if it don't work.<b>)</b>
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Anonymous
a b K Overclocking
February 28, 2003 12:05:20 AM

120RPM, that is impressive. I have to ask: was it stable? does it always start?

I have been having good success controlling a 10KRPM 5V fan motor with a PWM control, but it starts getting relatively unstable at below about 3000 RPM (possibly for the reasons you mentioned). I don't really think I would need much slower though, since I don't see much use for a really slow fan. My problem now is cost, as my design requires a processor.

The link you gave was indeed fan control central. Damn those are some expensive resistors they have there. Those pyramid things look interesting. They don't really describe what type of control they have though. Something like that would probably be the most cost effective in the end, since it is already designed and mass produced. That is of course unless two transistor designs are popping out of your head relatively quickly, heh heh.
February 28, 2003 2:40:11 AM

Yep it was stable and it started every time. The trick is in the way I designed the circuit... It would start the fan at full speed and then slow it down over a period of about 5 seconds to whatever speed I set (well, actually the speed that corresponded to the voltage I was feeding it). Of course that was purely experimental, you'd never run a fan that slow in practice.

Once you have it spinning, slowing it down is easy. It's getting it to start reliably that's the real trick. So, start the thing under full power and then turn it down...

That's what the capacitor in my cheapy circuit does... for a brief moment (a few milliseconds actually) the capacitor acts as a short, because it's discharged, giving the fan a burst of 12v, until the capacitor charges and the resistor takes over. It also provides a bit of filtering to keep the voltage even, but that's not really why it's there.

As for "fan control central"... why do you think I put up the little circuit... there is one on that page that is essentially what I posted ... and they want 6 bucks for it. Ouch!

The resistor trick really does work... Most manufacturer's over-spin their fans a bit because they know that over time the fan will slow a bit as things start to wear. Unfortunately this causes an effect known as "cavitation" where the blades actually create a vaccum and can't pull enough air to keep the airflow over the blades smooth, causing the noise we hear. If the blades could get a full grab of air every time, even a 6,000rpm fan would be whisper silent. Taking about 10% off the fan's speed with the resistor is merely a way of minimizing the cavitation effect.




<b>(</b>It ain't better if it don't work.<b>)</b>
February 28, 2003 3:10:39 PM

Will this curcuit work with a slow 120mm fan? I have one that runs at about 3000 rpm, wnated to try to take it down to around 1/2 of that during the winter months.

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
February 28, 2003 4:45:11 PM

It should work.

With the 10 ohm resistor, on a 12volt 200ma (.2amp) fan it will reduce the operating voltage to about 10 volts... Which should take less than 10% off the speed of the fan. This quiets most fans noticeably, because it reduces the cavitation effect. It does not significantly reduce airflow... in fact, on some fans it seems to increase it!

A 20 ohm resistor on the same fan would result in about 8 volts, taking about 20 to 25% off the speed of the fan, but it's also very near the minimum voltage where you can expect a fan to start reliably. (7.5 volts for most of them) With a 20 ohm resistor, I'd suggest you use a 220 uf (or bigger) capacitor.

I would not suggest running any fan at half speed... (which would occur around 5 or 6 volts) It may not start reliably and the reduction in cooling may be disastrous to your system.

The object is to maintain as much cooling as possible while quieting things down.


<b>(</b>It ain't better if it don't work.<b>)</b>
March 2, 2003 1:37:35 PM

But don't use this circuit on high power fans like my Delta 120HOP that draws 36W... the resistor can't handle the amount of heat it will create.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
March 2, 2003 1:46:40 PM

36Watts... That's 3 amps!

My god...

No, you can't use a simple resistor on something like that... But why would you want a fan that draws more juice than 3 hard disks in the first place?

BTW... how long did it take you to find that fan?

<b>(</b>It ain't better if it don't work.<b>)</b>
March 2, 2003 2:44:02 PM

Because he can? lol

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
March 2, 2003 2:44:08 PM

Pretty impressive fan isn't it? Puts out 197 cfm at full power with 4000rpm.

As for finding it... when I bought my watercooling I could opt a 120mm fan for my radiator. This was the only one they sold. So I bought it... did I know it was so power hungry.

Well you can imagine my first reaction once I used it... FVCK! I tried to slow it down with a rheostat... but that ended in a bloody hot rheostat. With a Pulsw Width Modulator the fan would make a very irritating wining noice so that wasn't an option. So I bought 4 5W and 4 4W resistors and put them parallel/serie... they use about 16W. Then I added the Rheostat and now I have a very silent fan that can move much air.

Luckily I use a secondary PSU to power all my fans and CDROMs.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
March 2, 2003 3:40:49 PM

now wonder the neighborhood dims!

Is there any good supplier online where I can get loose electronics parts? My local radioshack doesn't have much of a selection..

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
March 2, 2003 4:58:20 PM

I don't know for the USA but in Europe we got Conrad Electronics.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
March 3, 2003 1:06:55 PM

I know I'm being a pan in the ass about all of this, but I cant find any 2 watt resistors around. Now if I would have stayed awake in my 9th grade electronics class I would know how to get around this. Am I correct in that I will get a 10 ohm 2 watt load if I run 2 10 ohm 1 watt resistors in parallel?

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
March 3, 2003 3:44:53 PM

Nope for parallel you have to use the following resistance formula: 1/R+1/R=1/Rtotal.
So with 2 10 Ohm resistors you will get a 5 Ohm total resistance.

But putting 2 10 Ohm in serie will give you 20 Ohm resistance.

So I suggest you place two 5 Ohm 1W resistors in serie.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
March 3, 2003 3:53:37 PM

If you can't find the recommended 2 watt resistors..

you can:

a) Use a 5 watt resistor (they're easier to get)

b) Use 2 20 ohm 1 watts in parallell.


Here's the math...


The formula for parallell resistence is:

<b>1/(1/R1 + 1/R2 + 1/R3 + 1/R4 ... 1/Rn)== Ohms</b>

(i.e. the reciprocal of the summ of the reciprocals)

The result will always be less than the lowest resistor in the parallell group.

So If you were to use 2 x 10 ohms you would end up with:

1/(1/10 + 1/10) == 1/(.1 + .1) == 1/.2 == 5 ohms

A pair of 20 ohms gives you what you need...

1/(1/20 + 1/20) == 1/(.05 + .05) == 1/.1 == 10 ohms



And heres the math for a hypotetical 12volt 200ma fan...

(1 amp == 1000 ma so it's actually a .2 amp fan)

The voltage drop is calculated by ohms law:

<b>R == E/I</b>

R is resitance in ohms
E is voltage in volts
I is current in amps

To run a 12volt 200 ma fan on 10 volts you have to drop 2 volts across the resistor so you get:

(12 - 10)/.2 == 2/.2 == 10 ohms


The resistor's power rating is calculated for safety. When a fan first starts up <b>all</b> the voltage is across the resistor for a split second, so it must endure the full 12 volts...

The formula for power is:

<b>P == E X I</b>

P is power in watts
E is voltage in volts
I is current in amps


To safely run a 200ma fan you get:

12 X .2 == 2.4 watts.

Any resistor that meets or exceeds your calculated power will do fine... Resistors come in .1, .2, .5, 1, 2, 5, 10, 25, 50, 100, and 500 watt ratings... so round up to next standard value == 5 watts.


So... for our hypothetical 12 volt 200ma fan we need a 10 ohm 5 watt resistor.

Does that help???






<b>(</b>It ain't better if it don't work.<b>)</b>
March 3, 2003 3:55:05 PM

OR ... just use a 5 watt resistor.



<b>(</b>It ain't better if it don't work.<b>)</b>
March 3, 2003 3:57:54 PM

yeah, ofcourse. More watt wont hurt if you have the same resistance. But I don't know how easy he can find those.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
March 3, 2003 4:03:20 PM

Ill look around. I did find some monster 10 ohm 10 watt resistors at radio shack... the wire wound ceramic type. Each one was about an 1 1/2" long, minus the leads. I knew more wattage wouldnt hurt either. I just have an easier time finding the lower wattage resistors. Makes me wish I never got rid of those electronics hobby kits I had...
Btw, thanks for explaining that guys. It is a real help. :smile:

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
March 3, 2003 4:04:03 PM

5 watt resistors are usually easier to find than 2 watters, for some reason. Most warehouses don't stock the full line in all wattages... they base their inventories on sales and I guess low value 2 watt resistors aren't used very often.

C'set la vie :smile:


<b>(</b>It ain't better if it don't work.<b>)</b>
March 3, 2003 4:05:51 PM

Why not try a couple of TV repair shops or electronic wholesalers in your area... Can't speak for where you are but around here most will sell to hobbiests if they have the items in stock...

That 10watt monster may pose a curious new problem... <b>weight</b>... it may be heavy enough to put serious strain on the hair thin little wires used on some fans. (Ov course you could always disassemble and re-wire the fan :smile: ).




<b>(</b>It ain't better if it don't work.<b>)</b>
March 3, 2003 5:08:05 PM

Yeah, I didnt want that 10 watter sitting around, wont look too good in my case.

Ill looka round for one of those shops. Pity, there was one a few blocks from where I live, but much like most of the buisness in that ghetto place, its a nail / pager /cell phone store. Go fig...

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>
March 6, 2003 8:17:43 PM

Yep, I knew about that but it only works for 2 resistors...

Try it with 3 ... OOPS, wrong answer!



<b>(</b>It ain't better if it don't work.<b>)</b>
!