Sign in with
Sign up | Sign in
Your question

Which resistor to lower CPU fan speed?

Last response: in Home Audio
Share
Anonymous
June 14, 2005 3:34:49 PM

Archived from groups: rec.audio.pro (More info?)

I just purchased a new Antec rackmount PC case for my rig. It comes with
3x92mm fans and 1 80mm fan. They all spin at approx 4300RPM. I would
like them to spin at about 1600RPM. Is there a way to calculate which
resistor i need? I had a few kicking around and tried a 120ohm 0.25watt
but it slowed everything down to a useless speed.

Thanks!

Roach

BTW, i'm implimenting the resistor by interrupting the +12V power cable
and puting it in line.
Anonymous
June 14, 2005 3:34:50 PM

Archived from groups: rec.audio.pro (More info?)

give up
;) 

nace
Anonymous
June 14, 2005 3:56:36 PM

Archived from groups: rec.audio.pro (More info?)

Sorry, the subject line should read "Chassis fan speed" not "CPU fan speed."

Mike

Mike Rocha wrote:
> I just purchased a new Antec rackmount PC case for my rig. It comes with
> 3x92mm fans and 1 80mm fan. They all spin at approx 4300RPM. I would
> like them to spin at about 1600RPM. Is there a way to calculate which
> resistor i need? I had a few kicking around and tried a 120ohm 0.25watt
> but it slowed everything down to a useless speed.
>
> Thanks!
>
> Roach
>
> BTW, i'm implimenting the resistor by interrupting the +12V power cable
> and puting it in line.
Related resources
Anonymous
June 14, 2005 5:11:26 PM

Archived from groups: rec.audio.pro (More info?)

Nace wrote:
> give up
> ;) 
>
> nace
>

Hahaha, why i oughta! ...jerk!

Roach
Anonymous
June 14, 2005 7:48:17 PM

Archived from groups: rec.audio.pro (More info?)

Question... When you slow down the fan, are you certain the electronics
won't overheat?
Anonymous
June 14, 2005 8:50:42 PM

Archived from groups: rec.audio.pro (More info?)

Mike Rocha wrote:
> I just purchased a new Antec rackmount PC case for my rig. It comes with
> 3x92mm fans and 1 80mm fan. They all spin at approx 4300RPM. I would
> like them to spin at about 1600RPM. Is there a way to calculate which
> resistor i need?

You can get a clue from the label by seeing what current the fan takes
at 12V. 12/I gives you a notional resistance figure and a series
resistor of the same value will roughly halve the voltage, but that's
not accurate as the motor's V/I function isn't linear. And anyway 6V may
not be what you need, though actually it's often about right.

The short answer is trial and error...
The even shorter answer is 56 ohms.

> BTW, i'm implimenting the resistor by interrupting the +12V power cable
> and puting it in line.

You're on the right track there...

Anahata
Anonymous
June 14, 2005 9:13:07 PM

Archived from groups: rec.audio.pro (More info?)

William Sommerwerck wrote:

> Question... When you slow down the fan, are you certain the electronics
> won't overheat?

I found a couple fans at MCM (Parts Express)
that had a built-in thermister to provide
variable speed for changing temperature.
Not sure of the mm size but they are similar
to the chassis fans (OP) is discussing.
I used one in a power supply that was noisy.
The only caveat to using this type is that
the heat has to pass through the fan, i.e.
exhaust, obviously the heat sensor will not
work if the fan is at the intake.

rd
Anonymous
June 14, 2005 9:26:12 PM

Archived from groups: rec.audio.pro (More info?)

Mike Rocha wrote:
> I just purchased a new Antec rackmount PC case for my rig.
It comes
> with 3x92mm fans and 1 80mm fan. They all spin at approx
4300RPM. I
> would like them to spin at about 1600RPM. Is there a way
to calculate
> which resistor i need? I had a few kicking around and
tried a 120ohm
> 0.25watt but it slowed everything down to a useless speed.

Just pick up some Zalman fanmates. They have a little
adjustment knob. By provding a constant-voltage source, they
help guard against the fan stalling.
Anonymous
June 15, 2005 1:55:26 AM

Archived from groups: rec.audio.pro (More info?)

On Tue, 14 Jun 2005 11:34:49 -0400, Mike Rocha
<therealroach@rogers.com> wrote:

>I just purchased a new Antec rackmount PC case for my rig. It comes with
>3x92mm fans and 1 80mm fan. They all spin at approx 4300RPM. I would
>like them to spin at about 1600RPM. Is there a way to calculate which
>resistor i need? I had a few kicking around and tried a 120ohm 0.25watt
>but it slowed everything down to a useless speed.

This question was asked and discussed recently here:

http://groups-beta.google.com/group/rec.audio.tech/brow...

http://makeashorterlink.com/?R5C23534B


>Thanks!
>
>Roach
>
>BTW, i'm implimenting the resistor by interrupting the +12V power cable
>and puting it in line.

-----
http://mindspring.com/~benbradley
Anonymous
June 15, 2005 11:05:30 AM

Archived from groups: rec.audio.pro (More info?)

In article <11aunmob51mv54@corp.supernews.com> williams@nwlink.com writes:

> Question... When you slow down the fan, are you certain the electronics
> won't overheat?

Only if you measure the temperature before slowing the fan down and
then after. Unless it's the CPU fan and one of those newfangled
motherboards with the BIOS that lets you read the temperature of the
CPU, you really can't ever measure something to compare with what's on
the chip's spec sheet (as a maximum temperature rating). If you put a
temperature probe on the heat sink and measure that temperature with
the fan running at normal speed, then slow it down and see how much
the temperature rises, you can get an idea of how much "headroom"
you're taking away. Unless you're leaving your computer out in the sun
on a day like today (here), you can certainly take a 5 degree C rise
and still be safe. But if you make the temperature rise by 20 degrees,
you'd probably not slow it down that much.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
June 15, 2005 11:31:23 AM

Archived from groups: rec.audio.pro (More info?)

On Tue, 14 Jun 2005 11:34:49 -0400, Mike Rocha
<therealroach@rogers.com> wrote:

>I just purchased a new Antec rackmount PC case for my rig. It comes with
>3x92mm fans and 1 80mm fan. They all spin at approx 4300RPM. I would
>like them to spin at about 1600RPM. Is there a way to calculate which
>resistor i need? I had a few kicking around and tried a 120ohm 0.25watt
>but it slowed everything down to a useless speed.
>
>Thanks!
>
>Roach
>
>BTW, i'm implimenting the resistor by interrupting the +12V power cable
>and puting it in line.

That means 120ohm is too large, right? I think I hit on 30ohm as just
right for me. I used a 2W resistor if I recall- if it feels hot
replace it with a larger watt rated R. The size will be different if
all 3 fans are wired together. Get a 100ohm pot and dial it till you
can live with the noise and still stay within some kind of heat range
spec. We had a real hot day and the whole pc fried unfortunately when
I wasn't paying attention as I recall.
There is software that let's you set an audible alarm if the temp gets
too high (something monitor- maybe "mainboard monitor"- it's free).
I've had a DIY bucket system for 18 months now- what a relief. Keep
cookin'.
Anonymous
June 15, 2005 1:41:31 PM

Archived from groups: rec.audio.pro (More info?)

In article <1118794387.435306.122370@f14g2000cwb.googlegroups.com> annonn@juno.com writes:

> I found a couple fans at MCM (Parts Express)
> that had a built-in thermister to provide
> variable speed for changing temperature.

The problem with a variable speed controller is that when it decides
that things are getting too hot, it starts the noise. You're better
off with a constant low level noise than noise that stops and starts.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
June 15, 2005 2:17:36 PM

Archived from groups: rec.audio.pro (More info?)

I came in late here but..

Running at low voltage is one thing and starting reliably is another.
The Antec fans should start and run @ 5 volts so why use a heat
generating resistor. If it doesn't, you can try 7v (12v to + and 5v to
-) or replace the fan with a Zaleman (all of which run dead quiet on
5v)

Frank /~ http://newmex.com/f10
@/




On Wed, 15 Jun 2005 07:31:23 GMT, spud <oblahdee@blahdah.com> wrote:
>
>That means 120ohm is too large, right? I think I hit on 30ohm as just
>right for me. I used a 2W resistor if I recall- if it feels hot
>replace it with a larger watt rated R. The size will be different if
>all 3 fans are wired together. Get a 100ohm pot and dial it till you
>can live with the noise and still stay within some kind of heat range
>spec. We had a real hot day and the whole pc fried unfortunately when
>I wasn't paying attention as I recall.
>There is software that let's you set an audible alarm if the temp gets
>too high (something monitor- maybe "mainboard monitor"- it's free).
>I've had a DIY bucket system for 18 months now- what a relief. Keep
>cookin'.
>
>
Anonymous
June 15, 2005 3:26:32 PM

Archived from groups: rec.audio.pro (More info?)

Mike Rivers wrote:
> In article
<1118794387.435306.122370@f14g2000cwb.googlegroups.com>
> annonn@juno.com writes:
>
>> I found a couple fans at MCM (Parts Express)
>> that had a built-in thermister to provide
>> variable speed for changing temperature.
>
> The problem with a variable speed controller is that when
it decides
> that things are getting too hot, it starts the noise.

External conditions often have a strong influence. IOW a
hot day or a cold day with a space heater.

>You're better off with a constant low level noise than
noise that stops and starts.

That start-stop thing definately happens with laptops.
Anonymous
June 15, 2005 5:56:10 PM

Archived from groups: rec.audio.pro (More info?)

Frank Vuotto wrote:
> I came in late here but..
>
> Running at low voltage is one thing and starting reliably
is another.
> The Antec fans should start and run @ 5 volts so why use a
heat
> generating resistor. If it doesn't, you can try 7v (12v to
+ and 5v to
> -) or replace the fan with a Zaleman (all of which run
dead quiet on
> 5v)

I've found that various 12v fans are iffy when run from 5
volts. However the 7 volts you get by connecting the fan
from +12 to +5 results in more reliable operation and still
gives a definate loss of noise.

See my other comments about Zalmann FanMates. They are
basically an adjustable regulator, an adjustment pot and a
heat sink in a nice package for a fair price.
Anonymous
June 15, 2005 7:36:51 PM

Archived from groups: rec.audio.pro (More info?)

On Wed, 15 Jun 2005 13:56:10 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>I've found that various 12v fans are iffy when run from 5
>volts. However the 7 volts you get by connecting the fan
>from +12 to +5 results in more reliable operation and still
>gives a definate loss of noise.

I think this is less true than it use to be. It's been a while since
I've come across a fan that couldn't deal with 5v.

Right now I'm on my new video system that runs an Athlon 64 3000+,
10% overclocked, 2 gigs ram, 3 sata drives in a Cooler Master Cavalier
case (killer case (excellent airflow and a fairly heavy aluminum door,
the only one I use these days) with a Coolmax Taurus power supply set
to 'silient' mode. The stock 120mm exhaust and the 80mm intake fans
are running on 5 volts. The CPU has a Zalman 7000 with the included
fanmate run all the way down to minimum speed.

The MSI K8N Neo4 motherboard had a really obnoxious northbridge fan
that runs at 7000 RPM! I disconnected that and mounted an 80mm Zalman
(5v) in the case blowing on the chip's heatsink.

The video card is a BFG overclocked nvidia 6600 dual head that,
suprisingly, has a really quiet fan and I left it as is.

This system is as close to totally quiet as I have ever come. You
have to put your ear right on it tell it's running.


Frank /~ http://newmex.com/f10
@/
Anonymous
June 16, 2005 10:45:32 AM

Archived from groups: rec.audio.pro (More info?)

If the fans are fed from the drive power using
an inline connector, try to move the fan power
from the 12v line to the 5v line. I do this all the
time when I need a slower fan. Usually it is quite
simple to do, and as yet I've had no fans fail
to start or stall out.

Robert
Anonymous
June 16, 2005 4:45:47 PM

Archived from groups: rec.audio.pro (More info?)

On Thu, 16 Jun 2005 06:45:32 +0000 (UTC), Rv! <Rv@no.way.invalid> wrote:
> If the fans are fed from the drive power using
> an inline connector, try to move the fan power
> from the 12v line to the 5v line. I do this all the
> time when I need a slower fan. Usually it is quite
> simple to do, and as yet I've had no fans fail
> to start or stall out.
>
> Robert
>

I'd get a quieter cooler. My Zalman flower coolers came with a
speedcontrol, but it's quieter than my (admittedly too noisy) ambient
without it.

Take a look here:

http://www.endpcnoise.com/cgi-bin/e/scan/st=db/co=yes/r...

I'm using the Zalman copper flower coolers on Intel CPUs and consider
them well worth the lack of grief.
Anonymous
June 16, 2005 9:41:27 PM

Archived from groups: rec.audio.pro (More info?)

> I'd get a quieter cooler. My Zalman flower coolers came with a
> speedcontrol, but it's quieter than my (admittedly too noisy) ambient
> without it.

Most of the machines I build are on 24/7 and share bedrooms with
the owners, or are loft based servers. The bedroom machines must
be quiet as they will be on when sleeping. The loft based servers I
use slower fans and air filters to help keep dust contamination down.

These machines usually are very powerful systems so a large amount
of airflow is useful/needed. My last machine had two intake fans at
the HDD's and two output fans on the back, all running at 5v. None of
these could be heard above the ambient noise of a quiet processor fan.
On my personal PC I have swapped out the PSU fan for a quiet fan as well
so the machine is very quiet. On that subject the Dell 2400's seem to be
scarily quiet at times. Nice design.

My brother has three PC's setup for disco/karaoke use and these run
multiple fans at full speed and these can be quite noisy, but that's not a
problem when in that environment. These machines are also fully filtered
in and out.

I do agree with you that getting a quiet fan is probably for the best for
the
average user, however they can be expensive compared to a 5v running
basic bearing fan which can be bought for under £1/$1.8US.

Robertv!
April 25, 2009 7:40:39 PM

dude..you also need a transistor to stand the load for all those fans...what i would recommend is instead of running the fans at the same speed using the same resistor..using a transistor in combination with a variable resistor will give you a real adjustment type fan controller..

the connections are very simple

you need a soldering iron and soldering skills to make everything failproof nd snug.. :heink: 

then all you need to do is buy a Power transistor TIP122 will be around 50c.
a 200ohm resistor buy 4 of them it will cost you 30c.
and buy a variable resistor or control or potentiometer 15kohms.

connect 1st leg of the control to 1 end of resistor and the other end of resistor to the 1st leg of the transistor..
connect 2nd leg of the control with the 3rd leg of the control and connect it to the 2nd leg of the transistor..
also attach a wire to the 2nd leg of the transistor which will serve as positive (+) terminal.
the 3rd leg of the transistor should be connected to the positive terminal (+) of fans
the negative terminal(-) of the fans should be directly plugged into 12v (powersupply) and the spare wire from 2nd leg of transistor should be plugged into (+) of 12v powersupply..

and its all done..adjust the control to adjust the speed of fans as you wish...
please insulate all the open joints propely and dont let them come in contact with any of the parts inside the case and dont let it come in contact with the case itself..

btw the transistor runs hot..so please make it a point its there in some airy spot of the case...

TY..BEST WISHES..Dinu DeamonS

!