yellow fan wire

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have 2 90mm fans connected to 12V fan leads from power supply. there is
only one small 3 conductor plug to connect te yellow speed controll wire
to motherboard. one fan runs wide open. Can I splice the control wires
together safely to slow the one fan down, heat is not a problem and
don't need accurate speed control.
 

overlord

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Aug 29, 2001
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Hi Bob.... uh..... not really really sure what you're asking here.
If the fans were completely connected to the 3 pin connectors on the motherboard
then the MB would be controlling their speed by using the 3rd wire to monitor
their speed and adjust that speed based on the temps by varying the voltage it
was sending over that 3 pin connector.
Since your fans are running off the large 4pin molex connector from the power
supply, there is no adjusting of the speed. It doesn't matter that the 3rd wire
from the fans is run to the right pin on the 3 pin MB connector. That will only
let the MB monitor the speed, not control the voltage going to the fans.
Both fans are running wide open because they're getting the full 12 volts from
the PS connection: it doesn't matter what the MB thinks about it.
Splicing the 3rd wire, RPM monitor, (control wire?), of the 2 fans together and
connecting them to the Right pin on the 3pin MB connector is generally a
Bad Thing, but in your case won't accomplish squat anyway. You can.....

A connect the fan that runs too fast to all 3 pins of the MB connector in which
case the MB would be controlling it's speed/voltage based on temps.
or
B buy fans with the little adjustable resistors in the line to slow the fan speed.
or
C if you don't want to buy new fans or stuff, you can rewire the 4pin molex
connectors going to the fans to supply 7 volts instead of the 12 volts they're
getting now from the PS connectors.
The black center wires on the big 4pin connector are grounds. The wires on the
outside of the plug are +12 and +5 volts. Pulling the pins out of the plug and
putting them back so that ONLY the yellow and red are going thru to the fan
will give your fan +7 volts; the difference between +12 and +5.
They'll run slower on the lower voltage.
Some fans Need the 12 volt kick to start them spinning. So some 12v fans may not
spin up at all on +7 volts. You just have to try and see
It's not really recommended doing this to the CPU fan as like I mentioned it can
be less reliable for spinning up.

On Wed, 15 Dec 2004 23:38:51 -0500, y00h@webtv.net (Bob Y00h) wrote:

>have 2 90mm fans connected to 12V fan leads from power supply. there is
>only one small 3 conductor plug to connect te yellow speed controll wire
>to motherboard. one fan runs wide open. Can I splice the control wires
>together safely to slow the one fan down, heat is not a problem and
>don't need accurate speed control.
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On Wed, 15 Dec 2004 23:38:51 -0500, y00h@webtv.net (Bob
Y00h) wrote:

>have 2 90mm fans connected to 12V fan leads from power supply. there is
>only one small 3 conductor plug to connect te yellow speed controll wire
>to motherboard. one fan runs wide open. Can I splice the control wires
>together safely to slow the one fan down, heat is not a problem and
>don't need accurate speed control.

On typical computer/PC equipement the fan is not
speed-controlled by the third wire, it's only for RPM
sensing, that's all the motherboard circuit can do.
Therefore, the typical PC fan isn't built to provide the
speed-control function on the third lead either, only the
RPM sensing. Certainly there are fans with this function on
a 3rd lead, but for this reason that function isn't used in
PCs.

So, even if you acquired a fan with this RPM control via 3rd
lead, it's not supported connected to the 3 pin fan header.
To reduce speed on the typical fan you need voltage or PWM
change on the power leads, the third lead still going
directly to the motherboard 3 pin header. To accomplish
this most easily you might choose any of a number of fan
controllers on the market (those meant for "PC" fan
control).
 
G

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Dorothy,

running them is series sounds like a very good idea.

Indeed thinking about life span of fans, etc,
would you suggest that as a general rule of thumb in pc
cases with two fans, running them in series is a better
solution then running them both at 12vdc?
 
G

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Archived from groups: alt.comp.hardware.homebuilt (More info?)

> running them is series sounds like a very good idea.

Where lower noise is needed, and airflow remains at
a sufficient level it can provide an economic solution.

> Indeed thinking about life span of fans, etc,

Running fans at 50% will make them last longer,
unless of course they run at a higher temp :)

> would you suggest that as a general rule of thumb in pc
> cases with two fans, running them in series is a better
> solution then running them both at 12vdc?

o If cooling is sufficient yes
---- monitor HD temp, case-temp & cpu-temp
o If cooling is insufficient you may shorten life
---- of other components -- HD, Graphics, PSU
---- of the fan itself -- re air temp it is exposed to :)

So it is a matter of balance:
o Meet the cooling requirements
o Simultaneously meet the acoustic requirements

Both can be met with careful system integration.
--
Dorothy Bradbury
 
G

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On Thu, 16 Dec 2004 21:28:45 GMT, "Dorothy Bradbury"
<dorothy.bradbury@ntlworld.com> wrote:

>> running them is series sounds like a very good idea.
>
>Where lower noise is needed, and airflow remains at
>a sufficient level it can provide an economic solution.
>
>> Indeed thinking about life span of fans, etc,
>
>Running fans at 50% will make them last longer,
>unless of course they run at a higher temp :)
>


I don't recall which fans I tried, but one least one major
manufacturer's (I don't use generic fans, period) fans will
not work in series, while same single fan will work @ 6V.
 
G

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> I don't recall which fans I tried, but one least one major
> manufacturer's (I don't use generic fans, period) fans will
> not work in series, while same single fan will work @ 6V.

That can be a function of the fan's electronics, as well
as the start voltage - 6V is quite low, so always test.

PWM solutions commonly run a fan at 100% for a time,
to ensure all fans have started before dropping to 50%.

Start voltage varies with the fan spec/model/make:
o Fan microprocessor, number of poles & so on matters
o Stall management - some methods limit start torque
o Some 12V fans have recommended min of 9V (>> 6V)

Some fans use very soft start - a function of their locked
rotor protection, so little starting torque (even at 12V).
Others use very high power magnets, which has benefits
as well as costs - high torque is needed to get them going.

Not a negative, just a result of optimising the fan variables.
--
Dorothy Bradbury
 
G

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"Dorothy Bradbury" <dorothy.bradbury@ntlworld.com> wrote in news:Xjhwd.374
$hX.44@newsfe6-gui.ntli.net:

> To run 2 fans slowly at lower speed, you can run them in series:
> o Connecting two 12V fans in series runs each at 6V (if same spec fan)


I just tried this with two Panaflo 80mm. It was quite interesting to
watch.. there would spin for one second then stop, then start, then stop,
then start spinning properly.

Presumably 6V was borderline for thse fans and the Resistance of the fan
drops when it starts spinning, hence the little performance before starting
up properly?? I assume if one failed the other might stop???

Needless to say, I put them back in parallel on 7v :)

--
Lordy
 
G

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In article Bob Y00h says...
> have 2 90mm fans connected to 12V fan leads from power supply. there is
> only one small 3 conductor plug to connect te yellow speed controll wire
> to motherboard. one fan runs wide open. Can I splice the control wires
> together safely to slow the one fan down, heat is not a problem and
> don't need accurate speed control.

No. THe yellow wire sends a signal to the motherboard to monitor RPM.
The speed is controlled by voltage. You're not going to be able to alter
the speed on a header that isn't designed to without fitting a variable
resistor or using a fanbus.


--
Conor

A man alone in the forest is talking to himself and no women around to
hear him. Is he still wrong?
 
G

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On Fri, 17 Dec 2004 01:23:08 GMT, "Dorothy Bradbury"
<dorothy.bradbury@ntlworld.com> put finger to keyboard and composed:

>> I don't recall which fans I tried, but one least one major
>> manufacturer's (I don't use generic fans, period) fans will
>> not work in series, while same single fan will work @ 6V.

Perhaps the fans are not sharing the load equally, eg the voltage may
split 9V to 3V.

>That can be a function of the fan's electronics, as well
>as the start voltage - 6V is quite low, so always test.

I suspect the minimum voltage requirement would be determined by the
fan motor, not the fan electronics. Some (most?) commutation ICs can
operate down to 3VDC, although the motor may stall at this voltage.

See these datasheets for examples:
http://www.anpec.com.tw/products/download/pdf/APX9141a7.pdf
http://www.anpec.com.tw/products/download/pdf/APX9140a8.pdf

This picture illustrates the electronic commutation principle:
http://www.ece.msstate.edu/~hagler/May2001/02/FIG2.JPG


- Franc Zabkar
--
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G

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> I suspect the minimum voltage requirement would be determined by the
> fan motor, not the fan electronics. Some (most?) commutation ICs can
> operate down to 3VDC, although the motor may stall at this voltage.

Depends on which has the lower design voltage - motor or IC chip :)

Generally go by the voltage spec, then test if you go outside it.
If the fan is very high speed, don't go outside to the upside (heat).
--
Dorothy Bradbury
 
G

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Archived from groups: alt.comp.hardware.homebuilt (More info?)

> I just tried this with two Panaflo 80mm. It was quite interesting to
> watch.. there would spin for one second then stop, then start, then stop,
> then start spinning properly.

Panaflo use a stop/timer/restart motor stall management function.

NMB also use it on some fans (Minebea/Panaflo are now merged so you
will eventually see a broader Panaflo range - including S model & 38mm fans).

EBM-Papst use a different system - and so don't "do the dance" :)

Fans vary quite a lot in their operating range re intended market:
o Industrial fans typically 9-15V, 7-13.8V, 9-13.2V
o Higher speed fans a) have a narrower range or b) lower life at T-Max

A voltage range of 10.3-13.2V indicates a 24V fan rebadged as 12V for example.

Some fans have a very wide operating range - industrial 172mm fans I use tend
to have a 16-36V range, and one has 10-38V range despite being 24V nominal.

PWM will let you use an "exact" 50% cycle, in some cases 45%:
o The risk is you can end up with PWM noise
o They ensure starting by running the fan at 12V to ensure starting

Bearing design is also a factor in spec voltage:
o Typically ball/sleeve grow in noise over their service life
---- sleeve by 15dB(A) at T-Max over 1yr (if they even last that long)
---- ball by 5dB(A) at T-Max over 1yr
---- NMB ball by 3dB(A) at absolute maximum at T-Max over 1yr
o Fluid dynamic & top hydrodynamic bearings don't grow in noise
---- the disadvantage is they are not ideal at super-high rpm in fans
-------- unless you wish to pay 35$£/fan like some laptops use
---- in instances where you need say >6000rpm you use NMB ball
-------- an example would be a B8* or B7* model - special screamers

Anyone who has suffered a Dell which switched to full speed knows :)
If you think the old Apple 57dB(A) & 69dB(A) were bad, think again.


> Presumably 6V was borderline for thse fans and the Resistance of the fan
> drops when it starts spinning, hence the little performance before starting
> up properly?? I assume if one failed the other might stop???

The fan detected stall & reacted to it - and in doing so it can cause a series
connected fan to also go into stall. It depends on the exact model, and a 6V
supply is actually below spec - a 7V operation is more reasonable.

Yes if one fan did fail (rare re electronics) it may stop the other fan,
just like having 2 light bulbs in series, if one fails, other is not lit.

7V is the simplest system, although in some instances two inline is ok.
--
Dorothy Bradbury