power-supply fan

On Sat, 21 Aug 2004 17:12:46 +0200, "Fred Flintstone"
<fred.flintstone.RemoveThis@flintstone.dot.net> wrote:

 >hello,
 >is there any experience available regarding reducing the voltage for the
 >cooling fan of the power-supply ?
 >I have a HP Compaq Evo d330m and the fan of the power-supply is rather
 >noise.
 >if I could place a resistance in the power lead of the fan, this fan would
 >run slower.
 >the resistance of the fan motor is 40 Ohm, calculated from 12 V dc and 0,30
 >Amp.
 >any suggestions ?
 >thanks in advance
 >Fred

Resistance of fan motor cannot be calculated like that. In fact,
the fan won't use .3A in operation either. Why they provide this
spec? Good question, I think I once knew the answer but it
escapes me at the moment.

Anyway, yes you could add a resistor to the fan lead to reduce
it's speed, but only you can determine if power supply (or even
reset of system if PSU fan is the only exhaust point) can
tolerate airflow reduction, that is, how much reduction.

Generally speaking, a .3A spec'd fan may need roughly 47 Ohm
resistor, +- 20 Ohm, but you haven't mentioned if this PSU has
built-in fan speed control nor how much you want to reduce fan
speed... I provided the 47 Ohm figure because given the info
provided, it'd be the first value I'd try.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: power-supply fan 

kony wrote:
 > <fred.flintstone.RemoveThis@flintstone.dot.net> wrote:
 >
.... snip ...
  >> if I could place a resistance in the power lead of the fan, this
  >> fan would run slower. the resistance of the fan motor is 40 Ohm,
  >> calculated from 12 V dc and 0,30 Amp.
 >
 > Resistance of fan motor cannot be calculated like that. In fact,
 > the fan won't use .3A in operation either. Why they provide this
 > spec? Good question, I think I once knew the answer but it
 > escapes me at the moment.

Probably for fusing purposes, allowing for peak draw at startup or
stall.

--
fix (vb.): 1. to paper over, obscure, hide from public view; 2.
to work around, in a way that produces unintended consequences
that are worse than the original problem. Usage: "Windows ME
fixes many of the shortcomings of Windows 98 SE". - Hutchison<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: power-supply fan 

 > Anyway, yes you could add a resistor to the fan lead to reduce
 > it's speed, but only you can determine if power supply (or even
 > reset of system if PSU fan is the only exhaust point) can
 > tolerate airflow reduction, that is, how much reduction.
 >
 > Generally speaking, a .3A spec'd fan may need roughly 47 Ohm
 > resistor, +- 20 Ohm, but you haven't mentioned if this PSU has
 > built-in fan speed control nor how much you want to reduce fan
 > speed... I provided the 47 Ohm figure because given the info
 > provided, it'd be the first value I'd try.

the fan is AddA DC Brushless, model: AD0912US-A70GL
as far as I can tell it is not meant for speed control.
also I have not noticed any difference in sound.
I was intending to use a 33 Ohm resistance, just to be on the safe side.
regards,
Fred<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: power-supply fan 

If Compaq is not using a Power supply that is proprietary, then you
would be better off just replacing it with say an Antec Power Supply
assuming it would fit. I find the standard Antec 300 watt power
supply to be very quiet. I have a 350 watt model in my Asus
SLK3700AMB case and it is very quiet.

Some power supply companies sell after market noise reduction kits
where you put a larger fan on the bottom of the power supply.

You should not mod a case with a motherboard still inside it.
However, many cases do not have enough vent holes for the air to pass
through and it causes the fan to work harder or the air makes a
rushing sound trying to get through the inadequate vent holes.
Another problems can be the acoustice reverberations inside a badly
designed case, or a fan grill that vibrates.

On Sat, 21 Aug 2004 17:12:46 +0200, "Fred Flintstone"
<fred.flintstone RemoveThis @flintstone.dot.net> wrote:

 >hello,
 >is there any experience available regarding reducing the voltage for the
 >cooling fan of the power-supply ?
 >I have a HP Compaq Evo d330m and the fan of the power-supply is rather
 >noise.
 >if I could place a resistance in the power lead of the fan, this fan would
 >run slower.
 >the resistance of the fan motor is 40 Ohm, calculated from 12 V dc and 0,30
 >Amp.
 >any suggestions ?
 >thanks in advance
 >Fred
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: power-supply fan 

On Sun, 22 Aug 2004 10:44:07 +0200, "Fred Flintstone"
<fred.flintstone DeleteThis @flintstone.dot.net> wrote:

 >
  >> Anyway, yes you could add a resistor to the fan lead to reduce
  >> it's speed, but only you can determine if power supply (or even
  >> reset of system if PSU fan is the only exhaust point) can
  >> tolerate airflow reduction, that is, how much reduction.
  >>
  >> Generally speaking, a .3A spec'd fan may need roughly 47 Ohm
  >> resistor, +- 20 Ohm, but you haven't mentioned if this PSU has
  >> built-in fan speed control nor how much you want to reduce fan
  >> speed... I provided the 47 Ohm figure because given the info
  >> provided, it'd be the first value I'd try.
 >
 >the fan is AddA DC Brushless, model: AD0912US-A70GL
 >as far as I can tell it is not meant for speed control.
 >also I have not noticed any difference in sound.
 >I was intending to use a 33 Ohm resistance, just to be on the safe side.
 >regards,
 >Fred

"Meant" for speed control is suject to interpretation, just about
any DC brushless fan in that size (anything normally found in a
PC's parts) can vary RPM fine from voltage reduction.

I don't know what you mean by "... I have not noticed any
difference in sound." If your PSU has temp-based fan speed
control and fan wasn't formerly running near max RPM, then you
add a resistor and the PSU's RPM control circuit then sensing
higher temp, causes higher fan RPM, it could result in fan
speeding up again somewhat, but usually not as much as the
previous unmodified unit would.

33 Ohm could work too, one issue might be how well the PC chassis
allows passive intake, so effeciency of fan, air moved per RPM is
maximized. Typically some of the mid-to-older Compaqs didn't
have very good front air intake passages, if that is the
situation then modifying the front to allow more intake should
help.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: power-supply fan