Re: OK to use pwr fan connector for sys fan?


M

meow2222

My motherboard has a connection for the pwr fan, but my PSU doesn't have a plug
for that.  

mobo fan connector is for the pcu fan, not a power input. It supplies
the fan power and monitors its speed.

Is it usually OK to use that connection for a case fan instead?

yes - but then you wont have cpu fan speed monitoring, and the case
fan will change speed acording to cpu temp rather than case temp

 I've
heard "absolutes" on both sides, so am a little confused about it.

I have four case fans

why??


NT
 
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J

John Doe

OMG. This reminds me of the old school days when you'd wisper into
ones ear and then they would wisper into the next until you got to
the end and the story had changed completely.

The PWR connector on the board is to connect a cable from certain
Power Supplies to monitor temp and RPM and to control the fan in
the power supply.

Can you name a mainboard with that connector?
 
J

John Doe

I can name an older board, Asus A7N8X-E Deluxe.

Thanks for the citation.

It includes a three pin fan connector "PWR_FAN1" that senses fan
speed but not power supply temperature.
My Enermax PSU has a cable connector for it.

I guess. I wouldn't want to use one though, especially not if the
power supply has its own temperature sensor. If the power supply
doesn't have a sensor, the power supply fan should probably run at a
set speed (probably full). I can't see letting the mainboard control
the power supply fan speed unless it were able to sense power supply
temperature.
 
J

John Doe

Larc said:
....

| Can you name a mainboard with that connector?

This Gigabyte GA-EP35-DS3L has it, as did my Asus P5P800 SE that
went belly up. I think the main function is to control the PSU
fan,

According to Antec (condensed):
"... on an Antec TPII-550, the 2wire/3 pin connector/wire is the fan
sensor. It will report the speed of the power supply fan. You
connect this to one of the fan connectors on your motherboard"

Just reporting the fan speed would give feedback to the user, but
that doesn't even suggest it controls the fan speed. In fact, the
power supply fan can simply ignore the controlling voltage level
even if the mainboard tries to control the fan speed (probably why
it's only two wires instead of three) regardless of the mainboard
fan socket you connect it to.
 
P

Paul

John said:
Thanks for the citation.

It includes a three pin fan connector "PWR_FAN1" that senses fan
speed but not power supply temperature.


I guess. I wouldn't want to use one though, especially not if the
power supply has its own temperature sensor. If the power supply
doesn't have a sensor, the power supply fan should probably run at a
set speed (probably full). I can't see letting the mainboard control
the power supply fan speed unless it were able to sense power supply
temperature.

I have a similar setup. A7N8X-E Deluxe and an Enermax supply (a
replacement for a previous Antec, which also had a fan monitor cable).

The cable has two wires, from the power supply to the motherboard.
The connector is a three pin connector, where the +12V wire and pin
are not installed. That means the PSU is sending "RPM" and "GND" to
the motherboard. I have another system, where only "RPM" is sent,
because the "GND" connection is superfluous. There are plenty of
other ground paths, to establish ground.

The purpose for connecting the power supply fan monitor, to the
motherboard, is for people who have monitoring software that
checks temps, voltages, and fan speeds. A reading of zero RPMs
would be cause for concern, and a good piece of monitor software
can even send an email to the operator. Such would be good,
if the equipment was in a server room, and didn't normally
receive much in the way of attention from humans.

A power supply may shut off, if it gets too hot. But
at what temperature does it trigger ? And if you're using
the computer, how do you conclude what is wrong ? If you
get an indication that a fan speed is low or zero, then
that gives you one more hint of a problem. I connected
both my old and new power supply, just for the ability
to observe the fan.

On power supplies which have two fans, only one of them
is monitored by the two wire monitor cable. So in fact,
you could have a failure of the second fan, and not be
alerted. I've had at least one power supply, where the
second fan never seemed to run. So to this day, I don't
know if it is defective, or merely has a high
threshold setting for its controls.

Paul
 
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E

Ed Medlin

John Doe said:
According to Antec (condensed):
"... on an Antec TPII-550, the 2wire/3 pin connector/wire is the fan
sensor. It will report the speed of the power supply fan. You
connect this to one of the fan connectors on your motherboard"

Just reporting the fan speed would give feedback to the user, but
that doesn't even suggest it controls the fan speed. In fact, the
power supply fan can simply ignore the controlling voltage level
even if the mainboard tries to control the fan speed (probably why
it's only two wires instead of three) regardless of the mainboard
fan socket you connect it to.

The PWR connectors I have seen do not control anything.......They just give
you fan speed monitoring capabilities.


Ed
 
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J

John Doe

Ed Medlin said:
The PWR connectors I have seen do not control anything.......They
just give you fan speed monitoring capabilities.

Roger.
Apparently you can connect the power supply input to any of the 3
pin mainboard fan connectors because no power supply is going to let
the mainboard control its fan speed.

In response to the original poster, apparently Yes the power supply
fan connector can be used for any other ordinary system fan, but I
guess you might see that fan reported as "power supply" in a
monitoring/alarm utility. If the monitoring utility doesn't show the
fan speed varying, then you can guess the mainboard really isn't
trying to control it from that fan connector. Whatever, I wouldn't
hesitate to try.
 

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