Really low 1000-1100 RPM reported for Power Supply Fan on A7V8X-X

[Hupjack]

I just finished putting together my system, which I installed inside an
Antec SLK1600
http://www.antec-inc.com/us/pro_details_enclosure.php?ProdID=91600 This
case comes with an Antec 300W SmartPower ATX12V power supply.



I took the opportunity to install the ASUS PC Probe so I could make sure
that my temperatures, fan speeds, and voltages were in their proper ranges.
After noticing the PC Probe monitoring slot for power fan and chasis fan, I
realized my power supply had a cable that I could use to send the power
supply fan speed signal to the motherboard for monitoring. My Asus A7V8X-X
appears to only have fan connectors for the processor and a 2nd labeled for
the Chasis. I plugged the power supply fan cable into the chasis fan
connector, and the fan speed came through reported as the chasis fan just as
expected.



This note in the Antec Manual explains that the power supply fan may spin as
low as 1500 RPM and that motherboards might have problems with that.



Note: The speed of the fan may be as low as 1500 RPM when temperatures are
low. At these speeds some motherboards may not be able to properly detect
the fan speed and may generate false warnings of fan failure. Please refer
to your motherboard manual for proper fan monitoring set up.



Well it just so happens that right now PC Probe is reporting exactly 1500
RPM, but earlier it was reporting 1000 - 1100 RPM. Is this likely a
manifestation of the problem Antec warns is possible, or might I have a
funky power supply with a fan spinning slower than it should? From looking
at some posts on USENET, my impression was that for those who's mobos were
having trouble detecting the sub 1500 RPM speeds, the board simply wasn't
reporting anything at all, like 0 RPM though their fan was clearly spinning.
Since I'm actually getting 1000-1100 reported, I'm wondering if this is
accurate and just fine, accurate and bad news, or an inaccurate reading,
like reporting zero, just another possible result of troubled detection of
sub-1500 RPM fan speeds.



Another thought... Are all fan connectors created equally, or might using
the chasis fan connector to monitor the power supply fan be botching the
monitoring?



Thanks in advance,

-Ethan

 

[Noomie]

"I plugged the power supply fan cable into the chasis fan
connector"
That fan is not meant to connect to chassis fan connector, you are supposed
to connect it to PSU fan connector.

 

[Hupjack]

"I plugged the power supply fan cable into the chassis fan

That fan is not meant to connect to chassis fan connector, you are supposed
to connect it to PSU fan connector.

Sure.. obviously it's meant for the chassis fan... It's marked as such, but
I don't have a chassis fan.

Since my motherboard doesn't have a fan connector marked for the PSU fan, I
figured it probably would accomplish the exact same thing plugging it into
the chassis fan header. At least that way I could see the power supply fan
speed though it is, as expected, reported by PC Probe as the chassis fan
speed.

I messed up on this post... accidentally sent a different one to
alt.comp.hardware.pc-homebuilt and alt.comp.hardware.homebuilt

over there, Kony responded as follows:
-----------------------------------------
It's not a problem. Generally the lower the RPM the less accurate the
reading might be due to (any particular board's) sampling rate, and
sometimes the board will have a bios update that addresses compatibility
with lower RPM fans, but it's nothing to worry about. Just set the Asus
Probe alarm to a value lower than lowest RPM seen during operation.

The main thing to be concerned about is the chassis cooling, with a lower
RPM PSU fan you'd usually need at least 1 chassis exhaust fan too.
-----------------------------------------

so the question of "Are the chassis and PSU fan headers created equally"
remains unanswered.
Kony's response didn't address that, so I assume he didn't consider it an
issue.
Noomie's statement that you are supposed to connect the PSU fan to the PSU
header also fails to answer the question of weather the fan speed is sensed
and reported any differently when plugged into one or the other. Since I
have no PSU fan header, I obviously have no way of testing for a difference.

I expect Kony is right. But from reading other posts, people complained
that their boards reported zero RPM whereas mine was reporting 1000-1100
rpm. Perhaps there are others in my situation, but 1000-1100 rpm doesn't
get people concerned and posting to Usenet like 0 rpm does. The boards
(perhaps ASUS in particular) obviously don't report speeds accurately with
low RPM fans (which antec warned about in their manual). Perhaps the board
was just under reporting the speed, but this seems like a good thing to be
sure about rather than burn up a power supply. It's actually consistently
reporting a little over 1400 rpm right now. Can anybody say for sure
weather having used the chassis fan header for reporting the PSU fan speed
should have any impact on the reported speed?

I'll keep an eye on the PSU fan speed. Perhaps it's just a temperature
controlled thing, and it's able to cruise at 1000 rpm at startup when it's
nice and cool. The antec manual did say the PSU would spin as low as 1500,
but 1500 rpm is the highest it has reported so far. So once again... under
reporting?

Thanks for your help,
-Ethan

 

[Rob]

To help clear the water a little, I had a A7N8X-Deluxe board that had
it's original(1001) BIOS. It had both a Chassis and a Fan Header. The
Fan Header read 0 with my Antec PS hooked, so I moved it to the Chassis
Header and it worked fine there. I found that upgrading the BIOS
enabled the Fan Header and it, in fact, did read the same as the Chassis
Header. I guess it's safe to say that the symptoms you've read about
could be displayed, using the same board, under different circumstances.
So, I would use the Chassis Header, lower the threshold in Probe as
Kony suggested, monitor your temps and start enjoying your system.

Rob

 

[Hupjack]

thanks rob.. I actually spotted on some antec faq that you can stick that
fan monitoring cable on any available motherboard fan header. So bios bugs
aside, it looks like you are 100% correct.. It doesn't matter which header
you strap it to. Now I trust my PSU and system is behaving as it should, I
can tweak those monitoring settings and be on my merry way..

Thanks!