When is 100% not 100%-Fan speed question

Discussion in 'Asus' started by T.O., Mar 24, 2006.

  1. T.O.

    T.O. Guest

    The Set Up:
    Board-P5LD2
    Dual Core 3.0 Pentium
    Standard supplied fan and heat sink
    Using SpeedFan 4.27 to monitor

    The Situation:
    For 3 hours have been running stable and SpeedFan reports the CPU fan
    speed at 2600 when at 100%. When the CPU temp drops below the set level, it
    cuts the fan back. Fan speed picks up when the processor is loaded and the
    temp goes up. Works as advertised. So far-so good.
    But........this is with the case side off.
    I put the case side on...now....

    Within 10 minutes, STILL showing as 100%, the CPU fan will ramp up to a
    screaming 3600 rpm!
    No load on the CPU.
    CPU temp the SAME or cooler.
    Case temp the same.
    Hard drive temps the same.
    If I take the side off the case, it spools back down to 2600 rpm within 10
    minutes.

    The Question:
    So why now is 100%=3600 rpm, when 10 mins. ago----with all the temperature
    parameters the same---100%= 2600 rpm?
    Before, with the case side off, I could load the CPU up, run the temp up to
    55 or 60 degrees and it still sat at 2600 rpm. Now, with the side on AND at
    the cooler temps--47°-48°--, it's running at 3600 rpm. And even if I disable
    SpeedFan so that the MOBO runs it at 100%, it's still continues to run at
    3600 rpm.

    Mid tower case.
    1 small input fan blowing across the drives.
    1 small output fan in the back, with a duct positioning it right next to the
    CPU
    2 fans in the power supply pulling air out


    Anybody got any ideas?
    Anybody know what the max speed of the Intel supplied fan is supposed to be?
    Is something going on with air pressures inside the case? But even so, if
    the temps are holding, why the speed increase? And why is a reported 100%
    two different speeds?


    Thanks all


    T.O.
     
    T.O., Mar 24, 2006
    #1
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  2. T.O.

    Paul Guest

    Well, you know that something is not adding up there.

    The retail Intel fan has a thermistor in the fan hub, and
    that makes the fan sensitive to case air temperature. If
    the case air temperature is above 38C or so, the fan would be
    at max. Maybe if it is below 30C it would be at the Intel min.
    So, that is a sensitivity, not to CPU temperature, but to case
    temperature local to the fan.

    Asus Q-fan responds to the CPU diode temperature. At maybe 50C
    and above, the voltage supply to the CPU can header would effectively
    be increased (whether it is a PWM control method, or a linear
    control method).

    The two control methods "multiply together", to give the final
    fan speed.

    If the area around the CPU was a stagnant spot, the local air
    could be quite warm. The temperature there, might not be well
    represented by the monitor chip's measurement of case air temp.

    For example, some people get a bit of relief, by using a computer
    case where there is more space between the CPU heatsink and the
    PSU. While the PSU has a fan, the air velocity is insufficient
    to carry away all the CPU heat.

    Or, perhaps a duct can be used, leading from the side of
    the computer case, to feed the CPU area. It could even be
    just a fan bolted to the side of the case, with a long cable
    on it.

    Generally speaking, the fact that things go to hell when the
    case side is put back on, means there isn't enough front to
    back air flow. A computer case should run cooler with the
    side on, as then there should be a front to back flow. With
    the side off, there is no longer a controlled flow, and
    clouds of warm air just sit near where they are being
    generated. So, in theory, with proper fans in place, the
    computer should run quieter with the side on.

    I got a two channel digital thermometer at my local computer
    store for $30 CDN several years ago, and that is handy as
    a cross check of the other readouts. It fits in a drive bay,
    and you can move the sensors to where you need them.

    HTH,
    Paul
     
    Paul, Mar 24, 2006
    #2
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  3. T.O.

    T.O. Guest

    Thanks Paul. I wasn't aware of two fan controls--so that's probably the
    answer as to why I'm getting two different numbers, both being 100%.

    I think it's the CPU's thermistor that must be kicking in and out of high
    gear.
    When the case side is put back on, the case temp reported by SpeedFan may
    come up just 1° or 2° to around 36° or 37°. Allowing for a little difference
    in measurements, that would put it right at the 38° temp you mentioned.

    The one exhaust fan does have a duct that places it right within 1" or less
    of the CPU fan.
    The power supply's fan are also temp controlled by something internal in the
    supply. SpeedFan shows it running at only about 1100 rpm. I've never seen it
    any higher. It's an Antec 550 server supply.

    All of the bays are full. I have one small input fan blowing air over the
    drives. It has a space for another small input fan to sit right beside that
    one. May pick one up at the computer show tomorrow to see what happens.

    I was also looking this morning at the Intel supplied sink/fan. Looks like I
    might be able to wrap some tape around the top edge of the plastic fan
    housing creating a shroud of sorts. Maybe that will help pull more air
    through also. Ever tried anything like that?

    Thanks again.
    T.O.
     
    T.O., Mar 24, 2006
    #3
  4. T.O.

    Rob Hemmings Guest

    I had great results by using a short section of flexible plastic pipe,
    about 1.5" diameter (off of an old vacuum cleaner!) which had one
    end held close to where the front intake fan blew cold air into
    the case, and the other end held near the CPU HSF. This effectively
    made sure some cold air was ducted directly from outside the case to
    the HSF and so was sucked directly into the CPU fan. Resulted in a
    permanent 5C drop in CPU temp.
    HTH
     
    Rob Hemmings, Mar 24, 2006
    #4
  5. T.O.

    Bill Guest

    That may be the problem - the power supply fan is not running very fast.

    I had a similar problem where the PSU fan would only limp along at
    800-1000rpm most of the time because the PSU was not under a heavy load.
    The exhaust fan in the back of the case was blowing quite fast and
    sucking air out the back, but since it was working so fast, it sucked
    air BACKWARDS through the PSU and was drawing hot air back out of the
    PSU and over the CPU area.

    Since I didn't want to replace the case fan with a slower or 3-speed
    version (CPU was constantly crunching data), the solution was to replace
    the thermally controlled fan inside the power supply with a standard
    80mm fan that ran at full speed all the time.

    No more heat problems.
    Intake fans are not really needed if you have good exhaust flow. The
    cool air will be drawn in as the hot air is pushed out the back. Decent
    circulation is important, and having too many fans can be worse than
    just having good exhaust flow to get rid of the hot air.

    Having said that, I do have one fan inside my current case to push air
    over my hard drives, but it doesn't draw air into the case at all. It's
    strictly for cooling the drives, that's all.

    My exhaust fan is a 3-speed 120mm version, and I've found the best speed
    is actually medium. Turning it up to high doesn't improve cooling, and
    medium is less noisy.
    If CPU cooling is that critical, I think you have other issues you need
    to deal with before that.

    :)
     
    Bill, Mar 24, 2006
    #5
  6. T.O.

    T.O. Guest

    Thanks Bill.
    Actually the CPU cooling is not really an issue, it doesn't get that hot.
    I just couldn't understand why, when SpeedFan was reporting 100% speed on
    the CPU, it would vary between 2600 and 3600. Looks that the thermistor that
    Rob mentioned is the reason.

    And after watching it today, I'm convinced that's the culprit. No matter
    what the CPU temp is, I now see a correlation between case temp and CPU fan
    speed.
    It goes like this:
    Case up to 35°--2600 rpm
    Case at 36°--3300 rpm
    Case at 37°--3600 rpm
    The numbers aren't exact as it will vary a bit at each step. But in all
    this, the CPU temp can be 45° or it can be 55°, it doesn't matter.

    I need to see about getting that power supply fan to speed up a bit so I
    need to dig out the manual on it.
    It's an Antec 550 watt unit. It has two fans, but SpeedFan is only reporting
    one that it's picking up a signal from the MOBO where the fan speed signal
    is plugged into.

    Anybody know off the top of their head the answer to this one.
    Since SpeedFan is reporting around 1100 rpm on the supply, is that the upper
    fan, lower fan or both?
    And how am I going to speed them up?
    I'll dig out the manual later tonight, hope there is enough detail info in
    there.

    Thanks all.

    T.O.
     
    T.O., Mar 24, 2006
    #6
  7. T.O.

    T.O. Guest

    Thanks Bill.
    Actually the CPU cooling is not really an issue, it doesn't get that hot.
    I just couldn't understand why, when SpeedFan was reporting 100% speed on
    the CPU, it would vary between 2600 and 3600. Looks that the thermistor that
    Rob mentioned is the reason.

    And after watching it today, I'm convinced that's the culprit. No matter
    what the CPU temp is, I now see a correlation between case temp and CPU fan
    speed.
    It goes like this:
    Case up to 35°--2600 rpm
    Case at 36°--3300 rpm
    Case at 37°--3600 rpm
    The numbers aren't exact as it will vary a bit at each step. But in all
    this, the CPU temp can be 45° or it can be 55°, it doesn't matter.

    I need to see about getting that power supply fan to speed up a bit so I
    need to dig out the manual on it.
    It's an Antec 550 watt unit. It has two fans, but SpeedFan is only reporting
    one that it's picking up a signal from the MOBO where the fan speed signal
    is plugged into.

    Anybody know off the top of their head the answer to this one.
    Since SpeedFan is reporting around 1100 rpm on the supply, is that the upper
    fan, lower fan or both?
    And how am I going to speed them up?
    I'll dig out the manual later tonight, hope there is enough detail info in
    there.

    Thanks all.

    T.O.
     
    T.O., Mar 24, 2006
    #7
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