Two (or more) fans on the same motherboard fan connector
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From: kony on 2 Apr 2008 16:13 On Wed, 2 Apr 2008 11:01:18 +0100, "GT" <ContactGT_remove_(a)hotmail.com> wrote: >"kony" <spam(a)spam.com> wrote in message >news:n3d6v3pgqm6u71kll5t6otsom7sg1qmqlu(a)4ax.com... >> On Tue, 1 Apr 2008 15:59:22 +0100, "GT" >> <ContactGT_remove_(a)hotmail.com> wrote: >> >> >>>The yellow (RPM) wire is not used to control the fan throttling system. >>>The >>>fan speed is controlled by CPU temperature and threshold values in the >>>BIOS. >>>There is a warning on fan rotation speed which can be set to 'alarm' or >>>'shutdown system' or 'disabled'. So getting a speed reading from just 1 >>>fan >>>would be fine and shouldn't cause confusion >>> >> >> Normally this is true, but it wouldn't be impossible (and to >> some, even a more desirable way to implement the fan >> control) if the RPM signal were used to determine and change >> fan RPM to a threshold level. For example, at 50C, do what >> is needed to make fan RPM 3000. > >Absolutely - not impossible, but that would require the BIOS to have >knowledge of the thermal dissipation power of the heatsink and the CFM of >the fan, Not necessarily... you're still trying to think in terms of "try to keep the CPU at the same temperature", which is not necessary. The only thing truely necessary is to keep it below an absolute maximum threshold value which could still be programmically forced as (use max fan power @ threshold temp). > plus one or two other values concerning case temperature and >airflow through the heatsink. Not as simple as you think. > No it's simple, it's allowing the user to take control of the settings and decide these things, same as with many other bios settings.
From: GT on 3 Apr 2008 06:36 "kony" <spam(a)spam.com> wrote in message news:33q7v3htfbg1n1squvigui33d4beovuqsc(a)4ax.com... > On Wed, 2 Apr 2008 11:01:18 +0100, "GT" > <ContactGT_remove_(a)hotmail.com> wrote: > >>"kony" <spam(a)spam.com> wrote in message >>news:n3d6v3pgqm6u71kll5t6otsom7sg1qmqlu(a)4ax.com... >>> On Tue, 1 Apr 2008 15:59:22 +0100, "GT" >>> <ContactGT_remove_(a)hotmail.com> wrote: >>> >>> >>>>The yellow (RPM) wire is not used to control the fan throttling system. >>>>The >>>>fan speed is controlled by CPU temperature and threshold values in the >>>>BIOS. >>>>There is a warning on fan rotation speed which can be set to 'alarm' or >>>>'shutdown system' or 'disabled'. So getting a speed reading from just 1 >>>>fan >>>>would be fine and shouldn't cause confusion >>>> >>> >>> Normally this is true, but it wouldn't be impossible (and to >>> some, even a more desirable way to implement the fan >>> control) if the RPM signal were used to determine and change >>> fan RPM to a threshold level. For example, at 50C, do what >>> is needed to make fan RPM 3000. >> >>Absolutely - not impossible, but that would require the BIOS to have >>knowledge of the thermal dissipation power of the heatsink and the CFM of >>the fan, > > Not necessarily... you're still trying to think in terms of > "try to keep the CPU at the same temperature", which is not > necessary. The only thing truely necessary is to keep it > below an absolute maximum threshold value which could still > be programmically forced as (use max fan power @ threshold > temp). No, I'm talking about turning up the fan speed when the temperature goes over a certain threshold, but how would the BIOS know what voltages to turn the fans up/down to? Regardless of the actual temperature goal, the fan speed is controlled by varying the voltage. The BIOS has no information about the heat dissipation characteristics of the heatsink (it doesn't know what heatsink is on there) and the amount of additional cooling provided by turning the fan up and down (it doesn't know what the fan's flowrate is and how efficiently that airflow actually cools the heatsink), so it therefore won't 'know' what voltage to give the fan to achieve the required level of cooling. My point is that different fans move different amounts of air at different voltages - take a standard 775 cooler with a single 90mm fan versus the twin 120mm fan setup we are talking about here. If the BIOS sets the fans at 7v, the 90mm fan will shift something like 10-20cfm, but the twin 120mm fans at 7v will shift something like 60-80cfm. This extra airflow will cool the heatsink considerably more, but how will the BIOS know this? The BIOS would have to 'experiemnt' and store values to calibrate itself to do what you are suggesting. However, this would not be complicated and is a good idea!
From: kony on 3 Apr 2008 14:58
On Thu, 3 Apr 2008 11:36:50 +0100, "GT" <ContactGT_remove_(a)hotmail.com> wrote: >> Not necessarily... you're still trying to think in terms of >> "try to keep the CPU at the same temperature", which is not >> necessary. The only thing truely necessary is to keep it >> below an absolute maximum threshold value which could still >> be programmically forced as (use max fan power @ threshold >> temp). > >No, I'm talking about turning up the fan speed when the temperature goes >over a certain threshold, but how would the BIOS know what voltages to turn >the fans up/down to? If bios were set to hit a target RPM, the logic would be IF [(fan RPM) < (target RPM)] OR [ (CPU temp) > (max temp)] THEN increase voltage, ELSE IF (fan RPM) > (target RPM) THEN decrease voltage. > >Regardless of the actual temperature goal, the fan speed is controlled by >varying the voltage. The BIOS has no information about the heat dissipation >characteristics of the heatsink (it doesn't know what heatsink is on there) >and the amount of additional cooling provided by turning the fan up and down >(it doesn't know what the fan's flowrate is and how efficiently that airflow >actually cools the heatsink), so it therefore won't 'know' what voltage to >give the fan to achieve the required level of cooling. It doesn't need to. The control is not necessarily trying to hit a particular voltage (usually), it does not measure and adjust based on voltage, changing that is just the means to the end. >My point is that different fans move different amounts of air at different >voltages - take a standard 775 cooler with a single 90mm fan versus the twin >120mm fan setup we are talking about here. If the BIOS sets the fans at 7v, Which it doesn't, the bios or controller chip is usually ignorant of the voltage, instead setting higher or lower PWM rate or duration. >the 90mm fan will shift something like 10-20cfm, but the twin 120mm fans at >7v will shift something like 60-80cfm. This extra airflow will cool the >heatsink considerably more, but how will the BIOS know this? Again, it doesn't need to know this, you keep thinking in terms of trying to hit and maintain the same temp. All it needs to know is what the user wants it to do from a noise perspective and to start ramping quickly to full fan speed when a threshold temp is reached. This is almost what it does already, except that it tends to use a ratio or percentage of full power, not voltage, for control instead of a user input RPM value. >The BIOS would >have to 'experiemnt' and store values to calibrate itself to do what you are >suggesting. However, this would not be complicated and is a good idea! > No experimentation needed. It would work as mentioned above. Only difference is the value compared, that it would be RPM instead of (% or ratio of full power). Voltage is something it does not use at all, and in fact with a higher current fan the duty cycle would cause a lower voltage than with a lower current fan and yet the higher current fan spins faster at a lower voltage than the lower current fan would - so long as it's above the small region barely above it's stall voltage. |