HWMonitor/Speedfan not reading PWM fans

Calneon · 17 Dec 2013 at 18:05

I have a Gigabyte Z87X-OC with 4 PWM fans attached to 4 PWM fan headers. They're working fine, can hear them speed up when CPU temp increases, but neither HWMonitor or Speedfan pick them up. They both see two fans that hover around 1000 RPM (no matter what temp) and three fans on 0.

Anyone know why this could be?

Havana_UK · 17 Dec 2013 at 21:42

Calneon said:
I have a Gigabyte Z87X-OC with 4 PWM fans attached to 4 PWM fan headers. They're working fine, can hear them speed up when CPU temp increases, but neither HWMonitor or Speedfan pick them up. They both see two fans that hover around 1000 RPM (no matter what temp) and three fans on 0.

Anyone know why this could be?

Have you actually seen them speed up? I have the Z87X-UD3H and the CPU fan spins up just fine, but the (only other) fan plugged into sys fan 1 won't in up at all unless I get it running first by forcing the speed up. I think the system temperatures are so low that it just not getting a high enough duty cycle to actually get going.

Calneon · 17 Dec 2013 at 21:52

You're right, I have one fan plugged into CPU_OPT (pump is in CPU_FAN). That one increases and that's what I'm hearing, other others in the SYS_FAN ones don't speed up. I thought they were based on CPU too?

I have a 5 way splitter cable but it just runs every fan connected to it at max speed regardless of what the PWM is telling it...

Havana_UK · 17 Dec 2013 at 22:33

Calneon said:
You're right, I have one fan plugged into CPU_OPT (pump is in CPU_FAN). That one increases and that's what I'm hearing, other others in the SYS_FAN ones don't speed up. I thought they were based on CPU too?

I have a 5 way splitter cable but it just runs every fan connected to it at max speed regardless of what the PWM is telling it...

I believe that only the CPU_FAN and CPU_OPT headers control the PWM duty cycle based on CPU temperatures, and the other fan headers are driven from a different temperature sensor.

If I get my system fan spinning at about 200rpm then it's getting enough of a duty cycle to keep it rotating, but from stationary it's not getting enough to overcome the initial inertia to get it turning in the first place.

doyll · 17 Dec 2013 at 23:35

Many motherboard 4 pin fan headers are not PWM. Often the only ones that are PWM are
The CPU fan and CPU opt.. and often they are both using same PWM control.

Calneon · 17 Dec 2013 at 23:54

doyll said:
Many motherboard 4 pin fan headers are not PWM. Often the only ones that are PWM are
The CPU fan and CPU opt.. and often they are both using same PWM control.

Even if in the BIOS it lets you set the speed of those fan headers?

doyll · 18 Dec 2013 at 00:19

Fan speed can be set with variable voltage or PWM on fixed 12 volts.

Fans running at full speed on PWM splitter usually means no PWM signal. No PWM signal means 12 volt is constant.. no pulsing to lower the speed. Try plugging it into one of the CPU fan headers.

Calneon · 18 Dec 2013 at 11:11

Same deal in CPU_FAN and CPU_OPT. I'm also not sure why HWMonitor doesn't display CPU_FAN and CPU_OPT, and only shows 2 SYS_FANs when I have three plugged in...

Havana_UK · 18 Dec 2013 at 12:24

doyll said:
Many motherboard 4 pin fan headers are not PWM. Often the only ones that are PWM are
The CPU fan and CPU opt.. and often they are both using same PWM control.

The Gigabyte Z87X-UD3H (and presumably the Z87X-OC too) is definitely PWM on the 4-pin header. The BIOS has the option to adjust the PWM slope for those headers, and (at least in my case) the fan connected to sys_fan1 "twitches" at a regular rate. This is it receiving the PWM pulse, but it's not getting enough total power to overcome inertia and get moving.

Once moving the pulses are long enough to keep it turning, and you can adjust the fan speed quite accurately by adjusting the PWM duty cycle.

doyll · 18 Dec 2013 at 14:14

Page 27 of Z87X-OC manual gives fan header pin-out. It clearly shows only CPU_FAN has pin 4 with speed control (PWM)

SYS_FAN 1/2/3/4 show pin 4 as VCC. VCC used to mean Voltage at a Common Connector. Not sure what Giganbyte's meaning is, but I doubt it is PWM

SYS_FAN 5/6 do not have pin 3 RPM sensor function.

The Z87X-UD3H definitely has Speed Control (PWM) on CPU_FAN, but on SYS_VAN 1/2/3 pin 4 is also VCC.. so probably not PWM

Tealc · 18 Dec 2013 at 14:57

Code:

SYS_FAN1/2/3/4:
Pin No. Definition
1 GND
2 +12V /Speed Control
3 Sense
4 VCC

That doesn't look like a PWM controllable fan header to me either.

Speed control on Pin 2 suggests that Gigabyte have implemented variable voltage control you'd use with a 3 pin fan. The signal on pin 4 maybe designed that way to give 100% duty cycle to any attached PWM fan, or something. It is probably used in this case to designate it as the voltage input for the MOSFET on board the PWM fan.