If you connect a 3pin fan to a 4pin (PMW) header

NeilF · 14 Nov 2014 at 10:09

Can you still control the fan speed?

If I connect a regular 3 pin fan to one of the 4 pin headers on an MSI Gaming 5, does the mothboard somehow know it's a regular fan so varies the voltage instead of using PMW (as it would with a 4 pin fan connected)?

Or is the 3 pin fan simply run at 100% speed no matter what?

foster grant · 14 Nov 2014 at 10:33

I have an MSI GD65 Z87 Mobo....and i have two 140mm fans at the front of my case and both are 3 pin......and I can change the fan speed using either the BIOS or MSI Command Centre ....so they both run at about 75% which is about 800rpm

doyll · 14 Nov 2014 at 10:36

Probably not, but usually the only 4-pin fan header that is PWM is the CPU fan header. The other 4-pin fan headers are only using 3-pin pinout and are variable voltage controlled.

NeilF · 14 Nov 2014 at 10:48

doyll said:
Probably not, but usually the only 4-pin fan header that is PWM is the CPU fan header. The other 4-pin fan headers are only using 3-pin pinout and are variable voltage controlled.

Do you have tell your BIOS/MB it's a 3 pin fan to achieve that? I mean it can't use PWM on a 3pin fan so surely it must instead be voltage regulating them instead?

And I guess also, with a 3 pin fan it can't tell you the RPM? Where as with a 4 pin fan it can?

NeilF · 14 Nov 2014 at 10:53

doyll said:
Probably not, but usually the only 4-pin fan header that is PWM is the CPU fan header. The other 4-pin fan headers are only using 3-pin pinout and are variable voltage controlled.

All five of the headers on the MSI Gaming 5 are PWM.

Damo667 · 14 Nov 2014 at 12:11

from my somewhat limited experiences every time ive used a 4 pin header with a 3 pin fan it runs at 100% all the time and bios or speedfan wont change the speed. the only way ive done it is using a fan controller.

NeilF · 14 Nov 2014 at 12:19

Damo667 said:
from my somewhat limited experiences every time ive used a 4 pin header with a 3 pin fan it runs at 100% all the time and bios or speedfan wont change the speed. the only way ive done it is using a fan controller.

This is what I'm concerned about...

Tealc · 14 Nov 2014 at 13:03

Some motherboard headers and associated software allow control of 3 pin fans over 4 pin headers but I'm unsure of the level of control it affords, specifically whether it's as fine as % by % PWM duty cycle control or a much harsher level of control (ie 40% speed or 100% speed over a certain temp).

There are solutions that allow you to convert a PWM header into something that provides a fairly stable DC voltage. I have made some in the past and of course Phanteks offer their retail PWM fan hub which is based on a similar concept to mine that does a similar job, mostly.

doyll · 14 Nov 2014 at 15:13

NeilFawcett said:
All five of the headers on the MSI Gaming 5 are PWM.

You need to read chapter 1, part 21 of the manual. It clearly shows what the fan header pin-out is:

* CPUFAN1/CPUFAN2 are PWM .. pin-2 is 12v & pin-4 is speed control (PWM)

* SYSFAN1/SYSFAN2/SYSFAN3 are voltage control .. pin-2 is speed control (variable voltage) and pin-4 is NC (not connected to anything.)

clayer · 15 Nov 2014 at 22:04

you could use voltage reducers.

NeilF · 15 Nov 2014 at 22:12

doyll said:
You need to read chapter 1, part 21 of the manual. It clearly shows what the fan header pin-out is:

* CPUFAN1/CPUFAN2 are PWM .. pin-2 is 12v & pin-4 is speed control (PWM)

* SYSFAN1/SYSFAN2/SYSFAN3 are voltage control .. pin-2 is speed control (variable voltage) and pin-4 is NC (not connected to anything.)

Yes... Reviews stated 5 PMW fans... Where as in fact you are correct!

I'll want to use one of the PWM fan headers for the PWM --> 7 three pin hub in the Enthoos case, so I'll use the supplied Y splitter for the Noctua D14 PWM fans to run both PWM fans from CPU-1. CPU-2 can then be used to control the 7 three pin hub in the case

doyll · 15 Nov 2014 at 23:48

That should work, but if you have trouble with the PWM controlled fan hub, using CPU fan 1 for it and the D14 fans on the other one.

NeilF · 16 Nov 2014 at 14:45

doyll said:
That should work, but if you have trouble with the PWM controlled fan hub, using CPU fan 1 for it and the D14 fans on the other one.

What would be the difference? Surely this is the same really?

CPU-1 (PWM) --> Y-splitter --> D14 PWM fan 1 & 2
CPU-2 (PWM) --> PWM hub --> 3 pins fans

or

CPU-2 (PWM) --> Y-splitter --> D14 PWM fan 1 & 2
CPU-1 (PWM) --> PWM hub --> 3 pins fans

doyll · 16 Nov 2014 at 15:07

There you go .. making assumptions tghat both header are the same. They may be, but sometimes they are not.

NeilF · 16 Nov 2014 at 21:04

doyll said:
There you go .. making assumptions tghat both header are the same. They may be, but sometimes they are not.

Cryptic

doyll · 17 Nov 2014 at 11:28

LOL.
It's just that I have seen users have problems with Phanteks PWM controlled fan hub on 2nd CPU fan socket and it worked just fine on 1st CPU fan socket.

NeilF · 17 Nov 2014 at 11:34

doyll said:
LOL.
It's just that I have seen users have problems with Phanteks PWM controlled fan hub on 2nd CPU fan socket and it worked just fine on 1st CPU fan socket.

OK! Thanks for the heads-up!

ALXAndy · 17 Nov 2014 at 13:13

Four wires are -

pulse
sense
+
-

Pulse is the wire missing on a 3 pin fan and is how the board controls the speed of the fan (by increasing and reducing pulse width). The sense wire tells the board how many RPM the fan is travelling at and + and - are pretty obvious.

On a 3 pin fan you control the speed by increasing and reducing the voltage. So totally different to PWM. Motherboards only work PWM IIRC.

NeilF · 17 Nov 2014 at 13:16

ALXAndy said:
Four wires are -

pulse
sense
+
-

Pulse is the wire missing on a 3 pin fan and is how the board controls the speed of the fan (by increasing and reducing pulse width). The sense wire tells the board how many RPM the fan is travelling at and + and - are pretty obvious.

On a 3 pin fan you control the speed by increasing and reducing the voltage. So totally different to PWM. Motherboards only work PWM IIRC.

The manual for the MSI Gaming 5 suggests the 2 CPU 4-pin headers are PWM, but its 3 SYS 4-pin headers are voltage regulated (with the 4th pin not connected/used).

doyll · 17 Nov 2014 at 13:48

ALXAndy said:
Four wires are -

pulse
sense
+
-

Pulse is the wire missing on a 3 pin fan and is how the board controls the speed of the fan (by increasing and reducing pulse width). The sense wire tells the board how many RPM the fan is travelling at and + and - are pretty obvious.

On a 3 pin fan you control the speed by increasing and reducing the voltage. So totally different to PWM. Motherboards only work PWM IIRC.

Good explanation.

To clarify, the pin-4 pulse signal goes to a PCB in the fan that pulses the 12v power from pin-2 to the fan motor. The sensor pin-3 does indeed tell the motherboard the fan's speed, but on most motherboards it has any effect on PWM signal speed or the control of fan speed. It allows us to see what the rpm of the fan is, but the PWM signal is set at a percentage of 100%.

If we have a 50% PWM signal we do not have 50% of the fan's total speed.

For example, on GA-X58A-UD5, X58A-UD3R and X58-UD3R motherboards the PWM fan headers performance is below:

TY-143 fan 100% is 2480rpm and 50% is 1300rpm
TY-147 fan 100% is 1250rpm and 50% is 875rpm
TY-140 fan 100% is 1300rpm and 50% is 1025rpm
TY-140 fan 100% is 1260rpm and 50% is 885rpm

Unplug the rpm sensor lead from PWM header and other fans on splitter / hub continue run the same as when motherboard was reading the rpm that was going to PWM header.