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How do you control a 3 pin fan with a motherboard?

post #1 of 8
Thread Starter 
I have a MSI H81M-P33 mATX motherboard. It has a 3pin fan connector and a 4 pin fan connector. I have several 3 pin fans that I want to control the fan speed with the motherboard. Is this possible?

I heard some motherboards could control 3 pins with voltage instead of PWM?

https://us.msi.com/Motherboard/H81M-P33.html


I'm wondering if motherboard control is possible because I just realized my case that I just bought won't have external 3.5 slots for my fan controller. If worst comes to worst, would it be a bad idea to mount an external 3.5 fan controller internally?
Edited by Bluescreendeath - 8/29/16 at 8:05pm
post #2 of 8
Should be a fan control option in your BIOS
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post #3 of 8
Thread Starter 
Quote:
Originally Posted by claes View Post

Should be a fan control option in your BIOS

Yep, went to BIOS. It can read the speed but the RPM doesn't seem to change when I move the min and max sliders.
post #4 of 8
This might be possible easily. You could try using a bunch of "Y-cables" to connect all of your fans to the various fan headers of the board.

Some background that might be boring: Warning: Spoiler! (Click to show)
For 3-pin, the control works through changing the voltage that's put onto the second pin. It is 12 Volt for full speed of the fan. The board reduces the speed of a fan by supplying a reduced voltage. It is unclear what a board does exactly when you configure things in its BIOS menus, but you can guess a little. When you see a percentage setting and configure it, you can assume that it's simply a factor multiplied with that 12V voltage. This means if you set 0% speed, it means 0V and the fan stands still, gets zero power. If you set 40%, it means around 5V and the fans runs at some very reduced speed.

The 4-pin scheme is supposed to work differently. It is using a "PWM" signal on the fourth pin to control the speed and is always using a constant 12V on the second pin. If a fan header works like that, then 3-pin fans will always run at 100% speed on that fan header and you will not be able to control them.

Very often, the case fan headers on a motherboard will always do this "voltage control" second pin stuff to control fans, even if a fan header looks like it's 4-pin. They will never supply a correct PWM signal on the fourth pin. If this is the case for your motherboard (you should just try it), then you'll be able to control the speed of 3-pin fans even if connected to the board's 4-pin fan headers.

There might also be a setting to switch 4-pin fan headers of the motherboard between "voltage control" and "PWM control". This is often the case for the fan header intended for the CPU cooler.

You can connect multiple fans to a single fan header through using an "Y-cable". An Y-cable will wire everything needed to supply power to all connected fans. The speed signal that's sent back from one of the fans towards the motherboard will only be wired to a single fan. This means the speed you will see in BIOS screens or in software will be the speed of that particular fan. You can't know the speed of all of your connected fans.

When using Y-cables, you might want to look up power use in "A" = "Ampere" for the fans. From what I remember seeing somewhere, a fan header on a motherboard usually can supply 1A of power. If your fans each use 0.2A for example, you'll theoretically be able to connect a handful of them to a single fan header (I would be a bit scared).
post #5 of 8
My gigabyte X99 Phoenix SLI was the first board I've ever owned that did voltage/pwm on all the fan headers. Was really nice feature to have, but not all boards have that.

Easiest way would be like he said above, and use y-splitter from your cpu fan header probably
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post #6 of 8
Quote:
Originally Posted by Bluescreendeath View Post

I have a MSI H81M-P33 mATX motherboard. It has a 3pin fan connector and a 4 pin fan connector. I have several 3 pin fans that I want to control the fan speed with the motherboard. Is this possible?

I heard some motherboards could control 3 pins with voltage instead of PWM?

https://us.msi.com/Motherboard/H81M-P33.html


I'm wondering if motherboard control is possible because I just realized my case that I just bought won't have external 3.5 slots for my fan controller. If worst comes to worst, would it be a bad idea to mount an external 3.5 fan controller internally?
I assume you have the manual for your motherboard.
Page 11 show 3x fan headers; PWM control on CPUFAN & SYSFAN1 and 12v on SYSFAN2
Page 21 has more information and says you can use the Command Center utility to control your fans.

You can use splitters to run more than one fan off of a fan header, but be careful to not overload the fan header. Fan headers are typically able to supply up to about 1 amp (12 watts), but to be extra safe I never use them for more than 0.9A (10w). Most fans have their amp or watt rating on their labels. Add them up and let us know what they are.
post #7 of 8
Quote:
Originally Posted by Bluescreendeath View Post

Yep, went to BIOS. It can read the speed but the RPM doesn't seem to change when I move the min and max sliders.

Have you tried to actually save and restart? BIOS does not generally apply settings in real time.
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post #8 of 8
Quote:
Originally Posted by ronnin426850 View Post

Have you tried to actually save and restart? BIOS does not generally apply settings in real time.

I know on my board it would apply in real time, but this is generally true for most bios settings.
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