3pin fans

[lorcav123]

Does 3 pin fan work only on 5V,7V and 12 V voltage? nothing inbetween? I can buy bequiet Silent wings 3 120mm 3 pin for a good price, I was thinking of using this for my CPU cooler fan but it seems that I would have problem if there are only 3 speeds...

Can I set it to let say 10V?

 

[FreedomEclipse]

It works. It just runs slow/faster depending on the voltage. Some fans have a switch somewhere so you can set them to run at silent 5v, medium 7v and high 12v performance at a flick of a switch. if youre skilled enough to can rig up a potentiometer to a normal fan and run the fan at whatever speeds you want. anything between 1-12v.

 

[Metroid]

Does 3 pin fan work only on 5V,7V and 12 V voltage? nothing inbetween? I can buy bequiet Silent wings 3 120mm 3 pin for a good price, I was thinking of using this for my CPU cooler fan but it seems that I would have problem if there are only 3 speeds...

Can I set it to let say 10V?

It will likely run on 7v, on 5v not sure, it depends on the fan. 3 pin 10v, forget. only 5, 7 and 12v.

 

[timta2]

You can also buy a nice fan controller, that will allow you to adjust the fan speed easily. I think the last one I bought was like $20 USD and it has 4 channels, that can each control ~3 fans.

 

[Sybaris_Caesar]

Doesn't most PWM 4-pin headers can be changed to DC 3-pin in the bios?

 

[TheLostSwede]

Normally the UEFI of the motherboard can detect the difference between a PWM fan or a non PWM fan and then it simply adjusts the Voltage to adjust the fan speed instead of via PWM.
However, PWM is far more accurate than doing it the old fashioned way.

 

[lorcav123]

Thank you for answers. Yes I can change to DC control in BIOS. As far as I understood your answers it can only be on 5V, 7V and 12V, nothing inbetween. I won buy fan controller, I think I will buy a 4 pin fan, flexible controls.

 

[Flaky]

As far as I understood your answers it can only be on 5V, 7V and 12V, nothing inbetween.

No.
If motherboard supports fan control via DC, it will supply anything up to 12V.

The 5/7/12V refer to possible voltages which can be achieved manually, either by directly wiring the fan to psu output, or using a simple fan speed switch (calling those "controllers" would be too much).

 

[lorcav123]

No.
If motherboard supports fan control via DC, it will supply anything up to 12V.

The 5/7/12V refer to possible voltages which can be achieved manually, either by directly wiring the fan to psu output, or using a simple fan speed switch (calling those "controllers" would be too much).

ok, thn it will be 3pin. I have x470 strix, in BIOS I can change between auto, DC and PWM so that should be it.

 

[Ruyki]

DC control - fan speed is adjusted by adjusting voltage that is on 2nd pin of the fan header
PWM control - fan speed is adjusted by adjusting the PWN signal send to the fan on the 4th pin, the voltage on the 2nd pin stays at the normal level (12V)

If your mainboard has both of those options, you should be able to control any fan.

 

[kapone32]

I know that current GIgabyte boards allow you to install a 3 pin (water pump) or fan and control the RPMs just like a regualr PWM signal.

 

[Deathy]

Normally the UEFI of the motherboard can detect the difference between a PWM fan or a non PWM fan and then it simply adjusts the Voltage to adjust the fan speed instead of via PWM.
However, PWM is far more accurate than doing it the old fashioned way.

Really? If you want to go for a certain RPM I guess it might be easier with PWM, but if you just control the fan speed to achieve a certain temperature on a certain component, why would PWM be more accurate than voltage control?

 

[kapone32]

Really? If you want to go for a certain RPM I guess it might be easier with PWM, but if you just control the fan speed to achieve a certain temperature on a certain component, why would PWM be more accurate than voltage control?

Because the board communicates directly with the fan based on the PWM while the voltage is just putting less or more power into fan. So you could say brute force vs refined. Think of it as being more granular at voltage control so the PWM can the MBs temp sensors to adjust temp while a 3 PIN is not smart enough to do that.

 

[Vario]

Switching to all 4 pin is really nice ... not having to have a fan controller taking up space.

You can make a 4 pin PWM splitter for 3 pin fans theres a guide floating around, it uses an n-channel mosfet, I built one but it just didn't run the fans I wanted very well.

 

[Deathy]

Because the board communicates directly with the fan based on the PWM while the voltage is just putting less or more power into fan. So you could say brute force vs refined. Think of it as being more granular at voltage control so the PWM can the MBs temp sensors to adjust temp while a 3 PIN is not smart enough to do that.

That last part is just wrong. With DC voltage control on 3 pin fans (which works for 4 pin as well btw), the controller monitors some onboard temperature sensor that one specifies (usually CPU, chipset or case temperatures) and then regulates the voltage output of the fan header to correspond to enough RPM/airflow to keep the desired temperature in check. All that is different about 3 pin voltage control vs 4 pin PWM control is that PWM can be more efficient since it uses 12V all the time and doesn't require a voltage regulator. Though that is hardly "brute force" in my book. There are even voltage control schemes that work by adjusting the voltage to get a desired RPM from the fan, since the communication between fan and controller is done via one of the 3 pins, not the 4th pin.

 

[Bill_Bright]

Does 3 pin fan work only on 5V,7V and 12 V voltage? nothing inbetween?

The fan does not care. You just commonly see those settings because fan speed controllers used by motherboard, case, and fan makers that set the voltages to provide those low, medium, and high speed settings. These same fans can easily be used in a different application (not a computer) with a continuously variable speed controller (like a volume control).

Can I set it to let say 10V?

If your controller allows it, yes. But note if you set it to 2V, for example, that may not provide enough power to get it moving from 0 RPM.

 

[TheLostSwede]

The fan does not care. You just commonly see those settings because fan speed controllers used by motherboard, case, and fan makers that set the voltages to provide those low, medium, and high speed settings. These same fans can easily be used in a different application (not a computer) with a continuously variable speed controller (like a volume control).

If your controller allows it, yes. But note if you set it to 2V, for example, that may not provide enough power to get it moving from 0 RPM.

Actually, the 7V thing was because you can get 7V from a PC PSU, as odd as it seems. It's not a common PC Voltage and I'm not sure it's a good thing to do.

On the other hand, modern motherboards can deliver a wide range of Voltages to the onboard fan headers and don't give a squat about what "raw" Voltages are available from the PSU.

Also, the fan might care, as some fan motors aren't designed to work with lower Voltages, so they would simply stop if the Voltage is too low.

 

[Bill_Bright]

Actually, the 7V thing was because you can get 7V from a PC PSU,

That's the cart before the horse - discovered by some users who didn't want to use real fan speed controllers.

You cannot get 7VDC from any ATX compliant PSU. The ATX Form Factor Design Guide from June 2018 is quite clear. The only voltages are +12VDC, +5VDC, +3.3VDC, -12VDC (optional), and +5Vsb.

There are no "raw" voltages from an ATX compliant PSU. The ATX Form Factor requires all output voltages meet or exceed very tight regulation, as well as good ripple suppression. The ATX Form Factor standard stipulates those voltages must be regulated to not exceed ±5% tolerances.

Acceptable tolerance maximums:

​

12VDC ±5% = 11.4 to 12.6VDC​

5VDC ±5% = 4.75 to 5.25VDC​

3.3VDC ±5% = 3.14 to 3.47VDC​

​

If a PSU is outputting 7V, it is either faulty, modified and/or proprietary and thus, not ATX compliant.

I would urge anyone considering modifying their ATX compliant PSUs to NOT do it. Note it involves cross-connecting output "rails" (that is, not just that one connector). Do you really want to risk applying abnormally high voltages to your motherboard?

June 2018 ATX Form Factor Design Guide direct download link.

 

[TheLostSwede]

That's the cart before the horse - discovered by some users who didn't want to use real fan speed controllers.

You cannot get 7VDC from any ATX compliant PSU. The ATX Form Factor Design Guide from June 2018 is quite clear. The only voltages are +12VDC, +5VDC, +3.3VDC, -12VDC (optional), and +5Vsb.

There are no "raw" voltages from an ATX compliant PSU. The ATX Form Factor requires all output voltages meet or exceed very tight regulation, as well as good ripple suppression. The ATX Form Factor standard stipulates those voltages must be regulated to not exceed ±5% tolerances.

Acceptable tolerance maximums:

​

12VDC ±5% = 11.4 to 12.6VDC​

5VDC ±5% = 4.75 to 5.25VDC​

3.3VDC ±5% = 3.14 to 3.47VDC​

​

If a PSU is outputting 7V, it is either faulty, modified and/or proprietary and thus, not ATX compliant.

I would urge anyone considering modifying their ATX compliant PSUs to NOT do it. Note it involves cross-connecting output "rails" (that is, not just that one connector). Do you really want to risk applying abnormally high voltages to your motherboard?

June 2018 ATX Form Factor Design Guide direct download link.

As I said, it might not be a good idea, but that's how the 7V thing happened.
I mean "raw" as in standard Voltages that an ATX power supply puts out. If the motherboard has a good fan controller design, it doesn't matter what the input to the board is, as the fan controller IC will handle that.

I know the ATX spec very well, but you should go back and look at the picture provided in my previous post and you'll see how people did it.
Nothing about modifying the PSU.

 

[Vario]

You should just buy 4 pin fans from here on, most boards have PWM headers, PWM is more power efficient, has more granular speed adjustment range, with most motherboards, custom fan curves can be set that ensure a quiet PC at idle and adequate cooling when under load, all performed automatically based upon temperatures.

 

[Bill_Bright]

Nothing about modifying the PSU.

It is still modifying the output of the PSU. And since those cables do not isolate themselves from others on that same rail, it is still cross-connecting the outputs - not a good idea.

If the motherboard has a good fan controller design, it doesn't matter what the input to the board is, as the fan controller IC will handle that.

But it does not work that way. You are suggesting the fan controller IC will protect all the other components on the motherboard that may be exposed to that abnormal 7V. That is not how it works. The motherboard fan controller IC is isolated from other motherboard circuits and gets its supplied voltage from the board. It does not distribute the voltage to other points on the board.

My point is about that modified molex in your image does not contain any IC that might isolate the 7V from other devices connected on that same rail.

I also note typical 3-pin fan pinouts show there is either +5 or +12V. Not both. And 4-pin pinouts are just 12V as seen here. This means the actual output voltage is obtained by the IC's logic, not by mixing the PSU's +5 and +12V. Therefore, 7V is just an arbitrary number. It could have been 8 or 10V or continuously variable.

 

[TheLostSwede]

It is still modifying the output of the PSU. And since those cables do not isolate themselves from others on that same rail, it is still cross-connecting the outputs - not a good idea.

Which is what I said, no?

And it's not an arbitrary number, by cross-connecting the 12V and 5V, you get 7V, as the 5V acts as -5V in this scenario.
Again, not a good idea, but people have been doing it for years.
Plenty of guides out there on how to do it as well, please go bash them instead, I was simply trying to explain where the 7V number came from.