[SOLVED] How do I use PWM in fans??

Paperdoc

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Aha! COLGeek has found the big clue! In the photos in OP's other thread the RED header has 4 pins but it is NOT a standard 4-pin fan header. So what its pins do, and whether or not it even uses the new PWM method of fan control, is totally unknown. I can say you can NOT plug any standard 4-pin fan in there. The red plastic "tongue" sticking up beside the pins covers the FULL width of the header, whereas the standard "tongue" covers only the width of Pins 1 to 3.

The nearby three-pin header in white appears to have a label on it that says "FAN3", so it MAY be a standard 3-pin header. BUT we cannot know that for sure, considering that the 4-pin header is NOT standard.

Bottom line: IF the white 3-pin header really is a standard fan header, then you CAN plug in there the connector for a 4-pin PWM fan. There simply will not be any pin for the 4th hole in the connector, but the ridges in the connector side should fit around the white "tongue". IF you're lucky, and that header is standard 3-pin, the fan will run and have its speed controlled as if it were a 3-pin fan, but not using the new PWM control signal system.
 

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Almost all mobos now have ALL of the headers on them with four pins. Any 3- or 4-pin fan CAN be plugged into any of them. For CASE ventilation fans, you should be using SYS_FAN or CHA_FAN headers, not the CPU_FAN or CPU_OPT or PUMP header. The configuration of each of these headers can be adjusted in BIOS Setup to use either the older 3-pjn Voltage Control Mode or the newer PWM Mode to control the speed of the fans. Either option can control the speed of your 4-pin fan, but it is preferred that you use PWM Mode. SOME mobo headers can actually detect which fan design is plugged in and set themselves for this.

If you are not familiar with using BIOS Setup, post back here the maker and model of your mobo, and we can look at its manual and give precise instructions.
 
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Paperdoc

Polypheme
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Aha! COLGeek has found the big clue! In the photos in OP's other thread the RED header has 4 pins but it is NOT a standard 4-pin fan header. So what its pins do, and whether or not it even uses the new PWM method of fan control, is totally unknown. I can say you can NOT plug any standard 4-pin fan in there. The red plastic "tongue" sticking up beside the pins covers the FULL width of the header, whereas the standard "tongue" covers only the width of Pins 1 to 3.

The nearby three-pin header in white appears to have a label on it that says "FAN3", so it MAY be a standard 3-pin header. BUT we cannot know that for sure, considering that the 4-pin header is NOT standard.

Bottom line: IF the white 3-pin header really is a standard fan header, then you CAN plug in there the connector for a 4-pin PWM fan. There simply will not be any pin for the 4th hole in the connector, but the ridges in the connector side should fit around the white "tongue". IF you're lucky, and that header is standard 3-pin, the fan will run and have its speed controlled as if it were a 3-pin fan, but not using the new PWM control signal system.
 
Nov 11, 2021
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3
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Aha! COLGeek has found the big clue! In the photos in OP's other thread the RED header has 4 pins but it is NOT a standard 4-pin fan header. So what its pins do, and whether or not it even uses the new PWM method of fan control, is totally unknown. I can say you can NOT plug any standard 4-pin fan in there. The red plastic "tongue" sticking up beside the pins covers the FULL width of the header, whereas the standard "tongue" covers only the width of Pins 1 to 3.

The nearby three-pin header in white appears to have a label on it that says "FAN3", so it MAY be a standard 3-pin header. BUT we cannot know that for sure, considering that the 4-pin header is NOT standard.

Bottom line: IF the white 3-pin header really is a standard fan header, then you CAN plug in there the connector for a 4-pin PWM fan. There simply will not be any pin for the 4th hole in the connector, but the ridges in the connector side should fit around the white "tongue". IF you're lucky, and that header is standard 3-pin, the fan will run and have its speed controlled as if it were a 3-pin fan, but not using the new PWM control signal system.
What if I have the luck of a black cat under a ladder..
 

Paperdoc

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If the fan does work, and MAYBE if its speed also changes as your worload varies, then you ARE lucky. If it does not run when you try it there, unplug, because we have no way of verifying what that header is doing.

Thanks for Best Solution.
 
Nov 11, 2021
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3
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If the fan does work, and MAYBE if its speed also changes as your worload varies, then you ARE lucky. If it does not run when you try it there, unplug, because we have no way of verifying what that header is doing.

Thanks for Best Solution.
First of all, I haven't tried plugging in my existing fan (the one that is perfectly aligned with the strange RED 4 pin header) in the 3 pin header because I figured it wouldn't physically plug in, but now that I think about it (actually think about it) I think it would work!! (try that later though I'm super tired right now) Second, my existing fan used to change speeds (because it would literally be so LOUD when I'm playing a heavy game) but now after I unplugged it to see the header and then plugged it in again, it doesn't do that any more. It's just stuck on one speed (not the highest speed btw because it's very quiet) Why?
 

Paperdoc

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I don't recommend plugging the 4-pin fan you have (formerly on the red 4-pin header) into the 3-pin header. We have no way of knowing what the connections on all the pins are. And why? If I understand you original query, having just realized that the fan has FOUR pins on the red header, you assumed it must be a PWM-style fans and want to know how to make use of that. Well, it MAY be PWM, maybe not, but if it IS and was included with the mobo, the I would bet it ALREADY is being used as a PWM-stype fan. The main difference in that newer design (compared to 3-pin older fans) is a change in the electrical METHOD of controlling its speed, but NO change in the fact that is speed IS controlled according to a temperature measured on the mobo. The PWM method has slight technical advantages, but you would not notice them normally without careful experimentation. Now, IF that fan with 4 pins is really a PWM design and IF the pinout on its connector is "standard" and IF the white 3-pin header really is a standard 3-pin one, then that white header can NOT make any use of the PWM Method. IF all of those unknowns are true, plugging the 4-pin fan in there would would control it via the OLD Voltage Control Mode, and NOT make any use of the PWM feature!

As to why the old 3-pin fan on the white header now is running at a constant slow and quiet speed, I can suggest only that you MAY have "scrubbed" some oxide coating off the connector pins and improved its electrical connections to the header.
 
Nov 11, 2021
160
3
85
0
I don't recommend plugging the 4-pin fan you have (formerly on the red 4-pin header) into the 3-pin header. We have no way of knowing what the connections on all the pins are. And why? If I understand you original query, having just realized that the fan has FOUR pins on the red header, you assumed it must be a PWM-style fans and want to know how to make use of that. Well, it MAY be PWM, maybe not, but if it IS and was included with the mobo, the I would bet it ALREADY is being used as a PWM-stype fan. The main difference in that newer design (compared to 3-pin older fans) is a change in the electrical METHOD of controlling its speed, but NO change in the fact that is speed IS controlled according to a temperature measured on the mobo. The PWM method has slight technical advantages, but you would not notice them normally without careful experimentation. Now, IF that fan with 4 pins is really a PWM design and IF the pinout on its connector is "standard" and IF the white 3-pin header really is a standard 3-pin one, then that white header can NOT make any use of the PWM Method. IF all of those unknowns are true, plugging the 4-pin fan in there would would control it via the OLD Voltage Control Mode, and NOT make any use of the PWM feature!

As to why the old 3-pin fan on the white header now is running at a constant slow and quiet speed, I can suggest only that you MAY have "scrubbed" some oxide coating off the connector pins and improved its electrical connections to the header.
What exactly is the OLD Voltage Control Mode? Is it changing speeds of the fan according to the workload? And how do I make the 3 UNKNOWNS, known? Also, there is a misunderstanding. My existing fan is a FOUR pin fan! (The one that I said was running at constant slow and quiet speed. I have no idea if it's a PWM fan or not though) And it's plugged in the RED 4 pin header. The WHITE 3 pin header is not being used at all right now. My case only has only ONE place to put a fan in it anyways.
 

Paperdoc

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Ah, my mistake. Somehow I thought you had one fan plugged into each header.

MOST mobo fan headers can control the speed of their fan, and usually are set to do this by default. The choices are made available as items to set in the configuration of each fan header's details in BIOS Setup. All are based on using the TEMPERATURE measured by a sensor and adjusting the speed of the fan controlled by that header to cool that area with air flow. Note that, although we all use the phrase "Fan Speed Control", what really is happening is TEMPERATURE control, accomplished by manipulating fan speed. However, OP, you may NOT have any choices here. Many older HP and Compaq systems had very limited or no options for fan headers.

On modern mobos commonly bought by a user who is building their own system there are three main types of choices.

Profile is the Strategy of how to decide what speed the fan should run. The common (usually default) choice is Automatic (or Standard or Normal), in which the mobo has a pre-set "Fan Curve" of what speed signal to send to the fan for what measured temperature. A related option is "Custom", in which YOU get to specify your own version of the "Fan Curve" to use. Other common options are "Turbo" for full speed constantly, and "Quiet" for a fixed reduced speed. Some have a "Manual" option to let you set a fixed specified speed, although that term often gets used now for the "Custom" choice.

Mode is the method by which the fan speed is actually made to change to the value decided by the Profile. This may be Voltage Control Mode (aka DC Mode), in which the fan speed is determined by the voltage sent to it on Pin #2 - 12 VDC for full speed, down to 5 VDC for minimum speed without stalling. This is the ONLY Mode for controlling 3-pin fans. The other is PWM Mode for the new 4-pin fan design. In that system, the Voltage on Pin #2 is always the full 12 VDC, and the fan has a small chip that uses the new PWM signal from Pin #4 to modify the current flow from that source through the windings to effect speed control.

Temperature Source MAY be a choice offered. Almost all mobos have two groups of headers based on temp sensors. One group uses only the temp sensor built into the CPU chip itself and this guides the CPU chip cooling system. This group may include headers like CPU_OPT. The other main group is intended for cooling the case as a whole, and for that the most commonly used sensor is one on the mobo, placed where the maker has decided that's a decent representation of cooling needs throughout the mobo, and with their pre-set temperature setting. SOME mobos also include extra sensors for specific mobo components like the Voltage Regulator or North Bridge systems in case you want to custom-arrange cooling for specific areas. SOME also allow you to use the temp sensor inside the CPU chip if you need it for some cooling arrangement.

Some mobos also have a PUMP "fan" header intended to power and monitor the pump of a liquid-cooling system for the CPU, but this header always supplies the full 12 VDC because most AIO cooler systems keep their pump at full speed all the time.

Note that none of these headers uses the actual SPEED of its fan (or pump), as returned to that header, to control the speed. Their action is simply to send out a voltage or a PWM signal for some rough percent of whatever that fan can do. They do NOT care about the actual speed - they only change their instructions according to the temperature of the relevant sensor. HOWEVER, every header also has a SECONDARY and important function - monitor that speed signal for FAILURE for the fan. If that happens, they will pop a warning onto your screen. In the case of the CPU cooler system, it may take more drastic action to shut down your system if it believes the CPU has NO cooling available.

I used the phrase "old Voltage Control Mode" simply to refer to that MODE of controlling a fan speed, which is required by the older type of fans - 3-pin.
 
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