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Fan speed control how-to, 2-pin vs.3-pin vs. 4-pin
- Thread starter dwafford
- Start date
- Oct 6, 2014
- 22,021
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2 and 3 pin takes a fan controller to change the voltage, although some motherboards can do this on 3 pins.
4 pin is a true fan made to be controlled by the 4 pin connector on the motherboard that's what the extra wire is for.
4 pin fan connected to a 3 pin motherboard header has no controll unless your motherboard has the ability.
4 pin is a true fan made to be controlled by the 4 pin connector on the motherboard that's what the extra wire is for.
4 pin fan connected to a 3 pin motherboard header has no controll unless your motherboard has the ability.
2- and 3-pin fan speeds can only be changed by altering the voltage supplied to them. On both, the Black wire is Ground, and the Red wire is the + DC voltage supply. All fans in a computer are designed for max 12 VDC supply.
A 2-pin fan generally has on the end of its wires a male 4-pin Molex connector, but only 2 pins are used. That mates with a power supply connector directly from the PSU. Done that way, it always runs at full speed. Instead, if it is plugged into a third-party fan controller, that unit will supply a voltage that may be reduced (for slower fan speed) by changing the manual setting on the controller - usually, a knob that turns. It also might be possible to get an adapter to allow you to connect such a fan to a mobo 3-pin fan port, thus allowing the mobo to control the fan's speed (but see comment later on speed monitoring). 2-pin fans have no way to send out a speed signal, so you cannot measure the speed of such a fan.
A 3-pin fan is generally connected to a mobo fan port and its speed is changed by changing the supply voltage on Pin #2 of the mobo port. The third pin (Pin #3 on the port) is connected usually to a Yellow wire to the fan. The fan motor generates a pulse signal (2 pulses per revolution) which is sent on the Yellow wire back to the mobo for monitoring. The mobo can do 2 things with this. It will count pulses and generate a fan speed measurement for display by software. It also may check this signal for failure - that is, are there speed pulses coming or not? - and issue a failed fan warning if it gets no signal. For this reason, if you are using this fan port for some other fan type (like an adapted 2-pin fan) many mobos allow you to tell the fan port control system to Ignore this port's speed signal, thus eliminating false failure warnings.
A mobo case fan port usually has an automatic fan speed system available and activated by default. It works this way. The mobo has a temperature sensor built into itself somewhere the maker thinks is vital, (like close to the Northbridge chip) and its software setup has some control parameters like a target temperature and a controller gain, etc. pre-set. The automatic control system constantly compares the measured temperature to the target and alters the fan speed in an attempt to keep actual measured temp close to the target. On many mobos, you can alter the target and the fan speed control strategy if you so choose, either in BIOS Setup or using a software monitoring utility that comes with the mobo. You also have options to turn off automatic fan control and use fixed manually-set fan speed. NOTE that the actual fan speed as measured by the pulse signal is NOT used for control - it is only measured so you can see it if you wish. The mobo connector for a 3-pin fan is set up mechanically so that you can only plug the connector in one way - the correct way to get the right signals to the right pins.
A 4-pin fan works similarly, but with an important difference. The fan motor itself is different to work with this system. A mobo 4-pin fan port has the same three pins and signals on Pin #'s 1 to 3. One important difference, though, is that Pin #2 ALWAYS has the full +12 VDC on it. The added Pin #4 carries the PWM (Pulse Width Modulation) signal from mobo to fan. This is like a square-wave signal at about 25 kHz frequency, but it is not just 50% on. Its "% On" value is varied by the mobo control system. It is used as an "inhibitor" in the sense that an "On" state causes current flow to the fan motor to be interrupted so the fan slows down. Inside the fan motor casing there is a small chip that uses this PWM signal to control the flow of current (from the fixed +12 VDC supplied by Pin #2) through the fan motor, thus achieving fan speed control. The advantage of PWM control is that, since the voltage supplied to the motor is the full +12VDC for SOME of the time, it is much easier to start the fan and to keep it running at slow speeds.
The mechanical details of the fan connectors are such that you can plug any 3-pin fan or 4-pin fan into any 3-pin port or any 4-pin port. It's just that the result is not fully what you want if you mismatch them, but there is backwards compatibility. If you plug a 3-pin fan into a 4-pin port, it will receive a constant +12 VDC supply from Pin #2 at all times, and hence it will always run at full speed. It has no way to use the PWM signal, and it does not even receive it with no 4th wire. If you plug a 4-pin fan into a 3-pin port, it WILL run at changing speeds (unlike what Zerk2012 says above) because its +VDC supply on Pin #2 is being changed by the mobo, and it is NOT receiving any PWM signal from Pin #4 because the port does not have one. The only difference is that it is a little less easy to control it at low speeds because it is working exactly like a 3-pin fan. From this you can see that, although backwards compatibility is designed in for partial function, ideally you should connect to any mobo fan port exactly the type of fan it is designed for - 3-pin or 4-pin.
Fans for use on CPU cooling are exactly the same, but the mobo control system for the CPU_FAN port is different in important ways. The first is that the sensor for true measured temperature is built into the CPU chip (by its manufacturer) and NOT in the mobo. And of course, this means that the target temperature and control loop parameters are specific for the CPU chip type installed in the socket. The second has to do with fan speed monitoring. Many mobo's check more carefully the speed on the CPU cooling fan. On such systems, if it ever appears to have failed (no speed signal coming from motor to mobo) the system will send out an alarm signal (often with a big alarm sound) to tell you, then shut down the entire system almost immediately to avoid the possibility of overheating and permanently damaging the CPU chip. Such a system does not even wait for the CPU temperature measurement to go too high. On these systems, if you use some different CPU cooling system (like, the CPU fan is connected to a PSU Molex output and not the mobo port), you need to tell the BIOS NOT to use its automatic CPU cooling system and NOT to monitor that fan. For both of these reasons it is a good idea to use the CPU_FAN mobo port for the CPU cooling system and to allow it to do its automatic control (that is the default setting in BIOS). It is also important NOT to plug any other fan into this port - the port should ONLY be used for the CPU cooler.
On a mobo there normally is one CPU_FAN port (sometimes a secondary one, too, for an additional CPU fan), one or more SYS_FAN ports for case ventilation, and maybe a PWR_FAN port. The SYS_FAN ports are the ones guided by temp sensor(s) in the mobo and used for case fans. A PWR_FAN port is an odd one. It is designed for use with certain PSU units that have coming out of them a set of wires that look just like 3-pin fan wires, and end in a common 3-pin fan connector. The function here is ONLY to allow such a PSU to send to the mobo its internal fan's speed signal so it can be monitored and displayed by software. Such a mobo port does not supply the PSU fan with power, nor does it attempt to control that fan's speed. Some PSU's do have automatic speed control of the fan inside them, but that control is done entirely within the PSU. So if you have a PWR_FAN port on your mobo but no such wires from the PSU, ideally you connect nothing to that mobo port. However, many mobo makers have connected Ground to that port's Pin #1 and + 12VDC to its Pin #2, so that if you plug into it any 3-pin or 4-pin fan, that fan will run at full speed all the time. There is no control of speed, but it works.
A 2-pin fan generally has on the end of its wires a male 4-pin Molex connector, but only 2 pins are used. That mates with a power supply connector directly from the PSU. Done that way, it always runs at full speed. Instead, if it is plugged into a third-party fan controller, that unit will supply a voltage that may be reduced (for slower fan speed) by changing the manual setting on the controller - usually, a knob that turns. It also might be possible to get an adapter to allow you to connect such a fan to a mobo 3-pin fan port, thus allowing the mobo to control the fan's speed (but see comment later on speed monitoring). 2-pin fans have no way to send out a speed signal, so you cannot measure the speed of such a fan.
A 3-pin fan is generally connected to a mobo fan port and its speed is changed by changing the supply voltage on Pin #2 of the mobo port. The third pin (Pin #3 on the port) is connected usually to a Yellow wire to the fan. The fan motor generates a pulse signal (2 pulses per revolution) which is sent on the Yellow wire back to the mobo for monitoring. The mobo can do 2 things with this. It will count pulses and generate a fan speed measurement for display by software. It also may check this signal for failure - that is, are there speed pulses coming or not? - and issue a failed fan warning if it gets no signal. For this reason, if you are using this fan port for some other fan type (like an adapted 2-pin fan) many mobos allow you to tell the fan port control system to Ignore this port's speed signal, thus eliminating false failure warnings.
A mobo case fan port usually has an automatic fan speed system available and activated by default. It works this way. The mobo has a temperature sensor built into itself somewhere the maker thinks is vital, (like close to the Northbridge chip) and its software setup has some control parameters like a target temperature and a controller gain, etc. pre-set. The automatic control system constantly compares the measured temperature to the target and alters the fan speed in an attempt to keep actual measured temp close to the target. On many mobos, you can alter the target and the fan speed control strategy if you so choose, either in BIOS Setup or using a software monitoring utility that comes with the mobo. You also have options to turn off automatic fan control and use fixed manually-set fan speed. NOTE that the actual fan speed as measured by the pulse signal is NOT used for control - it is only measured so you can see it if you wish. The mobo connector for a 3-pin fan is set up mechanically so that you can only plug the connector in one way - the correct way to get the right signals to the right pins.
A 4-pin fan works similarly, but with an important difference. The fan motor itself is different to work with this system. A mobo 4-pin fan port has the same three pins and signals on Pin #'s 1 to 3. One important difference, though, is that Pin #2 ALWAYS has the full +12 VDC on it. The added Pin #4 carries the PWM (Pulse Width Modulation) signal from mobo to fan. This is like a square-wave signal at about 25 kHz frequency, but it is not just 50% on. Its "% On" value is varied by the mobo control system. It is used as an "inhibitor" in the sense that an "On" state causes current flow to the fan motor to be interrupted so the fan slows down. Inside the fan motor casing there is a small chip that uses this PWM signal to control the flow of current (from the fixed +12 VDC supplied by Pin #2) through the fan motor, thus achieving fan speed control. The advantage of PWM control is that, since the voltage supplied to the motor is the full +12VDC for SOME of the time, it is much easier to start the fan and to keep it running at slow speeds.
The mechanical details of the fan connectors are such that you can plug any 3-pin fan or 4-pin fan into any 3-pin port or any 4-pin port. It's just that the result is not fully what you want if you mismatch them, but there is backwards compatibility. If you plug a 3-pin fan into a 4-pin port, it will receive a constant +12 VDC supply from Pin #2 at all times, and hence it will always run at full speed. It has no way to use the PWM signal, and it does not even receive it with no 4th wire. If you plug a 4-pin fan into a 3-pin port, it WILL run at changing speeds (unlike what Zerk2012 says above) because its +VDC supply on Pin #2 is being changed by the mobo, and it is NOT receiving any PWM signal from Pin #4 because the port does not have one. The only difference is that it is a little less easy to control it at low speeds because it is working exactly like a 3-pin fan. From this you can see that, although backwards compatibility is designed in for partial function, ideally you should connect to any mobo fan port exactly the type of fan it is designed for - 3-pin or 4-pin.
Fans for use on CPU cooling are exactly the same, but the mobo control system for the CPU_FAN port is different in important ways. The first is that the sensor for true measured temperature is built into the CPU chip (by its manufacturer) and NOT in the mobo. And of course, this means that the target temperature and control loop parameters are specific for the CPU chip type installed in the socket. The second has to do with fan speed monitoring. Many mobo's check more carefully the speed on the CPU cooling fan. On such systems, if it ever appears to have failed (no speed signal coming from motor to mobo) the system will send out an alarm signal (often with a big alarm sound) to tell you, then shut down the entire system almost immediately to avoid the possibility of overheating and permanently damaging the CPU chip. Such a system does not even wait for the CPU temperature measurement to go too high. On these systems, if you use some different CPU cooling system (like, the CPU fan is connected to a PSU Molex output and not the mobo port), you need to tell the BIOS NOT to use its automatic CPU cooling system and NOT to monitor that fan. For both of these reasons it is a good idea to use the CPU_FAN mobo port for the CPU cooling system and to allow it to do its automatic control (that is the default setting in BIOS). It is also important NOT to plug any other fan into this port - the port should ONLY be used for the CPU cooler.
On a mobo there normally is one CPU_FAN port (sometimes a secondary one, too, for an additional CPU fan), one or more SYS_FAN ports for case ventilation, and maybe a PWR_FAN port. The SYS_FAN ports are the ones guided by temp sensor(s) in the mobo and used for case fans. A PWR_FAN port is an odd one. It is designed for use with certain PSU units that have coming out of them a set of wires that look just like 3-pin fan wires, and end in a common 3-pin fan connector. The function here is ONLY to allow such a PSU to send to the mobo its internal fan's speed signal so it can be monitored and displayed by software. Such a mobo port does not supply the PSU fan with power, nor does it attempt to control that fan's speed. Some PSU's do have automatic speed control of the fan inside them, but that control is done entirely within the PSU. So if you have a PWR_FAN port on your mobo but no such wires from the PSU, ideally you connect nothing to that mobo port. However, many mobo makers have connected Ground to that port's Pin #1 and + 12VDC to its Pin #2, so that if you plug into it any 3-pin or 4-pin fan, that fan will run at full speed all the time. There is no control of speed, but it works.
Hi , I really enjoyed reading such professional FAN KB . Now I have simple question :
- What happen if I connect 2-pin FAN ( not sure what type it was , possible from the server) into mobo CPU FAN connector ( 4-pin) ?
The reason Im asking because after this exercise my PC starts but no video output and no signs of working state.
Appreciate you help
- What happen if I connect 2-pin FAN ( not sure what type it was , possible from the server) into mobo CPU FAN connector ( 4-pin) ?
The reason Im asking because after this exercise my PC starts but no video output and no signs of working state.
Appreciate you help
Yes, I'd expect what you got.
First of all, I'm intrigued that you found a way to connect a 2-pin fan to a mobo fan port. All mobo fan ports I've seen for some time are either 3- or 4-pin in a particular arrangement of pins with a plastic tongue sticking up next to them. This is to ensure that the female connector from the fan wires fits onto it only one way. On the other hand, the only "2-pin" fans I have seen are those that have only 2 wires from the fan motor, but actually have a large male "4-pin Molex" connector on the end, to mate with an output connector from the PSU. That fan connector could not fit a mobo fan port. So, either you (or someone) custom-fitted a fan with a new connector (or used an adapter), or you have a very different fan entirely.
Anyway, irrespective of connectors, the wiring connections would have to be correct. Both 3- and 4-pin mobo fan ports provide the Ground connection on Pin #1, and +VDC on Pin #2. On a 3-pin port, the voltage on Pin #2 varies from 0 to +12 VDC. On a 4-pin port, that voltage is always +12 VDC. Your fan would have to connect to these two pins. IF you were to connect them in reverse, the fan would turn but in the wrong direction.
But here's the big problem that likely explains your non-functioning system. That fan you describe with "2 pins" obviously does NOT have a third wire to Pin #3. In 3- and 4-pin fans, this wire carries a pulse train signal from the motor back to the mobo for speed measurement. You plugged this fan into a CPU_FAN port. MANY mobos have by default (you can turn it off in BIOS Setup) a system on that CPU_FAN port to check the speed of that fan constantly. Of course, it is assumed that the fan plugged in here will be the real CPU cooler! If that fan ever fails to send a speed pulse signal to the port (which is what you created, OP) the system assumes that the CPU cooler has failed and initiates an immediate safety shut-down. First it sends out a warning beep on the mobo mini-speaker (PZO) and a message on the screen, then it shuts down the whole system. This is all to prevent the CPU from overheating and being destroyed for lack of cooling. This system does not even wait for the normal CPU temperature sensor to signal high CPU internal temperature. On a start-up, the warning sound and screen message may not last long before shut-down happens.
For people who have such a protection system in their mobos' CPU_FAN control system but who want to cool their CPU with some fan that is NOT connected to the CPU_FAN port (and hence will not supply the speed signal to that port), the BIOS Setup screens allow you to tell it to ignore that system. So you lose one extra CPU overheating monitor that way, but you system will run.
By the way, OP, since you do not know the origins of that fan, examine it very carefully. Look particularly for voltage and amperage specs on it. If it came from some very different application, it may not work the way common computer case ventilation fans do. Common fans operate on 12VDC (max) and consume typically 0.3 to 1.0 amps. Really high-performance fans for computer cases still use 12 VDC, but may consume up to 3 or 4 amps, and no mobo fan port can supply that.
First of all, I'm intrigued that you found a way to connect a 2-pin fan to a mobo fan port. All mobo fan ports I've seen for some time are either 3- or 4-pin in a particular arrangement of pins with a plastic tongue sticking up next to them. This is to ensure that the female connector from the fan wires fits onto it only one way. On the other hand, the only "2-pin" fans I have seen are those that have only 2 wires from the fan motor, but actually have a large male "4-pin Molex" connector on the end, to mate with an output connector from the PSU. That fan connector could not fit a mobo fan port. So, either you (or someone) custom-fitted a fan with a new connector (or used an adapter), or you have a very different fan entirely.
Anyway, irrespective of connectors, the wiring connections would have to be correct. Both 3- and 4-pin mobo fan ports provide the Ground connection on Pin #1, and +VDC on Pin #2. On a 3-pin port, the voltage on Pin #2 varies from 0 to +12 VDC. On a 4-pin port, that voltage is always +12 VDC. Your fan would have to connect to these two pins. IF you were to connect them in reverse, the fan would turn but in the wrong direction.
But here's the big problem that likely explains your non-functioning system. That fan you describe with "2 pins" obviously does NOT have a third wire to Pin #3. In 3- and 4-pin fans, this wire carries a pulse train signal from the motor back to the mobo for speed measurement. You plugged this fan into a CPU_FAN port. MANY mobos have by default (you can turn it off in BIOS Setup) a system on that CPU_FAN port to check the speed of that fan constantly. Of course, it is assumed that the fan plugged in here will be the real CPU cooler! If that fan ever fails to send a speed pulse signal to the port (which is what you created, OP) the system assumes that the CPU cooler has failed and initiates an immediate safety shut-down. First it sends out a warning beep on the mobo mini-speaker (PZO) and a message on the screen, then it shuts down the whole system. This is all to prevent the CPU from overheating and being destroyed for lack of cooling. This system does not even wait for the normal CPU temperature sensor to signal high CPU internal temperature. On a start-up, the warning sound and screen message may not last long before shut-down happens.
For people who have such a protection system in their mobos' CPU_FAN control system but who want to cool their CPU with some fan that is NOT connected to the CPU_FAN port (and hence will not supply the speed signal to that port), the BIOS Setup screens allow you to tell it to ignore that system. So you lose one extra CPU overheating monitor that way, but you system will run.
By the way, OP, since you do not know the origins of that fan, examine it very carefully. Look particularly for voltage and amperage specs on it. If it came from some very different application, it may not work the way common computer case ventilation fans do. Common fans operate on 12VDC (max) and consume typically 0.3 to 1.0 amps. Really high-performance fans for computer cases still use 12 VDC, but may consume up to 3 or 4 amps, and no mobo fan port can supply that.
Hi, I have pooled memory form the mobo to see if it will make a sound of parity failure and it did. but then when I put mem back its still beeping and now its just not stop 
. Have no idea what happened with this fan installation but i went to order new one ( not that expensive) with CPU and FAN.
Still try to understand what could happen to the board. I try to attach pics of the FANs here but could not see the option
. Have no idea what happened with this fan installation but i went to order new one ( not that expensive) with CPU and FAN. Still try to understand what could happen to the board. I try to attach pics of the FANs here but could not see the option
Marc Wolfe
Commendable
- Mar 15, 2016
- 4
- 0
- 1,510
You are right, but that does not apply to computer "PWM Fans" because they are not normal DC fans, and the method the mobo uses for controlling them is a special version of PWM designed to work with these non-standard fans.
Most small fans used in computer cases today are DC fans of the brushless type. That is, they do not have any commutator or brushes. Instead they include inside the fan motor case a small circuit board that simulates such a switching system electronically to "move" the magnetic fields of the field coils. The circuit also generates a pulse signal (2 pulses per revolution) that is sent back to the mobo port on the third wire (Pin #3 of the connector) for counting to yield fan speed. That same signal also is used by some mobos for fault detection - if the signal is missing, the mobo interprets that as a stalled fan. For the most part these things have little to do with whether that fan can be controlled via Pulse Width Modulation, but there is a link (later).
Since these small brushless fans already have circuit boards and components inside them, it was not a big stretch to add more circuitry for new functions. Now PWM control of a "normal" DC fan is accomplished by modulating the DC supply voltage with a PWM signal so that the supply to the fan is not constant DC, but a DC voltage that turns on and off rapidly with varying "% On Time". However, the so-called "PWM Fan" for a computer case does not accept this type of control. Instead it must have the full constant 12VDC supply on Pin #2 (and Ground on Pin #1, of course), plus the PWM signal from Pin #4 of the connector. Then the fan's own internal circuit board does the modulation of the DC supply as it is fed to the motor windings. In this way all the functions of the various circuits on that internal board have a reliable 12 VDC supply to use, AND the motor windings only receive a PWM-modulated DC current supply to accomplish speed control. The arrangement is such that, if there is no PWM signal supplied via Pin #4, the motor windings will just receive an unmodulated DC voltage of whatever value is supplied on Pin #2. This is one part of the "backwards compatibility" of the new 4-pin fan design so that it can run under mobo control by a 3-pin fan mobo port which operates only in Voltage Control Mode. That is, the 3-pin port supplies on Pin #2 a DC voltage which varies from 0 to 12 VDC to accomplish speed control, but supplies no PWM signal on a non-existent Pin #4.
Now the limit this imposes. Several manufacturers of these computer-style "PWM Fans" caution that you should NOT ever try to power such a fan from a "normal" PWM speed control system used with "normal" DC motors. The problem involved is that a pulse-modulated DC supply to a computer-type fan cannot be relied upon as a clean stable 12VDC supply to the components of the internal circuit board; in fact, its sharp pulse content may well damage the components of that board inside the fan case.
So, you could not use a PWM Speed Control system from other DC motor types to power the 4-pin fans used in computers. I am not clear whether you could use such a controller with older 3-pin computer fans, but I doubt it. The same concerns about a clean noise-free (i.e., without rapid voltage changes and mini-spikes) DC supply, and possible damage to components of the 3-pin fan's circuit board, would apply even though a 3-pin fan IS designed to work at voltages less than 12 VDC.
Most small fans used in computer cases today are DC fans of the brushless type. That is, they do not have any commutator or brushes. Instead they include inside the fan motor case a small circuit board that simulates such a switching system electronically to "move" the magnetic fields of the field coils. The circuit also generates a pulse signal (2 pulses per revolution) that is sent back to the mobo port on the third wire (Pin #3 of the connector) for counting to yield fan speed. That same signal also is used by some mobos for fault detection - if the signal is missing, the mobo interprets that as a stalled fan. For the most part these things have little to do with whether that fan can be controlled via Pulse Width Modulation, but there is a link (later).
Since these small brushless fans already have circuit boards and components inside them, it was not a big stretch to add more circuitry for new functions. Now PWM control of a "normal" DC fan is accomplished by modulating the DC supply voltage with a PWM signal so that the supply to the fan is not constant DC, but a DC voltage that turns on and off rapidly with varying "% On Time". However, the so-called "PWM Fan" for a computer case does not accept this type of control. Instead it must have the full constant 12VDC supply on Pin #2 (and Ground on Pin #1, of course), plus the PWM signal from Pin #4 of the connector. Then the fan's own internal circuit board does the modulation of the DC supply as it is fed to the motor windings. In this way all the functions of the various circuits on that internal board have a reliable 12 VDC supply to use, AND the motor windings only receive a PWM-modulated DC current supply to accomplish speed control. The arrangement is such that, if there is no PWM signal supplied via Pin #4, the motor windings will just receive an unmodulated DC voltage of whatever value is supplied on Pin #2. This is one part of the "backwards compatibility" of the new 4-pin fan design so that it can run under mobo control by a 3-pin fan mobo port which operates only in Voltage Control Mode. That is, the 3-pin port supplies on Pin #2 a DC voltage which varies from 0 to 12 VDC to accomplish speed control, but supplies no PWM signal on a non-existent Pin #4.
Now the limit this imposes. Several manufacturers of these computer-style "PWM Fans" caution that you should NOT ever try to power such a fan from a "normal" PWM speed control system used with "normal" DC motors. The problem involved is that a pulse-modulated DC supply to a computer-type fan cannot be relied upon as a clean stable 12VDC supply to the components of the internal circuit board; in fact, its sharp pulse content may well damage the components of that board inside the fan case.
So, you could not use a PWM Speed Control system from other DC motor types to power the 4-pin fans used in computers. I am not clear whether you could use such a controller with older 3-pin computer fans, but I doubt it. The same concerns about a clean noise-free (i.e., without rapid voltage changes and mini-spikes) DC supply, and possible damage to components of the 3-pin fan's circuit board, would apply even though a 3-pin fan IS designed to work at voltages less than 12 VDC.
Contiusa
Honorable
- Oct 8, 2013
- 33
- 2
- 10,530
Since the OP asked a general question about fan control, I have some doubts that I could not solve. In fact I can't find anyone talking about it. I hope to don't intrude or hijack it.
In terms of BIOS control (I am not talking about software control)
I am confused if the so called "voltage control" are just static voltage options -- when you have the option to set the header at a static "speed" of 5v, 7v or 12v (for example) -- or if the voltage can vary according to CPU load / system temp -- more or less like a PWM control.
And how do we recognize if the header (CPU-fan / SYS-fan / CHA-fan) has one or the other (static settings or curve settings for voltage control)?
My mobo (Z77X-D3H) has the usual options "quiet" / "standard" / "performance" / "Disable" for the SYS-fans. I know that "Disable" makes it run at 12v, but do the other options has a curve control according to the system temperature or are they static voltages that never change?
And how about the CPU-fan header? Can I plug a T2 Blizzard for example (3 pin cooler) and have it curve controlled by voltage? I have a 4 pin CPU cooler, I am just not sure how the 3 pin voltage control works in practice, not in theory.
Cheers,
In terms of BIOS control (I am not talking about software control)
I am confused if the so called "voltage control" are just static voltage options -- when you have the option to set the header at a static "speed" of 5v, 7v or 12v (for example) -- or if the voltage can vary according to CPU load / system temp -- more or less like a PWM control.
And how do we recognize if the header (CPU-fan / SYS-fan / CHA-fan) has one or the other (static settings or curve settings for voltage control)?
My mobo (Z77X-D3H) has the usual options "quiet" / "standard" / "performance" / "Disable" for the SYS-fans. I know that "Disable" makes it run at 12v, but do the other options has a curve control according to the system temperature or are they static voltages that never change?
And how about the CPU-fan header? Can I plug a T2 Blizzard for example (3 pin cooler) and have it curve controlled by voltage? I have a 4 pin CPU cooler, I am just not sure how the 3 pin voltage control works in practice, not in theory.
Cheers,
To review how the two main fan types (3-pin and 4-pin) differ, see my post above of Mar. 3/15, paragraphs 3 through 6. Control of speed of 3-pin fans can ONLY be done by changing the voltage supplied to it on Pin#2, so this system is called "Voltage Control Mode", or sometimes "DC Mode". A 4-pin fan is designed for control a different way, by giving it a fixed voltage supply and then a special signal called PWM on Pin #4. The 4-pin fan has its own internal circuit to apply that PWM signal to its power supply to adjust its speed. This means of control is called "PWM Mode". A design feature of 4-pin fans is that, IF one is connected to a mobo fan header that uses only Voltage Control Mode, it gets no PWM signal to apply BUT it also gets a DC supply that is NOT fixed. It varies, so the fan still changes speed. On the other hand, a 3-pin fan plugged into a 4-pin header that is using PWM Mode can only run full speed because it receives a fixed 12 VDC on Pin #2.
An "automatic" fan speed control system that runs a mobo SYS_FAN or CPU_FAN header works to change fan speed according to the actual temperature measured by a sensor, and a target for that temperature. The mobo has one sensor for the SYS_FAN control system (some mobos have more) at a critical point on the mobo; a second sensor built into the CPU chip itself is used for the CPU_FAN control system.
Many mobos offer four options for the fan control strategy that you can choose, for EACH fan header. Usually theses are: "Normal" or "Standard" or "Auto" for the automatic temperature-guided system; "Silent", "Low Noise", or "Quiet" for a fixed reduced fan speed that makes less noise BUT delivers fixed low cooling; "Turbo" or "Overclock" or "High" for a fixed high speed (and noise and cooling); and, "Manual" which allows you to set a fixed speed of your own choosing. (Contiusa, your mobo on p. 47 uses the label "Disabled" for the fixed full-speed option.) But that is the control STRATEGY, and not the control MECHANISM. The MECHANISM is the matter of Voltage Control Mode (necessary for 3-pin fans) or PWM Mode (best for 4-pin fans).
How can you tell which Mechanism a particular mobo fan header will use? Often the mobo manual is not completely clear and you need to decipher clues. The number of pins on a header is a start, but NOT a reliable indicator because there are mobos that use 4-pin headers for connection, but really only supply to the header the Voltage Control Mode signals on the first three pins. The first good place to look is where the Internal Connectors are diagrammed, and sometimes also diagrams of the pins and their functions for the headers on the mobo. First rule: if there are 3 pins for the header it is ONLY a 3-pin system using Voltage Control Mode. But if it has 4 pins, look closely at the pin labels IF there are any. Pin #1 is Ground. Pin #2 is the DC supply voltage. If it is ONLY shown to be 12 VDC, there's a good chance the header uses PWM Mode. Pin #3 is the speed signal being send BACK to the mobo for measurement - it is NOT really the speed CONTROL line as some labels say it is. The label on Pin #4 is important. If it says PWM Signal, this header can use PWM Mode. If it says a fixed DC voltage, it is NOT using PWM Mode, so it must be Voltage Control Mode. If it says unused or no signal, that also eliminates PWM Mode.
Now go to where your manual describes in detail the options for you to configure each mobo fan port. Almost all mobos now offer on the CPU_FAN port ONLY the choice to use EITHER control mode. Usually the choices for Control Mode are: "Auto", which lets the mobo figure out the correct mode of whatever fan is plugged in; "Voltage Control Mode" or "DC Mode"; and "PWM Mode". Ideally you should set this option to match the particular fan you have plugged into the CPU_FAN header.
Now look at the SYS_FAN header configuration options. Some current mobos also offer you a choice of either mode, but most do not. Most will use only one of them. Which one? The best clue usually is in the part where they tell you how to make your MANUAL settings if you choose the "Manual" speed control strategy. If it tells you to set a voltage, then surely it is using Voltage Control Mode. If it talks about "Slope PWM" and says you can choose values like "0.75 PWM value per C", then it is telling you that you set a PWM signal value in Manual Mode. Thus the header MUST be using PWM Mode, and pretty much guarantees that it does this when set to the Automatic fan speed control strategy.
This is the information you need when buying fans, because you really should buy 3-pin fans to connect to Voltage Control Mode headers, and 4-pin fans to connect to PWM Mode headers. The exception that works is that you CAN control the speed of a 4-pin fan with a header that uses Voltage Control Mode.
Contiusa, let's get to your specific system. p. 47 of your manual contains most of what you need. To start, for the CPU_FAN header it says you can choose whether to use Voltage Control Mode or PWM Mode. The T2 Blizzard CPU cooler system you cite comes only with a 3-pin fan, so you MUST set this to Voltage Control Mode. Then you can chose the strategy under CPU Fan Speed Control: "Normal" will have the mobo constantly change the fan speed if necessary according to the temperature measured inside the CPU chip, which is what you seek. IF you buy a cooler that uses a 4-pin fan instead, you can still control that fan using Voltage Control Mode. BUT you would be better in that case to set the CPU_FAN header to use PWM Mode, because it is a better control system if you have a 4-pin fan there.
Now on to the SYS_FAN headers. They show that manual control requires setting a PWM Slope value, so these headers all must be using ONLY PWM Mode. Thus, they can only control the speed of 4-pin fans; any 3-pin fan plugged into one of these SYS_FAN ports can only run full speed all the time. Assuming you are plugging 4-pin fans into these headers, you should set the System Fan Speed Control option to "Normal" again to use the automatic control system guided by the mobo's temperature sensor.
One final point. When you make changes in BIOS Setup screens, remember to SAVE and EXIT so that your changes are saved and used!
An "automatic" fan speed control system that runs a mobo SYS_FAN or CPU_FAN header works to change fan speed according to the actual temperature measured by a sensor, and a target for that temperature. The mobo has one sensor for the SYS_FAN control system (some mobos have more) at a critical point on the mobo; a second sensor built into the CPU chip itself is used for the CPU_FAN control system.
Many mobos offer four options for the fan control strategy that you can choose, for EACH fan header. Usually theses are: "Normal" or "Standard" or "Auto" for the automatic temperature-guided system; "Silent", "Low Noise", or "Quiet" for a fixed reduced fan speed that makes less noise BUT delivers fixed low cooling; "Turbo" or "Overclock" or "High" for a fixed high speed (and noise and cooling); and, "Manual" which allows you to set a fixed speed of your own choosing. (Contiusa, your mobo on p. 47 uses the label "Disabled" for the fixed full-speed option.) But that is the control STRATEGY, and not the control MECHANISM. The MECHANISM is the matter of Voltage Control Mode (necessary for 3-pin fans) or PWM Mode (best for 4-pin fans).
How can you tell which Mechanism a particular mobo fan header will use? Often the mobo manual is not completely clear and you need to decipher clues. The number of pins on a header is a start, but NOT a reliable indicator because there are mobos that use 4-pin headers for connection, but really only supply to the header the Voltage Control Mode signals on the first three pins. The first good place to look is where the Internal Connectors are diagrammed, and sometimes also diagrams of the pins and their functions for the headers on the mobo. First rule: if there are 3 pins for the header it is ONLY a 3-pin system using Voltage Control Mode. But if it has 4 pins, look closely at the pin labels IF there are any. Pin #1 is Ground. Pin #2 is the DC supply voltage. If it is ONLY shown to be 12 VDC, there's a good chance the header uses PWM Mode. Pin #3 is the speed signal being send BACK to the mobo for measurement - it is NOT really the speed CONTROL line as some labels say it is. The label on Pin #4 is important. If it says PWM Signal, this header can use PWM Mode. If it says a fixed DC voltage, it is NOT using PWM Mode, so it must be Voltage Control Mode. If it says unused or no signal, that also eliminates PWM Mode.
Now go to where your manual describes in detail the options for you to configure each mobo fan port. Almost all mobos now offer on the CPU_FAN port ONLY the choice to use EITHER control mode. Usually the choices for Control Mode are: "Auto", which lets the mobo figure out the correct mode of whatever fan is plugged in; "Voltage Control Mode" or "DC Mode"; and "PWM Mode". Ideally you should set this option to match the particular fan you have plugged into the CPU_FAN header.
Now look at the SYS_FAN header configuration options. Some current mobos also offer you a choice of either mode, but most do not. Most will use only one of them. Which one? The best clue usually is in the part where they tell you how to make your MANUAL settings if you choose the "Manual" speed control strategy. If it tells you to set a voltage, then surely it is using Voltage Control Mode. If it talks about "Slope PWM" and says you can choose values like "0.75 PWM value per C", then it is telling you that you set a PWM signal value in Manual Mode. Thus the header MUST be using PWM Mode, and pretty much guarantees that it does this when set to the Automatic fan speed control strategy.
This is the information you need when buying fans, because you really should buy 3-pin fans to connect to Voltage Control Mode headers, and 4-pin fans to connect to PWM Mode headers. The exception that works is that you CAN control the speed of a 4-pin fan with a header that uses Voltage Control Mode.
Contiusa, let's get to your specific system. p. 47 of your manual contains most of what you need. To start, for the CPU_FAN header it says you can choose whether to use Voltage Control Mode or PWM Mode. The T2 Blizzard CPU cooler system you cite comes only with a 3-pin fan, so you MUST set this to Voltage Control Mode. Then you can chose the strategy under CPU Fan Speed Control: "Normal" will have the mobo constantly change the fan speed if necessary according to the temperature measured inside the CPU chip, which is what you seek. IF you buy a cooler that uses a 4-pin fan instead, you can still control that fan using Voltage Control Mode. BUT you would be better in that case to set the CPU_FAN header to use PWM Mode, because it is a better control system if you have a 4-pin fan there.
Now on to the SYS_FAN headers. They show that manual control requires setting a PWM Slope value, so these headers all must be using ONLY PWM Mode. Thus, they can only control the speed of 4-pin fans; any 3-pin fan plugged into one of these SYS_FAN ports can only run full speed all the time. Assuming you are plugging 4-pin fans into these headers, you should set the System Fan Speed Control option to "Normal" again to use the automatic control system guided by the mobo's temperature sensor.
One final point. When you make changes in BIOS Setup screens, remember to SAVE and EXIT so that your changes are saved and used!
Contiusa
Honorable
- Oct 8, 2013
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Oh, that made all the difference! I had gone through this section before, but in my ignorance / tunnel vision I did not recognize the "Voltage Control Mode or PWM Mode". Now that you described it in layman terms all the pieces fell into place. It can even vary the SYS-fan voltage according to system temps. Cool.
Thanks a lot for the schooling!
I'm hoping that you are still looking at this thread three years later (!).
I am replacing the 120mm fan on my ORICO 9548U3 hard drive enclosure. It is a 2-pin connection. The replacement fan I bought is incredibly loud, so I'm trying to find a quiet one.
Most of the replacement fans, such as the SilenX EFC 12-15
https://www.newegg.com/Product/Product.aspx?Item=N82E16...
Appear to be 3-pin or 4-pin.
Is it a problem to cut the cable and splice in the 2-pin connector?
Thanks for your help and advice.
-sam
I am replacing the 120mm fan on my ORICO 9548U3 hard drive enclosure. It is a 2-pin connection. The replacement fan I bought is incredibly loud, so I'm trying to find a quiet one.
Most of the replacement fans, such as the SilenX EFC 12-15
https://www.newegg.com/Product/Product.aspx?Item=N82E16...
Appear to be 3-pin or 4-pin.
Is it a problem to cut the cable and splice in the 2-pin connector?
Thanks for your help and advice.
-sam
Not a problem, IF...
First of all, you need to know what voltage is being supplied to the old fan in that enclosure, AND its polarity. I see the enclosure comes with its own power supply and gets from that 12 VDC. So there is 12 VDC available inside that case - we just don't know whether that is what feeds the fan. I suggest you open the case, apply power, and use a voltmeter to measure the voltage to the fan. ALSO, take careful note of which wire going to the fan is positive.
Now, common computer case fans, whether 3- or 4-pin, use 12 VDC as their max voltage for full speed, so a fan of that type should do the job. What we ALSO do not know is how much air flow the old fan delivers, but if you are confident it blows like most computer 120mm case fans, then it can work.
For your purpose, a 4-pin fan is NOT necessary. That design is more complex and hence more expensive than a 3-pin fan. So, just go for a 3-pin model.
The one you linked, the SilenX EFX-12-15, will do well. I note that it has two connectors on the end of its wires, so that you can plug it into EITHER a 3-pin standard male fan header on a mobo OR a 4-pin Molex female power output connector from a computer PSU. You will note that the larger Molex male connector only has two of its "normal" 4 pins in it - that's because it only needs to connect to +12 VDC and Ground in the female connector. So that's the easiest way to splice on your old fan's connector. On the male Molex, the pin CLOSEST to the edge is the +12 VDC contact; it will mate with the Yellow wire of a female Molex output. The pin closer to the middle of the male is the Ground., and it will mate with a Black wire on the Molex female. Just be sure when you make your splices that the old connector's positive wire goes to the Molex male's OUTER wire. You will not need the 3-pin connector at all. (The third wire on the 3-pin connector is the fan speed signal, and your drive enclosure obviously does not have a way to connect that to anything. It is NOT needed for proper fan operation.)
BEFORE mounting the fan, examine its outer frame. It will have two arrows on it. One points AROUND the frame, and that's the direction of rotation when the fan power is wired correctly. The other arrow points THROUGH the fan, and that's the air flow direction. So mount the fan according to the arrow for air flow, and when you're done check the direction of rotation to be sure you did the splice correctly. If you get it backwards by mistake, no big problem - it won't damage the fan. Just re-do the splicing.
First of all, you need to know what voltage is being supplied to the old fan in that enclosure, AND its polarity. I see the enclosure comes with its own power supply and gets from that 12 VDC. So there is 12 VDC available inside that case - we just don't know whether that is what feeds the fan. I suggest you open the case, apply power, and use a voltmeter to measure the voltage to the fan. ALSO, take careful note of which wire going to the fan is positive.
Now, common computer case fans, whether 3- or 4-pin, use 12 VDC as their max voltage for full speed, so a fan of that type should do the job. What we ALSO do not know is how much air flow the old fan delivers, but if you are confident it blows like most computer 120mm case fans, then it can work.
For your purpose, a 4-pin fan is NOT necessary. That design is more complex and hence more expensive than a 3-pin fan. So, just go for a 3-pin model.
The one you linked, the SilenX EFX-12-15, will do well. I note that it has two connectors on the end of its wires, so that you can plug it into EITHER a 3-pin standard male fan header on a mobo OR a 4-pin Molex female power output connector from a computer PSU. You will note that the larger Molex male connector only has two of its "normal" 4 pins in it - that's because it only needs to connect to +12 VDC and Ground in the female connector. So that's the easiest way to splice on your old fan's connector. On the male Molex, the pin CLOSEST to the edge is the +12 VDC contact; it will mate with the Yellow wire of a female Molex output. The pin closer to the middle of the male is the Ground., and it will mate with a Black wire on the Molex female. Just be sure when you make your splices that the old connector's positive wire goes to the Molex male's OUTER wire. You will not need the 3-pin connector at all. (The third wire on the 3-pin connector is the fan speed signal, and your drive enclosure obviously does not have a way to connect that to anything. It is NOT needed for proper fan operation.)
BEFORE mounting the fan, examine its outer frame. It will have two arrows on it. One points AROUND the frame, and that's the direction of rotation when the fan power is wired correctly. The other arrow points THROUGH the fan, and that's the air flow direction. So mount the fan according to the arrow for air flow, and when you're done check the direction of rotation to be sure you did the splice correctly. If you get it backwards by mistake, no big problem - it won't damage the fan. Just re-do the splicing.
Thank you for the detailed and informative answer. I will do these things and report back. I very much appreciate the help and guidance.
I've done a lot of Googling for this issue. This forum post (your numerous replies) has become the comprehensive guide to computer case fans....
-sam
I've done a lot of Googling for this issue. This forum post (your numerous replies) has become the comprehensive guide to computer case fans....
-sam
I hope you can still help with a very similar problem. I was trying to get an additional fan to work and decided to test on the CPU port (bad idea, I know). I plugged in the normal 4-pin fan into the CPU fan port. Immediately after I started the machine (literally the moment I pressed the button) there was smoke coming from the CPU, so I immediately stopped it. After that I reconnected the CPU fan to the CPU fan port, started my system and everything runs ok with one exception. The CPU fan is always on full speed and extremely loud. The temp sensors show 30-40 degrees CPU temps while the CPU fan is still blasting at full speed. Any help will be appreciated.
I don;t know what type of new fan you tried to use on the CPU_FAN header. You say the smoke came from the CPU, but maybe it came from the mobo near the CPU, close to the CPU_FAN header. The fact that that header now seems unable to control the speed of the old "regular" CPU cooling fan suggest the header's circuitry was damaged. You could try this, just in case it works. Almost all recent mobos include a feature on the CPU_FAN header to be able to configure it to work with either the newer 4-pin PWM fans or the older 3-pin Voltage Control fans. A feature of the new 4-pin fans is that they CAN be controlled by a header that uses the older Voltage Control Mode (aka DC Mode) even though that is not ideal. So, on the hypothesis that the problem you have now is that the header for whatever reason cannot send out the proper PWM signal (and that would cause it to run full speed always), go into BIOS Setup to where you configure that CPU_FAN header. Change its control Mode from PWM to DC or Voltage Control, then SAVE and EXIT to save that setting. This might make the header use that older Mode and gain control of the fan speed.
- Dec 26, 2012
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None. That fan setup is intended for server support. It has a 7.2Amp rating and is not a standard 4pin motherboard setup but designed for more specialized applications.
Those connectors are nothing alike pwm, they just happen to be 4 pin because you have multiple speed options in the motor.
Why you'd want a 10k rpm fan in a pc is beyond me.
Those connectors are nothing alike pwm, they just happen to be 4 pin because you have multiple speed options in the motor.
Why you'd want a 10k rpm fan in a pc is beyond me.
- Dec 26, 2012
- 30,760
- 4,576
- 142,790
Then in order to do that, you'll need to know exactly what the wiring is for. It's not pwm. What does each wire do? 12v? 9v? Tach/sense? Being a back to back unit, it's almost certain to go to a splitter or controller that will operate the fan as a single unit, not seperates.
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