Extremely easy fan controller using PWM output of a MB

[TBSN]

SO, If I get lets say a sythe Ninja for a P5B-dlx (socket 775), will the three pin fan (I think it is a 3 pin fan..) fit into the 4pin connector on the board, or will I have to do some horrible solder job to get it to work? (please say no...) Thanks for the info

 

[Mark R]

Originally posted by: yiranhu
The interesting thing is that if you have a motherboard that has a 4-pin fan connector (my DS3 has 2 - one of them is unused because most of case fans do not come with 4 pins), then the temperature dependent PWM wave generator is build in. There is no need to replicate that on a separate board. All you need to do is to connect the 3 relevant pins of output of the 4 pin fan port to a MOSFET switch and then connect the switch output to the 3 pin or 2 pin fan. The extra pin in the 3 pin fan can be connected to the extra pin in the 4-pin connector to allow for RPM monitoring. Then the only thing you need to do is to enable temperature based fan control in the BIOS...

This should work fine. After all, that is exactly what '4-pin' PWM fans do internally.

The FAN has a built in MOSFET that turns the motor on/off in response to the PWM signal. The reason for 4 wires is so that the speed sensor doesn't get turned off by the PWM. If the speed sensor gets turned off, then speed readings will be spurious.

Just use an N-channel MOSFET as your switch (make sure you use a logic-level FET), and hook it up in open-drain configuration. You will need a pull up resistor connected to 5V on the PWM control signal, because it is an open collector output. Rather awkwardly this means you'll need a 5V regulator (or a 5V zener, to stop the 12 V supply to the fan sizzling the PWM controller on the mobo)

However, if you don't mind losing the speed monitoring funciton, you could build a 4 pin -> 2 pin PWM converter for about $2.

If you want PWM control and you want to measure the fan speed - you need a 4 pin fan, or you need a controller that converts the PWM output to DC.

 

[yiranhu]

Originally posted by: VinDSL

Originally posted by: yiranhu
3. what is ungodly racket? For me that's the noise when my case fans (3) runs at full speed.

Why don't you just undervolt them in a conventional manner?

Originally posted by: yiranhu
4. Who in here said intel PWM spec before VinDSL quoted someone saying that?

Um... See your title... reciprocal relationship, yes?

Actually, I think I see the original intent of this thread now...

I was working on an inverter at work yesterday. It supplies current to a conveyor motor (shaftless design). The inverter was working just fine, but it wasn't getting input from the encoder, so I threw a scope on it (spectrum analyzer actually). Nothing was coming out of the encoder except 60Hz background noise. I was looking for a square wave from the encoder... blah, blah, blah...

That's when it struck me!

I think you're saying... why not use the output of the spare mobo PWM header, as an input signal, to trigger a circuit that would control the speed of ALL fans in your computer, not just the HSF, e.g. using the mobo PWM output to automagically adjust the fan controller settings for your case fans, et cetera.

Is that 'the point' of this thread?

If so, I'll redact my statement about PWM being for lazy, stupid sheeple. That would be a great idea!

YES! that's all i'm saying. Since the computer is already creating a PWM control output, let's use it to power the fans... That's all i'm saying

 

[yiranhu]

P.S. Thanks Mark for that info. That's what I was looking for...

 

[TBSN]

...so If I buy a mobo with a 4pin cpu fan header, will a normal 3pin fan fit in the socket?

I don't care what it does, the fan just needs to spin to cool the cpu. After that I can worry about speed adjustments, etc.

 

[yiranhu]

Originally posted by: TBSN
...so If I buy a mobo with a 4pin cpu fan header, will a normal 3pin fan fit in the socket?

I don't care what it does, the fan just needs to spin to cool the cpu. After that I can worry about speed adjustments, etc.

If you just want it spinning, then you just need to apply a 12V power to the fan. Unfortunately 3 pin connectors do not connect into four pin connectors. So you have to rig a little connection yourself.

1. Take little pieces of wires (about the same gauge as the ones came on your fan), and connect the appropriate pins from the 3 pin connector to 4 pin connectors. It's extremely straightforward (+12 to +12, Gnd to Gnd, Sensor to Sensor). Note that if you don't care about the fan speed reading in BIOS, that sensor to sensor connection is not necessary.
Here's a tip on how to make this connection: If you have a old power supply somewhere that you can salvage for parts, find the floppy connector on it. It is a four pin connector. You need to file down the little notch so that it will fit in the 4 pin fan header on your MOBO. Then connector the wires and plug in!

2. If you don't have any motherboard fan headers available, you can always use the 4 pin molex connector on your power supply (I hope you have one of those available ). The 4 pin molex connector has +5 GnD GnD +12. So you only need to connect +12 to +12 and Gnd to one Gnd. If you don't want to do this yourself, you can go to microcenter and they have this conversion available commericially for 2 bucks or so (not worth it in my opinion since it's just 2 pieces of wire).

These two ways will get your fan running. Alternatively, you can buy a fan controller (Newegg has a few, compusa has a voltage based one really cheap, and so on). Then just plug the fan into that. Those will have 3 pin headers so your 3 pin fans will fit.

Hope this helps. Just remember, all you need to do to make a fan run is to apply 12 volts (actually anything above 5 will probably do it) to the fan.

 

[TBSN]

great, thanks for the info. I'm surpised this is so complicated, seeing as the CPU HSF should be able to connect seamlessly with the CPU fan header on the mobo. Does anyone know whether or not the fan headers on an Asus P5B/D would have 3 or 4 pins? Also, what about the CPU cooler fan? I know the Artic Freezer Pro has a 4pin fan, but what about Sythe coolers? Thanks!

 

[Operandi]

Originally posted by: TBSN
great, thanks for the info. I'm surpised this is so complicated, seeing as the CPU HSF should be able to connect seamlessly with the CPU fan header on the mobo. Does anyone know whether or not the fan headers on an Asus P5B/D would have 3 or 4 pins? Also, what about the CPU cooler fan? I know the Artic Freezer Pro has a 4pin fan, but what about Sythe coolers? Thanks!

Hold on... it's not that complicated at all.

You can connect a standard 3-pin fan to a 4-pin PWM header. The fan will run fine, some boards will just run it at 100% (no fan control) while others such as your Asus boards have any option in the BIOS to enable fan control over 3-pin fans.

 

[TBSN]

ahh OK, thanks.