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So you want PWM control of your 3-pin fan?

andrew124c41

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I just went back to the manual. My MBs do not support voltage contol....no way to do that1
 

dmax

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Whether it is the Resistor OR a Transistor, it still needs to dissipate the heat, that is why Switch Mode supplies are used today; As one runs at, say, 55% efficiency,
and the other at 90%
A MOSFET circuit will only work, if it's designed to be installed in the 12 volt supply line, as has been stated previously.
If your board is the M5A97, then it DOES have 4 Pin Chassis Fan connectors, which will be
PWM; If you have 2 or 3 pin fans, then use the Controllers that I Referenced earlier, on the
Molex 12 volt supply line.
 
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I just went back to the manual. My MBs do not support voltage contol....no way to do that1
If your board is an M5A97 it does. Isn't that what you have?

It even states that it in the manual. Duty cycle is voltage control for the chassis fans. :)
 
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dmax

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Just occurred to me, you could take one of the PWM units, and Hack it, by replacing the Variable Pot. with a Thermistor;
But it would need some experimentation.
The LE version has the same 3 x 4 Pin Chassis fan connectors.
 
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Thanks for this post that I've used for my 3pin CPU Fan and it works.
I found a used MOSFET transistor referenced NEC 2SK3299 that fits fine, look ahead !
Nice, very compact too. What model fan?
 

Florent

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The fan is a cooler master i117 in place of the standard Intel too noisy.
 

Tanotis

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Hello, its been great to know that this thread is living so long and still being commented and a great thread to know the PWM thing and electronic hack nicely. If anybody listen then help me to answer for the following. I drawn a similar circuit suggested by Lazzer408 on a online simulator and tried to run it, It was simulated nicely without any error. Can anybody suggest me any for mods, or can I go ahead to make on the board for real test?
falsetad.png
 

Welni

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Hello, its been great to know that this thread is living so long and still being commented and a great thread to know the PWM thing and electronic hack nicely. If anybody listen then help me to answer for the following. I drawn a similar circuit suggested by Lazzer408 on a online simulator and tried to run it, It was simulated nicely without any error. Can anybody suggest me any for mods, or can I go ahead to make on the board for real test?
View attachment 84940
I'm sorry, i'm not an expert, but if you still need it, you might want a bigger resistor at the output. This one will dissipate 1,44W at 12V output. I'd also think about a cap to flatten the voltage. Alternations in the voltage may couse the fan to stick to certain harmonic frequencies of the signal.

On the other hand i have a question. Why don't we just use a high switch mosfet driven by the PWM signal and flatten the output voltage with a low pass RC filter? Does the tacho readout work only on 12V(H) and 0V(L) signals? Or can it be downgraded to like 5V(H) and 0V(L)?
I hope i'll get my reply sooner than the last guy :D
 

norq

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I had to start a new thread because I couldn't update the old one.

Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.

Tested, working. Enjoy.

First, many thanks for sharing. Sorry for necro, but I built this circuit and used a SUP50N03 (instead of the IRL530N) which can source hefty amps even at Vgs=2v and has low Rds(on): http://www.vishay.com/docs/66570/sup50n03.pdf ... it doesn't say it's a logic level mosfet, but specs show it should work just fine, unless I'm mistaken! Please correct me.

I want to use this to drive 6 three-pin fans with high static pressure, each drawing up to 0.5A. The PWM from my motherboard swings between 0.08 and 3.5v.

At the output of this circuit (where the fans connect) I don't get a constant voltage but the same pwm signal, swinging between 0 and 12v (rather than 3.5v). It kind of works - the fans seem to have a large-ish capacitance on the input which almost converts the PWM-like signal into a constant voltage. However, the rotor of some of them, when all 6 are in operation (driven by this circuit) makes an audible clicking noise at lower speed - they don't make that clicking noise if I supply them with an actual constant voltage to achieve the same rotation speed. I suspect the noise is from one of the coils inside the small circuit board of the fan, rather than the actual rotor.

Is this sort of pwm-like signal safe for the fans? Can anyone comment please?
 
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Welni

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Hi there,
The clicking sound shouldn't be a problem. In fact, many cheap PWM controlled fans make it. It happens because of the steep signal edges. Better fans have some integrated ICs to power the motor more gently and reduce the sound level. Anyway if you check datasheets of same fans, one with PWM control and one without, the PWM fan should be rated as louder. (fe. BQ pure wings 2 are rated for 19.2dB and the PWM version for 20.2dB).
And if you're interested, high side switching + cap works well on arduino, so you can try it with your PC.
 
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norq

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Hi there,
The clicking sound shouldn't be a problem. In fact, many cheap PWM controlled fans make it. It happens because of the steep signal edges. Better fans have some integrated ICs to power the motor more gently and reduce the sound level. Anyway if you check datasheets of same fans, one with PWM control and one without, the PWM fan should be rated as louder. (fe. BQ pure wings 2 are rated for 19.2dB and the PWM version for 20.2dB).
And if you're interested, high side switching + cap works well on arduino, so you can try it with your PC.
Thanks for replying. I used a SUP50N03 which can source 5+ amps at 2.4v, and goes up to 50+ amps with higher Vgs (it's also a fast switching mosfet). I built the circuit in the 1st post to drive 6 powerful fans rated at 12v, 5.4w. At full speed these fans together draw about 2.5 amps.

The mosfet is:
  • cold to the touch when the PWM duty cycle is higher than 80% ... happily sourcing 2.5 amps and staying cold.
  • warm to the touch around 60% pwm duty cycle
  • super hot to the touch below 40% pwm duty cycle ... can't keep my finger on it for more than a fraction of a second
  • even hotter at 20% pwm duty cycle.
Using a scope I noticed (as expected) that the output signal is another PWM signal with the same frequency and duty signal as the motherboard's, but sweeping 0-12v.

Why does it get so hot at low pwm duty cycles, given that the mosfet switches on/off with the same frequency? Is it just because the time it stays on is shorter (bigger harmonics, so higher AC load?). Can I do something about it with simple components?

Any simple circuit (without using level converters, ADCs, etc) such that the output is close to a level voltage, rather than a PWM signal? That would also be better for my fans since with this PWM-like output signal, not all of my fans spin at the same speed for the same PWM duty cycle (I was expecting some variation, as they essentially switch on and off, but not as much).

EDIT: I found this (replace hxxp with http - the forum doesn't allow me to post links): hxxp://forum.arduino.cc/index.php?topic=12651.msg95289#msg95289

By the way - the circuit in the above hxxp link will not output a full 12v to the fans as there will always be a Vth drop on the final mosfet in that configuration when the bipolar is off (unless I'm missing something) ... it should output a fairly clean analogue voltage level though, rather than pwm like signal
 
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norq

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For the simple circuit in the first post is there any danger of killing the fan in time? Some of the fans when mounted onto this circuit are clicking since the fan receives a square wave between 0v and 12v

I had a bunch of Sunon Maglev MEC0251V1 fans (pretty powerful 120x25mm fan) mounted on this circuit, and some of them no longer respond to the signal ... they either spin very slowly at the same speed when the PWM has <100% duty cycle regardless of PWM value, or spin at full speed when PWM=100% (i.e. no square wave, just 12V).

I'm trying to rule out whether it was dust or the circuit that killed them.
 
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norq

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1 year. I'm aware alternatives exist, I'd just like to know if said circuit can kill fans
 
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