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landyacht318's avatar
landyacht318
Explorer
Jun 26, 2016

Speed controlling computer fans

For years I have been using the Silverstone fm121 as it comes with a remote mounted speed controlling potentiometer, goes as high as 110 CFM and 0.4 amps consumption.

It is fairly quiet for this amount of airflow and there are other fans that draw much more amperage for less airflow and make more noise doing so. I have a fm121 now in the process of failing after many years of faithful service in a harsh environment.


But since i first settled on the Silverstone fm121 as my favorite 120Mm computer fan, Noctua fans have come out. I put a Noctua NF-F12 on my Fridge condenser pushing instead of pulling, and duty cycle dropped while I saved 0.07 amps with this fan over the one provided, and of course it is much much quieter.

Noctua has now offered 2000 and 3000 rpm Industrial versions of the 1500 rpm original. Some are IP67 rated, some 3 wire some 4 wire pwm.

http://noctua.at/en/products/fan/industrial

I am not sure how the other two wires on the 4 wire versions control the speed. in the past when speed controlling non Silverstone computer fans, I used a 24khz PWM motor speed controller and life was good.

These 25KHZ PWM controllers met unfortunate ends due to a case of bumbling halfwitted jackassery, and the 13khz PWM LED dimmers I now have, cause that annoying humming sound from the motor.

Basically I want the 3000 rpm NF-f12 version on a speed control, A controller which is manually adjustable and not huge, does not waste significant amounts of power, and of course, will not cause the humming.

The Noctua NF-F12 3000 rpm version is rated at 0.3 amps and 186.3 cubic meters per hour which translates to 109.9cfm, basically the same as the silverstone fm121, but for 0.1amp less consumption. A little noisier at full speed but perhaps the Tone is more acceptable.

They have a 140Mm 3000 rpm fan capable of 158cfm too which interest me as well. I could cut a larger hole in my shroud to accept a 140Mm fan in place of a 120mm.

IAnother fan i'd love to control properly is an 'Original Delta TFC1212DE 12cm 120mm DC 12V 3.90A 252CFM 4pin PWM with Speed Sensor Server Inverter Axial Case Cooling Fan'
I affectionately call it the screaming banshee.

https://www.amazon.com/gp/product/B00L5XEKOS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1#Ask

This fan is insanely powerful, sending a dense narrow column of air a good distance at a good speed, but my PWM controller could not tame it enough. It would slow to about 65% speed then turn off, still consuming 2.6 amps, and moving too much air, and making way too much noise, and is mostly unused.

I'd love to be able to slow this insane ~ 4 amp fan down to near whisper quiet levels at acceptable wattage consumption, and also have the godmother of all white noise turbo boost jet engine fans being able to reduce barometric pressure, and drown out neighborhood screaming children having their frequent early morning chernobylesque meltdowns, and barking dogs inside my rig when exhausting at full speed.

IN general I want to learn more about how to best control these fans through the ways their speed/rpm was intended to be controlled by an actual computer via the 2 extra wires provided on these fans.

I am kind of a ventilation Nazi and my lack of understanding about how to best control these 3 and 4 wire fans for full manual speed control, without the sub 22KHZ humm, is bothering me.

Please Ventilate, I mean, enlighten. me.

35 Replies

  • One or three phases, the controller chip is still what you need to interface with unless you gut it and setup your own VFD.
  • The 120mm Noctra has a 3 phase motor, maybe the only one out there, so they are going to whine anyway, but it's almost inaudible even standing next to them, and I have four. Noctra pride themselves on SILENCE. If any of this was objectionable they wouldn't be doing it. I have no issues with anything whatsoever heating up or I wouldn't be doing this and turning current into heat in the first place.
  • The 4 wire fan is pretty easy to control, and shouldn't make any extra noise being controlled properly. Trying to pwm the power to such a fan will only result in headache, as the internal control chip will fight you the entire time.

    4-wire "pwm" fan:
    Connect just + and - the fan will run at minimum speed, which might be good enough?

    The remaining two wires are a hall-effect output and pwm input. The pwm input connects to the controller chip inside the fan, and controls the speed within a range defined by the manufacturer. The hall effect output is "open drain" emits a series of pulses corresponding to the fan's rpm.

    Connecting the pwm input to + through a 10k resistor will operate the fan at full speed. Connecting the hall-effect output to + through a 10k resistor will make it pulse low as the fan rotates. Without a "pull-up" resistor there is no output on this wire. This gives you a safe means to tell which wire is which.

    The following website details a few simple circuits to generate the PWM signal needed to interface with the fan's internal control chip.

    http://www.overclockers.com/pwm-fan-controller/
  • I have about 5 of those LED PWM dimmers on hand. They have made every fan I have used them with Whine annoyingly loud when the rpms are reduced. I can't tolerate the whine. I guess it is the windings in the motor whining. Perhaps the Noctua's IP67 rating would prevent the whining.

    The 25 KHZ PWM 10 amp motor speed controllers, well the whine was outside my hearing range, but they released their smoke due to bumbling jackassery on my part.

    These controllers had some heatsinks( with no thermal grease) and they would get quite hot powering the screaming banshee, but the LED dimmer had no heatsinks and had no issues powering this fan and did not get hot. No idea about this discrepancy. 13 vs 25KHZ?



    I think I once measured the output and it was the ground on the LED dimmer out, which did the PWM thing. Would it be possible to feed the fan battery voltage on the red and black and use the (-) output from the dimmer to the blue PWM wire?

    I see the computer fan speed controllers marketed as such are rather expensive.

    I just want the full speed control throughout the full possible ranges of the fans, including the screaming banshee, adjustable via a remote potentiometer. I thought perhaps it was better or allowed more rpm range to use the provided PWM wire on the fans to control speed rather than running red and black into a motor speed controller and then to fan.

    I could order more of the 25KHZ motor speed controllers but they are kind of bulky, exposed and fragile, and this led to their previous demise, with the addition of sufficient bumbling jackassery on my part.

    Also the Screaming banshee Fan was not able to be tamed sufficiently on these. I'd love to tame the screaming banshee to tolerable noise and amperage consumption levels, but at the minimum speed via the 25KHZ controller, it was still way too powerful, noisy and an Ampwhore.

    The LED dimmer, it would cut out at the same exact speed on the screaming banshee and read about 5.6 volts on my DMM when it cut out, though I know this is not an accurate voltage reading..
  • IMHO-- you don't need those extra wires in RV service unless you really wanna get anal with control systems, although that might be fun. One is an output tach, and the other is the PWM Control input from the control board that you don't have.

    You can do it two ways: Use something like THIS with all the 12v drivers stripped out and grab the PWM pulse direct to feed the fan, or do what I did and feed the PWM controlled voltage direct to the fan input and snip the other two wires. That's what I did and it works fine. I'm running 4ea. 2000 PPC from one of these eBay boxes to turn them around 40% and they start just fine. Running these on high I really worry about possible causing a flameout, and I think it's already happened. If I were to do it again I might grab the 3v waveform and play with it a tad. If you haven't bought them yet, take a look and see if they make a 120mm FLX version. That's the one I have in an 80mm version in the fridge box.

    The next step is to install the ARP and drive the Noctua's from the ext. fan control

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