brushless motor PC fan? - Page 1
Forum section: electronics / beginners

author: Lucky-Luka
author_rank: Unknown
timestamp: December 14, 2020, 09:32:04 am
content: Hi allShouldn't brushless motor have 3 wires?Is this a real bushless motor?https://www.amazon.com/uxcell-60mmx60mmx15mm-Brushless-Cooling-Cooler/dp/B01KTNU3ZYWhen I see 3 wires PC fans one wire is a pwm output, so it's the same question as before.https://www.amazon.com/Variable-Bearings-Computer-Receiver-Incubator/dp/B072NCYQRY/ref=pd_sbs_328_3/139-5993084-0046763?_encoding=UTF8&pd_rd_i=B072NCYQRY&pd_rd_r=952c839c-476d-4b69-a6e1-90aa8a0aebd8&pd_rd_w=UH2Bi&pd_rd_wg=ysKzE&pf_rd_p=ed1e2146-ecfe-435e-b3b5-d79fa072fd58&pf_rd_r=S450T06MTPYNNEPTR3A0&psc=1&refRID=S450T06MTPYNNEPTR3A0Maybe those with 4 pin (1 pin is a pwm input)?https://www.amazon.com/Noctua-NF-F12-PWM-4-Pin-Premium/dp/B00650P2ZC/ref=sr_1_4?dchild=1&keywords=noctua&qid=1607938249&sr=8-4Cheers

author: langwadt
author_rank: Super Contributor
timestamp: December 14, 2020, 09:40:26 am
content: hard to find a fan that isn't brushless, the driver is build in so it only needs two wires for power

author: Lucky-Luka
author_rank: Unknown
timestamp: December 14, 2020, 09:47:14 am
content: I am not an expert in brushless motor: I'm just beginning to understand how to control them using a PIC. Why do common brushless motors, those for drones for instance, have 3 wires then?https://www.amazon.com/DYS-Brushless-Outrunner-Multirotor-Quadcopter/dp/B06XBXRH6J/ref=sr_1_4?dchild=1&keywords=brushless+motor&qid=1607939220&sr=8-4

author: langwadt
author_rank: Super Contributor
timestamp: December 14, 2020, 10:12:52 am
content: Quote from: Lucky-Luka on December 14, 2020, 09:47:14 amthe pc fan has the driver build in

author: Zero999
author_rank: Super Contributor
timestamp: December 14, 2020, 05:20:00 pm
content: Quote from: langwadt on December 14, 2020, 10:12:52 amYes, that's true. Here's more information.https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/brushless-dc-motor/

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 15, 2020, 12:16:04 pm
content: Those fans have very simple motors. It's just a permanent magnet in the rotor, an electromagnet in the stator and a HALL switch. The magnet turns on, which rotates the rotor untill the magnetic fields are nearly aligned, and then the HALL switch turns of the electromagnet, and inertia keeps the rotor advancing, until it's so far away that when the HALL switch turns the magnet on again, the rotor keeps advancing instead of going back.So the motor is just pulsed, and has no continuous torque such as the 3-phase variants.

author: CaptDon
author_rank: Super Contributor
timestamp: December 21, 2020, 06:38:31 pm
content: Maybe they missed a simple point,Black = negative and return referenceRed = usually 5vdc or 12 vdcWhite = Tachometer wire to tell CPUthe fan is running and at what speed.Some fans also have a built in thermalspeed controller so tach speed becomessomething to watch via the white wireand is usually a square wave a 2 or 4pulses per revolution.

author: amyk
author_rank: Super Contributor
timestamp: December 21, 2020, 11:16:02 pm
content: Quote from: Doctorandus_P on December 15, 2020, 12:16:04 pmThey are usually bipolar, 4-pole, otherwise they could not be self-starting.

author: David Hess
author_rank: Super Contributor
timestamp: December 22, 2020, 06:02:38 pm
content: Those are actually brushless *DC* motors meaning that they include an internal inverter to produce the 3-phase AC required by the motor.Drone motors have the same construction but rely on an external inverter to produce the needed 3-phase waveforms.

author: wraper
author_rank: Unknown
timestamp: December 22, 2020, 06:05:20 pm
content: Quote from: Doctorandus_P on December 15, 2020, 12:16:04 pmIt's not that simple and you forgot about motor driver.

author: exe
author_rank: Unknown
timestamp: December 22, 2020, 08:15:34 pm
content: Yeah, most fans I touched could detect stalls, and restart after a while. Some of them also, afaik, tried to first check if it's still blocked, and only then start at full speed. The third/forth wires are to sense/control speed.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 23, 2020, 02:23:35 pm
content: Even the cheap ones have had more complex driver ICs for well over a decade now. The reason is, the IC is produced in masses and costs maybe a cent. The IC contains the MOSFETs to drive the phases, hall sensor feedback, stall detection & restart logic.The motor itself may be 2-phase (2 poles per phase, total 4 poles) or 3-phase (2 poles per phase, total 6 poles). I guess the 2-phase designs are still more usual. Either way, proper torque is delivered regardless of angle, because the motor never is 1-phase. There may be quite a lot of torque ripple, of course, but nowhere near 100%, more like 50%. With simple hall-based switching without interpolation, the electrical angle oscillates +/- 45 deg around the optimum 90 deg phase shift for the 2-phase, and +/-30 deg for the 3-phase variant.I wouldn't be too surprised to hear they interpolate the rotor location and chop a sine or even run a FOC today, or if not today, tomorrow.

author: exe
author_rank: Unknown
timestamp: December 23, 2020, 02:48:47 pm
content: I ask a question here about those dc motors. I wanted to use motor to cool down a linear power supply. I tested one motor, and it looked absolutely noiseless. I was impressed, looked like a resistive load. I bought a few more, but different fans. They all created considerable noise on the power rail with high-frequency spikes typical to smps (unfortunately, I don't have an oscilloscope screenshot to show, so hand-waving here). I wonder why I've seen such a difference.

author: xani
author_rank: Frequent Contributor
timestamp: December 24, 2020, 01:18:42 am
content: Quote from: exe on December 23, 2020, 02:48:47 pmThe other ones were most likely either brushless or driven internally by PWM. No idea what the "noiseless" one might be, might be just plain brushed DC motor with a cap.Either way you should just assume noise will be there and design circuit with that assumption, you certainly don't want to be looking for "that special fan" if it ever fails

author: Andrew LB
author_rank: Contributor
timestamp: December 31, 2020, 04:18:47 pm
content: All PC fans use brushless motors. The vast majority of which are single-phase motors using 4 poles, 4 stator slots. A few companies like Noctua use three-phase motors which are 4 pole, 6 stator slots. And apparently there are some new San Ace fans which have 12 stator slots but they're probably screamers made for industrial applications.Fan noise is due to a multitude of things such as RPM, bearing type, blade design, flow restriction, and the type of brushless motor.

author: Zero999
author_rank: Super Contributor
timestamp: January 01, 2021, 10:07:05 am
content: Brushless fans are generally less noisy, than brushed, because there's no arcing.I've never seen one with a single phase motor. They're all two, or three phase. Single phase would make it hard to start.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 01, 2021, 01:12:00 pm
content: Definitely two phases. 4 poles, 4 stator slots should give this away instantly.Since it has its own inverter (however simple) built-in, there is absolutely no reason to ever consider single phase. Two phases are enough to define the rotating vector properly. Extra phases bring extra smoothness (especially if the drive signal isn't sinusoidal, like it isn't with cheap BLDC motors), but two is the sane minimum. The phase difference in two-phase system is 90 degrees.

author: exe
author_rank: Unknown
timestamp: January 02, 2021, 09:17:17 pm
content: I did a very quick-n-dirty setup and measured noise of four random fans I had at hand. Beware of different vertical scale and timebase. I used AD2, ac-coupled with a 100n ceramic capacitor. Long leads all over my bench, no external decoupling applied. Even in this setup it's clear fans have very different noise. They also have different power ratings. I'm keen to try a Noctua, I think I have one laying somewhere, but I can't find it.