Take apart that PC Box Fan- see what’s inside brushless DC motor

PowMax brushless DC motor PC fan

I have been thinking about brushless motors for a while now, and I wanted to replace a small brush motor with a brushless one but wasn’t sure how to go about it. I looked up how they work to refresh my memory, then I thought I might make one out of permanent magnets and a few coils, but how was I going to control the switching of the coils? If I did use some kind of IC chip to do the logic it would add cost. Then I thought maybe I can just use some kind of analog circuit. Like maybe an infrared sensor tied to a transistor to time the pulses, or maybe a hall effect sensor. So Looked up “simple brushless motor” and found this site. It shows you how to make your own with all those sensors including a reed switch, pros cons etc.

I started to feel like making my own would be a pain and not efficient anyway, so I tried to think of a brushless motor I could find around the house and remembered that PC fans are brushless. I was pretty sure the PC only gave a voltage to the fan and did not offer any pulsing, so the motor must have some logic circuit built in. Perfect. I looked for photos online of PC fans opened up but a quick searched turned up nothing. I don’t know if a PC fan has enough power for what I’d like it to do. But I knew I was ready to take one apart.

So I found an old PC fan that I am pretty sure didn’t work and went at it.

I took pictures and video. Here we go.

Its called “PowMax” – well its dead now, so not so much Pow and not so much Max.

If you want to power it you need to offer 12Vdc. I am not even sure its speed would change if you gave it a less, since it’s a cheapo fan and it only has 2 leads. Black and Red. Which means its only for power and there is no third wire which can be tied to a sensor. This sensor usually gives feedback to the PC to make sure it actually running.

 

PowMax brushless DC motor PC fan

 

So if you pull up this nifty lil sticker on the back it also automagically picks up this little plastic disc that covers the shaft area.

PC fan de-labeled PC fan brushless motor de-labeled 2

So what you can see so far is a metal shaft and what looks like a plain plastic washer on its end. At first I wasn’t sure what this was and to remove the fan from its housing I started to pull and prod it, but it didn’t budge. So before I break the housing I figured I would check that plastic disc again. I poked it with a screwdriver and pried it off the shaft. Turns out its just a simple thin washer like disc split radially on one side. A very crude, simple, retainer ring. You can see it in this blurry picture below. And yes there is some grease in here, and as after pulling off the retainer you can see the bearing is an good old oilite brass bushing bearing. They are commonly used in motors and are the cheapest way to go. It’s a very good sign that this was a stock cheap-o fan.

p1050157-sm.jpg p1050158-sm.jpg

Now a tug at the fan and it comes off, but with some resistance. Its interesting because when it was all assembled the fan moved axially and bounced back when pushed like its on a spring. But there is no spring that resistance from axial movement is provided by the permanent magnets reacting to the wound coils iron core that the thin wire is wrapped around. The magnet in the fan actually keeps the fan in place, even without the retainer disc. Something to think about using in your own projects. You just wanna make sure your fan won’t lift itself right off the shaft when it reaches speed.. or maybe you do want it too.. Hmmm. Toy helicopter anyone?

 

So back to the dissection. Here is a view of the back of the frame and the back of the fan. At this point focus on the ring that is in the fan hub. This is a cylinder permanent magnet. That is what reacts to the changing magnetic field produced by the coils.

p1050159-sm.jpg

Now lets flip over the case and show you the coils. In a brushless motor there are two main parts, a rotor and a stator. Just like a brush motor the rotor spins and the stator stays put. But unlike a brush motor, the rotor contains permanent magnets and the stator has electromagnetic coils that turn on and off. Another important thing to note is that more brushless motor descriptions you find on the net will shoe the rotor and permanent magnets on the shaft and the stator in the shape of a ring surrounding the rotating shaft.

Here it’s a bit different. The shaft is spinning inside the electromagnets, but the permanent magnet is actually on the outside of the stator.

p1050160-sm.jpg

 

As for the magnet inside the fan hub, it seems to be made of similar material to what you would find on refrigerator magnets. Except this ring is magnetized in only 4 places equal distant to eachother. Its either that or the poles are alternating. You can test it yourself and let me know what you think. But I have a video here showing how my screwdriver skips to 4 places. So I think there are only 4 magnetized sections.

 

Anyway, now for some close ups of the stator.

The construction is pretty neat. There are 4 plastic posts that support the 4 electromagnets.

The electromagnets are made up of laminates, which are thin sheets of metal. This is pretty typical in motor construction. Its cheaper and easier to shape the laminates and stack them together than to make one big chunk of metal. A reader told me that the laminates are insulated from eachother to keep from overheating in larger motors. I am pretty sure there are only 6 laminates total. I think they are connected in the shape of a ring in the center which you cant see since its under the plastic. If I took out the laminate it would look like this…

laminate.JPG

 

 

The plastic is probably pressed on from the top and the bottom to complete the package before the wire is wound.

p1050162-sm.jpg

 

Also notice there is one transistor looking device on the board, but it has 4 leads, so I gotta see what it is. I will look up the code W41FB 7230.

The rotor is mounted to a PCB of sorts, but I am not sure there is any other circuitry on it. I haven’t been able to easily remove the stator from the housing. And I am not ready to break it, yet.

 

Take a look at this next pic. The bearing looks like its press fit into the housing. The housing is the darker colored plastic. Maybe I can just push it out. At first I thought the stator was press fit onto the bearing or the housing. But a closer look shows some space between the stator plastic frame and fan housing. Hmm dunno.

But if I pull hard enough I might break the housing.

p1050166-sm.jpg

On top of the bearing you can see gobs of grease doing absolutely nothing out there.

 

So what follows are two videos, one shows the fan staying on the stator without the retainer ring in place. And the other shows me searching for the magnetized sections of the magnet in the fan hub and discovering only 4.

 

 

Conclusion

 

Well since I didn’t remove the stator from the hub I am not sure you can just take the parts off and use them in your projects easily, but you could definitely replace the fan with a rotor of your choice. You would have to remove the magnet from the fan and install it into your new rotor. Or just clip off the fins and glue a new object to the fan hub.

 

Future project parts count = 2

  1. fan with magnetic ring
  2. brushless stator electromagnets with logic circuit

What’s next?

 

Give it 12Vdc and make sure its really dead.

If its alive give it 24 Vdc and see if it goes faster or blows the circuit.

If its really dead – take everything apart. Start with the fan magnet since you can use it later. Then try pulling the stator board off the casing. Then cut away the plastic stator frame to expose the laminates.

 

Questions for the public

 

Does anyone know what that chip transistor is?

Anyone know what the laminates probably look like?

Anyone try giving less or more than 12Vdc to obtain speed control?

 

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45 comments so far

  1. jesus on

    You should make a warning to other people that you don’t know anything about electronics and mechanics.

    Not knowing is not a sin, but don’t give stupid conclusions.
    Like what’s this washer do or it’s cheaper with laminates, no it isn’t I’m not going to explain it to you, but look little more carefuly and you would see an isolation between those ‘laminates’.

    ”But there is no spring that resistance from axial movement is provided by the permanent magnets reacting to the wound coils”

    wtf, are you crazy?! permanent magnet isn’t reacting to the wound coils, because there is no curent flowing trough them, they are reacting to the metal core, on which the coils are wound. omg

    That ‘chip’ is not a chip, because to name something a chip it has to have certain complexity.
    That is a transistor, or combination of two transistor which in turns are turning on the coils.
    Brushless motor does react to voltage minimum is mostly around 4volts, around 18Volts coils are starting to overheat and isolation burns, most PC fans will work till 35-40V and further, but in normal operation max is 13-14V.

    • Omar on

      If it’s free, don’t make complaints. I bet this article helped a lot of people to understand at least something about fans, even though information isn’t 100% accurate. It’s a starting point for a discussion.

    • Agustín Dall'Alba on

      That chip actually is a (analog) chip, and a fairily complex one. It’s a switching Hall (magnetic flux) sensor, with thermal compensation and all the bells and whistles. Pin 4 is ground, pin 1 is input, and the output switches from pin 2 to pin 3 when there’s a strong magnetic field going through the chip.

  2. jesus on

    Now I found out in your bio:

    “I am a Mechanical Engineer by trade. I design electro-mechanical products; consumer and industrial. I know a bit about gears, mechanisms, plastics, and some electronics and programming.”

    You design “electro-mechanical products”?! I only hope that you are joking, if you are not, I’m also electronic engineer and I must say you are a disgrace.

    Do not be offended but your knowledge is really weak for a title of engineer.

  3. prodmod on

    I know its not 100% right, that is why I have questions at the end.
    The title is “Take apart that PC Box Fan- see what’s inside”.
    It’s not called “How a PC Box Fan works 101″.
    I am a Mechanical Engineer, not electrical which is why I am asking what the transistor is.
    The article is left open so people can answer my questions and add comments, like you just did. So thanks.
    Try not to be such a grump next time. This isn’t wikipedia, it’s just a blog.
    If you have answers you should share them, that is the whole point of having a comments section.

  4. jesus on

    Yes, I over reacted, sorry.

    I was searching something and I couldn’t find it, I was mad and rest is history…

    Brushless motor can be divided in two main sections cheap and not cheap, that is sensorless and with sensor.
    PC fan motor, is(mainly) sensorless. A sensorless motor requires that the induced voltage in the un-driven winding be sensed and used to determine the current speed of the motor, or coils can be simply shifted.

    Brushless motors are used in such appliances because they don’t wear (as much as brush motors ), don’t make noise.

    Core on which are coils wound is made from several thin sheets of metal with good magnetic properties.
    Metal core is on purpose not from one picce, reason lies in electro magnetism, in short if the core would be from one picce induced current would melt(in bigger motors) the core. That is why they are isolated but needed for good magnetic properties.

    All motors, transformers and other electro-magnetic devices have cores of isolated sheets of metal.(and this is definitely not cheaper)

    Very good observation on permanent magnet on rotor(4 poles).
    Article is good but some mistakes do poke in the eye.

  5. prodmod on

    Thanks for the info. I remember an old colleague of mine mentioning something about eddy currents and how those insulated laminates help there too. Its that true for brushless motors? or was he maybe talking about something else, maybe AC motors?

    So what were you looking for? you might go ahead and post it here in case someone else comes along with the answer to your question.

  6. John on

    Yeah, the eddy currents will produce heat and create an opposing magnetic field which contributes to inefficiencies. The laminates are insulated from each other which reduces the volume of the conducting metal, therefore increasing resistance and reducing eddy currents.

    On the topic of the unidentified chip I’m going to have to disagree with jesus. First off a sensor-less controller for a brushless DC motor is usually going to be more sophisticated and expensive than one with a sensor. That is because a sensor-less system needs to read the back EMF field caused by the rotor to determine its position and speed. This is going to require additional circuitry involving a microcontroller, where as a system with a sensor is going to be a comparatively simple and cheap configuration. See your before mentioned website on “simple brushless motor”.

    Which brings me back to the mystery chip; I believe it is a Hall Effect sensor. A hall effect sensor detects magnetic fields and therefore would be able to determine the position of the rotor as the poles of the permanent magnets pass it. So unless I am wrong about this, calling it a transistor is not correct (although it does contain transistors in it to amplify voltage, most likely in the two transistor Darlington pair configuration). In my opinion calling it a chip is more accurate, but I think ‘component’ it is the most generic term and therefore the most appropriate in the case of an unidentified electrical device.

    Thanks for the article, the pictures were useful for clarifying a few concepts for me.

  7. prodmod on

    Thanks so much for your added info. And I am glad the pics helped you out.

  8. myke on

    thanks for the guide.
    i have been searching on how to remove the FAN of the dc fan for a long time.
    i have no clue on what to type in the google search.
    luckily found this one.
    helps alot man!

  9. Braden on

    I think Jesus is actually a 12 year old child!

  10. [...] in the way of air flow use the following link for the guide on how to remove the blades from a fan https://prodmod.wordpress.com/2007/02…less-dc-motor/ [...]

  11. Bushyetdah on

    Thanks for the info

  12. Harrirball on

    The circuit Board is a switch what reverses the magnetic poles of the copper wire causing the magnet to repel and spin it switches around 1000+ times a second

  13. slaska on

    That “chip” is a hall effect sensor. It detects the presence of a magnetic field on closes the internal switch to allow current to flow in a similar fashion that a transistor operates. This hall effect sensor allows for commutation (reversal of poles every 180 degrees) to take place.

    The sheets of metal reduce losses in the form of eddy currents. Losses here are basically the heat.

    Increasing the voltage probably won’t kill the fan unless very high but reversing the voltage ;however, will since the diodes on the circuit will break through and it simply won’t function as a diode anymore and you will have no commuation.

  14. Aliamyz on

    Hi guys,

    Nice blog.

    My question is,i’m going to build an Highland terrarium for growing highland nepenthes.(pitcher plant).
    So maybe i thought i can use these CP fans inside the terrarium for air circulation since it’s really cheap and unnoisy.
    Can you guys help me on how to install it inside the terrarium.
    I’m going to fix it in a 5 x 4 x1.6 feet terrarium.
    About two fans just for air circulation and nothing else.

    My main concern is HOW TO MAKE IT WORK?

    Thanx and regards,

    • Omar on

      I’m sure you have already made it work. But if you haven’t yet, all you need is an external power source (transformer + rectifier or switching) and some electronics if you want to be able to vary their speed. The rest are screws and a mounting hole.

  15. Reaver on

    Uh, so yeah my cooling fan crapped out on me today this was helpful since I’ve never taken apart a fan before. Almost ripped it apart with force.. Twice.

  16. muld3r on

    this “chip” or “transistor” is a hall sensor and it have to switch current into coils… it REALLY IS a hall sensor – I use it to measure rpm of my powerball…

    • Omar on

      The sensor showed in the pictures isn’t just a hall effect sensor. It has 4 leads and there are no transistors to interact with the coils…it’s an integrated controller with hall sensor included.

  17. James on

    Wow…

    all I can say is wow…

    to those first two reactions. I find the human race despicable sometimes. A guy puts forth an effort to learn something and two people attack him? I am just speechless that people like that even exist, it is unfortunate the internet seems to fuel them. O well, grumpy buggers tend to live a miserable life anyways, so I suppose their very existence is punishment enough.

    Good job prodmod on trying to figure this out on your own. I found it informative and myself too learned some things. I design high end servo drives and too was curious how they manage this in such a low cost an efficient package.

    Thanks

  18. James on

    Has anyone ever tried variable speed control on this type of fan? I assume the internal electronics will keel over if the voltage is varied?

    I’m just intending to LC low pass filter a 24V PWM to a 24V fan to vary its voltage from 12 to 24.

    • Omar on

      James, a PWM signal of low enough frequency can be applied to vary speed without harming the internal components. The low pass idea isn’t good by itself as the current needed by the fan will discharge the capacitor faster than it is charged. What you can do is use the “average voltage” after the low pass filter as a reference voltage to drive a transistor or operational amplifier.

  19. Omar on

    I think I found what those 4-leads chips are: two-coil fan drivers. They are a one-chip solution for driving two coil
    brushless DC cooling fans. The IC contains a Hall-effect sensor, dynamic offset correction and low side output drivers. Based on the information provided by the datasheet I found and the connections that the fans I have show, I think that both chips are equivalent. Hope this helps anyone interested in the subject. Regards.

    • Omar on

      adding to what I’ve already said.

      Questions:

      Does anyone know what that chip transistor is? —->

      “two-coil fan drivers”

      Anyone know what the laminates probably look like?—-> No idea what you are referring to…laminates look like laminates, thin pieces of metal.

      Anyone try giving less or more than 12Vdc to obtain speed control?—-> The correct answer could be found if you knew something about the bldc motor. But supposing that the fan has specified its operating voltage along with the current I wouldn’t go any further for a continuous operation as it has been design to work under those conditions. Higher voltages will make the IC logic blow (above 18V typical for those chips, absolute maximum rating) and could make the wound coils overheat and thus reducing the bldc life expectancy among other side effects. Lower voltages are allowed, but there’s a minimum voltage needed so that the bldc defeats the forces that oppose (like load inertia) to the torque that the motor produces. Typical values for a 12V fan with current consumption below 200mA is 7V to start spinning smoothly. Speed control can be achieved with PWM controlled switches (fets, transistors,…) without reducing the voltage applied to it (simplest way). Voltage regulators are another option (less efficient, higher power dissipation). The ultimate control is achieved through coils switching (most complicated but most effective and efficient).

      Hope all this info helps…I’m not an expert but I try to do my best according to the depth given here.

    • Omar on

      Time goes by and knowledge is gained. Some of my comments in reply to “jesus”‘s first comments were “moderated”. I’m very upset because I haven’t had the chance to freely express myself, as jesus had, but that decision isn’t mine. Extracting the main idea of what I said in that missing comment, that chip is a chip as some logic reside inside it. It is an integradted circuit that it has output transistors, switched by the hall effect sensor by means of a predriver. Arrogance isn’t a quality, so lets say that if an assumption of a “two transistor combination” is made, there has to be somw logic to control them (to do the switching) as the transistors by themselves can’t switch freely.
      I went on investigating those chips and I found that every cooler’s RPMs can be sensed, even though the “yellow wire” isn’t present. The yellow wire signal is just one of the transistors “on-time” pulse, so with another transistor and a pair of resistors, the output signal that is generally connected to the motherboards, can be generated. I’m thinking about testing one of those chips and put togheter a note with the information I found up to know. So if someone needs or wants to know how they work, send me an email and I will gladly share it.
      Regards.

    • omarai on

      I made my own blog going further in the electronics involved. Take a look at http://omarai.wordpress.com/.

      • Schnozzole on

        Thanks for taking the trouble to share your blog…. Spanish is not my mother tongue but you offer an opportunity to do some technical practice in a language I am trying to learn.

  20. Nipuna on

    LOL. I don’t know about you but here in Sri Lanka we learn about eddy currents and bits about hall sensors for high school physics.

  21. Nipuna on

    As for the power problem, you can try fixing some D400s for each coil and switching the current through them.

  22. Nipuna on

    BTW I discovered how to take out the circuit+stator assembly; just undo the wires from the grips and twist the stator until it comes off :) it’s held there by friction only.

  23. Wayne Sallee on

    I was just now able to fix a fan Hall sensor by using heat therapy. I don’t know how long it will last, but it’s working.

    I took a soldering iron, and touched each of the tips, alternating back and forth between the electrical connections soldered on the PC board. The idea behind this is that it heats up the components inside the sensor, causing realigning and reconnecting. After heating it up to what I felt was a safe amount, not too much, I let it cool, put the fan back together and tested it.

    And it works.

    I’ve done this heat therapy with a graphics processor chip, and a USB wireless chip.

    Keep in mind that this may only be a temporary fix, but it’s worth trying.

    Wayne Sallee
    Wayne@WayneSallee.com

  24. Joseph on

    This blog entry has been helpful since now I am investigating BLDC drive. I had taken apart a computer-type fan a few years ago, and so, I could only the still find rotor/blade. This blog answers a lot of the questions that I was wondering about.

  25. Lyndon Gonzales on

    Thanks for the article. I’m in the process of taking apart a 3 wire computer fan and I found your article helpful. I haven’t read the rest of your blogs, so, have you done anything with your disassembled computer fan?

    My plan is to make my own mini motors to replace the motors on those cheapo rc helicopters. I figure that the brushed motors those come out with are too weak and heavy and It’d be nice to do this kind of mod.

    Thanks again,

  26. Heya i’m for the first time here. I came across this board and I in finding It truly useful & it helped me out a lot. I am hoping to provide one thing back and aid others such as you helped me.

    • weasel5i2 on

      ^^^ Spammer. Please delete this comment and my reply as well.

      I’m looking for a way to make a brushless fan able to spin in both directions. Still reading the comments.. :)

  27. Raven on

    i was hoping this might help me in some of the problems i am having however, after seeing your pics and videos i realized that i may be able to help you, (which is nice). i have been trying to build the bedini circuit, but have been experiencing technical difficulties, anyways heres a video you might want to check out im not sure of the link you’ll just have to search for the title which is called…Imhotep – Bedini Fan Project Part 1, i would suggest checking out all 3 of them as im not sure which part contains the info youre looking for. i hope this helps and good luck

    • weasel5i2 on

      Raven, I built a Bedini/Imhotep fan circuit. It was not impressive at all. Voltage output was high, which is normal for a coil field collapse, but the current output was so insignificant I felt robbed for spending $20 on box fans. :P

  28. Vijay on

    do you data sheet of W41F IC?

  29. Moses on

    Hi, anyone know if the hall sensor can be modified to allow the fan to spin in different directions by alternating the current? I’m using PC fans to drive a boat controlled by an arduino. I need to be able to make the fans spin in both directions so that the boat can reverse when it senses an object in it’s way. At the moment the fans only spin in one direction and dont work if the current is switched.

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  31. Aloe Vera Hair on

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  32. Thunder Storm on

    That black square thing is a hal efect transistor that pick up the position of the rotor

  33. Sdijbjmj on

    Hey you really helped me out a ton. Thanks man… As for the “experts” on here mocking and belittling you about your knowledge…. Screw them! You helped me do exactly what I came here to do and that is take apart a PC fan. Thanks again

  34. Paul -Kiwinet on

    On closer inspection – the W41FB appears to be a fully integrated standalone motor driver IC, :-

    “W41F is designed to integrate Hall sensor with complementary output drivers and frequency generator together on the same chip, it is suitable for speed measurement, revolution counting, positioning. It includes a temperature compensated voltage regulator, a differential amplifier, a Hysteresis controller, two open-collector output drivers capable of sinking 400mA current load and an open-collector frequency generator capable of sinking 10mA current load. An on-chip protection diode is implemented to prevent reverse power fault.” – Quoted from the datasheet.


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