AC Motor Move Very Slow

Discussion in 'General Electronics Chat' started by alfa15, May 25, 2016.

  1. alfa15

    Thread Starter New Member

    May 25, 2016
    I've an air purifier (AP) 3M Filtrete FAP03-RS, work in 220v AC.

    But I found the fan is moving very slow these days.
    Even, I already shift the control speed's knob to maximum.
    It unable to take the air, pass to filter then blow out the air.
    The flow was very weak or no winds blows.

    I already put some oil into the motor but doesn't improve anything.
    then I read some sources on internet says about run/start capacitor.
    I found box shape cap, with value 2.5 microFarad, 440v.
    Beside above cap, there are two PCBs, I think both use for controlling the fan speed and LED indicator.
    In the PCBs, there are two ICs, two non-polar caps (box shape, yellow), two pollar caps, resistor, etc.

    I don't know whether the cap was run-cap or start-cap. So, I do some experiments as follow:
    1. I turn on the AP, the motor spin but very weak, then I twist the fan using hand as much as I can. The fan spin faster but only hold for few seconds just because I twisted it. After some seconds the fan slow down and reach the same slow constant speed.
    2. I'm removing the cable attach to the cap, and just connect the cable together (bypass the cap). Turn on the AP, and found the motor not moving at all. I try to twist it manually using hand, as fast as possible. but seems the motor wont start. The fan just spin then slow down until stop by itself.
    3. I put again the cable into the cap. turn on the AP. the motor start as before with very slow speed.
    4. Then, I check another component, something like speed sensor near the motor. IMG-20160525-WA0007.jpg I remove this sensor by cutting the cable. Note, the capacitor is still installed. Surprisingly, the motor now spin faster and I can feel the winds is blowing. I'm happy but still not satisfied. Because I'm feeling the motor was not spin at maximum speed.
    5. If I connect again the sensor, the motor again spin very slow.
    6. Removing both the cap and the sensor also wont make the motor spinning.
    I didn't touch the PCBs part because difficult for me to check it and I have very little experience handling such components.
    FYI, I've multitester with me (only support ohm, ampere, AC/DC).

    According to above experiment, could someone help me to identify the problem. My question are:
    1. what is the capacitor's type in this AP? is it start-cap or run-cap?
    2. is it possible the sensor create problem? how to test this component is fail or not using multitester?
    3. is it possible to turn on the motor by bypassing the PCBs? the motor has 4 wires (red, black, green, blue)
    4. is it possible to check the motor coil whether in good condition or not?
    I really appreciate if anyone in this forum can answer or give me some clues regarding above questions. Thanks.
  2. MaxHeadRoom


    Jul 18, 2013
    The fact you have a slot opto sensor indicates a controller of some kind.
    The motor sounds like a PSC type, Permanent Start Cap motor, if it is not a friction problem due to dry bearings etc, then you may have to reverse engineer the board, most likely a small handful of components.
    Measure the resistance between all windings could detect if it is just a identical pair of windings or a multi speed motor.
    alfa15 likes this.
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    There should be a disc mounted to the motor shaft that goes with that sensor. The disc will have eitir small holes or open slots in it. If those holes or slots are not open to let the light through it will give the wrong reading to the controller. This dust or dirt can happen in a fan or air mover environment.
    alfa15 likes this.
  4. alfa15

    Thread Starter New Member

    May 25, 2016
    Thanks Max, I'll check the winding's resistance.

    Thanks shortbus.
    yes, there is disc mounted with open slots. I don't have the real picture now. it's looks like this db6f9794-fa29-4870-b54d-70a526ad5349.jpg
    but I suspect the problem is on the sensor, because the disc has large gap. anyhow, I'll try clean bot the disc and sensor.
  5. AlbertHall

    Well-Known Member

    Jun 4, 2014
    In your list of components you did not include a transformer so I wonder where the power for the circuitry comes from. Those two non-polar yellow box capacitors may be part of the power supply and it is my experience that capacitors used that way are often the cause of the problem. Their capacitance reduces and this results in a lower supply voltage.

    This is the kind of thing that I mean:
    Can you check the capacitance and voltage rating of those yellow capacitors. That will tell us whether they are candidates for this or not.
    How you check them using only a multimeter is another problem ;)
    alfa15 likes this.
  6. alfa15

    Thread Starter New Member

    May 25, 2016
    Thanks AlbertHall.
    Yes, there is no transformer, I've disassembled all parts, consist only fan rotor, ac motor (cap + sensor) and 2 boards of PCB.

    Okay, I'll check the circuitry and give you the details today after I reach home.