How to test a 240vac floor fan motor?

Discussion in 'General Electronics Chat' started by CD-RW, May 21, 2011.

  1. CD-RW

    Thread Starter Member

    Feb 26, 2011
    33
    1
    I have a floor standing fan that's giving me some problems. At first I thought it was the 3 speed switch. But I noticed if I started the fan by spinning it by hand, it would then work OK.

    I then found a post telling me that if the starter capacitor (2uf > 250 vac) was kaput, this would be the symptoms.

    Putting a neon tester on each side of the cap shows live on both connections of the capacitor. Not done the standard capacitor test, as I'm sure it's the capacitor that has gone AWOL.

    Now the fan will not even run if I push it to start it.

    Before I buy a new starter capacitor, is there any way to test that the motor coils are OK please? If so I'll get a new starter capacitor and fit that.

    TIA :)
     
  2. Hagen

    Active Member

    May 8, 2010
    30
    1
    This simple test will check for continuity through both the starting and running winding. Isolate the motor from the power supply. Leave the capacitor disconnected. With your ohmeter, measure the resistance between the 2 wires that normally connect to the capacitor. This value indicates the total resistance of the running and starting winding in series. Next measure the resistance between the 2 points that normally connect to power. This is the running winding resistance. If you measure and open circuit in either case, you have motor problems. Also, make sure the shaft spins freely, and has little or no side to side play.
     
  3. #12

    Expert

    Nov 30, 2010
    16,337
    6,820
    Also check to see that there is no conductivity to the case from ANY motor winding. Motor windings sometimes get shorted to the case, and that means the motor is kaput, or soon will be.
     
  4. CD-RW

    Thread Starter Member

    Feb 26, 2011
    33
    1
    Thanks for that reply Hagen.

    I printed out your suggestion, and here are the results.

    I removed the starter capacitor from the fan, and the wires that were connected to the capacitor read .775 on the 2K range.

    I took the fan back off, and disconected the wires going from the motor to the switch.

    There are five wires going the the motor:

    Brown, Blue, White, Grey, and Green & Yellow (Earth)

    With the meter on the 2k range again, I took the following readings:

    Brown -> Blue .066
    Brown -> White .109
    Brown -> Grey 1. Nothing
    Blue -> White .175
    Blue -> Grey 1. Nothing
    White -> Grey 1. Nothing

    So is it fair to say the motor winding is at fault?

    There's not much side play on the motor shaft, but there is a good 5mm play backwards and forwards.

    This fan is at least 17 years old! So I guess I will have to buy a complete new fan now? :eek:

    Thanks for your help!
     
  5. CD-RW

    Thread Starter Member

    Feb 26, 2011
    33
    1
    Yes - checked that. There is no short from any of the 4 motor wires to the casing.

    Mains power In goes to a 3 connector terminal block. The Grey motor lead connects directly to the mains terminal block. Live goes via a red lead to the speed controller switch. The White, Brown and Blue motor leads connect to the speed controller switch. So I guess these are different taps on the motor windings to control the fan speed?

    Looks like Grey is the return lead, and maybe this is where the problem is?
     
  6. Hagen

    Active Member

    May 8, 2010
    30
    1
    If I am following correctly, it sounds like the grey lead going into the motor has continuity with absolutely no other wires. Yea, it sounds like its time for a new fan.
     
  7. CD-RW

    Thread Starter Member

    Feb 26, 2011
    33
    1
    Yes the Grey wire has continuity with nothing. So I guess it must have broken or burnt out in the windings? I can't be bothered to strip the motor and try to locate the break in the wiring. I have had 17+ years use out of it, so I guess I will bite the bullet and buy another fan soon. Argos has them for £25.00, and on ebay they are ~£17.00 including delivery.

    :D
     
  8. alim

    Senior Member

    Dec 27, 2005
    113
    1
    You should check if there is a thermal fuse in series with the the gray wire ,which has opened. It may not necessarily be the winding itself.
     
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