Microwave fan wiring?

Discussion in 'Technical Repair' started by wayneh, Jun 27, 2016.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
    12,101
    3,033
    I've just stripped a microwave of parts as it moves towards the recycler. It had a bad PCB and wasn't worth fixing.

    The vent fan is identical to the one here. It's marked 120V and has three wires, blue, orange and yellow. The blue wire is slightly larger gauge than the other two. The prongs on the motor terminal connect to blue, orange, yellow, in that order.

    I'm fairly certain the fan acts as a transformer and provides 21V AC for the turntable motor, with the other two being mains AC. But which is which?
     
  2. wayneh

    Thread Starter Expert

    Sep 9, 2010
    12,101
    3,033
    Oops. I think I just destroyed it. I tested the yellow and orange pair and this made the fan run. But the windings got hot and now there is no continuity between any poles.

    I couldn't get it to run with blue plus either of the other two. Maybe it's possible that the microwave failed because the vent fan died?
     
    cmartinez likes this.
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    It could be the transformer type, also if 3 wire it is can also be a PSC induction motor that requires a 6 to 10 micro farad cap.
    Max.
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,560
    2,527
    You had your 15 seconds of fun, I guess... but this is the first time I've heard of a fan doubling as a transformer. Very interesting.
     
  5. #12

    Expert

    Nov 30, 2010
    16,262
    6,769
    Have you heard of a speaker winding used as a choke for a DC supply?
    Really old audio amplifiers, vacuum tube type.
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,560
    2,527
    Nope... but when you say choke, do you mean as an inductor? And what's with those vacuum tube amplifiers?
     
  7. #12

    Expert

    Nov 30, 2010
    16,262
    6,769
    Yes, choke = inductor. especially in a DC power supply.
    Those are so old that I'm not sure I have a schematic for one that uses the speaker for a DC choke.
     
    cmartinez likes this.
  8. #12

    Expert

    Nov 30, 2010
    16,262
    6,769
    Here's one:
     
  9. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Here you go Waneh, its as you thaught. FAN MOTOR.JPG FAN & MOTOR.JPG FAN & MOTOR.2.JPG
     
    wayneh likes this.
  10. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,560
    2,527
  11. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Yes it is & its the same as the one waneh has, exept mine is a 240v ac motor. These motors with the 21V tap are common in microwave ovens.
     
  12. wayneh

    Thread Starter Expert

    Sep 9, 2010
    12,101
    3,033
    Since I couldn't get it to turn except by using the 21v, which promptly burnt out, I guess it wasn't much good anyway.
     
Loading...