clothes dryer problem
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  1. #1
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    Default clothes dryer problem

    hi, i am tying to fix a malfunctioning clothes dryer for a friend.
    it has been working (for years!), but fairly suddenly stopped rotating the drum.

    inspection showed that the fan and drive belt are intact, and the fibre bearings at the front of the drum were partially worn through. so there was excessive friction when rotating.

    anyway, i have replaced the fibre front drum bearings, and put in new belts just for maintenance.
    now, it will still not start rotating when the door is closed. that in turn is because the motor will not start. but if i spin the motor by hand (ie with fan cover off... ) to get it started, the drum will rotate, and seems to do so with some power. the new (and old) drive belt is tight, so it is not a case of it slipping.

    question: what could cause a the motor to not start properly, but function when it is spun by hand? i seem to recall from the thread i started when i bought a used pedestal drill, that it could be the big capacitor attached to the motor.

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    thoughts?

  2. #2
    1000+ Posts robmac's Avatar
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    I'm guessing a stuffed motor with a burnt out start winding.

    Most appliances have a dual winding motor (split phase induction motor). The first is the start winding. This is put into circuit by centrifugal switch (when not rotating or when at less than running speed). Once up to speed the centrifugal operates and disconnects start winding. Once the motor is spinning and the rotating magnetic field is established it will continue to run on second winding, the run winding.

    When a motor has load on the shaft greater than the motor rating (such as stuffed drum bearings) it may never reach full revs and thus stay in start mode.

    Start windings are not rated for continuous operation and soon burn up if left powered for a long time.

    If you are lucky, the centrifugal switch contacts will be cooked and the winding ok.

    Scratch a couple of marks on the end plates across to the casing (for re alignment) undo the 4x long studs and carefully take the non shaft end off , careful of the wiring. You will see the mechanical section of the centrifugal on the shaft and the switch on the back of casing.

    If the contact are OK the winding will o/cct.

    If the motor smells burnt (insulation cooked smell) then don't bother.

    Devices which need a more powerful motor use a PSC (permanent split capacitor) motor , like your drill press. Clothes dryer are designed on cheap-as-sh!t but still works principle so the cost of a PSC motor would blow ot the design cost!
    Last edited by robmac; 21st June 2013 at 08:40 PM.

  3. #3
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    Default Starting

    Hi Alexander

    All single phase motors need a start winding(s) as well as the main winding(s). The these can “burn out “ when the going is difficult . The motor can be started by spinning it and switching it on, and it may run OK or struggle depending on the type.

    There are several types of single phase motors and their start winding arrangements. From Wikipedia. There is plenty of information on the web.
    Single-phase induction motors.

    Shaded-pole motor
    A common single-phase motor is the shaded-pole motor and is used in devices requiring low starting torque, such as electric fans or the drain pump of washing machines and dishwashers or in other small household appliances. In this motor, small single-turn copper "shading coils" create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil. This causes a time lag in the flux passing through the shading coil, so that the maximum field intensity moves across the pole face on each cycle. This produces a low level rotating magnetic field which is large enough to turn both the rotor and its attached load. As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor.
    Split-phase motor
    Another common single-phase AC motor is the split-phase induction motor,[18] commonly used in major appliances such as air conditioners and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque.
    A split-phase motor has a startup winding separate from the main winding. When the motor is starting, the startup winding is connected to the power source via a centrifugal switch which is closed at low speed. The starting winding is wound with fewer turns of smaller wire than the main winding, so it has a lower inductance (L) and higher resistance (R). The lower L/R ratio creates a small phase shift, not more than about 30 degrees, between the flux due to the main winding and the flux of the starting winding. The starting direction of rotation is determined by the order of the connections of the startup winding relative to the running winding.
    Resistance start motor
    A resistance start motor is a split-phase induction motor with a starter inserted in series with the startup winding, creating reactance. This added starter provides assistance in the starting and initial direction of rotation.
    Capacitor start motor
    A capacitor start motor is a split-phase induction motor with a starting capacitor inserted in series with the startup winding, creating an LC circuit which produces a greater phase shift (and so, a much greater starting torque) than a split-phase motor. The capacitor naturally adds expense to such motors.
    Permanent-split capacitor motor
    Another variation is the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).[19] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,[19] and what correspond to the start windings (second windings) are permanently connected to the power source (through a capacitor), along with the run windings.[19] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where a variable speed is desired.
    A capacitor ranging from 3 to 25 microfarads is connected in series with the "start" windings and remains in the circuit during the run cycle.[19] The "start" windings and run windings are identical in this motor,[19] and reverse motion can be achieved by reversing the wiring of the 2 windings,[19] with the capacitor connected to the other windings as "start" windings. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also, provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding.

    You have to determine the type fitted because they look similar. However if the motor has a centrifugal switch you could check that it is operating correctly. On when stopped and breaks the circuit when the speed picks up.
    It probably is the last type; Permanent-split capacitor motor with a cap and no switch. Possibly the cap is stuffed but more likely the winding is ‘burnt out’. Your drill motor probably had a Capacitor start motor with a switch.

    jaahn

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    Thanks to both of you.
    I will have a look at the motor tomorrow.
    As it happens my drill is a centrifugal switch type and, rob, you have forgotten that you correctly predicted the switch to be the culprit, before i bought it on ebay. It took one good whack with the handle of a screw driver and has workes perfectly since.

    The windings on the dryer motor did not looked burnt, on a cursory look but shall see. It is a 15 year old simpson so i would think as low tech as they come.

    sent from my .GT110XZX589-P3 de luxe Peanut Butter Sandwich Hyper Tablet. not that you'd care.

  5. #5
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    ok, one repaired clothes dryer, and the culprit was the start capacitor.

    this motor had an 8uF capacitor with 2 pairs of tabs, and no centrifugal switch.
    from the above list, what sort of motor is it?

    that aside, the task reminded me that it is much cheaper buying the spares on ebay. i initially bought a set of front drum friction bearings (ie almost no value), a drive belt and a fan belt. shop price: $90. i checked on ebay, and the two belts can be had for more like $25. the capacitor i did buy on ebay for $20.

    i also found this very helpful website regarding white goods:
    Washing Machine Reviews | Washer & Dryers | Best Washing Machines

    part of which has a Q&A sections like this
    Simpson Sirocco series, 350, 450, 455, 500

    where someone who was (apparently) a repairman, just answers questions about repairs for the pleasure of doing so.

  6. #6
    1000+ Posts renault8&10's Avatar
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    or maybe the alleged repairman just has access to Google?
    KB


  7. #7
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by alexander View Post
    ok, one repaired clothes dryer, and the culprit was the start capacitor.

    this motor had an 8uF capacitor with 2 pairs of tabs, and no centrifugal switch.
    from the above list, what sort of motor is it?

    that aside, the task reminded me that it is much cheaper buying the spares on ebay. i initially bought a set of front drum friction bearings (ie almost no value), a drive belt and a fan belt. shop price: $90. i checked on ebay, and the two belts can be had for more like $25. the capacitor i did buy on ebay for $20.

    i also found this very helpful website regarding white goods:
    Washing Machine Reviews | Washer & Dryers | Best Washing Machines

    part of which has a Q&A sections like this
    Simpson Sirocco series, 350, 450, 455, 500

    where someone who was (apparently) a repairman, just answers questions about repairs for the pleasure of doing so.
    Probably PSC motor. (permanent split capacitor)). This style of motor is an alternative split phase motors. It will have twin stator windings and a single cap to give a phase shift.

    The lack of centrifugal switch, timer relay or two capacitors removes the possibilities of CSIR (capacitor start induction run) or CSCR (capacitor start capacitor run)

    It must be an ancient device and designed with some regard for longevity rather than cost.

  8. #8
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    could i trouble you to briefly explain how having this type of arrangement works?

    thanks

  9. #9
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    Quote Originally Posted by alexander View Post
    could i trouble you to briefly explain how having this type of arrangement works?

    thanks
    Google "psc motor" you will find someone far more versed than I in motor theory.

    However, in the briefest form, to make a motor rotate you need to create a rotating magnetic field. A single winding won't do this. If you have a second winding and create a leading (or lagging) current through it, ie phase shift between the windings, this creates a rudimentary rotating magnetic field. The inertia of the rotating armature does the rest.

    The phase shift is created by the capacitor. In an AC circuit capacitor current leads capacitor voltage (due the cap charging) by 90 degrees. (There is more to it when one considers the inductance of winding as well, I've just mentioned this is passing )

    So the current through the first winding is 90 degrees ahead of the winding with the capacitor.

    Essentially single phase motors are cr@p technically because they run rough due the cludges to get phase shift. They are quite inefficient as well.

    That's why three phase motors are used where smooth and vibration free drive is required. Three phase have three windings and field rotates from the AC supply.
    Last edited by robmac; 28th June 2013 at 07:40 PM.

  10. #10
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    Default Permanent-split capacitor motor

    Hi Alexander
    Robmac has given a reasonable explanation. In a single phase motor the main winding supplies an alternating magnetic field, not rotating as required to make it run in a direction. So a second winding has to be modified by some cunning method to give an advanced or retarded field relative to the main field. This biases the alternating field between the two windings to appear that it is rotating in one direction. Good enough for a simple squirrel cage rotor. That is the reason for the various types of single phase designs. Cost is always important in consumer goods.

    However each type has some disadvantages and disadvantages. Google. It has been my experience that PSC motors are used commonly where a higher start up torque is needed and also more grunt if the speed drops back a bit on a regular basis. Most other types need to run close to their design speed or burn out. PSC motors are currently used commonly when needed. It is not an old fashioned design.

    Robmac: "Essentially single phase motors are cr@p technically because they run rough due the cludges to get phase shift. They are quite inefficient as well. That's why three phase motors are used where smooth and vibration free drive is required. Three phase have three windings and field rotates from the AC supply." I guess that has some truth but not many people have a three phase dryer in the laundry. The inefficiency is also only relative.

    Jaahn

  11. #11
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    Quote Originally Posted by jaahn View Post
    Hi Alexander
    Robmac has given a reasonable explanation. In a single phase motor the main winding supplies an alternating magnetic field, not rotating as required to make it run in a direction. So a second winding has to be modified by some cunning method to give an advanced or retarded field relative to the main field. This biases the alternating field between the two windings to appear that it is rotating in one direction. Good enough for a simple squirrel cage rotor. That is the reason for the various types of single phase designs. Cost is always important in consumer goods.

    However each type has some disadvantages and disadvantages. Google. It has been my experience that PSC motors are used commonly where a higher start up torque is needed and also more grunt if the speed drops back a bit on a regular basis. Most other types need to run close to their design speed or burn out. PSC motors are currently used commonly when needed. It is not an old fashioned design.

    Robmac: "Essentially single phase motors are cr@p technically because they run rough due the cludges to get phase shift. They are quite inefficient as well. That's why three phase motors are used where smooth and vibration free drive is required. Three phase have three windings and field rotates from the AC supply." I guess that has some truth but not many people have a three phase dryer in the laundry. The inefficiency is also only relative.

    Jaahn
    Yep it's entirely relative.

    If you don't have three phase available you use a single phase motor.

    Three phase motors are definitely more efficient. The only losses are copper losses, hysteresis losses and friction! Three phase motors also have better starting torque, run much more smoothly and equally efficient at all loads.

    Single phase motors have all of the above losses,always vibrate, have lower efficiency (due varying capacitor current) at high loads and have very real power factor issues (I and V not necessary in phase).

    Three phase motors are always the choice for demanding applications.

  12. #12
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    Worn out fibre running strips on drum can be rectified short term by running the dryer upside down .PUGS

  13. #13
    1000+ Posts The Gonz's Avatar
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    Quote Originally Posted by robmac View Post
    Yep it's entirely relative.

    If you don't have three phase available you use a single phase motor.

    Three phase motors are always the choice for demanding applications.
    I have a $3000 3-phase aircon fan donated for my cadet squadron's wind tunnel project. However, even at the Royal Show, the pavilion techs were too frightened to crank up the 5m3 per sec beast - grossly underutilised as a result

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