ECN Forum Forums General Topics of the Trade General Discussion Area Reversing fans

I'm talking about the cheap exaust fans mounted in the bathroom ceiling that are vented with pipe.The motor is not enclosed and the shaded pole is achived by a little copper or brass plate(can't remember the type of metal)I The same idea as a shaded pole used on mechanical alternators for cycling condensate pumps.I think there are motors with shading poles but thought they aren't called shaded pole motors.Now I'm getting confused.I thought that the major reason for the shaded pole was to reduce magnetic flux and send the rotor in a given direction on start up.Am i confusing this with a compensating winding?Ok now have to go find out.

Found it."The shaded pole motor is an induction motor that utilizes a short circuited coil or copper ring called a shading coil to produce the starting torque.The shading pole is wound around one end of the stator pole face.
Current flowing in the primary stator windings will produce a magnetic field which induces a voltage into the shading coil and causes a high current to flow in the shaded pole coil.The magnetic field that is developed by the shaded pole current now opposes the magnetic field that initially created it.This shaded coil field is nearly 90 electrical degrees behinde the the main magnetic field and the interaction results in rotational torque.
The direction of rotation is determined by the shading coils with the motor turning toward the shaded pole.Reversing a shaded pole motor is very difficult.It involves either disassembling the motor and reversing the the stator end to end or moving the the shading coils".Page 350 of IPTs ELECTRICAL TRAINING MANUAL by Herb Puttz
Well not exactly what is thought but close enough i guess.A compensating winding is used i universal motors to reduce armature reaction,page 351.

[This message has been edited by frank (edited 09-12-2003).]

Frank,
That would have to be a cheap fan, indeed, if it were to use a Shaded pole motor!.
Normally these motors have next to no Torque and are really only for driving fans and other light loads, record players use them too!.

Trumpy,
yep it goes on to say that there is a low hp requirement 1/100hp to 1.5hp.Effciencies are 5% to 35% and operate at low power factors.Uses are small fans ,turn-tables clocks and valve operators.

There's quite a variety of 1Ø Motors.

The common Split Phase Induction Squirrel Cage Rotor type come in several flavors:
<OL TYPE=A>

[*] Split Phase-Resistance Start (no "compensation" in the Aux. Circuit,

[*] Split Phase-Capacitor Start (large value Capacitor in series with Aux. Circuit),

[*] Split Phase-Capacitor Start/Run (large Cap for starting, smaller Cap for running),

[*] Permanent Split (Phase) Capacitor-or "PSC" for short (Capacitor and Aux. Circuit always connected),

[*] Variations of the above for General Purpose, High-Torque and Two-Speed Pole Changing.
</OL>

Other Induction types include:
<OL TYPE=A>

[*] Shaded-Pole types (as previously discussed). These Motors do not have Starting Switches or Capacitors for the
Aux. Circuit, and the Aux. Circuit is always active in the operation via induction,

[*] Hysteresis Motors (typically used for Clocks and Phonographs). These are true Synchronous type AC Motors,

[*] Reluctance Motors - also Synchronous type Motors.
</OL>

1Ø AC Commutator "Universal" Motors include:
<OL TYPE=A>

[*] Series connected ("Simple Series"),

[*] Compensated Series connected,

[*] Repulsion Motors ("Simple" and "Armature-Excited"). These are Commutator type Motors with no external
connection to the Armature.

[*] Versions of the above with or without a speed Governor.
</OL>

And of course - DC Commutator Motors!

For the Repulsion Motors, the series AC circuit flows only thru the windings, not thru windings and armature.
The Armature is short circuited outside of the brushes. On the Armature-Excited type, there is a Variable Ratio Transformer in series with "½" of the Armature Circuit (it has 4 poles, or 4 brushes).

Variations of the Repulsion Motor are the Squirrel Cage Repulsion Motors. These "Brush-Shifting" Motors come in Series and Shunt wound arrangements, along with Single and Polyphase setups.

I would really like to add Schematics and description text for these types of Motors in the Technical Reference area.
Maybe sometime soon... maybe not

Scott35

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I pasted the Sigfile too!!!
(the text below "Scott35").

Oh well, it might make some interresting discussions!

Scott35

Repulsion motors are not universal motors
(Universal, meaining they need not work on line frequinecy sinusoidal AC.) Repulsion motors need 60Hz to operate. FWIW, they reverse by moving the position of the brushes on the chassis.

Ceiling fans are split phase type, the reverse by switching the polarity of one winding in relation to the other.

I have schematics at http://www.hurontel.on.ca/~taitg/pages/cfan.html

BTW, the 1PM04b is incorrect. In the high voltage configuration, the start winding is usually in parallel with one of the run windings, usually the one opposite the protector.

classicsat;


Not sure what you mean here.
The Aux. Winding is in Parallel with one end of one Run Winding.

I drew this the same way we've been hooking them up for many years. Maybe we were doing them all wrong???

Just a little cornfused on your reply.

Scott35

In the diagram, the entire start circuit is directly across the 240V line. That circuit is 120V (or else the motor wouldn't work wired for 120V), an paralleled with one of the two run windings, which are 120V each.