Permanent Split Capacitor (PSC) Motors

Hello, all, and especially the electric-motor savvy. I have an old Lakewood box fan, 120 VAC 1PH, with an airflow in/out switch that electrically reverses the motor rotation. I suspect that the motor is of a fractional-horsepower PSC design but there is no capacitor mounted anywhere external to the motor. Are these small fan motors manufactured with an internal capacitor or am I incorrect as to the motor type? Thanks for your time and comment. Sincerely,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337
Reply to
J. B. Wood
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It may be a non-capacitor split phase motor although that is not often found in the 1Hp range. However, the initial fan load would be small so the initial starting torque requirement would be small. Does it have a centrifugal switch to disconnect the start winding after it comes up to speed? .

Reply to
Don Kelly

If it does I certainly don't hear it functioning, Don. The fan is a standard 20" box fan with a 3-blade aluminum impeller. The motor was manufactured by McMillan Electric. There is a wiring diagram on the motor showing what wires to use for lo-med-hi speed and for CW/CCW rotation. No external capacitor is shown on the diagram nor does a capacitor appear to be mounted anywhere in the fan enclosure external to the motor. Mcmillan's website

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has a picture of a 4-pole PSC motor that looks like mine. There are no connection diagrams or further electrical info provided by the website, though. Sincerely,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337
Reply to
J. B. Wood

A commonly used but little appreciated technique that may describe your fan is the shaded pole motor with wound shading coils. Two shading coils are provided, one for each direction of rotation, but instead of being a single heavy turn they consist of multiple turns brought out to a switch. Short circuiting one or the other winding causes the motor to run in both directions. No centrifugal switches, no capacitors. Efficiency is poor, but on a fan of perhaps 1/15 HP nobody notices.

Reply to
BFoelsch

Hello, and thanks for responding. I actually thought this might be how it was done a while back but I could never find any reference books or other resources describing such a technique. The closest I've come is a statement in the "Standard Handbook for Electrical Engineers" published by McGraw-Hill: "Shaded-pole motors, unless of a special design, can be operated in only one direction of rotation." No examples of "special design" are provided. I am compelled to conclude that electrically-reversible shaded-pole motors must be rare beasts. Sincerely,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337
Reply to
J. B. Wood

The shaded pole motor also looks the same. However all the shaded pole motors shown are unidirectional. BFoelsch has one answer and the other is that it is a PSC with the capacitors well hidden in the frame.

For some reason (I think I read 1ph as 1hp- senility creeping in.) I thought that your motor was in the order of 1HP and a shaded pole motor wouldn't be used in that range.

Reply to
Don Kelly

My favorite book on small motors talks about this a bit; Cyril G. Veinott, Fractional Horsepower Electric Motors, McGraw-Hill, 1948, section 13-8, pages 306-308. Section 13-9 goes on to explain adjustable speed shaded pole motors.

Thanks in advance.

Reply to
BFoelsch

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Sincerely,

many if not most small fan motors are 'shaded pole' no start winding switch or capacitor...thats under 1/4 hp... your fan is probably under 1/6 hp ... could easily be 1/20 hp.

Phil Scott

Reply to
Phil Scott

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