My wife loves to pick up items other people throw out, because she thinks I can repair them. When she saw me starting to open the fan case she got close and rubbed on me told me how wonderful it was that I could fix this stuff and how smart I am. Well, I saw right through that! I'm trying to fix it anyway. So, she has a 20 inch 3 speed fan she wants me to fix. The motor just hums but does not spin. The hum get louder as the switch is moved to higher speed position. The hum in not excessive, just notifiable. I've checked the capacitor and it is ok. I don't see any defects in the stator, the rotor looks fine. Any other thoughts on how I could repair this.
amdx wrote in news:m46ch0$o9r$ email@example.com:
Humming (vibrating a little?) so some current is flowing. But the motor does not spin up nor fries itself so I think of an interrupted winding. To be more pricise in the main coil that is used in all three speeds. The screwdriver experiment seems to confirm this.
Here's the latest, With a little more research I note, my fan motor has 16 pole pieces and
16 slots. It has 8 coils, each coil span 4 slots. The problem? When moving a metallic screwdriver around the inside of the stator it is NOT attracted to every 4th pole piece. This is at all speed settings. I'm not making any sense of the defect yet, because I don't know how the
8 coils are connected to each other and to the power. I'd rather find a schematic then disassemble to the point where I might be able to trace the wires but not be able to put it back together.
If this schematic matches my motor,
then 4 of the coils would be in series and also in series with the capacitor. The other four coils, I don't know about. The 3 speeds have me scratching my head.
MikeK, I would suggest disregarding the 3 speeds at this point; they may be derived from high speed using capacitors or maybe even tapped windings. At this point, high speed is not working. As others have suggested, it sounds like a winding issue (although a capacitor is easy to replace). A typical PSC (Permanent Split Capacitor) motor has two main windings (four wires). One winding is energized from AC power, the other is fed AC power through the capacitor so that its trailing out of phase. If there is a short between the ends of one overlapped winding, you could end up with one in four poles being dead as described. An ohm meter should be able to tell you if there is a short. Aside from any common motor wires (same color) you should not have and motor wire combinations resulting in 0 ohms. A short in an overlapped winding would be 1/2 the ohms of the other winding (typically the windings should be similar in Ohms). Shorts most typically occur where the motor leads are soldered to the winding wires, or in the slot between the beginning coil and the ending coil of a winding. If the short is in the wire bundle the repair is usually trivial (unless carbonization has occurred). If it is a short between winding end coils, the spacing in dual overlapped coils often prevents pushing a divider in to insulate between windings, so that is more of a repair-or-destroy option. Good luck! Scott
Motor has 1 capacitor, so I think tapped windings.
I'm on the wrong computer, but the values for the defective fan are lower than my working fan. (they are different fans, but the motor frames are the same). So, I think there is a short.
Ya, I'm not concerned with repair, although If I find an easy fix great. I'm on a quest to know the schematic, right down to how all the coils are connected and wired to the switch. I can clearly see 8 coils, although there could be more, laid in the same slot and tied together looking like one coil. I do not understand how to get three speeds if there are truly 8 coils. I understand taps, but the factory would not do an actual tap, the would lay in a second coil and tap at the connection. (my opinion only) I'll know after I start disassembling the wiring. Thanks, Mikek
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Most likely there are two distinct primary windings, each ending with a motor wire. First a set of coils is laid in the stator wrapping four poles cw (0,1,2,3) then that same wire is wrapped onto 2,3,0,1 ccw (this gives an alternating field pattern). The second winding is then started cw on
1,2,3,0, then continued ccw on 3,0,1,2. Taps are either pulled off while the second winding is laid, or enough space is left to add additional coils overwrapping the primary coils.
Imagine these two coils, main (the one with taps) and drive. Main coil is wired to both sides of power to energize. Drive coil is also wired to both sides of power supply, but with the capacitor in-line on one end. Now interrupt one side of the primary with a switch. The first position energizes the entire primary coil. Connect the two taps to the other two positions on the switch for Med and Low.
Because you are getting three distinct noise levels, I would speculate the main winding and taps are working. Because it is not driven forward, either the capacitor is not lagging the sinewave properly (shorted or too early or too late) or the drive coil has a short rendering it bypassed. Because of the overlapped coils, a partial short could show some Ohms, but still not provide enough field strength to drive the rotor forward. The dead fourth pole does seem to indicate a short in the winding.