Electronics > Projects, Designs, and Technical Stuff

Variable-speed Single phase motor about to die.

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paul8f:
I suspect this single-phase motor for a blower-fan is giving trouble. It spins ok and sounds ok when running, but the system is bringing on a fault light. It looks like the fan is not spinning fast enough. I don't see any service ports to apply bearing lubricant.

Resistance measurements look ok....: resistance between the two electrical input terminals is low, and there is high resistance between the terminals to the metal case.

The motor is variable speed, and is driven by an ST TI 235 Triac. How do I figure out if the problem is with the motor or the driver circuit? Any help very welcome  :)

(I suppose the only real way to be sure would be to have a tachometer, and to know the RPM for a given applied voltage  :-//   :-//)

GeorgeOfTheJungle:
If there's a capacitor in series, replace that first. The failure mode is the capacitor becomes leaky => heats up => burns itself or the motors coil or both.

Ian.M:
Try a drop of SAE30 machine oil on the bearings applied where the shaft meets the bronze bush.   There's almost certainly another one the other side of the motor unless it doesn't have one and only has a bearing the far end of the fan rotor.  If they have been running somewhat dry, it will speed up.  if it doesn't make a difference you can assume the original lubrication is still sufficient.

Oilite bearings are pre-lubricated at the factory, but supplemental oil may be required during their life.  If the old oil charge needs to be replaced (to avoid the need for on-going regular lubrication) its a royal PITA and will require stripping down to remove the bearings which (if press fitted) may be left in metal housings or carriers but due to the need to heat them in oil, must be removed from all plastic or electrical parts.  See: http://www.loganact.com/tips/sleeve_bearings/oilube5.gif for the process.

MagicSmoker:
That's a shaded pole motor and they are nearly indestructible, electrically speaking. If the fan spins freely by hand then the problem is most likely with the triac-based speed controller. I would be especially suspicious of the capacitor in the gate circuit. See, for example, this page:

https://www.industrial-electronics.com/emct_2e_5a.html

duak:
Is the shaft of the motor horizontal?  If so, the weight of the impeller is causing more wear to the lower part of the inner bushing and the upper part of the outer bushing, the one visible in the image.  If this goes on long enough, the rotor can drag on the stator.  If the electronics checks out, remove the blower assembly, take it apart and check for score marks on the rotor.  If it's OK, the bushings should be good enough so clean the pieces, put a couple of drops of oil on the bushings, reassemble it and see what happens.  Quite often, the oil goes away and what's left gets thick.  Cleaning the old stuff away and relubing does wonders.  Also, I see a bit of debris on the winding so I expect there's also some on the impeller too.

Best o' luck,

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