Vacuum motors turned CCW by hand...

[superocd]

Why do they have a ratcheting effect when the shaft is turned by hand CCW? When changing the belt in my Kirby machines, my JCPenney Hoover Convertible or my Sanitaire, I notice that if I spin the spindle, the motor turns "smooth" one way and has a ratcheting effect the other way (I think it does this CCW on all types). However, my Royal does not "ratchet" when turned CW or CCW, even though it uses the same type of motor as my other machines (a universal motor). What is this phenomenon? Does it have anything to do with the bearings, commutator or brushes?

 

[texaskirbyguy]

I know what you are talking about...
It has to go with the way the carbon brushes wore in to the commutator. In CW rotation, the brushes are pushed slightly to one side due to slop in the holder. This gives an uneven wear. When turned CCW, the sharp edges are catching slightly on the commutator bars and are pushed slightly to the other side, giving the ratcheting feel you we experience.

I would suggest not to turn the motors opposite direction of motor rotation to avoid possible chipping of the brushes.

Also this is why brushes should be marked during removal so you know exactly how they were installed, should to plan to reinstall them. I use dots from a silver Sharpie pen.

 

[texaskirbyguy]

It is possible your Royal has tighter-fitting or different sized brushes that give more even wear. I have never torn down a Royal so not sure how they are made.

 

[broomvac]

texaskirbyguy hit the nail on the head. You are hearing the brushes catch just a bit in the spaces between the commutator bars. Some motors will make a louder sound than others. Some won’t do it at all. It’s just design.

I avoid doing this to my vac motors for the same reason texaskirbyguy brought up; I don’t want to potentially chip the trailing edges of my brushes. Have you harmed your motors? The likelihood is slim to none, but best practice is to not do it.

Thanks for the interesting topic!

 

[huskyvacs]

It won't hurt the motor to turn it backwards by hand - under power (reversing the motor) yes. But what it will do is like the guys above said - chip the brushes or file off the delicate pattern in the age wear that has bedded them to the shape of the armature. You don't want that, as it will cause excessive arcing and greater brush wear and risk of overheating damage to the armature. A few times wouldn't have hurt it, but definitely don't do it often.

 

[tolivac]

Universal motors turned backwards-----Keep in mind your corded VSP reversing drill does this all the time with NO harm.I have a VitaMix blender that has a reversing motor-B&D router motor-that is reversed while blending-Gives BETTER mix action.You will have to hold the machine while reversing-OK at lo speeds-you wait a second before reversing on High.The machine will jump!A large Forward-Off-Reverse switch in on the front of the motor base.And yes-reversible routers-these can be 15A!!

 

[texaskirbyguy]

Motors that are run in both directions and not run for much time will not have the issues mentioned. A sharp edge would not even get a chance to form.
Vacuums run at very high speeds for very long times in only one direction, which causes the wear patterns (and sharp edges) mentioned. Most of these machines are very old, so we are talking hundreds of millions of revolutions or more.

 

[kirbysthebest]

Texaskirbyguy

Well said, good explanation.

 

[madman]

As for why some motors don't do this... Some commutators don't have a trench between each contact, in those, the space between each contact is filled with epoxy. So there won't be a trench to catch the sharp edge of the brush. I'm fairly certain that's why.

Also, go ahead and turn it backwards. What's gonna happen? Chip off 1000th of an inch of carbon? Big deal.