AC Motor Changed Direction!

Something must be happening at startup. Single phase motor must have some starting arrangements. If not capacitor then start / run windings with centrifugal switch. Capacitor may be hidden inside?

In my curiosity (with the motor unplugged) I unscrewed two covers that were located on opposite sides of the shaft. I noticed one looked more worn than the other. Not sure what these are, though after putting them back in, the motor tried to run in the correct direction, then reverted back to the incorrect direction.

Thanks!

Kevin

What is it used on?

If it is on a fan, and the fan was back-spinning from an air draft, that can happen with 1 phase motors, you need to prevent the backdraft.

If it is a PSC (Permanent Split Capacitor) motor, the caps are inside the motor, you would not see the bulges. If so, it is probably a pump or fan. In that case, your starting cpacitor may be going bad.

Either way, take it to a good motor shop, they can fix it.

Those 'covers' sure sound like brushes! If you have never heard of them, this is going to be an educational experience for you. They wear and need replacing from time to time. Especially if one is more worn than the other. It might be a good plan to find out why the wear is uneven. You need to locate a source of replacements, which may not be too hard if the motor is a standard type. Worn or misaligned brushes can cause a number of motor problems. I didn't know that reverse running was among them, although I stand to be corrected.

I thought those might be brushes. There under the screw cap is a spring and then something down in under it. The motor is used on a band saw, so backdraft is not a problem.

So, how do I go about finding replacement brushes? Are the difficult to replace?

Thanks for everyone's insight!

Kevin

snipped-for-privacy@gmail.com wrote:

They are meant to be replaceable. They come with a spring and you undo a screw or two and kind of snap them in. Might be as well to inspect & clean the commutator or slip rings at the same time. (What the brushes press on - what does it look like?) The brushes may come with an instruction leaflet and there are plenty of websites with detailed instructions which we can direct you to. A first step would be to read the maker's name and the model number off the plate on the motor and post it on here. They are made in standard sizes. If the band saw is a well known make like eg Black & Decker, a local stockist may well have them.

Another strategy is to take one out and take it to an electrical spares place and show it to the guy behind the counter.

Wouldn't there be a full wave rectifier inside there somewhere?

Or justa diode somewhere, if the diode has melted and made a constant bridge you may get back current over the intended forward current. 1950's are not long after a diode's birth. Could be an early type.

Never seen the motor, nor remember one from the fifties but that's my thinking.

Here is the information on the motor plate:

Leland Motor, The Leland Electric Company, Dayton, OH Single Phase Induction Repulsion

Thanks!

Kevin

No diodes or anything like that in these motors. Wound rotor induction motors. A close relative of the repulsion/induction with its centrifugal "necklace" which shorts out the rotor.

During the startup, the brushes contact the commutator to induce a current in the rotor windings. The direction and torque depends upon the angle the brushes make with the stator field. The resultant start up is something like a series universal motor. After commutator segments short, it works like a single phase induction motor with counter rotating fields.

Maybe your worn/broken brushes are connecting the wrong commutator bars together, and possibly poorly at that. Get new brushes and install them with the correct contact and orientation.

Bill

-- Fermez le Bush

Have a look here. It is possible that one of the brushes illustrated will suit. If not, an email to them might be in order.