View Full Version : Why is my motor not working?

Dr. Rob
08-12-2003, 11:42 AM
Listen, the motor on my bench lathe just quit working properly. Thought I'd ask here first, since I'm just too tired to deal with it properly.

The trouble is this:

The lathe has an electric motor (described later) controlled by three switches on the control panel for forward, rev and stop. When I hit any button, nothing happens. If I hold down the button for start, and give the motor a good smack, it sometimes gets the idea and starts & runs fine. If I then let go of the button, it dies.

The symptoms are thereby similar to having worn carbon brushes or an electrical glitch or loose wire.

BUT this motor doesn't have any carbon brushes as far as I know. All electrical connections are screwed down tight. Opened the motor & electrical box and vacuumed all the dust & junk out. Fine. Also, the problem appeared suddenly rather than progressively.

!!Hey, I just saw a funnel cloud forming! Right on the horizon, out the window! Right in front of this approaching thunderstorm. Wow!!

Anyway...The sticker on the motor looks like this:

Output ½ hp.........Pole 4
Hz 50...........Heat 60*
Amp 4............Weight kg
RPM 1500..........Class A
Phase 1............Date 1989

Inside, it has an axle running through, with a big cylinder with annularly disposed holes (a lot like a revolver, really) which spins in a steel cylindrical housing, surrounded by a million miles of wound copper wire.

Four wires from the electrical cabinet attach somehow to the copper bit. All are solidly affixed, and not affected by jiggling them around.

NOW THE BIG PROBLEM: I don't know anything about electrical stuff- wouldn't know a capacitor if he walked up and introduced himself. Ohms? No. Watts? No. That's in L.A. Amps? No. Electrocardiogram? Um, no. Like speaking Greek to a Frenchman. No comprende.

I just want to know what to do about it. Garbage?

Thanks in advance.

[This message has been edited by Dr. Rob (edited 08-12-2003).]

08-12-2003, 12:10 PM
Is there an electrical device which is wired somewhere in the control circuit, cylindrical in form with wires attached to one end of it, often black in color but not necessesarily black and about 4 to 6 cm in diameter and about 10 cm tall? It will be marked with a uf (microfarad) rating.

08-12-2003, 12:13 PM
Did you notice any peculiar ozone/smokey odors at any time recently? If not I'd guess that you've got a problem in the switch. Maybe some of the contacts have arced and are welded in a fixed position.
But then I'm no electrical genius either...

08-12-2003, 12:13 PM
Evan is right, or the points that start it have corroded. And never work on anything of danger or value when you are too tired.

Now Dr. Evan, I have had this pain in my side. HA Ha.. yeah.. fix that..

08-12-2003, 12:18 PM
since this is single phase, also check for trouble with start windings and or centrifugal switch. You make no mention of horsepower, but with a 4 amp draw, its likely perhaps a 1/3 hp. It might be less expensive to replace if all indications suggest to do so.

08-12-2003, 12:35 PM
If there is a dead start capacitor and it is in the controller housing then replacing the motor will not cure the problem. This sounds like a type A induction motor with capacitor start (reversible). The sudden failure to start is most likely caused by a dead capacitor. The capacitor is often mounted remotely. The fact that the motor is rated at four amps does not mean 1/3 hp. You will note that it is a 50hz motor so it is almost certainly running on 220-240 volt single phase.

Nearly all countries (all?) that use 50hz ac power also deliver it at 220 to 240 volts. Pretty smart since it means they can use 16 gauge wire, smaller, cheaper, more flexible and less I^2R losses.

A few more considerations, the motor may have a remote energized start winding. In that case the controller will have a relay in older units or a triac in newer ones. In either case the relay or triac may have expired.

[This message has been edited by Evan (edited 08-12-2003).]

Dr. Rob
08-12-2003, 02:45 PM
Whoa, thanks for the fast replies!
Ooookay...just went at again.

Started at the beginning, with the switches. No prob, clean bill of health.

Inside the electrical cabinet there was indeed a capacitor (it introduced itself, as a representative of the Tong Fu Electronics Co. Amicable fellow- Nothing obviously wrong there either.)

A-ha! A wire had indeed come loose from the terminal it resides upon. Fix fix fix, test fire...No go. (maybe I knocked it loose just now?)

Give the motor a smack, and zzzzzzzzoom, away she goes.

Okay, but now I can see the individual electromechanical circuit breaker jumping up & down, goin' crazy in there, sparking and just rarin' to go. And sometimes it does connect, apparently.

Ergo, the motor is probably fine. The smacking part causes a secondary jolt to the electrical cabinet, which jolts the electromechanical componentry into action. (?) Fiddling with individual wires to switches, motor or capacitor does nothing.

All right- What then decides if the switch mechanism gets juice? Is that the capacitor? Another loose wire, hidden in there in the jungle?

I'll go have yet another look for obvious causes.

Thanks a-plenty for the great answers and deductive reasoning.

PS: Indeed, 220 volt.

08-12-2003, 03:26 PM
Dr. Rob,

The "circuit breaker" is likely the remote starting relay. For a quick fix REMOVE POWER and file the contacts with a points file. Do not use any sort of abrasive to clean contactors, it will leave small bits of nonconductive particles and will not work. Many of those relays have replaceable contacts with little sort-of cotter pins or similar holding the contacts in place. If so they are easy to replace, or, replace the relay.

The relay supplies power to the start winding of the motor. It must be of the correct type as it is the current delivered to the main winding that pulls in the relay. As the motor gains speed this current falls and the relay drops out automatically. The capacitor introduces a phase lead or lag which determines the start direction.

[This message has been edited by Evan (edited 08-12-2003).]

08-12-2003, 03:29 PM
I trust the tornado missed your house.

Forrest Addy
08-12-2003, 03:29 PM
Doc. It's my sad duty to inform you that your existing equipment is a total loss and will have to be replaced with new larger and better machine tools.

Save your self some agony. A long as the motor doesn't smell like burnt toast and the million miles of wire aren't charred down to bare copper, remove the motor and take it to a motor shop. $35 and three days later it will run. Trust me.

Dr. Rob
08-12-2003, 03:57 PM
Got it!
It has something to do with one of the cable bundles from the VCR to the rinse cycle, or something. When you hold it just SO! then everybody is happy- forw, rev, stop. Must be busted somewhere under the skin, or just an oxide pileup or something.

So, the case isn't completely solved, but we have a main suspect and modus operandi; just gotta find the motor-ive.

Sorry if I got everybody all revved up for nothing and caused sleepless nights all over the world.
But, all you guys get top points for being there in the front lines. Grazie.

Sorry, Forrest- Started laughing when I read your post; thought it was going to end with, "...send it to me so I can mourn it properly..." Yeah, RIGHT!

But no, there is no apparent damage to anything.

No damage from any tornado either. The funnel retracted and dissipated. I don't think anyone else saw it. Such things are an absolute rarity in this part of the world. I've seen one form in Finland, but had a hard time convincing people around me. Amazing things, but they kind of scare me- Ready to drop my stuff & go immediately. Thrud would remember Edmonton in 1987. Big one plowed through the tornado magnet park (trailer park) and suburbs. What a mess.

The lathe by the way is a SEA clone of an Emco Compact 8. Great little thing; my first lathe. Has handled everything I've thrown at it with a smile. Has since been supplemented by a Koping, a Lorch and a big beast of unknown origin (the one with the car transmission) but I'll never abandon it.

Thanks again; I'll let you know the final outcome.

Dr. Rob
08-12-2003, 05:34 PM

Dig this: It wasn't a relay, cable, coil or spark plug.

Inside the stop button unit, there is a mechanism with a coil spring-loaded yoke that makes contact onto a couple of connectors.

That coil spring (like ballpoint pen size) was broken partway up, so not enough force was available to provide proper contact. Ergo, it wasn't a matter of not getting started, as a matter of constantly / intermittently being told to stop.

Geez. Sheesh. But you know what? I don't feel the least bit dumb for not looking there first.

Whatever. All well now.
Thanks again.

John Foster
08-12-2003, 06:16 PM
Hey, it is always the last place you look!

08-12-2003, 06:52 PM
Told you so. My guess was right...but for wrong reasons. http://bbs.homeshopmachinist.net//biggrin.gif

08-12-2003, 07:29 PM
Dr. Rob:
"Geez. Sheesh. But you know what? I don't feel the least bit dumb for not looking there first."

You should. My IQ dropped 50 points just by reading this. http://bbs.homeshopmachinist.net//biggrin.gif

Everyone knows you look for the one thing that "obviously" could never cause the problem...first!

[This message has been edited by Thrud (edited 08-12-2003).]