Electric Motor Problems ?

[randyjaco]

I am finishing up restoration of a Walker Turner 900 drill press. It has the original 1/2 hp 120 vac motor, which I checked prior to starting the project. As you can see from the pictures, everything is hooked up and I started to do a run-in to check everything out. The motor will run for nearly a minute and then will trip the breaker
The motor is under minimum load. Mechanically everything is running smoothly. I do notice that the cord feels a little warm, but other than that, there is no blue smoke and there is no burning smell. It just appears that it is using too many amps.
Warning, I am electrically challenged, but I do have a VOM and an amp meter.
Any suggestions as to what the problem may be and how to fix it? I do have other motors, but I would like to use the Original motor if possible.

TIA
Randy

 

[markba633csi]

Hi Randy- it sounds like the starting circuit is not cutting out like it should- do you hear the centrifugal switch clack as the motor comes to a stop?
The mechanism might be stuck or the contacts could be welded together
One test you could do would be to disconnect one of the capacitor leads after the motor is started and running. This should be safe if done carefully. You could install a temporary switch in one of the leads or use an alligator clip lead, wearing gloves. If the capacitor uses slip-on terminals, you could loosen one so it's just barely holding on enough to start the motor, then pull it off while wearing a glove.
If the problem goes away then you know it's the internal start switch that needs attention
-Mark

 

[graham-xrf]

You are in the right place. There are motor experts here.
If you have as much as a meter, you are not at all in the pits of being electrically challenged!

Just to throw in from the start, I suspect old deteriorated capacitor. These things can have the kind of "breakdown after a while" coupled with running AC currents when they shouldn't. Fortunately, getting another, in modern construction, better rated and more robust than the old kinds, is a low cost affair. You can get them from eBay. Various capacitor setups are possible. Some motors have a double capacitor arrangement of "starting capacitor", and a section that is the "running capacitor". They depend on a internal centrifugal switch to change over when the motor spins up.

First we go carefully. Get all the info you can from the nameplate. Do not be afraid to take the motor apart. There are a few things to check. There are so many wires in a bunch, and I can't see any capacitor. 3-phase motors don't need them, but I was thinking 120V 1/3HP would be a single phase. The stuff that motors are made of are kinda fundamental. Iron, copper, and insulation. Unless the insulation deteriorates and starts breaking up, or some kind of overheating happened, and things start burning up, there is not much that can go wrong.

Unpowered, and without the belt, does the motor spin freely? One possible reason for overheat and quit are binding in the bearings. Listen for bearing noise.

Some motors have a starting run-up controlled by a centrifugal operated switch . Motors can appear to get going, and then quit if they have this type of "run-up" circuit that gets things going using lower power coil configuration, and then once spinning, the centrifugal switch operates to get it into full power mode. Full power into a motor when starting up from a standstill can take a huge current surge, which is why this method is used. If the centrifugal switch contacts mess up, get burned, or some stay welded together and won't let go, then overheating, high currents, and other bad stuff happens. There may be a thermal cutout in there as well. The mechanism, if there is one, must operate freely, without sticking. Look for corroded mechanism, broken or missing springs and suchlike.

 

[randyjaco]

Thanks for the replies. I was out of the shop today, but should be back in tomorrow.
The capacitor is brand new.
The motor turns freely. The assembled drill press turns freely, so there is very little frictional torque on the motor. The motor has excellent start up torque. I will give the centrifugal switch a check. (sounds like a likely candidate)

 

[tq60]

Simple check.

Plug in and turn on, as soon as it is at seed turn off and listen.

Should hear a click as it slows down.

Sent from my SM-G781V using Tapatalk

 

[CluelessNewB]

Check wire colors carefully, old wire colors fade and change over time, sometimes they can be very deceiving. Good bright sunlight can sometimes be enlightening!

 

[randyjaco]

I got it fixed. It was the centrifugal switch. Getting it apart was no picknick. Since it had been together for 78 years, it was reluctant to come apart. It took a lot of judicious hammer blows to get it to separate .
Thanks again for the replies and help.

 

[Janderso]

I got it fixed. It was the centrifugal switch. Getting it apart was no picknick. Since it had been together for 78 years, it was reluctant to come apart. It took a lot of judicious hammer blows to get it to separate .
Thanks again for the replies and help.

Did you replace it?
Fix it?

 

[markba633csi]

I'm curious too- was it stuck? broken? contacts welded?
-M

 

[randyjaco]

Somehow water got on the shaft and the rust prevented the slide from moving. I cleaned it up and added a little grease. It now works like a champ
I love it when I can fix electrical problems mechanically