Induction motor gone bipolar?

Bipolar? Lubricate it with lithium grease!

Probably a bad start cap or a fault in the starting circuit.

An induction motor without the starging winding energized will do exactly as you describe - have no real preference for direction and no starting torque.

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Thanks Sam! That's the answer I was hoping for.

--
David Farber
David Farber\'s Service Center
L.A., CA

I didn't get any results by searching the GE number provided, but your description sounds as though the motor is a common capacitor start split-phase AC motor, David.

Some of these types of motors have 2 AC capacitors.. a higher value start capacitor (typically over 100uF), and a low value run capacitor (generally under 30uF)

The behavior you've described sounds as though there is a fault in the start circuit, as you suspected, and Sam suggested. These motors will exhibit the symptoms you experienced as far as humming when they fail to spin up, but run when the shaft is spun by external means.

This type of motor consists of a start capacitor, in series with a start winding, a start/run centrifugal switch, and a run winding. At rest, the start winding (and series capacitor) is connected in parallel with the run winding, by the centrifugal switch.

If your motor doesn't include a centrifugal switch, then it's a different type of motor than a split-phase motor.

In properly operating capacitor start split-phase motor, when power is applied, the start winding spins up the rotor, the weights of the centrifugal switch overcome the tension of the springs associated with the switch, and the switch opens, allowing the run winding to take over. When the power is removed, the rotor begins to slow, then a distinct click is heard, when the centrifugal mechanism resets as the rotor approaches the lower switch point speed as it continues to coast to a stop.

These types of motors aren't instantly reversible. If for some reason power is re-applied before the rotor stops (not the usual start/stop procedure), the motor will continue to run in the same direction the rotor was coasting. This is a characteristic of these motors, in that the rotor needs to stop before power is re-applied. This is important for applications where the motor is wired to be reversible.

For visual inspection, you'll want to examine the areas of the shaft where the bearings are situated in the case of sleeve bearings. If the sleeve bearings are worn, the motor may have to be replaced, as these aren't usually a service part. When the sleeve bearings are badly worn, it may be noticable by looking for signs that the rotor has been contacting/rubbing on the sectors of the stator.

Another important component is the centrifugal switch. If the contacts are badly pitted and/or burnt from arcing, the switch should be replaced (if it's available as service part). Some folks are comfortable with filing or dressing the contacts with abrasives (emery or sandpaper), then burnishing the contacts. If the contacts' connection has become high in resistance due to pitting from arcing, the motor could fail to spin up in the way you've described.

When these motors fail to spin up, a very likely cause is the start capacitor. Depending upon what type of tester was used, the results indicated when testing AC capacitors may be inconclusive as to the quality of the capacitor. Testing the motor with a new AC capacitor is a better approach.

If a fault has developed within the start winding of the motor, the motor will most likely have to be replaced.

-- Cheers, WB .............

How did you test the start cap? If it's flaky it's not going to advance the phase to start the motor and could possibly start backwords.

I tested the caps with my Bob Parker ESR meter. There are two 130uF 330V capacitors in parallel. I checked them out of circuit to make sure. I'm fairly certain I tested them for shorts because the ESR was very low. I'm going to have another visit with the gate this afternoon and specifically test out the motor starting circuit.

Here is a schematic that I drew up a while back. Except for my head scratching of what's energizing relay "B", I think the rest of the diagram is accurate. It doesn't help that about 75% of the wires are all the same color!

Schematic:

For other pics of the electronics:

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA

Wild_Bill wrote:

Interesting point about the "click." I do here click(s?) when the gate stops moving. I had always thought the click was being caused by the mechanical movement of the switching relays.

There is about a 30 second delay before the gate starts to automatically close after reaching the fully open positioned. I don't think it is possible for the rotor to continue to turn if the gate has stopped unless there is some intermediate transmission in the motor itself.

If for some reason

If it is the centrifugal switch, I'm hoping it easy to remove and replace. What are the chances of that happening?

I think the easiest and most telling test will be to hook up an ohm meter between the two start windings and see if there is continuity, then go from there.

Hi WB,

You're right about the two capacitors. However they are wired in parallel in this situation. Since I am not the original service guy on the gate, perhaps it's not supposed to be that way. Here is the wiring diagram that I drew from tracing out the connections.

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA

Hi David, I think I should've mentioned that my motor comments were related to testing a motor that's been isolated from any controls, as in bench testing. Bench testing would be where the click of the centrifugal switch mechanism would be very noticeable.

I dunno if the motor in the gate controller is a typical motor, or a special-purpose motor built for this particular appliance (custom built for the OEM/gate control company's specific requirements). If all of the switching circuitry is separate from the motor, then it's probably a typical motor. Typical meaning that the internal switches in the motor would just be the centrifugal switch, and a thermal protection device.

Testing the controls (wuuf! that's a lot of contacts) may be simplified by placing test lamps at the motor connector, instead of the motor. Light duty test lamps won't absolutely confirm that the main contactor for the motor is capable of passing the motor's required current, but the lamps should indicate that the basic open and close functions are taking place. There are probably some devices (possibly a single device) that act as travel limit switches for the gate arm/linkage.

So, I would suspect that if you place lamps where the motor would be, when you select Open, the one lamp would be on until you give the controller the limit signal (it's open, so stop). Then if I understand, the controller delay will cause a pause before the controller will auto-cycle to Close, so the other lamp should light until you give the controller the limit signal (it's closed, so stop).

Starting these types of motors repeatedly is severe duty for the start windings and the start capacitor(s). What I mean by repeatedly would be the motor starting more than 6 or 8 times per hour. And since each opening is actually starting the motor twice, using test lamps for testing may be a good idea. If you had some heavier loads (6 to 10A) to substitute the motor with, that would be more of an actual test of the controller, as the motor will draw some serious current very briefly each time it starts.

Typically, the centrifugal switch for the start winding is located in the end bell of the motor opposite the output shaft end (usually the end where the leads enter the motor). The switch contacts are generally secured to the end bell of the motor.

Removing the end bell of a general purpose utility-type motor usually means removing the nuts from four long screws that secure the end bells and center (stator section) together, by running thru the case with screw heads at one end, and nuts at the other. It's always a good idea to mark the orientation of the end bells to the case by making distinct marks at both ends of the case and the end bells, where the end bells meet the case.

Maybe Bob Parker would know the specific differences, but I believe that the characteristics of AC capacitors used in induction motors are significantly different than electrolytic capacitors typically found in electronic equipment.

Other signs to look for in this type of unit would be discolored terminals on wiring connections, which generally always indicates high resistance connections that have overheated.

-- Cheers, WB .............

Yes check the centrifugal switch.

ESR meter isn't telling you the full story... You need to know the Farad value.. ESR is not a factor here.

Wild_Bill wrote:

I had another look at the motor and mechanism this afternoon. The motor start ciruit measured open. Whether it's the centrifugal switch or it's the start winding, it needs repair. As for right now, I'm going to call some local motor repair shops next and see if it can be fixed. I like the idea have having an experienced person look at it and not having to worry about for another 30 years. The capacitors look ok physically. No swelling, cracking, or discoloration. The relays show a tiny bit of wear but nothing too bad.

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA

It's not rocket science. It's a GE fractional horsepower induction motor. If the start cap is ok then the mechanical switching inside the motor is bad. And I don't recall ever seeing the need to parallel two

130's together to get a 1/6 HP motor to start. Maybe one for run and one for start but usually smaller value for the run cap. Find a drawing for the motor.

Here are some additional specs I found on the motor label:

1/3 hp

Von Weise Gear Co., St. Louis, Missouri Model V00358AG10

6 (six!) rpm.

Time Rating: cont.

I still cannot find any info regarding what value capacitor should be installed with this motor. The motor with pulley and case weighs 30 pounds. I saw a hefty spring inside the casing via an air vent near the bottom.

Thanks for your reply.

-- David Farber David Farber's Service Center L.A., CA

Von Weise gear motor.

Von Weise Gear Company Industrial Park Saint Clair, MO 63077

Tel. 636.629.1010

They should have info on their unit.

I've repaired several Baldor 10/15 horse / 230 volt single phase repulsion/induction motors. Repulsion motor on start for high torque commutator is shunted at speed and then runs as repulsion motor. No caps needed. When I say repair I mean assembled rebuilt parts and dressed the comm. This motor weighs 370 lbs.

You are going to have to find someone familiar with the gearmotor call Von Weise.

I was wondering earlier, if the motor was a gearhead motor. With an output of 6 RPM, there wouldn't definitely be a need for high starting torque for the motor shaft, since the geartrain provides output shaft torque.

So, the capacitors that were found may not be the original ones, and are not likely to be for a 1/6 HP motor. The motor shop where I get parts told me that a general guideline for start capacitor (value) sizing is 500uF for 1 HP, for capacitor start split-phase motors. The capacitor value you found would be adequate for a capacitor start split-phase motor of 3/4 HP to 1 HP. Anything is possible with used equipment, and if the capacitor had failed in the past, someone may have confused the resistors-in-parallel rule, with capacitors in parallel.

Since the gear reduction unit provides a considerable amount of torque, it's possible that the motor may be a PSC permanent split capacitor type, and not a capaitor start split-phase motor.

The capacitor value would still be wrong for a PSC motor that size. PSC motors are often used with gear reduction boxes to provide low RPM outputs, but the capacitors used are very low values, as in single or double-digit values, not 100+uF.

PSC motors are fairly simple, in that the stator is made up of two identical windings in series, with the 3 terminals arranged like a center-tapped transformer winding. The connection of one of the capacitor's leads is changed for CW or CCW rotation.

Commercial application PSC motors are very reliable, they often have ball bearings for the motor shaft, and nearly always have internal thermal protection, and they are commonly designed with impedance protection.

The PSC types don't have centrifugal switches, and the spring you saw thru the vent is likely to be part of the mechanism for a centrifugal switch.

-- Cheers, WB .............

Wild_Bill wrote:

Just to update what I found out in the past few days: The label on the motor says 1/3 hp. I called some repair shops and asked if they knew about the start capacitance value. One tech told me that the GE 5KH series was a split phase motor and did not require any start capacitor. I finally found a local guy who was able to come to my shop and call me back with an estimate. He said the aluminum start windings were bad and that he would replace both the start and run windings with copper wires. As to the question of starting capacitance, he said adding a capacitor wouldn't hurt especially if it was running that way for a long time. I'll be getting the repaired motor back tomorrow and hopefully it will be as good as new.

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA

I'm glad you found a solution, David. From what I've been hearing in recent years, shops that are interested in repairing small motors are becoming scarce.

I realized that I'd mis-stated the HP rating you stated from the motor label after the reply was sent. Still, that value of capacitance is excessively high for a small motor.

The guy that said a split-phase motor doesn't require a start capacitor is correct, although when S-P motors are manufactured with a start capacitor, they're capable of being used in applications that require higher starting torques, hence the CS,S-P naming. Many heavy duty motor applications, such as industrial-duty air compressors require motors with both start and run capacitors.. CS,CR,S-P type.

Because of the high gear ratio to attain the 6 RPM output, the starting torque requirement wouldn't be very high. The ratio is over 250:1 for a 1700 RPM motor.

-- Cheers, WB .............

Hey Wild Bill,

Elsewhere in this thread you mention adding a start capacitor to a split phase motor, I'm wondering how one goes about gaining access to the proper wires to hook it up, that is, is it usually straight forward and easy to ID the proper hookup points, are the leads you need to hook into usually long enough, or do you have to go digging into the windings and add some wire and such?

Thanks, Mike

Wild_Bill wrote:

In the typical utility type split-phase motor, the 120VAC line lead would go directly to the centrifugal switch. The centrifugal switch is in series with the start winding. So, the terminals are generally available at the terminal board, although it may be necessary to access the connections by removing the end bell from the motor. This usually makes it much easier to see/confirm the actual connections, and check them with an ohm meter. The capacitor can be prepared for connection by adding suitable leads to the terminals, which will allow the connections to be made inside the motor's case.

If the connection points are unclear, a motor book or the manufacturer's wiring diagram may be helpful in determining the correct connection points. Seek the help of a person that's qualified and experienced with motor wiring if any of the comments mentioned here are unclear.

A suitably sized (value) AC capacitor with the properly rated working voltage can be added in series with the AC line terminal and centrifugal switch connector, which may just be quick connect, push-on terminals or leads attached to screw posts with nuts. Most fractional HP split-phase motors have these types of terminals, if other types of connections are made, one would need to add some connections that are properly insulated and isolated from rotating parts of the rotor.

Since the motor wasn't originally equipped with a starting capacitor, the capacitor will need to be securely mounted to the motor case or near the motor, with the terminal connections insulated. An electrical workbox makes a good enlosure to house an external capacitor in.

Thermal protection feature: Fractional HP motors generally have self-resetting thermal protection devices buried in the motor's windings, although larger output motors may have manually resettable thermal protection switches which are externally accessible, usually a red button marked Reset. Thermal protection will help prevent damage to the motor caused from overheating, from conditions such as reduced/blocked air flow or load increase on the motor, but may not offer any protection in the event of a jam or stall that takes place quickly.

Current protection devices can prevent motor damage by interrupting the input power connections when over-current conditions take place.

-- Cheers, WB .............