Induction motor gone bipolar?

[David Farber]

I have an automatic gate which uses a GE 5KH36HN62T motor to open and close
the gate. The gate intermittently will not open. You can hear the motor buzz
and it will start moving if given a gentle push. The motor uses a capacitor
start circuit to get it going. The other fault with the motor is that
sometimes it turns in the wrong direction. This is my analysis of the
situation so correct me if I'm wrong. The fact that the motor buzzes and
will start turning with a gentle assist probably means there is a fault in
the start circuit. I tested the capacitors and they are ok. So I'm thinking
the internal motor start switch is sticking open. As far as the motor
occasionally turning the wrong direction, that too can be attributed to the
faulty start circuit because not only does the start circuit get the motor
going from a stopped position, it determines the direction that motor will
turn. If the load is light enough, the motor now may turn in either
direction if the start windings are not giving it its initial boost. Does
this make sense?

Thanks for your reply.

 

[William Sommerwerck]

Bipolar? Lubricate it with lithium grease!

 

[Samuel M. Goldwasser]

I have an automatic gate which uses a GE 5KH36HN62T motor to open and close
the gate. The gate intermittently will not open. You can hear the motor buzz
and it will start moving if given a gentle push. The motor uses a capacitor
start circuit to get it going. The other fault with the motor is that
sometimes it turns in the wrong direction. This is my analysis of the
situation so correct me if I'm wrong. The fact that the motor buzzes and
will start turning with a gentle assist probably means there is a fault in
the start circuit. I tested the capacitors and they are ok. So I'm thinking
the internal motor start switch is sticking open. As far as the motor
occasionally turning the wrong direction, that too can be attributed to the
faulty start circuit because not only does the start circuit get the motor
going from a stopped position, it determines the direction that motor will
turn. If the load is light enough, the motor now may turn in either
direction if the start windings are not giving it its initial boost. Does
this make sense?

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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[David Farber]

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.

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

 

[David Farber]

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: http://www.pbase.com/mrfixit/image/81687434
For other pics of the electronics: http://www.pbase.com/mrfixit/gate

Thanks for your reply.

 

[David Farber]

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.

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.

These types of motors aren't instantly reversible.

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

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

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.

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.
http://www.pbase.com/mrfixit/image/81687434

Thanks for your reply.

 

[Jamie]

I have an automatic gate which uses a GE 5KH36HN62T motor to open and close
the gate. The gate intermittently will not open. You can hear the motor buzz
and it will start moving if given a gentle push. The motor uses a capacitor
start circuit to get it going. The other fault with the motor is that
sometimes it turns in the wrong direction. This is my analysis of the
situation so correct me if I'm wrong. The fact that the motor buzzes and
will start turning with a gentle assist probably means there is a fault in
the start circuit. I tested the capacitors and they are ok. So I'm thinking
the internal motor start switch is sticking open. As far as the motor
occasionally turning the wrong direction, that too can be attributed to the
faulty start circuit because not only does the start circuit get the motor
going from a stopped position, it determines the direction that motor will
turn. If the load is light enough, the motor now may turn in either
direction if the start windings are not giving it its initial boost. Does
this make sense?

Yes
check the centrifugal switch.

 

[Jamie]

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.

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

 

[David Farber]

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.

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]

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]

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.

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]

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.

I got a reply from Regal Beloit regarding my wiring inquiry. I've uploaded
the diagram here:
http://members.dslextreme.com/users/farberbear/GE_motor/Motor-wiring.jpg

Interestingly enough, in the reply from the support representative, he said
that this motor does not require a capacitor nor is it likely it will
operate if one is used. So why is there a capacitor drawn in the diagram?

By the way, I reinstalled the repaired motor exactly the way it was
previously installed, with the two capacitors, and it is working fine.

 

[David Lesher]

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.

I'll take exception to one part of Bill's otherwise great wording....

As you can see in the diagram linked in this thread; the running winding
is always on [...when the motor is powered up, obviously...] but the
starting winding is soon turned off.

The starting winding is on only for the ~~~100-200 ms it takes the motor to
spin up. (I measured the time once in Machines Lab. Hi Prof Klingshirn!)

(You can work all this out with copious amounts of math but the following
will do.)

What makes it all work is phase shift, both electrical and physical.
The starting winding jerks the motor shaft slightly, then 90 degrees
later [electrically] the running winding [offset physically around the
path of the rotor] follows up with a second one. That one-two punch is
what starts the motor in the correct direction. If you want to go the
other way, flip the running winding around so the running jerk is the
opposite side of the starting peak.

The capacitor also limits the starting current to some finite value;
more capacitance in parallel is more current. Since it's used for only
200 ms, the starting winding can get away with much higher current
than the running one. But hold the motor stalled; and smoke will soon
arise...unless the breaker trips.

Now a shaded pole motor fudges in the phase shift without a cap, but
gives far less torque. If you recall analog electric clocks; that's what
they use.

Three phase makes it all trivial. You get 3 peaks for the three windings,
each peak offset by 120 degrees [electrically] and the winding offset by
120 degrees physically; so you get ABCABCABCABC and the motor needs no
starting winding nonsense at all....it just goes.