Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Capacitor Start, Capacitor Run Motor

I havd an air compressor that has the Subject line type of motor,
115vac. It only has about 200 hours on it. I had left it on for a
couple of days recently and found that my circuit breaker in my garage
was tripped. I restet it and the compressor started(surprised me
because I didn't remember leaving it on.). It ran about 2 seconds and
the circuit breaker kicked, again.
Before I tore into the compressor, I made sure it wasn't the circuit
breaker by plugging into the utility room circuit, 23 seconds later, it
kicked that breaker.
The strange thing is that it sounds different than before. It did have
a deeper, stronger sound when the motor was running, now it sounds
kinda puny. When the motor starts and runs, it turns the compressor
pump an actually builds a small amount of pressure before it kicks off.
I have pulled the starting cap and the run cap to get the numbers off,
and have found them online. However, before I buy them, I was wondering
if this sounds more like the main winding (not the startup winding) may
be burned out. I haven't opened the case on the motor to look, yet, but
I wouldn't think that the winding would NORMALLY short (thus more
current), but sometime during the few days that I had left the
compressor on, we had a lightning hit that destoyed a dvd player and an
audio amp.
It could be coincidence.
Anyway, what would cause the motor to pull excess current. Would the
run cap being bad cause this?
I have checked both caps with a DMM, and all I can say is that they are
not shorted.

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Default Capacitor Start, Capacitor Run Motor

Short answer: replace the capacitors.


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Default Capacitor Start, Capacitor Run Motor



On Oct 15, 2:48 pm, "Charles Schuler"
wrote:
Short answer: replace the capacitors.


I agree. The capacitors are cheap to replace. In general the run
capacitor value is much less than the start capacitor value.

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Default Capacitor Start, Capacitor Run Motor



On Oct 15, 5:17 pm, "Ken Layton" wrote:
On Oct 15, 2:48 pm, "Charles Schuler"
wrote:

Short answer: replace the capacitors.I agree. The capacitors are cheap to replace. In general the run

capacitor value is much less than the start capacitor value.

So, a bad capacitor could cause a hi current condition?

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Default Capacitor Start, Capacitor Run Motor


"Robowang" wrote in message
oups.com...


On Oct 15, 5:17 pm, "Ken Layton" wrote:
On Oct 15, 2:48 pm, "Charles Schuler"
wrote:

Short answer: replace the capacitors.I agree. The capacitors are cheap
to replace. In general the run

capacitor value is much less than the start capacitor value.

So, a bad capacitor could cause a hi current condition?


Not exactly ... see my short answer. Circuit breakers have two trip times.
A stalled motor can evoke the longer trip time because a capacitor failure
does not get the motor turning.




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Default Capacitor Start, Capacitor Run Motor

I ordered the caps.
However, The motor does start. It actually gets to where I would guess
that the start winding is cut out, maybe 50-60% of it's speed. then it
kicks the circuit breaker.
When the compressor is first started, it is very easy to rotate the
pump. Of course, as the pressure is built up in the tank, the
compressor is going to work the motor harder. But it kicks out almost
immediately.
To pull that much current, the main winding would have to be near
shorted. I have seen older motors lose the coating on the windings,
partially shorting the windings and lose resistance due to losing wire
length in the winding. This will cause the motor to not be as efficient
at the same current draw. Or I have seen an open in the winding, which
kills the motor, totally.
Also, if the start capacitor is bad, wouldn't that just cause the motor
not to turn at start up and just hum and jiggle? I think the start cap
on a single phase motor is just to cause enough of an out of phase
condition to get the rotor to start rotaing, then once it starts
turning, the start winding (and start cap) is cut out and the main
winding will continue the rotation in the direction the start winding
phase pulled the rotor orignally.
It's all smoke and mirrors. I'll get back when I get the caps. I hope
it is just the caps, as a new 6hp peak motor is close to $200.00.
thanx guys.

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Default Capacitor Start, Capacitor Run Motor

Of course the motor could be bad ... but the point is that the capacitors
are more often bad. It is simply a matter of statistics, which is what
you'll mostly get when posting here.

My experience with motors and capacitors is 10:1 capacitor failures versus
winding failures. Just me ... no science ... just statistics.

Good luck.



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Default Capacitor Start, Capacitor Run Motor

Hi!

As has been mentioned, your compressor's problem is likely the run
capacitor. Even if the start cap were bad as well, the motor might still be
able to start and get up to running speed just fine.

I don't think you can stress the capacitor enough with a simple meter test
to make it fail. It sounds like the run cap breaks down with stress and time
before turning into a short or more load than the circuit can handle. With
time it might get worse, such that your meter test would reveal a short
circuit.

I think you will find the replacement capacitors solve the problem, but I
would still like to hear how it goes.

William


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Default Capacitor Start, Capacitor Run Motor

I had almost the exact same problem about a month ago and it was just a bad
run cap.

- Mike

"William R. Walsh" m
wrote in message news:UYEYg.1024713$084.883077@attbi_s22...
Hi!

As has been mentioned, your compressor's problem is likely the run
capacitor. Even if the start cap were bad as well, the motor might still
be
able to start and get up to running speed just fine.

I don't think you can stress the capacitor enough with a simple meter test
to make it fail. It sounds like the run cap breaks down with stress and
time
before turning into a short or more load than the circuit can handle. With
time it might get worse, such that your meter test would reveal a short
circuit.

I think you will find the replacement capacitors solve the problem, but I
would still like to hear how it goes.

William




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Default Capacitor Start, Capacitor Run Motor



On Oct 16, 1:51 am, "Michael Kennedy"
wrote:
I had almost the exact same problem about a month ago and it was just a bad
run cap.

- Mike

"William R. Walsh" m
wrote in messagenews:UYEYg.1024713$084.883077@attbi_s22...

Hi!


As has been mentioned, your compressor's problem is likely the run
capacitor. Even if the start cap were bad as well, the motor might still
be
able to start and get up to running speed just fine.


I don't think you can stress the capacitor enough with a simple meter test
to make it fail. It sounds like the run cap breaks down with stress and
time
before turning into a short or more load than the circuit can handle. With
time it might get worse, such that your meter test would reveal a short
circuit.


I think you will find the replacement capacitors solve the problem, but I
would still like to hear how it goes.


William

That makes me feel better.
Yeah, I think if it is a cap that it's likely that it's the run cap. I
just don't have any experience with electric motors. The only thing I
have ever experienced was replacing a start cap in a refrigerator. It
wouldn't start up, just hum. The motor was a low rpm version and you
couls actually start it by spinning the shaft until it got up to speed.
A start cap fixed it.
I just wasn't for sure about the run cap. It's been along time since I
had any training in that area, but it seems like I remember that the
run cap was to help the motor make torque efficiently once it reaches
peak speed.
I have used a heavy duty cap checker and even it wasn't effective. The
best way to check big cap is substitution. But you gotta have an extra.
I know a DMM is pretty useless for a cap out of the circuit, but it's
all I have.
I should have the new caps by the end of the week, So I'll let everyone
know what happens.
Thanx for the input.



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Default Capacitor Start, Capacitor Run Motor

"Robowang" writes:

I ordered the caps.
However, The motor does start. It actually gets to where I would guess
that the start winding is cut out, maybe 50-60% of it's speed. then it
kicks the circuit breaker.


Can you confirm that the start winding is actually cutting out. It
may be that the centrifugal switch is the problem.

When the compressor is first started, it is very easy to rotate the
pump. Of course, as the pressure is built up in the tank, the
compressor is going to work the motor harder. But it kicks out almost
immediately.
To pull that much current, the main winding would have to be near
shorted. I have seen older motors lose the coating on the windings,


Not really. All you need is a few shorted turns which then act as the
shorted secondary of a transformer.

partially shorting the windings and lose resistance due to losing wire
length in the winding. This will cause the motor to not be as efficient
at the same current draw. Or I have seen an open in the winding, which
kills the motor, totally.
Also, if the start capacitor is bad, wouldn't that just cause the motor
not to turn at start up and just hum and jiggle? I think the start cap
on a single phase motor is just to cause enough of an out of phase
condition to get the rotor to start rotaing, then once it starts
turning, the start winding (and start cap) is cut out and the main
winding will continue the rotation in the direction the start winding
phase pulled the rotor orignally.
It's all smoke and mirrors. I'll get back when I get the caps. I hope
it is just the caps, as a new 6hp peak motor is close to $200.00.
thanx guys.


One simple (in principle) test would be to remove the compressor load entirely
and power only the run winding. Then, spin it by hand and apply power while
it's still turning. It should come up to speed and run without tripping the
breaker if the windings are good.

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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Default Capacitor Start, Capacitor Run Motor

I read all of the posts and I find it odd that no one asked about both
the size of the breaker and if this compressor motor was plugged into
an extension cord? If an extension cord is used, amperage drop over
distance maybe...just a thought!
Cheers, Steve
Sam Goldwasser wrote:
"Robowang" writes:

I ordered the caps.
However, The motor does start. It actually gets to where I would guess
that the start winding is cut out, maybe 50-60% of it's speed. then it
kicks the circuit breaker.


Can you confirm that the start winding is actually cutting out. It
may be that the centrifugal switch is the problem.

When the compressor is first started, it is very easy to rotate the
pump. Of course, as the pressure is built up in the tank, the
compressor is going to work the motor harder. But it kicks out almost
immediately.
To pull that much current, the main winding would have to be near
shorted. I have seen older motors lose the coating on the windings,


Not really. All you need is a few shorted turns which then act as the
shorted secondary of a transformer.

partially shorting the windings and lose resistance due to losing wire
length in the winding. This will cause the motor to not be as efficient
at the same current draw. Or I have seen an open in the winding, which
kills the motor, totally.
Also, if the start capacitor is bad, wouldn't that just cause the motor
not to turn at start up and just hum and jiggle? I think the start cap
on a single phase motor is just to cause enough of an out of phase
condition to get the rotor to start rotaing, then once it starts
turning, the start winding (and start cap) is cut out and the main
winding will continue the rotation in the direction the start winding
phase pulled the rotor orignally.
It's all smoke and mirrors. I'll get back when I get the caps. I hope
it is just the caps, as a new 6hp peak motor is close to $200.00.
thanx guys.


One simple (in principle) test would be to remove the compressor load entirely
and power only the run winding. Then, spin it by hand and apply power while
it's still turning. It should come up to speed and run without tripping the
breaker if the windings are good.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.


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Default Capacitor Start, Capacitor Run Motor

The breaker size is 20 amps.
I am not using an extension cord.
I did connect to seperate circuit with a 20 amp breaker and it tripped.
also.
I hope to get the caps this week, but I still haven't been notified
that they were shipped.
I have a decent Electronics store about 30 miles away, so if I don't
hear from the net store today, I will cancel my order and go to the
local store this weekend.
Thanx guys.

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