Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr

Tor Tveitane wrote:
Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr



I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

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"Tor Tveitane" wrote in message
...
| Hi,
|
| Can I use a LCR bridge in inductance mode to measure difference in
| inductance if I suspect one of the windings in an electrical motors to
have
| shorted turns...?

Sure. Compare the ratio of inductance to resistance.

| What is the preferred way to check for shorted turns within an
inductor...?

For shorted turns in a motor use a growler.

N

On Sun, 07 Nov 2004 19:25:13 GMT, CJT wrote:

Tor Tveitane wrote:
Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr



I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

That was my thought/guess as well.

Tom

"Tom MacIntyre" skrev i melding
...

I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

That was my thought/guess as well.

Any urls and info to show how to setup this and to diagnose the response..?

Tor

"Tor Tveitane" wrote in message
...
| "Tom MacIntyre" skrev i melding
| ...
|
| I don't know what's preferred, but one way might be to ring it like
| a flyback and look at the response.
|
| That was my thought/guess as well.
|
| Any urls and info to show how to setup this and to diagnose the
response..?

http://repairfaq.ece.drexel.edu/REPAIR/F_appfaqi.html

What sort of motor? What's shorted, field or rotor?

N

Tor Tveitane wrote:
"Tom MacIntyre" skrev i melding
...


I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

That was my thought/guess as well.


Any urls and info to show how to setup this and to diagnose the response..?

Tor


This is the kind of thing I had in mind:

http://repairfaq.ece.drexel.edu/sam/flytest.htm#flyadv

--
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minimize spam. Our true address is of the form .

"Tor Tveitane" wrote in message
...
Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to
have
shorted turns...?

What is the preferred way to check for shorted turns within an
inductor...?

Thanks for clues

Tpr




I've never used one but isn't a growler used for this purpose.

electronic hints and repair briefs
http://homepages.tcp.co.uk/~diverse

"N Cook" writes:

I've never used one but isn't a growler used for this purpose.

Yes, though it would be hard to justify the expense to fix one small
motor.

See, for example: http://www.sotcher.com/mre/520.html

It's just the primary of a transformer connected to 60 Hz along with
a hacksaw blade, so you could probably build one or improvise from
something else.

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On 08 Nov 2004 08:11:57 -0500 Sam Goldwasser
wrote:

"N Cook" writes:

I've never used one but isn't a growler used for this purpose.

Yes, though it would be hard to justify the expense to fix one small
motor.

Yes, but any electric motor shop, or automotive electric shop will
have a growler and would charge only a very small fee to test an
armature for you.

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

If you bring it over here, it would take me less than 2 minutes to
check it out. ;-)

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

Does anyone know if this happens?

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

"Jim Adney" wrote in message
...
| On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
| wrote:
|
| Disassemble the motor and just take in the rotor, so that they don't
| have to do any significant work.
|
| IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
| variety.
|
| I was wondering about that. Wouldn't a squirrel cage motor still have
| the same magnetic properties? I'm not sure, but I'd bet that such a
| rotor would still pass the growler test, but it's hard to imagine a
| squirrel cage rotor with a short in it, which, I believe is what the
| OP asked about.

I don't know how to 'growl' a squirrel cage motor. I'd just fire it up and
check the amps on each leg.

NM

"Jim Adney" wrote in message
...
On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

Does anyone know if this happens?



I've never even heard of a rotor failure on any type of induction motor,
usually it's the starting switch, capacitor, or bearings that fail. The
stator windings can burn out but it's rare.

Jim Adney writes:

On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

By definition, a squirrel cage rotor is all shorts.

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"James Sweet" writes:

"Jim Adney" wrote in message
...
On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

Does anyone know if this happens?

I've never even heard of a rotor failure on any type of induction motor,
usually it's the starting switch, capacitor, or bearings that fail. The
stator windings can burn out but it's rare.

The only way a squirrel cage rotor could fail would be for one or more
of the shorting bars to open. A quirrel cage rotor is based on all
the bars being shorted at the end-plates.

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On 11 Nov 2004 08:08:07 -0500 Sam Goldwasser
wrote:

Jim Adney writes:

On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

By definition, a squirrel cage rotor is all shorts.

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Jim Adney writes:

On 11 Nov 2004 08:08:07 -0500 Sam Goldwasser
wrote:

Jim Adney writes:

On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

By definition, a squirrel cage rotor is all shorts.

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

Nah. A commutator motor happens to be shorted but that is a byproduct
of how it's wound, not a requirement. A squirrel cage rotor is a bunch
of copper bars embedded just under the surface of a solid steel rotor
running length-wise. They are shorted at the end plates. Since these
are induction motors, they depend on the current flowing in the bars
as the secondary of a transformer to provide the torque.

For brush-type motors, current is applied to the rotor windings via the
brushes. It's possible to build such a motor without "shorted" windings.

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"Jim Adney" bravely wrote to "All" (11 Nov 04 20:57:04)
--- on the heady topic of " Detect shorted turns in motor windings..."

JA From: Jim Adney

JA On 11 Nov 2004 08:08:07 -0500 Sam Goldwasser
JA wrote:

Jim Adney writes:

On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
wrote:

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

By definition, a squirrel cage rotor is all shorts.

JA Right, but so is a regular commutator rotor. The only difference, I
JA think, is that the squirrel cage rotor is wound with much more rugged
JA "wire."

The squirrel cage rotor is really a rotating transformer with a very
low resistance secondary. Any phase difference (slip) between the
applied field and the transformed field generates very high currents
in the range of 100's of amperes. To say the rotor is wound with much
more rugged wire is really an understatement. It is this high current
that causes a counter emf, applying a mechanical torque to the shaft,
and results in the desired motor action.

A*s*i*m*o*v

.... Electrical engineers deal with current events.

On 12 Nov 2004 08:27:24 -0500 Sam Goldwasser
wrote:

Jim Adney writes:

On 11 Nov 2004 08:08:07 -0500 Sam Goldwasser
wrote:

By definition, a squirrel cage rotor is all shorts.

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

Nah. A commutator motor happens to be shorted but that is a byproduct
of how it's wound, not a requirement. A squirrel cage rotor is a bunch
of copper bars embedded just under the surface of a solid steel rotor
running length-wise. They are shorted at the end plates. Since these
are induction motors, they depend on the current flowing in the bars
as the secondary of a transformer to provide the torque.

I'm in total agreement with the last part of this paragraph.

For brush-type motors, current is applied to the rotor windings via the
brushes. It's possible to build such a motor without "shorted" windings.

Can you put your money where your mouth is? I've certainly never seen
a commercial motor which was wound this way, and it strikes me that
such a motor would quickly destroy its commutator as you tried to
suddenly turn off the current in each winding segment.

I'm prepared to eat my words, however, if someone can come up with an
example. ;-)

Note that I put in the word "commercial" so that you guys don't point
out the home-build from 2 nails and a bunch of wire type motors which
are used to demonstrate basic motor principles. Yes, I agree that it's
not "necessary" unless you want to make a practical motor.

I'm not trying to be pedantic, just sticking to the original question
about a shorted turn in a motor, which I was willing to assume was a
commercial motor of some kind.

So, to get back to my question: Has anyone ever seen an
electromagnetic failure in a squirrel cage rotor? Does it EVER happen?

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Jim Adney writes:

On 12 Nov 2004 08:27:24 -0500 Sam Goldwasser
wrote:

Jim Adney writes:

On 11 Nov 2004 08:08:07 -0500 Sam Goldwasser
wrote:

By definition, a squirrel cage rotor is all shorts.

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

Nah. A commutator motor happens to be shorted but that is a byproduct
of how it's wound, not a requirement. A squirrel cage rotor is a bunch
of copper bars embedded just under the surface of a solid steel rotor
running length-wise. They are shorted at the end plates. Since these
are induction motors, they depend on the current flowing in the bars
as the secondary of a transformer to provide the torque.

I'm in total agreement with the last part of this paragraph.

For brush-type motors, current is applied to the rotor windings via the
brushes. It's possible to build such a motor without "shorted" windings.

Can you put your money where your mouth is? I've certainly never seen
a commercial motor which was wound this way, and it strikes me that
such a motor would quickly destroy its commutator as you tried to
suddenly turn off the current in each winding segment.

I didn't say that any commercial motors were built this way. I don't
know. What I'm saying is that the motor will turn, which would not
be the case if the squirrel cage rotor were open.

I'm prepared to eat my words, however, if someone can come up with an
example. ;-)

Note that I put in the word "commercial" so that you guys don't point
out the home-build from 2 nails and a bunch of wire type motors which
are used to demonstrate basic motor principles. Yes, I agree that it's
not "necessary" unless you want to make a practical motor.

I'm not trying to be pedantic, just sticking to the original question
about a shorted turn in a motor, which I was willing to assume was a
commercial motor of some kind.

So, to get back to my question: Has anyone ever seen an
electromagnetic failure in a squirrel cage rotor? Does it EVER happen?

I have a bench grinder that seems to have such a fault. I have eliminated
mechanical causes as best I can and it still intermittently stops and
hums loudly when the rotor gets hot.

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"Sam Goldwasser" wrote in message
...

| I have a bench grinder that seems to have such a fault. I have eliminated
| mechanical causes as best I can and it still intermittently stops and
| hums loudly when the rotor gets hot.

Bearings?

NM

"NSM" writes:

"Sam Goldwasser" wrote in message
...

| I have a bench grinder that seems to have such a fault. I have eliminated
| mechanical causes as best I can and it still intermittently stops and
| hums loudly when the rotor gets hot.

Bearings?

That's what I thought originally but I couldn't find any problems.

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"Sam Goldwasser" wrote in message
...

| | I have a bench grinder that seems to have such a fault. I have
eliminated
| | mechanical causes as best I can and it still intermittently stops and
| | hums loudly when the rotor gets hot.
|
| Bearings?
|
| That's what I thought originally but I couldn't find any problems.

If it's a cap run motor maybe the cap is shorting, otherwise a shorted turn
in the motor I think.

NM

"NSM" writes:

"Sam Goldwasser" wrote in message
...

| | I have a bench grinder that seems to have such a fault. I have
eliminated
| | mechanical causes as best I can and it still intermittently stops and
| | hums loudly when the rotor gets hot.
|
| Bearings?
|
| That's what I thought originally but I couldn't find any problems.

If it's a cap run motor maybe the cap is shorting, otherwise a shorted turn
in the motor I think.

Could be though the effect seems to depend on the position (angle) of the
rotor. It's a split phase motor.

Also should note that if the rotor gets up to speed before it heats up,
the motor runs fine. Once it gets into funky mode, though, it can't
be spun up by hand unless it's done with power off.

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"Sam Goldwasser" wrote in message
...

| Could be though the effect seems to depend on the position (angle) of the
| rotor. It's a split phase motor.
|
| Also should note that if the rotor gets up to speed before it heats up,
| the motor runs fine. Once it gets into funky mode, though, it can't
| be spun up by hand unless it's done with power off.

Dead squirrel? Seriously, if the squirrel cage bars are soldered, perhaps
they have failed.

N

"NSM" writes:

"Sam Goldwasser" wrote in message
...

| Could be though the effect seems to depend on the position (angle) of the
| rotor. It's a split phase motor.
|
| Also should note that if the rotor gets up to speed before it heats up,
| the motor runs fine. Once it gets into funky mode, though, it can't
| be spun up by hand unless it's done with power off.

Dead squirrel? Seriously, if the squirrel cage bars are soldered, perhaps
they have failed.

That's what I thought might have happened but there certainly isn't
any visual evidence of it. I even tried to heat the rotor up with a
propane torch but that was a joke - it barely got warm.

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On 15 Nov 2004 08:26:06 -0500 Sam Goldwasser
wrote:

Jim Adney writes:

So, to get back to my question: Has anyone ever seen an
electromagnetic failure in a squirrel cage rotor? Does it EVER happen?

I have a bench grinder that seems to have such a fault. I have eliminated
mechanical causes as best I can and it still intermittently stops and
hums loudly when the rotor gets hot.

Do you have access to a growler? If so, I wonder if you could remove
the rotor and check it cold and then again after warming in an oven.
Might a simple physical inspection reveal something, perhaps even
something that could be fixed.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

"NSM" writes:

"Sam Goldwasser" wrote in message
...

| Physically it looks fine. It's not that important to spend time on
| at this point. I picked up another grinder for $6.
|
| Probably no need to put it in an oven. Just run it up a couple times
until
| it fails and let it cook in that state. Then pull the rotor and test.

It sure sounds like it's pulling out of sync, so there's no out-of-phase
current to keep it running. Does it have a capacitor?

No capacitor. Split phase meaning two windings, one with much higher
resistance to produce the phase shift.

The thing is, it's not only stopping. It acts as a very good brake
when the condition occurs - hard to turn. This unlike an induction
motor with only one winding energized which will turn freely and
then spin up to normal speed once its going fast enough. This one
will slow down if you try to spin it by hand. Then make a loud hum
or buzz at a certain angle of the rotor.

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"Sam Goldwasser" wrote in message
...

| No capacitor. Split phase meaning two windings, one with much higher
| resistance to produce the phase shift.
|
| The thing is, it's not only stopping. It acts as a very good brake
| when the condition occurs - hard to turn. This unlike an induction
| motor with only one winding energized which will turn freely and
| then spin up to normal speed once its going fast enough. This one
| will slow down if you try to spin it by hand. Then make a loud hum
| or buzz at a certain angle of the rotor.

I wonder if the centrifugal switch is failing, but I don't see why that
would slow it down. Most odd.

N

"NSM" writes:

"Sam Goldwasser" wrote in message
...

| No capacitor. Split phase meaning two windings, one with much higher
| resistance to produce the phase shift.
|
| The thing is, it's not only stopping. It acts as a very good brake
| when the condition occurs - hard to turn. This unlike an induction
| motor with only one winding energized which will turn freely and
| then spin up to normal speed once it's going fast enough. This one
| will slow down if you try to spin it by hand. Then make a loud hum
| or buzz at a certain angle of the rotor.

I wonder if the centrifugal switch is failing, but I don't see why that
would slow it down. Most odd.

If it failed to cut out, then the motor would just smoke.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
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"Sam Goldwasser" wrote in message
...
| "NSM" writes:

| I wonder if the centrifugal switch is failing, but I don't see why that
| would slow it down. Most odd.
|
| If it failed to cut out, then the motor would just smoke.

I've heard of them closing randomly while the motor is running.

N

"NSM" writes:

"Sam Goldwasser" wrote in message
...
| "NSM" writes:

| I wonder if the centrifugal switch is failing, but I don't see why that
| would slow it down. Most odd.
|
| If it failed to cut out, then the motor would just smoke.

I've heard of them closing randomly while the motor is running.

But all that would do is create smoke when the starting winding overheated!
The motor would still run.

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

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