Motor problem 1

[Rick9]

Hello..

We have a small single phase motor which operates a dust collector. The motor is 3kw x 240V x PH-1
This motor has an FLA rating of 19 amps. It is run on its own 30amp circuit and all wiring is appropriate in size .. less than 25 feet from the panel.

The problem is that the motor has been shutting off (magnetic starter) due to over current.

The motor is made by ABT in Germany and is only 3 years old. The starter is made by Klinger and Born also in Germany.

Its a bit of an odd motor. In order to start it, you hold the power button for 3-4 seconds. There is no centrifugal switch. The start and run capacitors are mounted inside the dust collector cabinet, they are separate from the motor as well.

I put a meter on a single wire between the starter and the motor and left 1 x 6" Blast gate open in the system. When the motor reached full speed, it was drawing 13.1 Amps..

I opened a second gate and the amperage increased to 13.8 Amps.

This all seemed normal so I shut it off.

I then opened 6 gates and started the motor again. This time the amperage settled at 23.4 Amps . Almost 20% over current .. I shut it down before it tripped the starter.

I then closed all the gates, expecting the current to be 13 amps or a bit lower, instead when I started it up, it settled at 17.4 Amps. At this point I am confused.

So I opened that original gate, the one where the current was 13.1 amps. The motor jumped to 20.5 Amps.

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The machine is in a shop where most all the tools are 3 phase, the compressor and DC are Single phase because they assist other machinery and the entire shop is run off a Digital Phase converter. The DC and compressor would use up 3 phase power.

Could the run capacitor failing cause the motor to draw excessive current ?
What else should I consider ?

 

[Rick9]

Swapped out the Run Capacitor with a new one .. Machine fired up just fine ..

Read the current off the two hot wires.. One is 14.9 amps .. the other is only 11.7 amps.. Sigh ..

If I remember correctly, the amperage should be within 10% ??

The amperage is different by 21%

Anyone have any ideas ?

 

[wayne440]

Run it for a while; if it works and doesn't overheat, I would return it to service and wait for the next thing to worry about.

 

[waross]

When you have different indicated current on the lines to a single phase motor, it is probably a metering error. Not unheard of with clamp-on type ammeters in tight locations. Possibly you were measuring motor only current on one line, and motor plus capacitor current on the other line.
Let's hope so because the other possibility is a faulty motor. If that is the case, expect total failure soon. On a single phase motor the current will be equal on both lines.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

One source of error is not getting the jaws all the way closed.

It's probably obvious, but I'll mention that if the measurement is correct, that would seem to suggest that you either have another wire to the motor that you didn't see, or else current finding a path to ground in the motor (through a ground-connected cap or winding).


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(2B)+(2B)' ?

 

[ScottyUK]

If this is a capacitor run motor then it's not unreasonable to expect the winding with the capacitor to have a slightly different current compared to the 'straight' winding. Maybe the OP could clarify if this is what he meant, or as Bill and Pete have interpreted that what goes in on one end doesn't appear to come out of the other end. That latter state is indeed bad.

 

[electricpete]

You're right Scotty, I didn't read the post closely enough. Somehow I got the idea that there were only two leads running from the supply to the motor, but reading it again the op never said that, and that wouldn't make sense anyway. Disregard my previous post.

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(2B)+(2B)' ?

 

[Rick9]

Yes.. I was being pointy headed.. I was checking the amperage in a place with the capacitors in the circuit.

With brand new capacitors, we checked the amperage at the lock out .. before the starter.. There is no improvement.. Its still running over current..

The only thing left is the motor winding's..

The machine is just over 3 years old and it appears the motor needs to be re-wound.. Pretty poor ..

 

[badservo]

Could also be that odd start switch sticking closed when you release the button.