DC Motor Trouble 1

[ProWinder]

We are working on a Westinghouse motor.
Frame 620-MCA Volts 230 DC
rise 75 Deg C Series Wound
HP 275 RPM 370 Amps 975 Hrs 1
HP 360 RPM 340 Amps 1280 Hrs 5


Looking at the com side of the motor it will run ccw and draws 150 amps
the motor will turn in the cw direction. The motor draws 500 amps.
When the power is turned off it appears that the armature turns ccw about the distance of one bar segment of the comm.
We tried switching A1 and A2 from the test panel. The motor will still only turn ccw. With A1 and A2 in the correct spot, we changed S1 and S2. The motor will now turn in the cw rotation, but not ccw.

We tried connecting the A1 and A2 test panel leads directly to the brush holders and the motor will still only rotate ccw.

We did do a polarity test of the frame. The series fields are correct. The inter poles are also correct. All the brushes are properly seated to the comm.

Any thoughts?

 

[rbulsara]

With one set of connections, the motor will turn only in one direction. You interchange A1 and A2 for reversing the direction. (assuming the original connections/polarities were good)

In your second sentence, what are you doing to turn it in cw direction when it draws 500A?

 

[waross]

I had a DC motor in a printing press that would not reverse. One of the connections was loose and was so badly heat corroded that the copper oxide was rectifying the current. When the connection was cleaned and tightened the motor ran in both directions with no problems.

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

 

[ProWinder]

The motor will not (sorry) turn in the cw direction. We are using a drum controller to test run the motor. With this we can change motor direction without moving the motor leads. We did try out a different motor to see if the test panel had a fault. The other motor ran just fine.

All of the connections inside the motor look to clean and well connected.

 

[DickDV]

It this is a series wound field motor as the nameplate data implies, and you have the series field wired in series with the armature, then, reversing the polarity of the two free leads, one an S and the other an A, will not result in a change of direction because you effectively have a double reversal, of the field and also of the armature.

To get reversal, you have to break the series connection between the S and A leads, bring them both out to the outside, and then reverse only one, either the two S leads or the two A leads.

If that doesn't result in reversal of rotation, then something very strange is going on. The first thing I would be absolutely sure of is that this is really a series wound motor. Because of the difference in forward and reverse amps, I half suspect you have either a comp shunt or stab shunt motor. Both of them will have S and A leads but also F1 and F2 leads.

Let us know.

 

[Marke]

Check to see what sort of motor this is.
Shunt motors can be easily reversed by the controller. Series can not and neither can some compound motors.(combination of series and shunt)

Your information says series.

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[ProWinder]

This is a series motor. I did change just the a1 and a2 leads, no change in direction. Change s1 and s2 and the motor will turn the other way. This is done and the drum switch that we are using is switched the same way with the motor leads in different locations.

The strange part of this is that the motor will turn no problem in the ccw direction but won't turn cw. That is said with A1 positive A2 negative S1 positive S2 negative. Change the drum switch to A1 negative A2 positive S1 positive S2 negative the motor hums and draws 500 amps and does not turn.
We tried turning the motor with no power to get it moving and turn on the power and it stops the armature.
I have seen something similar to this and we had a problem with the span of equalizer trays being 1-117 when it should have been 1-118. This was on a compound motor.
I was thinking we have a problem with the armature, but I was told this motor was in service and was taken out of service because the brake wheel was cracked. So we are at a loss of what is wrong.

 

[rbulsara]

Post your wiring diagram. It is not clear as to how your drum switch is wired.

Also see

http://www.joliettech.com/connections_dc_motors.htm

Does it match that?

In reverse it will be (+)A2----A1->S1---S2(-).

 

[ProWinder]

The wiring diagram for the drum switch I don't have. The connection does match the diagram you posted.
I have run other series motors without any troubles of reversing direction with the test panel we are using. This motor is should be easy to test run but doesn't make any sense.

 

[waross]

You probably have mislabled leads. If an A1 and S1 lead had the markings interchanged, you would expect these results.
That is you may be interchanging A1 and S1 instead of A1 and A2. You can end up with full voltage across the armature and the series field shorted end to end, or vise versa.

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

 

[ProWinder]

Waross, if this was the case should the motor still turn ccw or would it just not run at all?
With the motor apart I did trace the leads and did not see any thing stand out to be out of place.

 

[rbulsara]

I am no DC motor winding expert... but relying on my basic understanding here.

You said the motor is reversing (cw rotation) when S1 and S2 are interchanged. What does it draw then?

Is the issue only when interchanging A1 and A2?

If it works with no issues with S1/S2 interchanged, the motor should be OK. May be something gets messed up (interpole winding?) while reversing A1 A2.

 

[ProWinder]

when s1 and s2 are switched the motor changes direction. however it will not change direction when we switch the drum switch to reverse the motor.

 

[rbulsara]

Fix the switch and the test setup.

or test the motor without the "switch" or any of your test set up in both directions. If it works fine, then fix the switch!

 

[ProWinder]

The drum switch is part of out test panel. The test panel was built 40 years ago. I think I will have to try running the motor from a welder to avoid using the test panel.
I don't think the test panel is the problem, or the drum switch for that matter.
Thanks for the help I will try a few of these suggestions on Monday.
I will post what we find out to let you all know.

 

[waross]

Disconnect the motor and check out the connections on the drum switch with a continuity tester. That should be quick and easy.
Make sure that the leads from the motor to the controller have the same numbers on each end.

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

 

[edison123]

I think S1 & S2 are really A1 & A2. Check again.

And this being a series field motor, it should not be run without a load to avoid run-away speeds. Do you any have load on the motor ?

 

[ProWinder]

Well we found out the problem. The internal connection of one inter pole was pinched against the series winding leads. This gave us bucking fields. Once we isolated the two the motor ran just fine.

 

[ScottyUK]

Thanks for the feedback - far too many people don't bother. Star for doing that.


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If we learn from our mistakes I'm getting a great education!

 

[edison123]

I second Scotty. But I am still trying to understand how it worked in one direction and not the other. I will get it tomorrow.