Hi,
Is there any definite test for burnt windings either in the field or in the armature? Like an ohm meter?My concerns are related to an Lionel 1945-6 2-6-2 steam Prairie (single AC motor - Lionel #: 2025) and an American Flyer magnetic crane.The Prairie motor does not move at all. The crane motor makes hesitant moves, but no spinning.
Burnt Windings?
If the windings are burnt, a visual check may reveal discoloration and/or visible charing, however not every portion of the windings may be visible.
However, a better check would be a continuity check of the armature and field coil.
The field coil, being basically a wire wrapped around a plate, is checked like this:
Using a multimeter set to read resistance (Measured in Ohms), and the leads properly hooked up, check the continuity of the wire, it should have very low resistance, usually in the order of zero to a few ohms, as it is a wire. A very high resistance, for example hundreds of Ohms or above, would indicate an open circuit, i.e. a broken wire.
Also check the resistance between the field coil wire and the field plates. This should indicate a very, very high reading, typically infinity, or whatever the full scale reading is on the type of meter you use.
If there is a low/no reading between the wire and the plates, it means that there is a short between the wire and the plates, which would prevent the fild coil from building a magnetic field, which would yield a motor that will not run.
As far as the armature is concerned, check the resistance between commutator segments. Each reading should be zero/very low. Also, at this time it may be a good idea to check each of the segments for pitting, and looseness.
Check the resistance between the commutator segments and the shaft. This should be very very hich/infinate. A low reading would indicate a damaged armature. It may be possible to fix said damage at home, but unlikely, and is usually a PAIN.
While the motor is apart, check the condition of the brushes, and the brush holders. If there is insufficent pressure on the brushes, the motor will not run or at least run terribly.
When reassembling the motor, ensure that the motor turns easily and smoothly, if there is any binding, it can yield overheating which CAN burn out windings if left unchecked.
If you do not
Hi Railroader Sailor,
Thanks, very much for your detailed answer. I do have OHM meters and will make these tests later this week. And I will report the answers.
From your message, I assume that it is impossible to check for shorted windings in which the enamel is burnt and the short is only between the windings and not to the iron. Is that true?
Regards, Richard
Are you sure the windings are burnt?
Maybe you need to do some maintenance such as cleaning the brushes and the armature plate. Also I would check the wiring to the device, such as track side hookups, before trying to say that the windings are burnt. What about wiring in the 2-6-2 or the crane?
If the windings really are burnt you will smell it, smells worse than rotten eggs being burnt on a gas burner.
Lee F.
The only way to test for shorted windigs on such a small motor is resistance. And thats not to reliable either. the difference between a good coil and a shorted one could be less than one thousandth of an ohm. Most meters are not sensitive enough to tell the difference.
A shorted or open armature will usually have a lot of sparking at the commutator.
I did repair an armature one time that had a bad solder connection. The connection from winding to commutator was bad
A test of AC impedance is far more sensitive than a test of DC resistance.
How do you do that?
Put a 10-ohm 10-watt (minimum) resistor, an AC voltmeter, and your transformer output all in series. Then connect the voltmeter in parallel with two of the commutator segments, with the armature out of the motor. Don’t leave the armature connected longer than 1 second as you note the voltage measurement. Do the test on all three pairs of commutator segments. If the voltage is nearly the same for all three, the armature is very likely okay.
I just did this test on a good armature from a 2026, using 16 volts from a 1033 transformer. I read 1.8 volts on all three segment pairs.