Bad Motor Poles

[tehachapifan]

Thankfully this doesn't seem to be a very common problem, but I believe I may be experiencing my second bad motor pole. In both cases it basically caused the (DCC) loco to behave extremely erratically and with both I surmised it was a bad motor pole because the motor would occasionally not start from a stop unless I nudged the motor poles to get them going again. I also noticed with tonight's loco that the poles would do this in a certain position only, leading me to believe it is indeed a bad pole. Aside from these telltale(?) signs, are there any other more definitive tests to rule-out or confirm a bad motor pole?

[Steveruger45]

Hey Pete, where are you?   , Russ is asking about bad Poles.   

[daniel_leavitt2000]

He's busy making more poop joke threads in the Crew Lounge.

[tehachapifan]

Hey Pete, where are you?   , Russ is asking about bad Poles.   

I wondered if that might come up!

[peteski]

Sure, we always get blamed! 

Without taking the motor apart and measuring the resistance between pairs of the commutator segments I don't know of any reliable way to verify if a winding is open or shorted.  Trying to do this without taking the motor apart, but through the brushes contacting the commutator will not work. The brushes will likely contact more than one commutator segment giving unreliable readings.

But whatever causes the problem, the bottom line is that the motor seems unreliable and you'll probably end up replacing it.

[Doug G.]

I have connected to the brushes before and checked for repetitive resistance measurements as the armature is rotated. If there is an open coil, there will be a fairly gross difference in resistance at that spot but, I don't like doing it that way. It doesn't seem to be conclusive enough. Checking adjacent segments is the best way. As Pete indicated, if you have to give the armature a manual start sometimes, something is certainly wrong.

About the only other thing that can cause that symptom is if there are spots on the commutator segments that are dirty and the brushes aren't making reliable contact. You would have to disassemble the motor enough to check that out, too, or, I have stuck toothpicks soaked in Lacquer thinner against the armature while it is turning to scrape off contaminants but it has to be a motor where you have access to the commutator. That's not usually the case with modern motors (mine have been the motors used in Treble-O-Lectric locos).

Doug

[rrjim1]

I've replaced several Kato motors that had a broken wire. Motors usually run hot, but dirty clogged commutators will act the same way. Back in the old days I would drill a 1/8 inch hole in the side of the end bell so I could clean the com. I have also had some new Atlas scale speed motors that would not start without help. These were all bearings being a little tight, lube and running them correct the problem. 

[Cajonpassfan]

He's busy making more poop joke threads in the Crew Lounge.

I'm not touching this one with a ten foot one...
Otto K.