I bought a set of rubber stamped 2333 F3's that are in excellent condition. Before even running them, I disassembled and cleaned as I've done countless times before with Postwar equipment. After all my work, I looked forward to running them.
After only 2 minutes and no car load, I saw smoke. The wiring on the motors was not burned, and the brushes were new and commutator cleaned of any residue. The motors were very hot for only having run 2 laps. Again I tried recleaning the commutator thinking oil made its way on there and replaced the brushes again. I also cleaned the windings with a q-tip to make certain that no oil was burning. Only after a few minutes it happened again.
I would think that a motor requiring a rewind would have dark/burned wiring. The wiring looks good with no burn spots, but the smoke eminates from the wiring and they are getting hot in a very short period of time, moreso than my other horizontal motors.
Anyone have a similar experience? Do I need to rewind them?
The easiest way to test one is to check the resistance across all three possible combinations of commutator segments. If any one is lower and higher than the others, you likely have a bad segment. You should also check the core, although it's very unusual for it to go bad.
You can then go from there.
When I looked into it about a year ago, it was running around $40 an armature to have one rewound. I ended up finding a replacement armature for a fraction of that cost. You might check into that before spending big bucks on a rewind.
Could you tell whether the smoke was coming from the armature or the field coil?
A single shorted turn is enough to do what you saw. If it is buried in the coil, you wouldn't see the damage, only the smoke. If you happen to have a DC supply available, you could try running with that. If it works okay on DC, a shorted field turn (or two) is probably the culprit. (DC won't help an armature short.)
Bob Nelson
Thanks for the input guys, unfortunately this one has more problems than I thought.
The smoke is coming from the armature, and now I'm seeing burn marks. Upon a closer look, one motor has a loose rivet causing the armature to come into contact with the "wobbling" encased metal field housing with each rotation. It's only off by a bit, but enough to cause big problems. That motor runs slower, and causes the other to work harder and has grinded the wheels down on the other truck (slight groove) which I also had not noticed as I only checked the wheel wear on the lead truck.
I wedged a piece of electrical tape (carefully folded) between the motor housing and the metal field to temporarily tighten the casing and it ran smooth. But I don't have the tools to replace the wheels, permanently fix the loose motor rivet, and rewind the motors. This one might be a shelf unit unless I decide to pour more money into it.
Thanks again.
If the armature needs to be rewound it is cheaper and easier to have it sent out than do it yourself. There repair shops listed in the back of CTT magazine.
Lee F.
lionelsoni wrote: If you happen to have a DC supply available, you could try running with that. If it works okay on DC, a shorted field turn (or two) is probably the culprit. (DC won't help an armature short.)
If you happen to have a DC supply available, you could try running with that. If it works okay on DC, a shorted field turn (or two) is probably the culprit. (DC won't help an armature short.)
Wow, I've been around motors all my life and I didn't know that! Can you explain why the problem surfaces when running on AC but not on DC? And why DC won't help an armature short?
Joel
Happy to.
The field coil is normally like an inductor. The current through it is determined by the voltage and frequency applied and by the impedance of the coil, which is partly resistive and partly inductive. When operated on DC, the inductive component vanishes, but the resistance remains.
When a turn or two are shorted, the field coil turns into an autotransformer with a low-voltage short-circuited secondary winding. Running on AC, a lot of current flows in that shorted winding, which can explain the smoke. But on DC, there is no current induced into the shorted-turn "secondary", which therefore remains cool; and, if most of the turns are okay, the field coil functions almost normally.
The armature of even a DC motor is actually excited with AC. That is the function of the commutator, which connects and disconnects coils as the armature rotates. So, even though the motor as a whole is running on DC, the armature sees AC. If the armature has a shorted turn, that turn will always behave as a shorted transformer secondary winding, and overheat.
statistician,
I saw this auction, and I thought you might be interested:
http://cgi.ebay.com/Field-Studs-for-2333-100-Motor_W0QQitemZ220063153923QQihZ012QQcategoryZ4146QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
That ebay aution is mine! LOL. Those studs are impossible to find so I've started making my own. They actually require very tight tolerances as the field alignment and brush height are all affected by these little studs. A few thousands of an inch off and things can start to get a little weird. If you'd like you can bypass the auction and I'll sell them to forum members for $5.00 each. I also make them with the rivet type ends instead of the thread and nut for those that insist on an original look and have to correct rivet press. Just send me an email.
jpelosi@optonline.net
Jim
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