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I was wondering about the windings of the stationary coil on pre post war motors. I have had a couple of motors that I have put together from yard sales that the PO has unwound a few of the turns(the last one at least eight). How does this affect the running of the motor. This last one I just hooked it up, cleaned it, put new brushes in and tested it. I put it on the test stand and let it run for an hour and it didn't seem to have any effect. It ran fine, didn't get hot granted it was just free running no weight  but it seemed fine. Any thoughts?

Thanks Jim

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Johnbeere is correct. Reducing the field strength will result in higher speed. Under this condition the armature current is increased, so care has to be taken not to overheat the armature. It would be easy to splice on a short piece of magnet wire and replace the missing wire. The turn to turn voltage difference in the field is very small so insulating the splice could be ignored or done with a thin layer of varnish.

Robert Hannon's book titled "O-Gauge Reference Manual 1" contains specific data on the wire size and number of turns for both the field and armature windings on most postwar locomotives. Scanning through this reference, a typical number of windings on a field is approximately 160 +/-. So, if you lost 8 turns, that is only about a 5 percent change (perhaps a little more on the outer layers due to the increased winding circumference). I doubt that would affect performance noticeably.

Last edited by GregR

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