Isolation of motor brushes: FM H20-44 switcher

[gmpullman]

tstage

Is is logical to say that the brushes are sufficiently isolated from the frame?

Hi, Tom

I would agree with you that the motor brushes themselves are isolated from the frame and that method you show is pretty common among brass manufacturers for collecting current from each rail, thus each truck is "hot" to the corresponding rail and only a pair of wheels on each truck are insulated at the axles. There may be fiber "thrust" washers at the end of the axle at the insulated side as well to prevent the insulated wheel from touching the side frame.

In its simplest form you could place the black and red wires to each bolster screw and the orange and gray wires to each motor lead and you're done.

To be sure, remove the wires at the bolster screws, power the motor with a 6-to-9 volt DC source, a battery works fine, then check for voltage between each motor terminal and any metal on the frame/trucks.

This engine is a good candidate for a keep-alive capacitor, too, since you only have a total of four wheels collecting current.

I might suggest placing strips of Kapton tape on the bottom-side of the frame, above the truck side frames, to help prevent any short-circuits in the event of a derailment.

Have fun with your new H20-44!

Ed

[tstage]

Greetings -

I received one of my "new" acquisitions in the mail today: A brass Alco Models FM H20-44 switcher.  I removed the shell and used my $20 Sears multimeter to check the motor brushes and points on the frame for continuity.  Below is a picture of one half of the chassis:

I get continuity between the screw (that the red motor wire is attached to) and only the areas in the red circles.  The opposite end of the chassis is a mirror image of this one and I get identical readings from the same contact points; the one exception being the wipers on the opposite corner truck.  All other points from either screw show an open circuit.

Is it logical to say that the brushes are sufficiently isolated from the frame?

Thanks,

Tom