400 HP DC Motor

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since 05/27/07

I was at Jerry's Electric Motor service awhile back when a 400 HP motor came in for repair. As I usually do, I pitched in to help. I also had a camera handy. I thought that EV types might be interested in how a really big motor is constructed.

This motor is a compound wound 600 VDC, 1800 RPM unit. It is fairly old and some of the design techniques are obsolete. Nonetheless the construction is typical and interesting. This also shows what is necessary to produce 400 HP continuously and reliably.

The photo to the upper left shows Jerry Brown of Jerry's Electric Motor Service (423 472-5959) loading the repaired motor onto his delivery truck. Jerry's has a service area within about a hundred mile radius of Cleveland. If you're within that radius I highly recommend their services.

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This is the armature. In this case we found a NOS armature so we didn't have to rewind the old one.

A closeup of the armature construction. This photo shows how the windings are bound together. The orange color is GE Glyptol dielectric paint. It greatly reduces the incidences of tracking.

Here is the large economy sized commutator. As is evident by the shading, there are 4 brushes in each bank.

The compound field failed catastrophically so we decided to section it and take some photos.

A closeup of the cut. This photo shows the construction of the field. The vertical laminations are in the center with both the series and shunt fields inside the orange tape.

A cross-section of the pole. The various parts are identified. Several features are of interest. First is the hexagonal cross-section of the shunt windings. Second is the small number of series turns. Note that the shunt field runs on 600 volts.

This photo shows a couple of failure points in the shunt field. The arrows show the failure points. The inner surface (lower arrow) was directly against the pole piece. Not a great design for a 600 volt coil. Note the voids in the potting.

Another field failure. Once a fault occurs the high voltage and large amount of inductance makes the arc fault propagate rapidly.