The railroads seem to like the engine/generator/electric motor
setup. . . . and have used the arrangement for over 75 years.


John Duncan

Do your home work and tell us why railroads use diesel generators and
electric motors.

Paul Lamar



Question:  What type of motor develops maximum torque at 0 rpm?

Chris Cosman


Excellent Chris, directly to the point.

The number of cars a locomotive can pull is directly related to it's
weight.

Paul Lamar

With a controller, and the size generators used, one can apply a
large amount of current to a motor, and thereby get it to turn
without "spin". This is based on a multiple pole motor (as I
recall, an odd number of poles are used).

With that said, I forget exactly how this is done with a train,
but part of the motor is actually built as part of the axle of a
wheel. So if a truck (the thing that houses the wheels) has n
axles, it will have x power generating wheels.

These guys are not using something as small as 10 gauge wire,
they are using something larger because they apply something like
80 Amps to those coils (been too long since I've studied these
motors).

The amount of Gauss generated (magnetic lines per "inch") is
quite large and will actually react with the immediately adjacent
axle (so there may not be as many "power" axles as total axles in
a truck).

This type of torque makes the startup and stop of a
locomotive(movement wise) very very smooth.

This smoothness is very important because all other systems
(non-electric drive) causes the wheels to spin and "scallop" the
rails. This was most notable at signals and just before and just
after switches.

That results in damage to the wheels of the cars being pulled.
This is high maintenance because those damaged wheels do damage
to the rails. So track crews had to replace those rails at those
locations (high maintenance cost by itself). Thanks to electic
drive we get to enjoy tracks/rails that are "continuous welds".

Diesel drive to the wheels would have a similar effect as steam
even with a clutch, because the power moments from each piston
would be directly transferred to the wheels (think of the same
for a propeller).

To help make this real for you, ever notice how some highways
have potting or rippling just before a traffic light (and maybe
starting about 60 feet before the light) where the temperatures
get high enough for the asphalt to get a bit loose. This is
caused by semis when they first start up, they have a tremendous
amount of torgue applied to their driving wheels which is what
gets them moving and allows them to accelerate.

This was the long story of why diesel electric locomotives (or
electric locomotives).

Regards,
Steve Thompson


sort of. They do not generate power. That is the job of the diesel.
They are electric motors and as chris points out above they generate
max torque at zero RPM to get a 100 car train moving. It is about the only possible
way of doing it other than a steam engine. Other wise you would need a huge gear
box with many possible gear ratios starting at 100 to one.. A truck may have as many as
ten speeds forward.

The navy tried it in ships and it was too inefficient because, like aircraft, they
were driving propellers


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