[sdiy] OT: Generator?

[KHeck73 at aol.com]

In a message dated 4/25/2001 2:43:23 AM Eastern Daylight Time, 
john.l.marshall at gte.net writes:


> The generator-motor approach solves the gear shifting problem. Kenworth
> trucks have up to 16 forward gears to start rolling and then get up to
> speed. Imagine the gear box for three locomotives that are pulling a hundred
> cars!
> 
> 
> > throughout this thread, I've been wondering why locomotive engines in
> > america don't do this... (regenerative braking).  AFAIK, even though
> > trains are diesel in america, the diesel powers generators and the
> > locomotion is created by big electric motors (don't ask me why!), so
> > it makes sense to me to use regenerative braking, unless of course,
> > there aren't any batteries, just the generators to the motors (through
> > a controller or two no doubt)
> > -ben
> 
> 

(I'm sort of beating a dead iron horse to death on this). Another way of 
looking at it is that an electric motor provides  tremendous torque from a 
dead stop. It wants to turn in a big way when power is applied, or it will 
dissipate the energy as heat. Piston driven motors physically can't run when 
they're not turning, so there's no torque available. They have to be running 
at some higher speed to generate torque. That's the main reason the 
horsepower of a diesel is converted to electricity for electric motor torque 
in locomotives. You need torque to pull the tremendous weights, and you need 
it from standstill. Notice when you hear a diesel train engine, it's rumbling 
at about the same RPM all the time? That's horsepower available to generate 
current for electric motors, regardless of train motion. The diesel generator 
eliminates the need for the overhead lines (or powered rails in a subway 
engine).

There's a CSX railroad shop near me that rebuilds both the diesel engines and 
electric motors. Pistons almost the size of 5 gallon buckets, and the motor 
armatures are bigger than 55 gallon drums! Pretty impressive stuff. 
-Karl.
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