"Jon Elson" wrote in message
...
I was at the local ice cream place that is adjacent to one of the local
train tracks.
The Amtrak pulled up to exchange passengers at the nearby station. A
bit after it stopped, I heard a very familiar and unexpected sound.
It was a large air compressor driven by a 60 Hz 3-phase motor. I'd
guess from the sound it very well could be a Quincy, and I'd guess maybe
15-25 Hp 4-cyl 2-stage, with pneumatic unloaders.

Anyway, it struck me as just a tiny bit odd they'd use an electric
compressor, as they have mechanical power available off the Diesel engine.
I also noticed the Diesel didn't seem to change speed when the train
accelerated, so I'm guessing they run a single engine at 60-Hz
synchronous speed all the time, so they can distribute 60-Hz power for
air conditioning, etc. to the coaches. So, no aux engine for the
non-traction power.

Anybody know anything about this?

Jon

From http://science.howstuffworks.com/diesel-locomotive.htm

This 270,000-pound (122,470-kg) locomotive is designed to tow passenger-train cars at
speeds of up to 110 miles per hour (177 kph). The diesel engine makes 3,200
horsepower, and the generator can turn this into almost 4,700 amps of electrical
current. The four drive motors use this electricity to generate over 64,000 pounds of
thrust. There is a completely separate V-12 engine and generator to provide
electrical power for the rest of the train. This generator is called the head-end
power unit. The one on this train can make over 560 kilowatts (kW) of electrical
power.

See also http://en.wikipedia.org/wiki/Diesel_locomotive
about 1/2 way down "Propulsion system operation"

Art