danmitch wrote:


Amtrak's locos now provide high-power 60 Hz AC to the entire train.
This is locally available in each car. It runs local lighting, air
conditioning, heating, cooking, refrigeration, etc. it's also
available (sometimes at each seat) as 115VAC for personal appliances
(laptop computers, TVs and such).

This is called "Head End Power" since it all comes directly from the
locomotive. In olden days, each car had it's own low voltage (often 32
volt) DC generator and batteries.

With lots of electrical power available it's no wonder that electric
air compressors are now in use. In older units, the compressors were
mechanically clutched to the engines, and engaged as needed.

To maintain the 60 Hz power, older Amtrak locomotives needed to
maintain engine RPM even when the train is not moving. They did this
by cutting out cylinders in the main engine reducing power and fuel
consumption, while maintaining RPM. This was complicated. Newer units
use large inverters to produce the 60 Hz power, and thus allow the
engines to reduce RPM while still generating 60 Hz power (assuming
higher speeds are not needed to move the train). They can't drop to
full idle, but can slow revolutions to save fuel.

These locos seem to be quite new, in fact I hadn't seen this type until
last week, but I have also seen several of them while driving up to
Chicago last week. They have a BIG round "nose" on the front.

One thing I noticed is that the engine RPM seemed to stay the same as
the loco arrived and then later pulled away from the station.
I'm used to the typical Diesel-electric locos increasing RPM as they
need power for acceleration.

I did notice very familiar Carrier V4 semi-hermetic Air Cond.
compressors on each of the coaches, so there's one of the places a lot
of the AC power goes to.


Jon