john smith wrote:
I was pondering a similar question earlier this week as I watched
gasoline prices increase.
The conversion from horsepower to kilowatts is 1:0.75, so a 400 hp
engine is 300 kw.
I was curious as to how large a 300 kw motor is and how massive the
power cables are to provide the requisite voltage and current.
1000 V and 300 A?
How much energy is lost to heating?
How does one reduce this heating loss?
How many kw does it take to start a given mass moving?
I am guessing there is an initial surge current, followed by reduction
in current once the mass is in motion and to keep it moving.

To give you a couple of size references, we had a 25 hp DC motor that
was set to move a carriage that could weigh as much as 1500 pounds up
and down a column. The engineering requirement was for the motor to be
able to accelerate the carriage from a stop to the furthermost position
(12 feet up)in something under 4 seconds and the placement be within
..1". The power was provided by a high voltage DC unit producing 900 VDC
and up to 100 amps current. The motor case was about 10" in diameter
and about 20" long and weighed over 75 pounds. The power supply was a
little bigger than a 21" monitor but required 220/3Phase to operate.

An air compressor that I used to run had a 1750 hp open frame motor
for the main drive. It was 10 feet in diameter and 3 feet thick. It
took a special 1700 VAC/3P feed and took nearly 2 minutes to come up to
steadystate speed.

What they are going to find in the end, is that putting some kind of
electric taxi system on the individual aircraft is going to backfire
and cost them seat and cargo capacity that outweighs the supposed saved
fuel costs.

Craig C.