On 5/10/2011 8:25 AM, Mark Borgerson wrote:

"Some Basic factoids about 3 phase.... Most of the electric power in
the world is 3 phase. The concept was originally conceived by Nikola
Tesla and was proven that 3 phase was far superior to single phase
power. 3 phase power is typically 150% more efficient than single phase
in the same power range. In a single phase unit the power falls to zero
three times during each cycle, in 3 phase it never drops to zero. The
power delivered to the load is the same at any instant. Also, in 3
phase the conductors need only be 75% the size of conductors for single
phase for the same power output."

http://www.windstuffnow.com/main/3_phase_basics.htm

"To provide direct current with low ripple, automotive alternators have
a three-phase winding. In addition, the pole-pieces of the rotor are
shaped (claw-pole) so as to produce a voltage waveform closer to a
square wave that, when rectified by the diodes, produces even less
ripple than the rectification of three-phase sinusoidal voltages."

http://en.wikipedia.org/wiki/Alternator

There's a plot of the output voltages at:

http://www.alternatorparts.com/under...lternators.htm

You can see that the voltage, and thus, the current, never
drops below about 10V.
/snip/
The ripple on a three phase alternator output is only about 15%.

Mark Borgerson


Interesting inputs. If voltage and current doesn't drop below 10 volts
(and presumably peaks at 14 volt or more?) then the power variation
might be 10X10 / 14X14 - a ratio of 1:2 possibly??

Brian W