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Mark Borgerson

In article .com,
llid says...

Some Rube posted that current from an alternator never goes to zero.

WRONG.

1) an alternator produces alternating current.

2) alternating current alternates directions.

3) every time the current reverses, it MUST stop and go to zero.

4) if it did not stop and go to zero it could not reverse - it could not
alternate.

When you rectify this stop-and-go current through a bridge setup of diodes,
all that happens is the direction of the current is is made to flow the same
direction via the correct placement of diodes which allow current one way
but not the other. However, re-routing the current to all the same direction
(DC) does not and cannot eliminate those finite periods of time when the
original alternating current stops and reverses directions. This alternating
current is produced by the north and south poles lines of flux cutting
through a coil of wire. It goes one way, stops between poles, and then goes
back the other way.

Walk forward, then walk backward. There will be a finite period of time when
you're not moving because you have completely stopped when you reversed
directions. You can never eliminate the stop.

What you've said is true for a single-phase alternator. Most auto and
marine alternators are at least 3-phase systems that combine the output
from the three phases through multiple diodes. In those systems one
phase is always providing current through the diodes and the output
voltage never drops to zero.

Mark Borgerson