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From: gvcormack@watdaisy.UUCP (Gordon V. Cormack)
Newsgroups: net.auto
Subject: Re: Alternators
Message-ID: <6912@watdaisy.UUCP>
Date: Sat, 2-Feb-85 09:07:09 EST
Article-I.D.: watdaisy.6912
Posted: Sat Feb  2 09:07:09 1985
Date-Received: Sat, 2-Feb-85 14:43:22 EST
References: <776@sdcsla.UUCP>
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 31

> I read an article about how some guy invented a box that cuts out 
> his alternator most of the time thus saving gas by not having the
> device under a load when not needed.
> 
> Dave Wargo
> U.C.S.D.

The regulator that comes with the car does this.  The field strength
is varied depending on how much output is required from the alternator.
The output from the alternator goes directly (actually through
some rectifiers) to the battery without any further regulation.
Aside from the friction of the alternator the energy consumed by
the alternator is proportional to that required.

The regulator can easily sense when more output is required.  The
voltage at the battery terminals is maintained at 13.5 volts.  If
the battery is discharged (or there are a lot of accessories to drive)
it will require a lot of current to bring the voltage to 13.5.  If
the battery is fully charged, it will require almost none.

This method of control was the major advance of alternators over
the generators found in cars until the mid-60s.  Generators have
permanent field magnets and therefore the output cannot be adjusted.
The regulator has to discard some of the output of the generator.
This also can be done without appreciable power loss by making and
breaking the connection between the generator and the battery, but
this control circuitry must switch very high currents.
-- 
 
Gordon V. Cormack      CS Department, University of Waterloo
   gvcormack@watdaisy.uucp     gvcormack%watdaisy@waterloo.csnet