Alternator drain

[John Hess]

Non-permanent magnet alternators need a battery.  Honda made an 
alternator at one time that used a permanent magnet rotor.  This unit 
would generate electricity any time it turned.

The difference is simple.  The automotive alternator produces 
(generally) a three phase Alternating Current electrical signal.  The 
average DC component of these AC signals will be 0 volts (equal 
duration/level positive and negative).  A generator produces a DC 
 (pulsating though it may be).  The average DC component of this 
signal will always be the same polarity and will generally vary with 
the speed of the unit.  The fact that an earlier writers alternator 
produced pulsating DC was due to the rectifiers generally included in 
the alternator package, not to a function of an alternator.

----------
From:  Sandy[SMTP:sganz at wgn.net]
Sent:  Tuesday, April 01, 1997 8:48 PM
To:  diy_efi at coulomb.eng.ohio-state.edu
Subject:  Re: Alternator drain


Alternators need a battery, where as the generator does not, so if you 
have
a totally dead battery, the alternator will not have voltage in the 
field
coils to start charging. The Generator, has magnets, so, it needs no 
field
excitation to get it going.

Sandy

At 01:27 PM 4/1/97 -0600, you wrote:
>Fred, 'splain this me ..... sssslowly
>
>>My Humvee has two alternators, well, actually and alternator and a 
generator
>>attached to the engine block, the alternator runs the vehicle 
normally, and
>>the generator provides a seperate feed to all the lights, stereo, 
and
>>anything that's not "mission critical" to the operation of the 
vehicle.
>>
>>Fred
>
>lessee .... both provide pulsating DC.  One just uses rectifiers
>and the other doesn't.  Both have regulated outputs (both current
>and voltage, I assume).  So why not use both the same type???
>
>Tom Cloud <cloud at peaches.ph.utexas.edu>
>
>