From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Avionics transient
To: lml
Date: Sun, 18 Jun 2006 01:54:29 -0400
Message-ID: <web-1182236@logan.com>
In-Reply-To: <6F23F936-CAC7-4E11-B6E3-48780657AF83@adelphia.net>
References: <list-1181500@logan.com>
 <6F23F936-CAC7-4E11-B6E3-48780657AF83@adelphia.net>
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Posted for Gary Casey <glcasey@adelphia.net>:

>
  In my opinion it is not advisable to put a pullable breaker in the
  alternator output ("B") lead.  And yes, if you pull that breaker with  the
field being powered the alternator output voltage will go to a  very high
level - certainly well over 100 volts (with the engine at  high rpm).  If the
voltage regulator over-voltage sense lead is  connected to the alternator
output it presumably shut itself off,  popping the alternator field breaker.
  If not and if it is  reconnected, though, it may or may not result in an
unacceptable  system over-voltage, depending on the capacity of the battery to
  absorb the sudden high current.  I installed a fuse in the B lead in  the
event that a stator winding gets shorted to ground.  In the first  scenario,
with an alternator charging into a dead battery the B lead  breaker should
never blow.  The alternator is a current-limited  device and can never produce
a higher current than its rating  (approximately - the ratings aren't exact).
  If your friend had the  breaker blow repeatedly it either had too low a
rating or the breaker  itself was defective.  I recommend a fuse with a rating
at least 10%  higher than the rating of the alternator.  20% is better.
  
  Gary Casey