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Date: Fri, 09 Sep 2005 14:32:21 -0500
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Overvoltage control (help Ed A)
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If my crowbar overvoltage opens the B+ circuit, there's NO current 
flowing out of the alternator.  Absent current, there can be no heat 
generated.  The field can go to max output, there will be high voltage 
at the B+ terminal, but no heat generated.  Sounds to me like a bogus 
concern.  I think the key issue is "... Nuckolls expressed dislike ..." 
and no further support is "needed".

Still looking for a "real" reason ... Jim S.

Mark R Steitle wrote:

>Jim,
>I first explored this issue after Bob Knuckols expressed a dislike of
>internally regulated alternators...because they can fail in such a way
>that you cannot shut them down.  Yes, you can interrupt the "B" lead,
>but this will not shut down the alternator.  I imagine it could get hot
>enough to self-destruct and possibly catch fire.  
>
>The modification I use removes the internal regulator assembly and puts
>a direct (external) feed line to one of the brushes.  The other brush is
>tied to ground.  Nothing else is connected to the field.  With this
>arrangement, can you explain how removing power from one of the brushes
>will allow the alternator to continue producing power?  I've tested my
>modified alternators with the engine running and it does in fact stop
>producing power when I cut the power to this lead.
>
>Another benefit to an external regulator is that you can precisely
>adjust the voltage, provided you use an adjustable regulator.  
>
>Mark S.  
>
>-----Original Message-----
>From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
>Behalf Of Jim Sower
>Sent: Thursday, September 08, 2005 5:31 PM
>To: Rotary motors in aircraft
>Subject: [FlyRotary] Re: Overvoltage control (help Ed A)
>
>I've always been puzzled why folks would go to all the trouble of 
>disabling a perfectly good internal regulator so as to install an 
>external unit.  If the Field circuit gets somehow internally shorted to 
>the output circuit, the alternator is going to run away and create an 
>over voltage condition.  In that event, there's no way that turning off 
>current to the Field is going to help you.  Other than a short 
>described, I don't know how an over voltage can occur.  So my question 
>is:  is an internally regulated system all that much more apt to have an
>
>over voltage type failure, and if so why?  I've had lots of trouble with
>
>externally regulated alternators, very little with internal regulators.
>
>My crowbar over voltage system is bullet proof.  It's the only scheme 
>that prevents damage caused by an internal short in the alternator.
>What, exactly, is the big attraction of external regulators? ... Jim S.
>  
>
>  
>