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Date: Thu, 24 Feb 2005 09:40:22 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: E-shaft permanent magnet alternator
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Russell Duffy wrote:

>Is there any way to control the PM alternator?  In other words, can you turn
>it off?  
>
>Say you add one of these as a backup, and your normal alt is an ND or some
>other type that can be turned on and off.  As a part of pre-flight, you
>could turn off the main alt, and verify that you still had charging voltage,
>but would you ever be able to turn off the PM alt and verify that your main
>alt was working?  With the type of voltage alarm that many of us use, I
>don't think you'd get a warning unless both alts were down.  
>
>Cheers,
>Rusty (I still like it though)
>  
>
>
Rusty, a PM alternator won't experience the overvoltage problems of a 
standard one.  The whole issue of controlling the field current (which 
controls the output) goes away.  Instead, you'll get undervoltage until 
you get it up to rated RPM.  The voltage warning lamp should be on the 
entire time your taxing, and go out when you rev the engine during the 
runup.  If that isn't good enough, I'm sure Bill could easily throw in a 
disable switch to the regulator he'd design (see, Bill, I'm looking out 
for ya' 8*)