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Subject: RE: [FlyRotary] Re: Overvoltage control (help Ed A)
Date: Fri, 9 Sep 2005 10:27:20 -0500
Message-ID: <87DBA06C9A5CB84B80439BA09D86E69E0267E617@MAIL01.austin.utexas.edu>
Thread-Topic: [FlyRotary] Re: Overvoltage control (help Ed A)
Thread-Index: AcW1QuX79mnZWhX1S2GBslr5/ZdWWgAAGp8w
From: "Mark R Steitle" <mark.steitle@austin.utexas.edu>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>


=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Mark,

The self destruct fire item is the only reason that I see to go beyond
interrupting the B lead.

Interesting my ND alterator does shut down when I shut the power field
off and it is internally regulated. I thought that was normal, but there
were potential internal failures that could trigger the runaway
alternator and then I would not be able to shut it down. Is that
confused
thinking or why am I able to shut it down while running?

Bernie=20
>=20
>
Bernie,
If the internal regulator's I/C decides to act up, who knows what the
results will be, depends on how it fails.  Ninety-nine percent of the
time everything works as designed.  Its that other one percent that
we're talking about.  With the internal regulator, you have no way of
stopping the current from flowing into the field windings if/when the
I/C malfunctions, therefore you can't shut it down. =20

So, what would happen to your electronics if this happens?  I don't know
the maximum voltage limit on the EC-2 or EM-2, but the alternator is
capable of producing over 100 volts.  I doubt the EC-2 or EM-2 can
tolerate anywhere near this.  (Years ago when I was working as a fleet
mechanic, we tried a device that hooked up to the alternator that would
allow you to run 110v tools off the vehicle's charging system.  It
worked, but was unreliable.  But that's another story.)  The specs on my
SL-30 nav/com say 32v is max.  So, if the alternator malfunctions and
starts over-charging, you will likely start letting the smoke out of
your expensive electronics.  And it won't take long and things will get
real quiet (after the smoke is out of the EC-2).  So, this is enough
reason for me to go with the external regulator and OVP. =20

My system uses two ND alternators and two RG batteries, with a crossfeed
relay between the batteries.  So, if one alternator self-destructs, the
OVM will automatically shut it down, and turn on a warning light on the
panel.  At that point I would activate the x-feed relay (connecting both
batteries to the remaining "good" alternator and continue on my way.  I
can repair/replace the alternator at my destination.   =20

Mark S.