Return-Path: Received: from fed1rmmtao02.cox.net ([68.230.241.37] verified) by logan.com (CommuniGate Pro SMTP 4.2.4) with ESMTP id 455601 for flyrotary@lancaironline.net; Wed, 06 Oct 2004 20:17:59 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.37; envelope-from=ALVentures@cox.net Received: from BigAl ([68.107.116.221]) by fed1rmmtao02.cox.net (InterMail vM.6.01.03.04 201-2131-111-106-20040729) with ESMTP id <20041007001726.LFOS6045.fed1rmmtao02.cox.net@BigAl> for ; Wed, 6 Oct 2004 20:17:26 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Voltage overload Date: Wed, 6 Oct 2004 17:17:32 -0700 Message-ID: <000001c4ac03$0a18e6e0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C4ABC8.5DBC58D0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C4ABC8.5DBC58D0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 Al, you are right about now having the lack of over-voltage protection. = All I have in line is a fusable link rignt now. Fortunately, all of my expensive avionics can tolerate voltages of at least 28V without being affected. =20 =20 If a voltage regulator fails, how high can the voltage go? =20 Until something fails. The assumed failure is full-on field current, so = the alternator puts out max rated current until . . . . The stock built in regulators adjust the output by doing a fairy high frequency, = square-wave, on-off switching of the field current; with the on time adjusted to = maintain ~14.5 volts. The most common failure mode is no "on" time, and the = battery voltage drops. I don't know by direct experience, but Bob Nuchols says = they can fail full "on". =20 Al =20 =20 =20 Dave Leonard Dave; =20 That's interesting. Makes me wonder whether I should put a scope on = voltage and see if it is smooth. =20 =20 The downside of connecting the field to the output, as I'm sure you = know, is that you now have the risk of a runaway voltage condition if the VR = fails. I guess the odds are low, but the costs could be high. Avionics? =20 I assume that you have a breaker (or fuse) in the alt field circuit. = You can put a "crowbar" circuit between the field lead and ground that will = trip the breaker in an over-voltage condition. I got one from Aeroelectric. =20 Al =20 ------=_NextPart_000_0001_01C4ABC8.5DBC58D0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

Al, you are right about now having the lack = of over-voltage protection.  All I have in line is a fusable link = rignt now.  Fortunately, all of my expensive avionics can tolerate = voltages of at least 28V without being affected. 

 

If a voltage regulator fails, how high can = the voltage go?

 

Until something fails.  The = assumed failure is full-on field current, so the alternator puts out max rated = current until . . . .   The stock built in regulators adjust the = output by doing a fairy high frequency, square-wave, on-off switching of the field current; with the on time adjusted to maintain ~14.5 volts.  The = most common failure mode is no “on” time, and the battery voltage = drops.  I don’t know by direct experience, but Bob Nuchols says they = can fail full “on”.

 

Al

 

 

 

Dave Leonard

=

Dave;

 

That’s interesting.  Makes me wonder whether I should put a scope on = voltage and see if it is smooth. 

 

The downside = of connecting the field to the output, as I’m sure you know, is that = you now have the risk of a runaway voltage condition if the VR fails.  I = guess the odds are low, but the costs could be high. Avionics?

 

I assume that = you have a breaker (or fuse) in the alt field circuit.  You can put a “crowbar” circuit between the field lead and ground that = will trip the breaker in an over-voltage condition.  I got one from = Aeroelectric.

 

Al

 

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