X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 5.0c2) with ESMTP id 715706 for flyrotary@lancaironline.net; Thu, 08 Sep 2005 15:24:36 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.100; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-065-188-083-049.carolina.res.rr.com [65.188.83.49]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id j88JNnWf022273 for ; Thu, 8 Sep 2005 15:23:50 -0400 (EDT) Message-ID: <001701c5b4aa$da434990$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Overvoltage control (help Ed A) Date: Thu, 8 Sep 2005 15:23:54 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0014_01C5B489.52E55E50" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0014_01C5B489.52E55E50 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message On alternators with internal regulators (most Auto = alternators), breaking the low current Field circuit may not (will = likely not) stop the alternator from producing current. Most of the = alternators need the field coil current to "bootleg" their start in = producing voltage, but once generating - do not need the external field = coil current to continue. That is why if you have an alternator with an = internal regulator, you can not depend on opening the low current field = coil circuit to kill the power and why you would need a method similar = to the one described in this thread of breaking the high current (Power = lead usually referred to as the "B" lead) through a high capacity relay = (Contactor) or a "fuse". There are always side effects when interrupting a high current flow = (less if the current flow is minimal). If there is a large inductive = load (such as a large DC motor) then the back EFM can produce a high = voltage spike. There are reports that alternators may increase their = voltage dramatically if there is a sudden loss of load -but, its never = been clear to me if that is a malfunctioning generator or caused by the = lost of load - never been tempted to experiment. However, I once had = two batteries which connected to the alternator through their = contactors. I could switch the batteries on and off the alternator line = without any ill effects - not quite the same as dumping a large load - = but, after starting on just one battery, the load was fairly high when = put back on line. However, one battery was always on-line. So not certain what effect breaking the "B" lead would be (since it = would depend on conditions) but since many designs have a "fuse" in the = "B" lead for that purpose, I am going to hazard my opinion that the = effects of breaking the "B" lead may be less serious than what-ever bad = situation is causing you to want to do that in the first place. = Ideally, of course, is to have an externally regulator alternator (or a = modified auto alternator with the internal regulator disabled so unable = to provide the field coil internally) and a low current circuit breaker = tripping mechanism for the field coil. =20 Ed ----- Original Message -----=20 From: WALTER B KERR=20 To: Rotary motors in aircraft=20 Sent: Thursday, September 08, 2005 2:14 PM Subject: [FlyRotary] Re: Overvoltage control (help Ed A) If you don't have a low current way to break the field current, and = need to break the high current line, then you have to used this OV = module to trip a breaker that's holding in a main contactor for your = high current "B" lead. If any of that was confusing, Ed can explain it = :-) Cheers,=20 Rusty=20 = =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 Help Ed. I almost understand Rusty's comments, but Mark S left me in = the dust. Us old dogs are sometimes hard to train! I think that with an internal regulator; just because you break the = field current supply , a failed regulator may keep powering the field = with the internal alternator voltage. The continous breaker in the big = alternator line can protect the battery and airplane except what happens = to the alternator in the meantime if the interal regulator is applying a = large field current to the field will the alternator burn up quiet = rapidly and possible start a fire? Bernie, soggy Treasure Coast although we had a bonanza just taxi in = so must be drying out a little ------=_NextPart_000_0014_01C5B489.52E55E50 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
  On alternators with internal = regulators (most=20 Auto alternators), breaking the low current Field circuit may not (will = likely=20 not) stop the alternator from producing current.  Most of the = alternators=20 need the field coil current to "bootleg" their start in producing = voltage, but=20 once generating - do not need the external field coil current to=20 continue.  That is why if you have an alternator with an internal=20 regulator, you can not depend on opening the low current field coil = circuit to=20 kill the power and why you would need a  method similar = to the=20 one described in this thread of breaking the high current (Power lead = usually=20 referred to as the "B" lead) through a high capacity relay (Contactor) = or a=20 "fuse".
 
There are always side effects when interrupting = a high=20 current flow (less if the current flow is minimal).  If there = is a=20 large inductive load (such as a large DC motor) then the back EFM = can=20 produce a high voltage spike.  There are reports that alternators = may=20 increase their  voltage dramatically if there is a sudden loss of = load=20 -but, its never been clear to me if that is a malfunctioning generator = or caused=20 by the lost of load - never been tempted to experiment.   = However, I=20 once had two batteries which connected to the alternator through their=20 contactors.  I could switch the batteries on and off the alternator = line=20 without any ill effects - not quite the same as dumping a large load - = but,=20 after starting on just one battery, the load was fairly high when put = back on=20 line.  However, one battery was always on-line.
 
So not certain what effect breaking the "B" lead = would be=20 (since it would depend on conditions)  but since many designs have = a "fuse"=20 in the "B" lead for that purpose, I am going to hazard my opinion that = the=20 effects of breaking the "B" lead may be less serious than what-ever bad=20 situation is causing you to want to do that in the first = place. =20 Ideally, of course, is to have an externally regulator alternator (or a = modified=20 auto alternator with the internal regulator disabled so unable to = provide the=20 field coil internally) and a low current circuit breaker tripping = mechanism for=20 the field coil.
 
 
Ed
----- Original Message -----
From:=20 WALTER B = KERR
Sent: Thursday, September 08, = 2005 2:14=20 PM
Subject: [FlyRotary] Re: = Overvoltage=20 control (help Ed A)

  If you=20 don't have a low current way to break the field current, and need = to=20 break the high current line, then you have to used this OV module = to trip=20 a breaker that's holding in a main contactor for=20 your high current "B" lead.  If any of that was confusing, Ed can explain = it=20 :-)

 

Cheers,=20

Rusty=20

 

=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=

Help Ed. I almost understand Rusty's = comments, but=20 Mark S left me in the dust. Us old dogs are sometimes hard to=20 train!

I think that with an internal regulator; = just=20 because you break the field current supply , a failed=20 regulator may keep powering the field with the internal = alternator=20 voltage. The continous breaker in the big alternator line can = protect the=20 battery and airplane except what happens to the alternator in the = meantime=20 if the interal regulator is applying a large field current to the = field will=20 the alternator burn up quiet rapidly and possible start a=20 fire?

 

Bernie, soggy Treasure Coast although we = had a=20 bonanza just taxi in so must be drying out a=20 little

 
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