Return-Path: <13brv3@bellsouth.net> Received: from imf16aec.mail.bellsouth.net ([205.152.59.64] verified) by logan.com (CommuniGate Pro SMTP 4.1.6) with ESMTP id 2715831 for flyrotary@lancaironline.net; Sun, 09 Nov 2003 00:28:22 -0500 Received: from rad ([68.212.11.237]) by imf16aec.mail.bellsouth.net (InterMail vM.5.01.05.27 201-253-122-126-127-20021220) with ESMTP id <20031109052821.CVXW20018.imf16aec.mail.bellsouth.net@rad> for ; Sun, 9 Nov 2003 00:28:21 -0500 From: "Russell Duffy" <13brv3@bellsouth.net> To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Murphy's law of precautionary landings Date: Sat, 8 Nov 2003 23:28:23 -0600 Message-ID: <004601c3a682$4b2ceaa0$6001a8c0@rad> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0047_01C3A650.00927AA0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Importance: Normal In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_0047_01C3A650.00927AA0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable A 100 A fuze is pretty stout. There was a recent bit on the Velocity = forum to the effect that a 60 amp alternator needs an 80 amp fuze at a = minimum. If your alternator is over 75 A, you might want to go to a 120 A fuze. = I think current limiters are only supposed to come into play if you get a = dead short in the alternator output so some overkill (as much as 30%-40%) shouldn't hurt. I'm installing a 100 A fuze to protect my [allegedly] = 75 A alternator.=20 How big is your alternator anyway ... Jim S.=20 =20 The alternator is 100A, and I originally wondered if a 100A fuse would = be enough. As you mentioned, I had a larger fuse than the alternator = rating on my RV-8. I decided to try the 100A fuse here, since I figured I'd never have reason to draw that much current. If the battery had been more run down than usual today, or there was some other reason to suspect that I would have been requiring extra current from the alternator, then I'd = figure the fuse was too small. As is, it's still sort of a mystery for now. =20 =20 My leading theory is fatigue. The fuse is flimsy, and I have a bracket built to keep it from flexing. While this looks like it would work, I = can't be sure that it doesn't still vibrate, and flex a tiny amount. If = that's the case, it may have just fatigued the element until it cracked, and = lost capacity. I'll probably find out more tomorrow. =20 =20 FWIW, there will be some changes in the fuse installation for the rev-2 arrangement. For now, if it works OK tomorrow, I'll just continue = flying it and will keep a close watch on the volt meter. Even with my draggy cowl = and lack of wheel pants, I'm never more than 9 minutes from the edge of my = test area to my home airport. =20 =20 Cheers, Rusty =20 ------=_NextPart_000_0047_01C3A650.00927AA0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
A 100 A fuze is pretty stout.  There was a recent bit on the = Velocity=20 forum to the effect that a 60 amp alternator needs an 80 amp fuze at a=20 minimum.  If your alternator is over 75 A, you might want to go to = a 120 A=20 fuze.  I think current limiters are only supposed to come into play = if you=20 get a dead short in the alternator output so some overkill (as much as = 30%-40%)=20 shouldn't hurt.  I'm installing a 100 A fuze to protect my = [allegedly] 75 A=20 alternator.
How big is your alternator anyway ... Jim = S. 
 
The=20 alternator is 100A, and I originally wondered if a 100A fuse would = be=20 enough.  As you mentioned, I had a larger fuse than the=20 alternator rating on my RV-8.  I decided to try the 100A fuse here, = since I=20 figured I'd never have reason to draw that much current.  If = the=20 battery had been more run down than usual today, or there was some = other=20 reason to suspect that I would have been requiring extra current = from the=20 alternator, then I'd figure the fuse was too small.  As is, it's = still sort=20 of a mystery for now.  
 
My leading=20 theory is fatigue.  The fuse is flimsy, and I have a bracket = built to=20 keep it from flexing.  While this looks like it would work, I = can't be=20 sure that it doesn't still vibrate, and flex a tiny = amount. =20 If that's the case, it may have just fatigued the element until it = cracked, and=20 lost capacity.  I'll probably find out more=20 tomorrow.  
 
FWIW, there=20 will be some changes in the fuse installation for the rev-2=20 arrangement.  For now, if it works OK tomorrow, I'll just=20 continue flying it and will keep a close watch on the volt = meter. =20 Even with my draggy cowl and lack of wheel pants, I'm never more than 9 = minutes=20 from the edge of my test area to my home=20 airport.  
 
Cheers,
Rusty
 
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