X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 10 Jun 2006 00:32:18 -0400 Message-ID: X-Original-Return-Path: Received: from sj-iport-5.cisco.com ([171.68.10.87] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1148094 for lml@lancaironline.net; Fri, 09 Jun 2006 17:23:49 -0400 Received-SPF: pass receiver=logan.com; client-ip=171.68.10.87; envelope-from=jmacknig@cisco.com Received: from sj-dkim-4.cisco.com ([171.71.179.196]) by sj-iport-5.cisco.com with ESMTP; 09 Jun 2006 14:23:05 -0700 X-IronPort-AV: i="4.05,224,1146466800"; d="scan'208,217"; a="292488801:sNHT46802030" Received: from sj-core-2.cisco.com (sj-core-2.cisco.com [171.71.177.254]) by sj-dkim-4.cisco.com (8.12.11/8.12.11) with ESMTP id k59LN4J7025097; Fri, 9 Jun 2006 14:23:04 -0700 Received: from [128.107.150.249] (dhcp-128-107-150-249.cisco.com [128.107.150.249]) by sj-core-2.cisco.com (8.12.10/8.12.6) with ESMTP id k59LN4ke021859; Fri, 9 Jun 2006 14:23:04 -0700 (PDT) X-Original-Message-ID: <4489E6B8.4040904@cisco.com> X-Original-Date: Fri, 09 Jun 2006 14:23:04 -0700 From: Jim MacKnight Organization: ATG Hardware Engineering User-Agent: Thunderbird 1.5.0.4 (Windows/20060516) MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: [LML] Re: LNC2 Field Breaker Popping -- Solution at Hand! References: In-Reply-To: Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit DKIM-Signature: a=rsa-sha1; q=dns; l=7114; t=1149888184; x=1150752184; c=relaxed/simple; s=sjdkim4001; h=Content-Type:From:Subject:Content-Transfer-Encoding:MIME-Version; d=cisco.com; i=jmacknig@cisco.com; z=From:Jim=20MacKnight=20 |Subject:[LML]=20Re=3A=20LNC2=20Field=20Breaker=20Popping=20--=20Solution=20at=20 Hand!; X=v=3Dcisco.com=3B=20h=3DogXtFW/Pr5nZ2quBvT9wZP1c8aU=3D; b=JjC/t1qG7zzLii/HtS5HCiD8gyLmDq7kkp9m4BIaNxeVCC/EZQTNXreRAg420PCf0oRVHe3r xEOrKVXJTA47mDfN/pyZT8fmXvtfV3UXY1XLhPbLKbbupuyQ0qqJFUSU; Authentication-Results: sj-dkim-4.cisco.com; header.From=jmacknig@cisco.com; dkim=pass ( 16 extraneous bytes; sig from cisco.com verified; ); Just a note to all the Lancairians,
Finally found it -- brushes were worn in the alternator to < 1/2 their normal length, causing "brush hop" -- solution $19.95 for new brushes (even bought a spare set). I guess the old adage, "When there's a problem, think horses not zebras". I know, I know; this is is only for us N.A. folks ;-)

Tried all of the normal things: bench tested with VR twice, soldering all terminals, checking grounds, replacing some suspect crimps, replacing a circuit breaker, bypassing the ALT position on the Master switch, etc. Nothing helped and it just kept getting worse. Was just about to the point of hooking up an oscilloscope to the VR/alternator combo (with a 200' foot extension cord) to find out what was starting the failure mode.

The generator/alternator person stated this was the first time he'd ever seen the kind of symptoms for having bad brushes. Normal symptoms is the alternator working correctly on light loads but blowing the field breaker with heavier output loading -- my issue was just the opposite! Guess with 20/20 hindsight, the failure makes sense. Excess vibration being transmitted to to the brushes at specific RPMs caused the brushes to hop away from the commutator just long enough to let the output voltage drop. Then when the brush again made contact, the alternator output spiked to over 16.1V for >50msec, causing the VR's SCR OVP to trigger, popping the Field circuit breaker. Since even B&C Specialties could not tell me the time constant for the VR/alternator closed loop system, the differing vibration frequency from certain engine RPMs would cause a long enough hop.

Thanks again to everyone who had some thoughts on this. Also to Ben at Gilgen in Gilroy, CA for his perserverence and specialized test equipment and finally to Tim at B&C Specialties in Missouri for providing invaluable information on how the LR3B internals were actually working and timings.

jim...
N1222K, LNC2, 597.6 hrs

Thanks Jeff, really appreciate the inputs -- I'll check it. Had the original battery in since April 2000 and finally replaced it in September 2005.

Thought I had the problem licked when I did the following about 2 weeks ago:

pulled out the alternator & VR, had them tested as a pair on a bench for 15 minutes at 60A load with no problems,
thought I found a nicked wire (on the field wire between the VR and Alternator side of the split Master switch),
cleaned up some minor dissimilar metal corrosion (on VR bolts and ground screw from alternator into the engine crankcase),
re-routed a wire bundle, and
then flew for 10+ hours with no issues.

Then went to Baja and it started again. Just barely made it back to home base. Now the field circuit breaker trips 12 times in just going once around the pattern. Right now it seems to be heavily weighted towards vibration sensitivity since it's now occuring when the oil temp is just barely 100F and cylinder head temps are 250+ with no heat soaking required.

We're using a B&C Specialty voltage regulator (VR), LR3B, with a built-in OVP (65A SCR that is triggered with a 50msec pulse/intermittent). This then shorts the alternator field lead to ground, tripping the alternator field breaker. The alternator is a 90A Bosch, AL9971N replacing the original alternator in late 2001 (the original aviation grade alternator went bad in the first 100 hours or so).

Talked with the voltage regulator designer at B&C and his input was that the OVP is most likely tripping the field breaker. This can be caused by a very large number of things:

a very fast open circuit intermittent in either the field or B lead (+12V output lead from the alternator);
a poor ground (a real possibility in our fiberglass birds);
bad crimp in any one of the wires; a bad master switch;
misaligned commutator brushes in the alternator;
etc.

As a note, the previous time I put it together I found some mild dissimilar metal corrosion underneath the washers bolting the VR to the backside of the firewall (a fine, whitish opaque powder in some places).

I thought the next steps would be (before shotgunning it by replacing the alternator & VR):

Solder ALL the crimp joints in the field and ground system,
jumper the Alternator side of the split Master switch to be ON all the time,
add a separate ground wire from the VR unit directly to ground, i.e. not relying on the firewall bolts to get the good ground), and
have the alternator person open the alternator and see if the commutator brushes are not misaligned or too short)

I'm going to try and do that all tonight then test fly it Thursday. If that doesn't improve things, then get out the ol' shotgun...

I guess the good news is that now it's happening often enough that it should be much easier to find ;-)

Any other ideas are definitely welcome.
jim...
N1222K
LNC2

VTAILJEFF@aol.com wrote:

Jack,

If you have not found the problem I would try the battery. Sounds like a problem I had with a bad cell in the battery on my IVP. It would crank the engine fine but about 5 minutes after takeoff it would cause the field cb to trip. I went through troubleshooting everything you mention here and found it was a bad cell in the battery.

Regards,

Jeff Edwards

LIVP

Marvin Kaye wrote:

Posted for "Mark Ravinski" <mjrav@comcast.net>:

Jim,
Maybe your field breaker has mechanical issues. Try swapping that out.

Mark Ravinski
N360KB

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