X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 17 Apr 2006 22:41:48 -0400 Message-ID: X-Original-Return-Path: Received: from test-iport-2.cisco.com ([171.71.176.105] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1070879 for lml@lancaironline.net; Mon, 17 Apr 2006 13:13:27 -0400 Received-SPF: pass receiver=logan.com; client-ip=171.71.176.105; envelope-from=jmacknig@cisco.com Received: from sj-core-4.cisco.com ([171.68.223.138]) by test-iport-2.cisco.com with ESMTP; 17 Apr 2006 10:12:41 -0700 Received: from cisco.com (dhcp-128-107-149-164.cisco.com [128.107.149.164]) by sj-core-4.cisco.com (8.12.10/8.12.6) with ESMTP id k3HHCfYg021854; Mon, 17 Apr 2006 10:12:41 -0700 (PDT) X-Original-Message-ID: <4443CC88.7040205@cisco.com> X-Original-Date: Mon, 17 Apr 2006 10:12:40 -0700 From: jmacknig User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20030208 Netscape/7 X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: LNC2 Field Breaker Popping References: Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Have an alternator issue with my LNC2. Wondering if anyone has run across this type of issue.

Symptoms

Starting about 4-6 weeks ago the alternator field breaker (10A) has been tripping after 20min or so of flight. Can immediately reset (within 5-10 seconds) and the alternator comes back on line everytime and will stay on for another 15-30 minutes.
External vibration tends to make it happen more quickly.
When operating correctly, field current is 0.5 - 0.6A for 16A output load and 1.3A for 50A output load (measured)
10A circuit breaker is not "weak". Tripped 15A ultra-fast blow fuse in Fluke meter (put in series to make above measurement) and breaker didn't trip
Researched alternators over the weekend, found the Sacramento Sky Ranch website, ran the static checks and everything's OK from that end.
9 months ago had the alternator field breaker trip once. Found primary feed wire from the battery plus side had slowly chaffed against the ground case of the voltage regulator (VR), causing a momentary battery short to ground. Replaced the primary battery feed, improved the spacing, added better wire insulation and never saw an issue again until 4 weeks ago (yes, checked that and no sign of chaffing).

Equipment:

Bosch 95A alternator, ~450 hours time in service (replaced the original non-Bosch at ~100 hours when the PMA'd unit failed)
External voltage reguator, single wire setup. May have an internal OVP but not sure (should have the datasheet here on Wednesday)
10A field reaker feeds the VR high side input.

Some Ideas:

Have checked all wiring from alternator to VR and have found no chaffed wires.
Checked the field wire from the alternator to the VR for intermittents or shorts with DVM and didn't see any sign. Yep, did the wire giggling trick, pulled, pushed and prodded but everything seemed solid.
Alternator or VR (just behind firewall) could be getting heat soaked but then would expect failure rate to increase as time goes on
Could the momentary shorting of the +12V battery to the VR case have weakened the main VR output regulating transistor?
Pulling alternator and VR out as a pair and have them checked at our local alternator/generator shop. Spoke with the owner (has over 45 years experience with motors, alternators & generators) and the symptoms didn't ring any bells.

Any other ideas out there?

Thanks,
jim...
N1222K
LNC2, 571 hours
(wow, didn't realize this ended up being such a ramble)