Hi Dave, It's possible your alternator is internally wired differently. As for the rest of us (again, what I was told) the diodes are supposedly there meant to both turn the a/c current into dc for use by the batteries and act fuse-like to prevent the possibility some kind of much worse (Overheat / fire perhaps? ) alternator self destruction. All I knew at the time was for 78 bucks and 45 or so minutes of wrenching I could make it all good again and have the peace of mind associated with replacing a 20 year old alternator with a brand new unit.
Now that I'm looking into it that appears the catastrophic failure would to be related to the field coils which are energized as the alternator turns and their voltage is regulated by the battery / voltage regulator. Apparently, if left unchecked (With a disconnected battery, open "ignition" circuit) the output voltage could go to a couple hundred volts which could potentially make the regulator circuitry immolate itself or something to that effect. With the typical setup the diodes burn-out first and prevent catastrophic damage. See here for more details: http://www.pangolin.co.nz/node/16 -Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA Message: 2 Date: Mon, 18 Jul 2016 08:38:01 -0400 From: Dave Syer <syerd...@gmail.com> To: "C&c Stus List" <cnc-list@cnc-list.com> Subject: Stus-List Relocating the Yanmar key now alternator.. Message-ID: <CAD7ywJNLTLNEHS97dz1oBPaK74ymNc-TLCLL=zsojmhkart...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Interesting discussion. So, I have run my 1985 2gm Yanmar briefly with the key removed and no apparent harm was done. The manual does say never to run it with the battery disconnected. Now, when I check the schematic, (and my engine) there is a 30A tubular fuse in series with the key switch. Therefore a blown fuse = an open key switch, and would cause the same damage to the alternator. This does not make a lot of sense to me. Other than adequate knowledge, am I missing something? See below.
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