Thanks JF. An interesting read here.
http://www.autoshop101.com/forms/alt_bwoh.pdf A decent corrected alternator diagram here. Post #15 http://www.ybw.com/forums/showthread.php?224370-What-s-the-R-connection-for-on-a-Yanmar-Hitachi-alternator/page2 So, if I understand correctly the key switch energizes the starting circuit, the warning indicators and provides a reference battery voltage to the voltage regulator, which regulates the voltage to the field coil and thereby the alternator output. More study required to truly grasp the theory, but am still grappling with why "no key/blown fuse = alternator destruction", and why some have had alternators fail and some did not. Also, keyless operation is not discussed (that I could find) in the owners manual or the shop manual, which seems strange. Is it possible that OE Yanmar alternators are of a design that incorporates safeguards appropriate to this situation, and that the failed alternators are of a different type? > On Jul 18, 2016, at 1:25 PM, Jean-Francois J Rivard <[email protected]> > wrote: > > 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 <[email protected]> > To: "C&c Stus List" <[email protected]> > 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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