Hi Dave,
Here's how I understood the whole thing. An alternator's design is basically the reverse of a regular DC motor with an added twist.. On a regular DC motor the windings (Electro magnets) are on the spinning armature and there are permanent magnets attached to the housing. You add voltage to it: The windings are energized, they produce a magnetic force opposite to the permanent magnet on the housing, the motor spins. The more voltage, the stronger the electro magnet on the armature becomes, the faster it spins On an alternator, the windings are on the housing (Stator) and the magnets are spinning with the shaft (Rotor). You spin the alternator, the magnets fields excite the windings, A/C electricity is produced. The alternator's added twist is that the magnets are not permanent, they are electro-magnets with their own winding. The genius here is that it makes the magnets adjustable where their strength (And the Alternator's output) can be controlled by varying the voltage applied to them while still being driven at the same RPM.. Voila :-) The alternator I burned was most assuredly the original Yanmar unit.. It had the funky looking fan, was stamped 'Yanmar", and was painted the same color as the rest of the engine. I guess the one on your 2GM is somehow different than what was on my 3GM.. -Francois 1990 34+ "Take Five" Lake Lanier, GA From: "syerd...@gmail.com" <syerd...@gmail.com> To: Jean-Francois J Rivard/Atlanta/IBM@IBMUS Cc: cnc-list@cnc-list.com Date: 07/19/2016 08:14 AM Subject: Re: Relocating the Yanmar key now alternator.. 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 <jfriv...@us.ibm.com> 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 <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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