Hi Dave,
Thanks for the added stuff. Actually it seems to explain it all: Why some alternators fry and some don't: The key here is the "Self Exciting" part. The self exciting alternators don't need the ignition return side at all. Basically all your key does is turn-off the instrument panel (And annoying buzzer) and disable the starter. Your alternator's function is truly not affected by the key . This other site I saw explains that very clearly : https://alternatorparts.com/what-is-a-self-exciting-alternator.html That also explain the runaway voltage situation: It says: "Remember the diagram of the pulsed DC output from the alternator and the fact that the battery acts as a large filter or cushion in the system. " so basically from looking at the schema you can see that in the non-self exciting alternator like mine the ignition / charging light is connected straight into the alternator. If you switch the battery off while the engine is running since it's a diesel it keeps chugging / the alternator keeps producing juice and the voltage regulator will take the brunt of the stator's output which causes the voltage spike.. Bottom line, it appears the 2QM 2GM engines have self-exciting alternators and the 3GM's don't. -Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA "While this clarifies the role of that supply and why the engine will run fine, (and for many of us, without apparent damage) with the key removed. (once spinning, the alternator excites itself,) it does not explain the failure experienced by only some of us, or the absence of warning in the various factory docs. Based on my extensive online research ;-) the failure experienced is as if the alternator is seeing no load, (i.e. battery disconnected) or as if it is running unregulated, with a fully energized field coil. I wonder if the failing alternators have an issue (i.e. failed regulator?) that is hidden by the presence of the independent field current supply, and only becomes exposed in its absence" Regards François Rivard 4111 Northside Pkwy, Nw Big Data Black Belt Certified Level 3 IT Specialist Thought Leader Atlanta, 30327-3015 USA IBM Sales & Distribution, Software Sales Mobile: 770-639-0429 e-mail: [email protected] From: Dave Syer <[email protected]> To: "C&c Stus List" <[email protected]>, Jean-Francois J Rivard/Atlanta/IBM@IBMUS Date: 07/19/2016 01:35 PM Subject: Re: Stus-List Relocating the Yanmar key now alternator.. There is a great explanation of all this here: http://www.pirate4x4.com/tech/billavista/Wiring/Part2/ And, to complete your commentary below, a lucid explanation of the role of the key switch circuit in our engines. >>>snip Field Current Supply The field current supply is provided from one of two different sources, depending on the state of the alternator. When the engine is not running and the alternator is not spinning and producing electricity, the field current supply comes from the vehicle's battery, via the ignition switch and alternator warning lamp (if equipped). We'll go into more detail on the warning lamp shortly. The process of supplying battery voltage to "kick-start" or "prime" the alternator is known as "exciting" the alternator, and the wire that carries the current from the alternator warning lamp to the appropriate voltage regulator terminal is known as the "exciter" wire. A few special alternators do not have this wire and are known as "self-exciting" - we'll cover this in more detail in the wiring section. After the engine is started, and the alternator is generating electricity the diode trio feeds the alternator output back to the voltage regulator to serve as the field current supply. Theoretically, once up to speed, the alternator is self sustaining, and the car will run without a battery until it is shut off (as long as system demand does not exceed alternator output capacity). However - you should never disconnect the battery in a running vehicle as doing so can cause voltage surges that can damage not only the voltage regulator, but also other on-board electrical equipment - particularly computer-controlled devices. Remember the diagram of the pulsed DC output from the alternator and the fact that the battery acts as a large filter or cushion in the system. Note that the field current is much smaller than the output current produced in the stator windings. For example, to produce 70 amperes of DC, the field current required will be less than 2 amperes. >>>snip While this clarifies the role of that supply and why the engine will run fine, (and for many of us, without apparent damage) with the key removed. (once spinning, the alternator excites itself,) it does not explain the failure experienced by only some of us, or the absence of warning in the various factory docs. Based on my extensive online research ;-) the failure experienced is as if the alternator is seeing no load, (i.e. battery disconnected) or as if it is running unregulated, with a fully energized field coil. I wonder if the failing alternators have an issue (i.e. failed regulator?) that is hidden by the presence of the independent field current supply, and only becomes exposed in its absence? Dave Message: 2 Date: Tue, 19 Jul 2016 09:21:52 -0400 From: "Jean-Francois J Rivard" <[email protected]> To: "[email protected]" <[email protected]> Cc: [email protected] Subject: Re: Stus-List Relocating the Yanmar key now alternator.. Message-ID: < of4343dba2.fa97e163-on00257ff5.004567a8-85257ff5.00496...@notes.na.collabserv.com > Content-Type: text/plain; charset="us-ascii" 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..
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