Posted by Bob on December 31, 2008 at 18:38:36 from (69.178.228.68):
In Reply to: Re: DUMB posted by John B. on December 31, 2008 at 17:20:13:
Guys, bear with me on this. What I am talking about is REAL, and I am giving you sound and reasonable advice the MAY prevent trouble and $$$ down the road.
OK, here's the deal... You will NEVER find an OEM GM alternator circuit WITHOUT a resistor or lamp or diode, in the "switched excite circuit" just as I'm trying to explain. AFAIK, the engineers at GM never intended for the alternators to have the #1 terminal directly connected to the battery (though the ignition switch). If someone can find such an OEM diagram, I'll gladly "eat crow". If such an example DOES exist, it is certainly a rarity.
Here is how a diode, idiot lamp, or resistor protect the internal VR and diode trio in case there's a poor connection, resistance/voltage drop in the charging circuit between the alternator's output stud and the battery.
With a DIRECT connection between the alternator's #1 terminal and the battery (though the ACCY side of the ignition switch) if there's ANY voltage drop in the main charging circuit, current will then flow through an alternate path consisting of the diode trio, the internal VR, out the #1 terminal and on to the battery.
The diode trio is only intended to supply probably up to about 4 Amps to "excite" the rotating field, and if it DOES begin to supply charging current though internal wiring in the VR and out the #1 terminal it will overheat/be destroyed and, likely the VR as well.
You may very well GET BY with the "ACCY" hookup, as long as the charging circuit wiring is LARGE, in good shape, and never develops a loose or poor connection.
HOWEVER, choosing to do so opens up a possible "failure mode" for the alternator's diode trio and internal VR that will NOT EXIST if a lamp, resistor or diode are used to limit or eliminate the possibility of current "backfeeding" out of the alternator's #1 terminal.
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