I'm going to agree with Ken on this one. The GMC alternator works hard, but is our engine compartment really much hotter than a Toronado on a sunny
day? (Huge steel hood soaking up sun within an inch of the alternator, A/C cranking, maybe towing a trailer, etc?)
I'd like to suggest a possible alternate cause for some of these failures. Our alternators are remote-sensing. A separate wire goes (indirectly)
to the chassis battery, and the regulator uses that voltage to decide how much output is needed. A failure of the sense lead will send the alternator
into full output. Like any automotive alternator, the Delcotron is capable of over 100 volts at full field/no current. Years ago "they" sold a
clever device for externally-regulated alternators which allowed you to plug in your electric power tools so long as they had a "universal"
(brush-type) motor. The device disconnected the alternator from the battery and regulator, full-fielded it, sent its output to a voltmeter and 120V
socket, and provided a hand throttle for the engine. You plugged in the tool, eg; electric chain saw, and revved the engine until it read 120 volts
(DC). The stock output diodes withstood this voltage in most cases. An internal regulator might not.
Returning to our GMCs, we have an absurd 10ga wire carrying the full alternator output to a marginal 60 amp diode isolator. Can you say major
voltage drop? If the sense wire isn't seeing 14 to 14.5 volts at the coach battery, it's going to call for "MORE" power, which the alternator tries
to supply. Might this produce voltage enough to damage a regulator or diode trio?
FWIW, one of the first mods I did to my Eleganza 20 odd years ago was to install an 8ga wire in parallel with the 10ga to the isolator center post.
I also replaced the 60A isolator with a 120A unit from J.C.Whitney. (It just fits mounted horizontally on the firewall.) I've had only one
alternator failure in 20 years, and that due to the internal buss bar from the diodes to the B+ terminal working loose, with an effect similar to that
described above.
HTH, My .02, YMMV
--
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien