| Alternator resistor [message #273991] |
Wed, 18 March 2015 22:50  |
Bullitthead
Messages: 1411
Registered: November 2013
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This is a pic of the innards of a 100 amp alternator from a Cadillac that I cannibalized the diode trio from to repair the 80 amp alternator in the GMC.
http://www.gmcmhphotos.com/photos/alternator/p57563-100-amp-alternator-innards.html
See the precision wire-wound resistor attached to the regulator assembly? It is grounded on the top screw and the other end attaches to the output of the diode trio which also is the input to the field (which is the rotor in alternators). I think it measured 4.72 ohms. The 80 amp alternator from the GMC did not have the resistor. Is the one in the 100 amp there to take the place of the nichrome resistor wire that the GMC has in the harness? I ask because I cannot get my alternator to sense the battery voltage and raise the output to compensate for the isolator diode and the system barely maintains the battery voltage. Turn on the lights and the battery voltage steadily drops. I have an ammeter in the alternator output that shows when the charge drops off, and this happens when I have 14.3 at the isolator input and 13.6 at the battery. Only losing a tenth of a volt between the alternator and the isolator because of the wire and ammeter, right at the alternator terminal is 14.4V. Jumping the brown wire (without interrupting it) to the battery upped the output voltage of the alternator to just the right level, until I turned the headlights on and blew the diode trio! That's why I had to swipe the one from the Caddy alternator. Really would like to know if that resistor has anything to do with the output voltage. The 100 amp unit is not in my wiring diagrams. Anybody know?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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