Posted by John T on November 06, 2011 at 05:45:00 from (173.243.181.15):
In Reply to: Elementary Electrical posted by equeen on November 06, 2011 at 05:21:11:
I think Bob M has a good picture of that switch and what wires go where, I'll let him or others handle that part of your question and I'll just address this one:
3. Alternator #1 spade switch wire to ignition. Wiring options appear to include somewhere along the length of the wire: A filament style marker lamp bulb, or A 15 ohm resistor, or A 3 amp 50 volt PIV diode
Of course I could be confused with the above, but my question remains...... What is the purpose of something in this stretch of wire?
ANSWER:
OKAY, voltage is required to the No 1 terminal (on the GM 3 wire 10 SI alternator family) in order to "excite" the alternator prior to sufficient RPM such that it becomes self "excited"
So, why a diode or resistor or incandescent idiot light???
One or more of those are required becasue if you feed that No 1 terminal from the ignition system, like the IGN output on an ignition switch or the high input (NOT to distributor) side of the coil or the high input (NOT to coil) side of a ballast resistor THE TRACTOR MAY CONTINUE TO RUN AFTER YOU TURN THE IGN SWITCH OFF because the alternator might still back feed the coil i.e. independant from the ign switch.
NOTE Ive seen this work with no resistor at all in that wire, it depends on the idle RPM and other factors but many tractos would run on without this feature
I suggest either an incandescent lamp or a resistor as they provide at least some small degree of current limiting versus use of a diode like most use. Also an idiot light (small incandescent tail marker) provides a visual indication if shes charging or not the diode or resistor cant. Also some "dudes" use an idiot light in paralell with a resistor so the alternator still excites even if the lamp burns out.
NOTE some dudes (like if its a diesel) rig up an oil pressure switch and use it to excite the alternator verus the ignition but id still sue a resistor to give soem degree of current limiting.
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