Posted by Don Williams [108.162.237.59] on Sunday, June 26, 2016 at 12:29:03 :
In Reply to: Wiring Diagram Question posted by Greg Coffin [172.68.34.167] on Saturday, June 25, 2016 at 17:00:49 :
Short answer -- polarity on the field terminals does not matter. A little more explanation.
The "I" terminal on the voltage regulator is simply sensing the voltage level of the system. We will call that the reference signal.
Going back to elementary school science fair, do you remember the kid who made an electromagnet using a 6V lantern battery and a nail with wire coiled around it? You could magically pick up ferrous metal objects with it when both ends of the wire were connected to the battery. Polarity did not matter, just hook them up.
The field coil inside the alternator is essentially an electromagnet. The field coil is creating a magnetic field. As the magnetic field strength increases the electrical current output of the alternator increases. The electronic voltage regulator is simply controlling the current flow through the field coil by turning transistors on and off inside the regulator and completing the circuit back to the battery through the regulator case ground. This increase and decrease in field current is what makes the alternator charge more or less. Of course engine RPM plays a part but lets just assume a constant RPM for this explanation. As with the science fair experiment, polarity does not matter to an electromagnet.
The voltage regulator determines how much field current to allow to pass based on the voltage reference signal at "I". If voltage is low at "I", the field current is higher in order to put more charge to the system. If the reference signal is high then field current goes down because less charge is needed.
On a side note, if you have trouble with the system overcharging on an older vehicle using this system it may be the reference signal. Over time the resistance through the circuit will increase causing a voltage drop at "I". Seeing a low voltage at "I" causes the regulator to call for more charge. I found a good fix for this is to use the reference signal to turn on a relay. Run a new wire from the battery through the relay contacts to the "I" terminal on the voltage regulator. Field current on this system can be as high as 5 amps or so. I suggest fusing the new wire from the battery at about 10 amps.
Hope this helps.