Reprinted from i Saluti, August 1999,
from the Alfa Digest
Polarizing a Generator
by Simon Favre
I have a �62 Giulietta 1300 normale. It originally had a Lucas generator with positive ground. This has recently been replaced with a Bosch generator. For some reason the Bosch generator is not charging. Someone told me I should �polarize� the Bosch generator for positive ground. How do I do this?
Positive ground is a myth. Polarizing a generator is a myth. You polarize it every time you turn the ignition on. There are no permanent magnets in a generator. The regulators on these cars, both Bosch and Lucas, are only relays. There are no permanent magnets in the relays either. The way it works is this: When you turn on the key, the battery provides power to both the armature and the field of the generator through the charging light. When you start the motor and rev it up past a certain point, the generator is putting out more voltage than the battery. At a trip point determined by the regulator (relays), the regulator connects the generator output (the armature) directly to the battery. This shorts out the charging light. When the voltage rises to a second trip point, the regulator starts chopping the field coil to reduce the generator output to prevent overcharging. The default mode of the regulator is to ground the field terminal through the overvoltage relay contacts. When the max voltage is reached, these contacts open up, taking away the field current. This causes the output voltage to drop, which makes the regulator close the contacts again, etc. etc. etc. There�s also a resistor across the overvoltage points, so the field isn�t completely cut off, but the field current drops way down.
The key point here is that Alfa, in a fairly smart move, specified that all the instruments on Giuliettas work in positive or negative ground. The generator and regulator don�t know the difference. It�s really as simple as reversing the battery. Your problem may lie with either the regulator (if it�s Lucas, that�s a given), or the wiring. Note that if the generator light does NOT come on when you turn the key, the generator will NEVER start charging! Double check the wiring against a schematic, and make sure the generator light functions properly. My advice is to scrap the Lucas regulator and put in a decent Bosch unit. You can use one from a Porsche 912. The early 105 cars with a generator had a Bosch regulator that is more correct. The only difference is the shape of the terminals. The Lucas had screws you stuck the wire in, so you have to add some terminal connectors either way if you put in a Bosch regulator.
Data point: My �62 had the Lucas crap in it at first, too. I switched the battery and had a Lucas generator happily putting out negative ground before I replaced it all with Bosch. I had a Lucas regulator go bad and burn out a perfectly good generator. Bosch is the way to go.
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