Polarizing Alternator

[lummert]

To my knowledge Polarizing is done to Generator charging circuits anytime the battery is disconnected or any charging parts replaced. First time I've heard it being done to an alternator. But if it works for you.

I saw where you've been asked about the battery light on the dash. On '87 and back BMW's if the battery light on the dash does not light there will be no charging. Starting in '88 a resistor was added across the battery bulb leads so the battery would get the exciter wire circuit hot so the alternator would still charge with a burnt out bulb.

IIRC correctly a 5 ohm resistor can be installed in place of the indicator lamp.

[Angeou]

Alternator Usage specification

(1) The polarity of the battery must be the same as that of the alternator. The consequence of not using according to the specification is that the diode is damaged due to the large current discharge of the diode.

(2) When the six diodes of the rectifier are connected to the stator winding, it is absolutely forbidden to check the insulation of the alternator with a megger or 220V AC power supply. Otherwise, the diode is easily broken down and damaged.

(3) After the engine is turned off, the ignition switch should be turned off. If the flame is not turned off in time, the battery will continue to discharge, which will affect the magnetic field and shorten the battery life.

(4) When the alternator is running, it is not allowed to use the fire test method to check whether it generates electricity. Otherwise, it is easy to damage diode and electronic components.

(5) The regulator must be the same as the alternator in the form of iron, otherwise the alternator will not be able to output voltage due to no magnetic field current. And the voltage level of the two should be the same, otherwise the charging system can not work properly.

(6) If the alternator is not generating electricity or the charging current is small, the fault should be eliminated in time, and the wire connection between the alternator and the battery should be firm. Otherwise, it is easy to damage diodes and electronic components.

(7) When the alternator is mounted on the engine, the center of the alternator with pulley groove and the center of the engine with pulley groove should be aligned, and the appropriate degree of triangular belt tightness should also be set.

When installing the V-belt early, force to pry the front cover of the alternator. Otherwise, it will crush the element.

This article is helpful: https://www.dieselgeneratortech.com/gen ... -work.html

[lummert]

But does the charge light work?

[jimmy57]

Polarizing an alternator is ENTIRELY a different thing than on a generator. Generators are series wound and the armature needs to have maximum magnetizing in order to have the correct output, especially at lower speeds. When a generator is rebuilt some of the operations could lead to the armature getting magnetized wrongly. Applying current to the brushes in the correct polarity will assure that the potentially reversed residual magnetism is corrected.
Polarizing an alternator is really a wrong use of the term. The rotor (equivalent sort of, to armature) is magnetized and the claw poles will be the two magnetic poles, N and S as usually described. There will be no issues of residual magnetism. What is needed is properly called Exciter Current. In order to get the alternator to have a low rotation speed start of current output it needs a current applied to the brushes that lead to the winding in rotor so the rotor has the needed magnetism to induce current in the stator windings. The warning lamp bulb circuit can be that current or on some systems it is a dedicated circuit for only that purpose. Once the alternator spins up and current flow in stator commences then there is a set of diodes, not the rectifier large amperage set, called the magnetizing diodes that supply the voltage regulator and thus the brushes with the current used for rotor magnetic field current. This current is what the Voltage regulator controls to limit the voltage. The maximum current of an alternator is set by the length and gauge of stator windings supported by an appropriate length and gauge of wire wrapped in rotor and then the capacity of the rectifying diodes to sort the alternator current motion into pulses of direct current. The multiple phases in the alternator, owing to the multiple poles of rotor and offset multiple phase windings in stator, yield pulses with their peak currents (and voltage) occurring close cyclically yielding small ripple voltage of no consequence.
BUT, absent that initial exciter supply the alternator will start charging anyway but ussally the alternator speed may have to exceed 8000 RPM which would be over 3000 RPM with the overdriven ratio used on most gasoline engines.