Re: 49 Packard polarity change

Posted by HH56 On 2015/7/19 20:56:01

Ordinary solenoids and relays of our vintage don't really care about the polarity. The voltage just makes them an electromagnet to attract a piece of metal so it generally doesn't matter whether a north or south pole of a magnet does the attracting. Modern units are sometimes equipped with internal diodes or other back emf suppression means across the coil and those would care.

The ign coils themselves also do not care but the loss of efficiency comes in to play at the spark plug. The spark is much more efficient when it jumps from the hot center electrode to the cooler side wire because the electrode heat causes electrons to be in a state where less energy is required to "break them free". If the coil polarity is reversed the spark will still jump the gap but has to jump the other direction starting at a colder electrode so has to work harder. If another part of the electrical system is marginal that tiny bit more effort required may be enough to cause the spark to be weak or in worst cases not be able to jump the gap at all.

Regular stock Packard motors do not care about polarity since the relationship between the field and the armature is hard wired inside the motor. For example, a north pole on the field will attract an opposite south pole a few degrees away on the armature and will spin the shaft. If you change the polarity of the input to the motor, while the north and south poles internally will change they are still hard wired together in the same rotational relationship and will both change at the same time so opposites will still attract. Where motor issues arise is on motors where the field and armature are wired separately and one changes but the other does not. Those motors will run backwards as will permanent magnet motors where the field never changes. In those, the armature only can reverse polarity depending on input so it will run either direction. Modern power window motors take advantage of that whereas our era motors used either separate forward and reverse wound field windings or else a separate field winding with a reversing relay to change the relationship.

To polarize the generator have the engine and key off then use a decent size wire to momentarily connect -- 1 or 2 seconds -- between the BAT terminal and the ARM or GEN terminal of the regulator.

The momentary voltage applied back to the generator turns the field and armature into an electromagnet and results in a tiny residual magnetic field of the proper polarity being "stored" on the generator pole shoes. Because the generator and field coils are disconnected when the generator is still the generator uses that tiny residual magnetic field to produce a small low current voltage of the correct polarity when it first starts turning. Once there is some voltage out it can energize the cut out contacts in the regulator which connects the generator to the battery. When it is connected the regulator then can feed battery voltage to strengthen the field so the generator can produce to the capacity required.