How to polarize a generator
Steve Cowell
polarizing generators, since I received inquiries about it.
Ken wrote:
Here is what my literature, "Auto Mechanics Fundamentals" by Stockel
and Stockel, says regarding dc generators.
"DC GENERATOR POLARITY
Polarity can be defined as the directional flow of current leaving
the generator. When the generator is stopped, a certain amount of
residual magnetism remains in the pole shoes. The polarity of the
shoes at this time, depends on the direction of current flow in the
field coil windings prior to stopping.
If, during generator testing, current is accidentally caused to
flow in an opposite to normal direction, the pole shoes will change
polarity. N becomes S, and S becomes N. When the generator is
installed and the engine is started, the reversed polarity will cause
current to flow in the wrong direction.
The reversed current flow will damage the cutout relay points by
doubling system voltage at the points (generator and battery will be
in series). The operating coil magnetic strength will be insufficient
to hold the cutout points closed. As a result, they will vibrate and
burn. In time, they will actually weld together, and the battery will
discharge through the generator. A dead battery, as well as possible
damage to the generator, will result. To prevent this, the generator
should be polarized before starting the engine.
GENERATOR POLARIZING
When a DC generator has been disconnected and reinstalled, it must
be polarized prior to starting the engine.
When the generator grounds the field circuit externally, the
generator is polarized by connecting a jumper wire acrossthe Gen. and
Bat. terminals of the regulator. Hold one end of the wire against the
generator terminal, and scratch the other end across the battery
terminal. This one flash causes current to flow through the field
coil in the proper direction, insuring correct polarity.
To polarize the internally grounded field circuit [Ford],
DISCONNECT the field lead from the regulator and momentarily scratch
it on the battery terminal of the regulator.
Remember this rule for polarizing generators - ALWAYS PASS CURRENT
THROUGH THE FIELD COILS IN A DIRECTION THAT WILL CAUSE THE GROUND
SIDE OF THE COILS TO BE CONNECTED TO THE GROUND SIDE OF THE BATTERY.
Remember, always polarize a generator after installation!"
- - - -
There are some illustrations in the text which show the "A type" and
"B type" generator winding diagrams. The "A type" grounds the field
winding externally. The "B type" (Ford, Motorcraft) grounds the field
internally.
End of quote from Ken....thanks again, Ken.
--
Steve.......scowell@aoc.nrao.edu...............