From: Bjorn Brandstedt (super_deuce@hotmail.com)
Date: Wed Jun 02 2004 - 07:49:58 PDT
For those of you wondering about the polarization business, this is more or
less what I incuded in a recent article about solid state devices for the
deuce (MVM Feb 2004):
“Polarizing the generator” refers to aligning the magnetic fields in the
permanent magnets within the generator, putting the north and south poles
where they need to be for a positive output voltage with respect to chassis
ground.
Within the generator are permanent magnetic pole pieces that set up the
magnetic field,
through which the armature rotates and creates electric energy. If there was
no magnetic
field, then there would be no output from the generator.
The batteries are not part of the picture during start-up. They are not
connected to the
generator courtesy of the regulator, which breaks the circuit when the
generator voltage is
less than the battery voltage.
So, when the armature begins to rotate, the only way it can produce an
output is to rely
on the “residual magnetism” of the pole pieces. Once there is an output, it
is fed back to
the field windings through the regulator control transistor, which is
biased, or turned
“on” right from the start. The regulator runs on power from the generator,
not from the
batteries.
The transistor has a built-in shortcoming as a switch compared to a relay
contact in that it
requires a minimum of about ˝ a volt to operate. This means that a strong
residual
magnetic field is of added importance when the solid state regulator is
used. The old
electromechanical regulator with its relay contacts offered an almost zero
loss in
voltage across its contacts.
The voltage fed back to the field now builds the magnetic field, which in
turn produces a
greater output voltage and so on until the regulator kicks in and begins to
control the
voltage to the field by turning the control transistor off. The generator
voltage then drops
and the control transistor is again turned on. This takes place at a rate of
over 1000 times
each second. If there was no residual magnetic field, the process could not
begin and
there would not be any output from the generator.
The pole pieces may lose their magnetism from extended storage (perhaps a
year or
more), exposure to extreme heat or cold or if the generator is dropped or
even just
whacked with a hammer.
When we polarize the generator, we restore the residual magnetism to the
pole pieces. It
has to be done properly. If the pole pieces become magnetized in the wrong
direction, the
generator output will be negative or erratic, which may destroy the control
transistor in
the regulator.
To polarize the generator, make sure that the generator and the batteries
are properly
grounded then, momentarily, apply the battery voltage (positive 24 volts) to
the field
terminal. That's all.
Bjorn
>From: "John Brian Seeling" <JBSeeling@cox-internet.com>
>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>Subject: [MV] generator woes
>Date: Tue, 1 Jun 2004 15:13:56 -0500
>
>half-track 12-volt generator isn't putting out. changed the voltage
>regulator but that accomplished nothing.
>i thought the generators were pretty tough, and that replacing the
>regulator
>would solve my problems.
>now that i've paid my "dumb-tax," can anyone offer some advice/suggestions
>on how to trouble-shoot and fix this problem?
>any advice to the electrically-challenged? I've got to get the old girl
>running before Friday, since she has to be in New Orleans for the D-Day
>anniversary, and I don't want to start "experimenting" without some idea of
>what i should be doing.
>Thanks in advance,
>-John Brian Seeling.
>
>
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