From: David Cole (DavidCole@tk7.net)
Date: Thu Jun 03 2004 - 20:36:36 PDT
FWIW, brush equipped AC generators can have the same problem. The
residiual magnetism in the rotating field (armature) goes away after a
while and sometimes they have to be flashed or polarized in order to make
them come alive again. I had this problem with an old John Deere AC
generator that looks similar to the newer Coleman plastic housed AC
generators ends.
Dave
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
On Wed, 02 Jun 2004 10:49:58 -0400, Bjorn Brandstedt
<super_deuce@hotmail.com> wrote:
>
> 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 ½ 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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>
>
>
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>
-- Dave
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