> Surprising that the car would run without it being connected
Car should run fine on just the battery. In fact it has to, as the
generator does almost nothing at idle.
> and was even
> still charging 8-9 volts.
Seems a little bit high; should be only 2-4 volts with the field
disconnected. Perhaps the wire was hanging and still letting a bit of
current through? Not really a cause for concern, but you might want to keep
an eye on the ammeter. If it goes higher than +20 for very long, there may
be an internal short in the generator.
It really is a clever system; the problem is that there is no real
difference between a DC motor and a DC generator except how fast it is
turning. So, the generator must be disconnected from the battery with the
engine stopped (or turning very slowly) so that it doesn't draw current out
of the battery (and try to turn the engine). The problem is, how to know
when to connect the generator to the battery.
So, when you first start the engine, the generator gets no field current and
works on strictly a slight magnetism remaining in the iron housing from the
last time it was used. (Setting up this magnetism is what 'polarizing'
does.) That generates a small voltage, which is fed only to the field
windings to increase the output, and so the output quickly rises to battery
voltage. When it gets there, the cutout contacts in the control box close
(connecting the generator output to the battery).
Now, how to 'know' when to disconnect the generator, since it's output is
now always battery voltage, no matter how much it is, or is not, producing?
There is another winding on the cutout relay that monitors the current
to/from the generator. If the current rises to 3-5 amps going the 'wrong
way', the current winding opposes the voltage winding; the cutout opens; the
red light comes on (which basically just monitors the state of the cutout
relay vs the ignition switch) and the whole cycle repeats when the generator
rpm comes back up.
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