Onan MJA Series Service Manual page 97

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When current flows in the control windings, it decreases the magnetism
in the core, reducing the current flow in the gate winding. Therefore,
the control regtllates the current in the generators' field, which controls
the generator's output. More de-magnetizing current in the control
winding, less current in the gate winding and gene.rator field and a lower
ou tput voltage.
Next, we must introduce a regulator so that the current in the control
windings will depend on the voltage output of the generator. The reg ­
ulator must allow little or no current flow up to a certain output voltage
and a large flow above that voltage. That is the purpose of the circuit
shown in Fig. 4.E. This circuit uses rectifiers, to allow the current.
to flow in only one direction, and a control reactor. The control reactor
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GEJllERATOR OUTPUT VOLTAGE
FIG 4.E - CONTROL CIRCUIT
FIG 4. F - CONTROL REAC­
TOR CHARACTERISTICS
is the voltage sensitive control of the regulator. Its characteristics
are shown in Fig. 4. F. Below the proper voltage, little eurrent flows
through the reactor, so little current flows in the control windings.
This allows full current to the field windings. When the reactorsatur- .
ates magnetically, it suddenly allows a lot of current to flow through
the control windings, reducing the current to the field Windings. This
reduces the generators' output voltage, which, in turn reduces the CUr­
rent through the control reactor and control windings· back to the set re­
quirements. The regulator then holds voltage at a pre-set level deter ­
mined by the control reactor.
This is the basic circuit, but some refinements have been added. Com ­
pounding windings on each large reactor, help to retain voltage control
thr.ough changes in load and an output voltage control resistor allows ad­
justment 01 the output voltage by changing the voltage across the control
reactor (Fig. 4.G). .