Generac Power Systems 75, 55, 65 7.- Generator Operating Diagram, Section GENERATOR FUNDAMENTALS

Section 1

GENERATOR FUNDAMENTALS

Figure 1-7. – Generator Operating Diagram

NOTE: AC output frequency at 3720 rpm will be about 62 Hertz. The “No-Load” is set slightly high to prevent excessive rpm, frequency and voltage droop under heavy electrical loading.

Generator operation may be described briefly as fol- lows:

1.Some “residual” magnetism is normally present in the Rotor and is sufficient to induce approximately 7 to 12 volts AC Into the STATOR's AC power windings.

2.During startup, an engine controller circuit board delivers bat- tery voltage to the ROTOR, via the brushes and slip rings.

a.The battery voltage is called “Field Boost”.

b.Flow of direct current through the ROTOR increases the strength of the magnetic field above that of “residual” magnetism alone.

3.“Residual” plus “Field Boost” magnetism induces a voltage into the Stator excitation (DPE), battery charge and AC Power windings.

4.Excitation winding unregulated AC output is delivered to an electronic voltage regulator, via an excitation circuit breaker.

a.A “Reference” voltage has been preset into the Voltage Regulator.

b.An “Actual” (“sensing”) voltage is delivered to the Voltage Regulator via sensing leads from the Stator AC power windings.

c.The Regulator “compares” the actual (sens- ing) voltage to its pre-set reference voltage.

(1)If the actual (sensing) voltage is greater than the pre-set reference voltage, the Regulator will decrease the regulated cur- rent flow to the Rotor.

(2)If the actual (sensing) voltage is less than the pre-set reference voltage, the Regulator will increase the regulated cur- rent flow to the Rotor.

(3)In the manner described, the Regulator maintains an actual (sensing) voltage that is equal to the pre-set reference voltage.

NOTE: The Voltage Regulator also changes the Stator excitation windings alternating current (AC) output to direct current (DC).

5.When an electrical load is connected across the Stator power windings, the circuit is completed and an electrical current will flow.

6.The Rotor's magnetic field also induces a voltage Into the Stator battery charge windings.

a.Battery charge winding AC output is deliv- ered to a battery charge rectifier (BCR) which changes the AC to direct current (DC).

b.The rectified DC is then delivered to the unit battery, to maintain the battery in a charged state.

c.A 1 ohm, 25 watt Resistor is installed in series with the grounded side of the battery charge circuit.

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