ARMY TM 9-6115-673-13&P
AIR FORCE TO 35C2-3-512-1
1.23.
GENERATOR CONTROL CIRCUIT.
1.23.1. The generator control circuit (Figure 1-11) consists of a dynamo (G1), the generator control unit (A2),
discharge varistor (V1), HOURS meter (M3), and diode (CR2).
1.23.2. The dynamo (G1) generates power for the generator control circuit. The dynamo consists of a stator mounted
to the diesel engine block and a dynamo wheel mounted to the engine flywheel. While the diesel engine is running,
magnets mounted on the inside surface of the dynamo wheel provide the field magnetism necessary to generate
current flow in the stator. The dynamo (G1) generates AC current which is connected via the engine wiring harness to
the generator control unit (A2) at A2 pins VMAG1 and VMAG2.
1.23.3. The generator control unit (A2) rectifies the dynamo alternating current to direct current which exits at A2 pin
VMAG+. This direct current is used to power the HOURS meter (M3), which maintains the cumulative time for
generator set operation (e.g., the total time that the diesel engine dynamo generates power). The current is also used
to energize the low oil pressure solenoid (L4) at L4 pin Y.
1.23.4. The generator control unit (A2) also detects a short circuit fault condition and trips the load circuit breaker
(CB1). Under normal operating conditions, rectified DC current exits A2 at pin VMAG+ and provides current to the
load circuit breaker (CB1) trip coil via an auxiliary shunt (part of CB1). Whenever CB1 is closed (connecting the
generator set with the load), the auxiliary shunt closes enabling current to flow to the trip coil. The trip coil will not
energize however since the circuit terminates at the generator control unit (A2) pin STC which is not grounded. While
the generator set is operating, generator control unit (A2) continually monitors the current flow at A2 pin VINAC (or
VINDC for MEP-501A). When a short circuit occurs (or when the generator set is shutdown), the input at VINAC (or
VINDC) drops or goes low. The generator control unit (A2) reacts by grounding the CB1 trip coil circuit at A2 pin STC.
When the coil is energized, it opens the load circuit breaker (CB1) to isolate the generator set from the load.
1.23.5. Discharge varistor (V1) is connected across the dynamo wires leading to generator control unit (A2) pins
VMAG1 and VMAG2. It protects the generator control unit (A2) from inductive voltage surges generated by the
dynamo. It accomplishes this by limiting the peak discharge voltage to a safe value.
1.23.6 Diode (CR2), in MEP-531A, protects generator control unit (A2) by suppressing any spikes generated by the
trip coil in circuit breaker (CB1).
