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connecting the DC power assured bus to the battery
Inverter isolated.
emergency bus.
No loads are shed.
(4) Battery Failure. 2-66. BATTERY SYSTEM OPERATION.
The battery supplies power to the battery emergency
bus when the ESNTL BUS switch (fig. 2-8) is in the
Caution Message:
HOT BATT 1 START position. When two batteries are installed,
HOT BATT 2 either battery will supply bus power. In the event of
(CDS2/CDS3) HOT BATT 1 & 2 total generator failure with the ESNTL BUS switch in
(CDS4) HOT BATT 1, 2 the RUN position, the battery supplies power to all DC
buses. Battery loading can be reduced by placing the
ESNTL BUS switch to the START position, thereby
No loads are shed.
eliminating DC power assured and DC essential bus
(5) TRU Failure. loads from the system.
2-46
TM 1-1520-248-10
2-67. DC EXTERNAL POWER SYSTEM (1) MD-3: 28V at 1500 amps.
OPERATION.
(2) MD-3A: 28V at 1500 amps.
During ground operations, external power may be
connected to the electrical system through an external
power receptacle (71, fig. 2-1) located on the lower (3) MD-3M: 28V at 500 amps.
side of the nose. An external DC power sensor
monitors external power input and protects aircraft
systems from out of tolerance voltages, fluctuations,
and spiking. For application of external power, the DC 2-68. AC ELECTRICAL POWER DISTRIBUTION
GEN switch must be in the OFF position. The external SYSTEM.
power relay will then close and allow distribution of
external power to all DC buses and the inverter. A GPU
rated at 200 ampere, 28 Vdc is required for continuous a. Primary AC power. The primary AC distribution
ground operation and 500 750 ampere, 28 Vdc is system feeds AC generator power through the AC
required for starting. The following are the maximum generator transfer relay to the TRU, which is controlled
GPU settings: DC power output by a rectifier remote control circuit breaker (RCCB),
and to the essential bus through the inverter relay. The
a. AGPU-DOD model # MEP-360A (TM 55-1730- 115 Vac essential bus supplies power to the 26 Vac
229-12). bus through the 115/26 Vac transformer. Distribution
(1) 28 Vdc 700 amps (1000 amps for 30 seconds) from the Vac buses is controlled by circuit breakers
with no AC. located on the center post circuit breaker panel (fig. 2-
8).
(2) 28 Vdc 50 amps from battery chargers with
27.5 kwAC available.
b. Secondary AC power. When the AC generator
b. MD-3 series generator set (MIL-HANDBOOK- is not operating. AC power is provided by the inverter
300). through the inverter relay to the 115 Vac essential bus.
2-47
TM 1-1520-248-10
2
2
2
1
1
406075-1494-3
J2334
3
R
3 R
Figure 2-21. Electrical System Schematic
2-48
TM 1-1520-248-10
2-69. AC GENERATOR. 2-71. AC EXTERNAL POWER RECEPTACLE.
An AC external power receptacle is provided for the
At approximately 95% Nr and with the AC GEN switch application of AC power from an auxiliary AC power
(fig. 2-8) in the AC GEN position, the engine mounted unit. The receptacle is located on the lower right side of
AC generator provides power to the TRU. The TRU the aft fuselage. A 10 kVA external power source of
supplies primary DC power to the DC power assured three-phase, 120/208 Vac, 400 Hz output is required.
bus, DC essential bus 28 Vdc essential bus and the
battery emergency bus. 2-72. ELECTRICAL SYSTEMS CONTROLS
AND INDICATORS.
2-70. INVERTER. a. Electrical Systems Indicator (fig. 2-22). The
MPD contains a selectable-parameter digital indicator.
Display of AC voltage (ACV), rectifier voltage (RECT
a. Description. A single-phase, 115 Vac, 400 Hz V), rectifier load percentage (RECT LD%), starterinverter
is provided to supply power to the AC essential generator load percentage (S GEN LD %), battery
bus when the AC generator is not supplying power. The voltage (BATT V), and starter voltage (START V) may
inverter is powered by the battery generator bus and is be sequentially selected for display on the MPD by
protected by the INV circuit breaker located in the pressing the SEL switch.
overhead console (fig. 2-8).
b. Electrical Systems Controls (fig. 2-8).
(1) DC Power Control. DC power is controlled
b. Operation. The inverter is energized through by the BATT 1 and BATT 2 switches; DC GEN switch;
the BUS INTCON circuit breaker (fig. 2-8) when either DC GEN FIELD and RESET circuit breakers in the
external DC power is applied or the DC generator is overhead console; and a 9TH CELL circuit breaker (for
supplying power. With the BATT 1 switch on, battery battery preheat monitoring) located in the forward
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(26)
