96-20 External Power
A 28-volt MS3506-compatible external power receptacle is located inside the right engine cowl
door. When the battery is switched ON, the external power relay and the battery relay both
close, connecting external power to the aircraft electrical system and battery The external
power relay will not close if reverse polarity is provided to the receptacle.
A separate wire from the external power receptacle to the battery bypasses the external
power and battery relays. This wire allows battery charging via the external receptacle with
the battery switch OFF. A 10-amp circuit breaker at the receptacle opens if current exceeds
normal charging levels, and a diode provides polarity protection.
96-30 Starter and Ignition System
A single starter-generator is used for engine starting and electrical power generation. A
generator control unit (GCU) controls starter-generator function. During a start, the GCU
latches the starter on until N
1
reaches 58 percent RPM. Therefore, the pilot is not required to
hold the start button down throughout the start sequence. Above 58 percent N
1
RPM, the GCU
automatically switches out of start mode, but the generator switch should not be switched ON
until idle RPM stabilizes to prevent the generator load from bringing the RPM down.
When the igniter key switch is in the enable position, depressing the start button causes a
normal start sequence with the starter latching on and the igniter firing. Above 58 percent N
1
RPM, the igniter will fire while the start button is depressed.
When the igniter switch is OFF, the engine can be motored by the starter by depressing the
start button without the starter latching or the igniter firing. This is useful for performing
a compressor wash or rinse. If the igniter is switched OFF during a start, the starter will
disengage. If the igniter is switched OFF while the engine is running, the engine will continue
to run; however, this is not recommended.
NOTE
Start button is active when battery switch is ON, even if igniter
switch is OFF. Rotor brake may be left engaged after shutdown
to disable start button.
SEP 2012 R66 Maintenance Manual Chapter 96 Electrical System Page 96.5
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