Electrical System; Master Switch - Rotax CESSNA 150 Manual

Airplane Flight
Manual Cessna F150L
Nr. 160
Converted with kit 1-10
NS402S with ROTAX 912 S3 and Page:
HOFFMANN HO-V352F/170FQ+10 Revision 1

ELECTRICAL SYSTEM

The airplane is equipped with a 14-volt, direct current electrical system with one internal
generator (Generator 1) and one externally mounted generator (Generator 2) (see Abb. 1 - 4).
A 12V battery is located right in front of the firewall immediately under the engine cowling. The
power is supplied to a bus bar. A master switch controls this power to all circuits, except the
engine ignition system and the optional built-in clock and hour meter (which only operates
when the engine is running).

MASTER SWITCH

The master switch is a split-rocker type switch labelled MASTER and is ON in the up position
and OFF in the down position. The right half of the switch, labelled BAT, controls all electrical
power to the airplane. The left half, labelled ALT, controls the alternators., Alternators are
provided with separate indicator lights and circuit breakers. The generators are separated
individually from the electrical system by their own circuit breakers
During normal operations both halves of the switch should be switched simultaneously on.
However, if devices are to be tested on the ground, the side of the switch labeled "BAT" can be
set to "ON." If the side of the switch labeled "GEN" is set to "OFF," both generators are
disconnected from the electrical system. In this case, all the electrical load will be on the
battery. If the alternator switch in "OFF" position for extended periods, the battery current will
be reduced to the point where the battery contactor will disconnect the current from the
generator field winding and prevent the generator to be reconnected
AMMETER
The ammeter indicates the current flow, in amperes, from the generators to the battery or to
the electrical system. When the engine is running, and the main switch is turned on, the
ammeters indicate the amount of the current drawn from each generator. The maximum
charging currents are 28A for generator 1 and 44A for generator 2.
OVERVOLTAGE WARNING AND WARNING LIGHT
The aircraft is equipped with an overvoltage protection system consisting of a warning device
behind the instrument panel and a red "OVER VOLTAGE" warning lamp below the ampere
meter
If an overvoltage occurs, the overvoltage alarm automatically shuts off the alternators by
removing the power to the generator winding. As a result, the red warning lights illuminate,
indicating to the pilot that the generators are no longer providing power and all the electrical
power is being supplied by the on-board battery.
The overvoltage warning can be reseted, by. setting the main switch off and then turned on
again. If the warning light does not come on again, the generator has resumed normal power
generation. However, if the lamp lights up again, there is a fault and the flight should not be
continued and landing performed as soon as possible.
The overvoltage warning light can be checked by briefly switching off the half of the main
switch labeled "GEN", while leaving the "BAT" switch half switched on.