Maintenance Manual STEMME S10-VT
Date of Issue: Jan. 01, 1998
Page 3-36
Amendment Nr. 0
Date: --
A4011121_B23.doc
Doc. No. A40-11-121
3.7.4 Structure of Grounding
Engine housing and fuselage steel-tube framework are the central a/c ground. More ground busses are
installed at several positions in the a/c, combining local components and equipment.
Ground Bus 1VN
Ground Bus 1VN mechanically protects the battery connector. It is connected to the battery „minus“
and via a 16 mm
2
/ 0.025 in
2
cable to the engine housing. Also the ground of the starter-relays and
ground bus 2VN-1 are connected.
Ground Bus 2VN-1
Ground Bus 2VN-1 is installed in the junction box (E-box) and connected to 1VN.
Ground Bus 2VN-2
Ground Bus 2VN-2 is installed in the cockpit on the RH electronic plate and is ground for electronic
equipment in the cockpit supplied by the Main Bus 2VV and for the relays in the E-box, which are
selected by switching to ground in the cockpit. Ground Bus 2VN-2 is also connected to the fuselage
steel-tube framework.
Ground Bus 2VN-3 and 2VN-4
These two busses are ground for the landing gear control; they are installed on the relays plate and
connected to the fuselage steel-tube framework.
Ground Bus 3VN-1
Ground Bus 3VN-1 is the central ground for all systems at Engine Bus 3VV. It is installed on the RH
electronic plate and connected with the fuselage steel-tube framework.
Ground Bus 3VN-2
Ground Bus 3VN-2 is the central ground for the engine instrumentation. It is installed on the backside
of the RH instrument panel and connected with the fuselage steel-tube framework.
Ground Bus 4VN
Ground Bus 4VN is central ground for all avionic equipment including headsets. It is installed on the
RH electronic plate and connected with the fuselage steel-tube framework.
3.7.5 Generation of Electric Energy
Electrical power sources are the main battery, capacity 26 Ah, the optional additional battery, 7.2 Ah, for
supply of avionics during soaring and two engine-driven generators generating 600 Watt and 250 Watt. The
external, V-belt driven, generator (600 Watt) supplies the Main Bus 2VV. When the engine is running, it can
be selected via relays by a switch on the instrument panel (refer to description of switches, section 3.7.11).
Voltage control is by an internal voltage regulator. As recommended by the engine manufacturer, the
generator output is buffered by a capacitor of 22.000 F.
The internal generator is driven directly by the crankshaft. It is an integrated unit with the coil for the supply of
engine ignition and transmitters for ignition points. Because of the low power of 250 W it is used only for the
supply of systems required for engine operation (ignition, main fuel pumps, TCU). The internal generator is
generating power whenever the engine is running and cannot be switched on or off. Voltage is regulated by a
separate voltage regulator. As recommended by the engine manufacturer, the generator output is buffered by
a capacitor of 22.000 F.
The voltage regulator requires a reference voltage to regulate a generator output at the moment of starting.
This is realised by an electric interconnect in between the main system and the system of the internal
generator. Overload and reverse current of this interconnect is prevented by a CB (10A) and a diode. By this
design, the systems are separated in case of a malfunction and supply of the main fuel pumps and the TCU
is assured, when ever the internal generator is below the voltage limit.
