CGS Ground School Technical The Vigilant Electrical System © Crown Copyright 2012 No Part of this presentation may be reproduced without the permission of the issuing authority. The views expressed in this presentation do not necessarily reflect the views or policy of the MOD.

TERMINOLOGY A/C – Alternating Current. With alternating current, the flow of electricity periodically reverses direction. D/C – Direct Current. With direct current, the flow of electricity is only in one direction. Alternator – An engine driven system whereby a magnet is rotated inside a wire coil. The alternator produces alternating current (A/C). Generator – This is simply an alternator fitted with a device called a rectifier. The rectifier converts the A/C output into D/C output. Circuit Breaker (c/b) – A circuit breaker is a device within an electrical circuit that can either be activated by the pilot ‘pulling’ it, or by the aircraft system ‘popping’ it. A c/b will be rated to a certain amperage, if this figure is exceeded the c/b will ‘pop’ and stand proud in its housing. Fuse – A device within a circuit similar to a c/b but a fuse can’t be reset.

A generator fuse. This is a 50 ampere circuit breaker labelled ‘GENERATOR FUSE’. Despite it’s name it is actually a circuit breaker and is also referred to as the Alternator c/b. All of these devices are linked via an electrical circuit. Three busbars: A busbar is a series of conductors carrying all power to or from a station. A main fuse. This is a 40 ampere circuit breaker labelled ‘MAIN FUSE’. Despite the name it is actually a circuit breaker ve - ve 12 V MAIN FUSE GEN FUSE +ve from load bus Main busbar Avionics busbar Load busbar The Vigilant electrical system has a number of components: A 12v 28a battery An engine driven generator to provide D/C. A mainswitchA starter motor PARTS OF THE SYSTEM

With the generator relay energised, the electricity from the generator flows into the main circuit. When the ignition key is turned, the started motor is earthed and turns the engine which then turns the generator. This energises a relay which connects the battery to the main circuit. With the engine running the oil pressure increases. The load busbar provides electricity to the generator relay. Although this looks complex, it operates very simply. When the mainswitch is switched ‘ON’, part of the circuit is earthed. MAIN FUSE GEN FUSE +ve from load bus Main busbar Avionics busbar Load busbar + ve - ve 12 V An oil pressure switch then connects the main circuit to the load busbar. START UP

When the engine is switched off, the oil pressure switch disconnects the link between the main circuit and the load busbar. To allow the testing of the lights during maintenance, this disconnect can be by-passed by a guarded switch under the engine cowling. Main busbar Avionics busbar Load busbar BUSBARS The Vigilant has three busbars. The Main busbar. The Avionics busbar. And the Load busbar. The main busbar supplies electricity to the: ►Electric fuel pump ►Fuel quantity sensor ►Artificial horizon ►Outside air temp gauge ►Turn and slip indicator ►Instrument lights ►Engine instruments ►RPM Gauge The avionics busbar supplies electricity to the: ►Radio ►Transponder The load busbar supplies electricity to the: ►Strobe lights ►Landing lights ►Navigation lights ►Engine hours counter ►Generator relay All of these electrical devices are further protected from surges by independent c/bs. The c/bs have different ratings depending on what piece of equipment they are protecting. All of these c/bs are located in the foot well underneath the right hand instrument panel

As such the ammeter will show a discharge and the voltmeter will indicate a reducing voltage. Reducing electrical loads will prolong the battery life. Switching off all of the lights will have the biggest effect. +ve from load bus MAIN FUSE GEN FUSE Main busbar Avionics busbar Load busbar + ve - ve 12 V MALFUNCTIONS Overvolting If the voltmeter reads above 15v or the ammeter indicates above +20 amperes charge, pull the alternator c/b (generator fuse). This is usually caused by the failure of the voltage regulator on the generator. This then disconnects the generator from the main circuit. The aircraft electrical circuit is now fed purely by the battery.

+ve from load bus If the c/b pops again or if it hadn’t popped initially, reduce the electrical loads (all lights in the first instance) and then land as soon as practicable. This could also be caused by the alternator belt snapping. Undervolting If the voltmeter reads less than12v or the ammeter indicates below -5 amperes charge, ensure the generator c/b is in. If the generator c/b has ‘popped’, the aircraft will be using battery power only. Initially push the c/b back in. ONLY EVER RESET A C/B ONCE MAIN FUSE GEN FUSE Main busbar Avionics busbar Load busbar + ve - ve 12 V MALFUNCTIONS If the alternator belt does snap, the RPM gauge will read zero despite the engine running normally.

+ve from load bus Main c/b If the main c/b pops it is trying to protect the electrical components on the busbar against a surge (more than 40 amps). Be aware that if it has popped again, none of the electrical services provided by the busbars, including the radio, transponder and the RPM gauge will work. MAIN FUSE GEN FUSE Main busbar Avionics busbar Load busbar + ve - ve 12 V MALFUNCTIONS Initially reset the c/b. ONLY EVER RESET A C/B ONCE If it pops again, land as soon as practicable.

THE END Any Questions?