Cessna 172 Electrical System

The system consists of the battery, stand-by battery, alternator, Bus Bars, circuit breakers, fuses, ammeter/loadmeter, and voltage regulator.

What are the main components of a C172's electrical system?

24 volts

How many volts does the main battery have?

60amp or 28volts. The volts are higher so that the alternator is able to charge the battery (24v).

How many amps/volts is the alternator? And why are those numbers the way that they are?

6 total bus bars:

Main Bus 1 & 2

Avionics Bus 1 & 2

Essential Bus

Crossfeed Bus

How many bus bars are there? And what are the main Bus Bars?

Direct Connect System (DC)

What kind of electrical system does the C172 have?

The electrical current is sent one way and does not return to the source.

What does a DC system mean?

Fuel Pump

Flaps

Beacon light

Landing Light

Cabin Lights

Avionics 1

Explain the electrical components in/on/around the aircraft that are associated with Main Bus 1.

Pitot Heat

Nav Lights

Taxi Lights

Strobe Lights

Panel Lights

Avionics 2

Explain the electrical components in/on/around the aircraft that are associated with Main Bus 2.

PFD

ADC/AHRS

COMM 1

NAV 1

Standby LIGHTS

What does the ESSential bus power?

PFD

ADC

AHRS

Engine/Airframe unit

Nav 1

Explain the electrical components in/on/around the aircraft that are associated with avionics 1?

MFD

Transponder

Nav 2

Comm 2

Audio

Explain the electrical components in/on/around the aircraft that are associated with avionics 2?

WARN system:

Stall Warning

ELT

Main bus voltmeter

hourmeter

Starter relay

Standby battery

Main bus sense circuits

Explain the electrical components in/on/around the aircraft that are associated with the Crossfeed Bus?

It acts as a tie between the buses, a crossroads to keep the main buses isolated from one another, while also having the capability of providing power to failed components in the event that one bus loses power.

What is the purpose of the Crossfeed Bus?

Protection varies anywhere from 5 - 15 amps from the circuit breakers.

If you were to scale the amount of amps used by the circuit breakers to protect each electrical component, what would it be?

What is the purpose of the circuit breakers?

They provide a level of protection from overloads, short circuits, and ground faults. This is why circuit breakers will pop out when their max amp protection is reached/tripped.

Which bus(s) can receive power from the STANBY Battery? (Can the power from the standby battery flow throughout all the buses?)

The ESS (Essential Bus) is the only bus that can receive power from the standby battery. It will not allow power to flow through to the other buses. (so in the event of a main batt, and alternator failure). Standby will only give power to the ess buss components.