Electrical

The design of the electrical system provides multiple power paths to essential equipment so that there is a simple pre-planned procedure available to positively reduce the electrical load requirement when needed.  The architecture follows Figure Z-14 in the AeroElectric Connection (www.aeroelectric.com).  Much thanks go to Bob Nuckolls for his tireless contribution to the expansion of understanding of aircraft electrical systems in the homebuilt community.  The electrical requirement is divided into a three bus architecture:  The battery bus provides connection for critical to flight components; alternator, ignition, fuel pump and the Endurance Bus.  There are two battery busses that are each completely independent of each other in operation.  Battery Bus #1 is equipped with a 40 amp alternator and  Battery Bus #2 is equipped with a 20 amp dynamo.  The Endurance Bus is the minimum equipment other than engine-critical equipment, required for safe completion of the current flight.  The Endurance Bus is fed through a diode pack from both battery buses.  There is also an alternate Endurance Bus power switch from Battery Bus #2 in the event of a failure of the diode pack.  The main bus is comprised of all of the other electrical equipment.  The Main Bus is connected to Battery Bus #1 because it's alternator has the capacity to power these additional loads.

The objective behind the electrical system architecture is to have sufficient reserve power to carry the engine-critical and the Endurance Bus loads to the exhaustion of the fuel on board with no anxiety to the pilot.  With electronic ignition and electric fuel pump the power required to meet this objective would make battery only option prohibitively heavy.  For that reason there are two engine driven sources of electrical power each with it's own battery.   There should be no diagnosis of electrical problems while in flight.  If a low voltage event occurs then immediately follow the low voltage checklist:  

    1.  Identify low voltage system

     2.  If #1 battery is low voltage turn off alternator field and OV sense circuit breakers.  Turn off Main Bus circuit breaker.  Turn on #2 ignition and fuel pump.  Turn off #1 ignition and fuel pump.  If the #1 battery voltage is above 12VDC, close the battery interconnect circuit breaker.  Verify low voltage event is concluded and continue to next planned stop else go to step 4.  Document alternator field and diode pack temperature.  Document alternator voltage regulator temperature.  Document #1 battery temperature

    3.   If #2 battery is low voltage turn off dynamo relay circuit breaker.  Turn on #1 ignition and fuel pump.  Turn off #2 ignition and fuel pump.  If the #2 battery voltage is above 12VDC, close the battery interconnect circuit breaker.  If low voltage event is not concluded turn off main bus circuit breaker.   Verify low voltage event concluded and continue to next planned stop else go to step 4.  Document dynamo field temperature.  Document dynamo voltage regulator temperature.  Document #2 battery temperature

    4.  If low voltage event continues verify the electrical system is configured for battery only operation and current draw is < 16 amps then land immediately!   If the battery interconnect circuit breaker was not closed above your reserve capacity is 12 1/2 minutes so get it on the ground now!

A fully charged 100% capacity battery will provide 25 minutes of battery only operation.  Considering there are two batteries available this gives a battery only run time of 50 minutes.  Prudent planning says that you do not plan on 100% battery capacity being available so with 50% capacity there will be 25 minutes from beginning of low voltage event till electrical reserve exhaustion.  Part of the annual condition inspection is to run a battery capacity test to insure that the batteries currently meets the endurance needs of the aircraft.  Planned replacement of the battery based on capacity testing is a critical component of the electrical system reliability for this aircraft.  Electrical system reliability in this context means the ability to safely complete the current flight, not the prevention of all failures.  Things will break;  it's controlling the impact of those failures on safe completion of flight that makes reliability of the system as a whole.  Reliability is achieved by the combination of design and pre-planned procedures that insure successful landings.

Electrical Power Distribution

Electrical Ground Distribution