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

Battery

    Hog Battery  (wet cell lead acid)

The battery mount on the firewall was made using a Harley battery for sizing.  I thought it was a good idea because you can always find an inexpensive replacement at Wal-Mart!  The original battery has gone bad but it did prove that it could turn the engine over and also provided a power source for testing during the construction of the instrument panel.

Panasonic Battery (sealed lead acid )

I have determined that the RG series of batteries is a much better choice for aircraft use.  It is a sealed lead acid battery that does not have the acid vapor issues or spillage issues associated with regular wet batteries.  In addition, the electrical characteristics are much better.  This type of battery technology yields a much lower internal resistance which gives more cranking power per pound as well as longer reserve capacity for endurance loads.  I decided on two 12AH 12V Panasonic batteries.  Panasonic markets their line of these batteries under the trademark VRLA Batteries (Valve Regulated Lead Acid).  A good competitor here is the Odyssey (http://www.odysseybatteries.com/files/techbook.pdf) from a performance perspective it is equal to the Panasonic but you need to play the cost/weight game to get the best value. 

Books

The AeroElectric Connection by Bob Nuckolls is an excellent reference for how to wire up your homebuilt.  It is available from aeroelectric.com

Circuit Breakers

  This circuit breaker panel was designed and constructed before I ran across the AeroElectric Connection, Bob Nuckolls excellent reference manual.  As a result, I have had to redesign the entire electrical system.  Check WD0002 sheet 4 below for the current Circuit Breaker/Switch Placement.

Dimmer

The Instrument Panel Light Dimmer was made from a Sport Aviation article from the February 1992 issue.  As is the case with everything, technology waits for no KR to be completed.  There is now very inexpensive voltage regulator integrated circuits.  Aeroelectric.com lists a circuit using a lm-317 that is better than the one I have in it's tolerance to short circuits.  Mine works fine so until it fails there's no need to upgrade.  If it ever fails, I'll replace it with a lm-317.

The first electrical power source is a 20 amp dynamo installed on the flywheel inside the Diehl accessory case provided by GPASC.   The choice for the second electrical power source has been narrowed down to two options.  The first option is a John Deere dynamo (permanent magnet alternator).  The second choice is a Hitachi LR140-707 alternator.   This alternator is a 40A 14.00V unit that is set up to run from 400 to 4000 rpm in it's application.   This alternator choice is currently under investigation to be driven off the magneto drive boss of the Diehl accessory case.   I have determined that cutting down the front plate of the alternator will provide a mounting adaptor to the magneto drive. The current task is to make the end of the alternator look like a magneto to the engine. The main alternator has been decided to be the Hitachi LR140-707.  It took 27 months but it now looks like a magneto to the engine.  I have made a composite page of my diary entries showing the modification process for the alternator.

alt0001 Alternator Drawings

  Sheet 1:  Alternator Magneto Adapter

  Sheet 2:  Diode Pack And Brushes

  Regulation for the main alternator will be with a B&C Specialty Products LRC-3 Linear Regulator.  Linear regulation provides a much quieter electrical system that is advisable for composite aircraft.

Tie Wraps  

Here's the full line catalog on Thomas and Betts nylon cable ties. Notice that the Tyrap name covers a wide range of products. The product you're looking for is the Ty-Fast low profile version on page J46.  http://tnbelectricalworld.tnb.com/contractor/docs/tyrap.pdf

WD0001 Wiring Diagrams  (Superseded by WD0002 and WD0003)

WD0002 Power Distribution And Grounding Wiring Diagrams   (Superseded by WD0004)

This diagram shows the dual alternator single battery Z-13 configuration previously designed.  This is now replaced by WD0004 which is a dual alternator dual battery configuration.

     Sheet 1     Power Distribution Wiring Diagram

     Sheet 2     Grounding

     Sheet 3     Wiring Diagram

     Sheet 4     Circuit Breaker / Switch Placement

WD0003 Auto Pilot Schematics And Wiring Diagrams

    Sheet 1     Autopilot Single Cannel Schematic

    Sheet 2     Autopilot Motherboard Schematic

    Sheet 3    Autopilot System Interconnect Wiring Diagram

WD0004 Power Distribution And Grounding Wiring Diagrams

     Sheet 1     Power Distribution Schematic

     Sheet 2     Main Bus

     Sheet 3     Endurance Bus

     Sheet 4     Grounding

     Sheet 5     Circuit Breaker / Switch Placement

     Sheet 6     Power Distribution Wire Diagram

     Sheet 7     Micro-Monitor

Alternator Over Voltage Disconnect Schematic

Temperature Annunciater

A suggestion that I picked up in reading the AeroElectric Connection was that you need to monitor temperatures of several points on the aircraft during to the test flight phase to make sure that things are ok.  Among them were alternator field and regulator temperatures as an example.  I looked into some data acquisition interfaces for a laptop PC and found that the best price point available was on the order of $30/point.  running this up the the 30 or 40 collection points I was interested in having quickly put the price of this type of information over a thousand dollars and out of my reach.  That is when I came up with the idea of a simple annunciater that would indicate if these data points were in the acceptable range, marginal range or bad range.  This would be indicated with indicator lights that were shown as one segment of a ten segment LED.  A green LED would indicate normal, a yellow LED would indicate marginal, and a red LED would indicate bad.  This brought the price/point down to the $5 range which made the price for the system on the order of a couple of hundred dollars.  The schematic for this system is linked to the title line above.

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