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Old 08-11-2017, 02:05 PM
leok leok is offline
Join Date: Apr 2013
Location: Clarkston, MI
Posts: 435
Default Electrical System Design and Build continued

I control the heat vents, fore/aft and left/right with servos managed by an Arduino mini-computer. I have heated front seats


I have roll, pitch and rudder trim with roll and pitch integrated into the Garmin autopilot and auto trim system. Both the Garmin autopilot and the VPX can provide speed scheduling for trim speed to roll and pitch.

Getting this all together was an iterative process with thoughts and ideas incorporated over time, with imagined flights, thought and study.

Designing the System – Step One

As a beginning, I made a list of all functions I wanted. This included everything from IFR flight to boarding and loading the airplane in the dark. It is important to get this as comprehensive as possible as each design step grows out of the previous. Later changes are laborious to incorporate. I did the initial step in Excel so I could move things around easily.

1) Make a list of functions
2) Separate the list into functionally related groups
• Avionics related (I subdivided into 3 groups)
• Interior lighting
• Exterior lighting
• Stuff I always want power to (door entry lights, USB charge receptacles)
• Stuff I want power to only when the Master switch is on
• Stuff I need to provide back up and/or levels of redundancy and/or emergency

From the function list, I created a list of the avionics boxes I would be needed to accomplish the various functions. Based on my list I found the total price from each supplier to be within 2 AMU. I did not find price a significant differentiator for the functionality I had worked out.
I chose Garmin because it was the only provider with a full integrated lineup. That choice was further strengthened as I learned more about the CAN communications buss and backup pathways built into the G3X system. I also wanted easy integration with one stop support. Your choices may be different based on your circumstances/priorities.

With the list of avionics, I then separated then into three groups as I have three levels of power/redundancy.
1) Items absolutely required to get me on the ground in case of with the loss of both alternators ;
• G5
• Radio 1
• GPS/Nav source
• 1 electronic engine ignition
• ADAHR/Magnatometer
2) Items nice to have if power supplies are reduced (to be switched off when on battery only);
• Auto Pilot
• Transponder
• Engine Monitor Module
• Roll/Pitch Servo
3) Items I could do without and continue happily on my way (to be switched off when on the smaller back up alternator);
• Radio 2
• Intercom/Audio Panel
• Rudder Trim

Grouping the functions and assigning to individual VPX switches, then organizing the physical switch locations for logic and ergonomics is an iterative process. I stepped through many flights, eyes closed, comfortable in an easy chair, to slowly refine how I wanted the ‘flow’ and ergonomics to function.


Designing the System - Step two

The first section of the design was to complete a drawing of the ‘backbone’ or primary power distribution system. As you can see in the attached drawing, I included all or the details necessary to provide normal, back up, and emergency power distribution and the related switches. I stopped short of detailing the individual wiring loops as they are detailed in the next steps.


I created spread sheets detailing every device that required power to operate, every switch and what current rating was needed. Using the VPX planner tool (online at the VPX web site) I assigned each power output and decided how I wanted to switch them. The switching is a key decision because the VPX has only 10 assignable switch inputs. I had more items to switch than switch inputs even after grouping the avionics into three groups. I grouped all interior lights, exterior lights, pitot heat, and seat heat to mini power busses with VPX switched power leads feeding individual small blade fuse holders. One benefit of using the VPX for switching, is that on/off switches carry only small amounts of power, so any switch rating will do.


With everything grouped, I designed each sub-buss as an individual system. With a single VPX switch input, and single power feed from the VPX, each sub-buss was designed, wired and tested.
Building started Oct 5th 2014, Flying since 1/16/2020
RV Hotel, come by and visit if you're in town
Dues paid 2020

Last edited by leok : 06-25-2018 at 03:25 PM. Reason: fix picture links
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