13.3.0 Electrical System

I’ve started to work on the electrical system for the airplane. This is going to be interesting. I’ve decided to install a fully redundant electrical system using two batteries and two alternators. That should work out nicely since the Garmin G3X avionics system I’m planning on installing generally has dual power inputs for most of its modules. Therefore, the main distribution bus goes to the ‘A’ power inputs while the aux distribution bus goes to the ‘B’ power inputs.

Generally, both systems will run concurrently but I’ve added in the ability to cross connect the buses if needed. I’m also adding a shore power connector so that I can power everything up without running down the batteries while programming or troubleshooting the system. 

The complexity increases substantially when I started adding connectors for the various sub-assemblies. This first schematic, VELO-ELEC-01 is basically complete, unless I find some mistakes or need to make changes fro some reason. Although I’m not showing it here, I’m also making a huge spreadsheet that helps to track switch, lamp, circuit breaker and connector numbers. Trying to track all of that without a spreadsheet is nearly impossible.

This schematic (VELO-ELEC-02) is both for engine start and the annunciator lamps. Even though the Garmin system I’m installing includes annunciator functions, I’ve decided that there’s still nothing better than warning lights to quickly get your attention.

The system lighting schematic (VELO-ELEC-03) shows all lighting, both internal and external. The Garmin GAD 27 Electrical Adapter Unit adds some complexity, but it also adds functionality and cuts down on current flow through some of the switches.

The drawing below (VELO-ELEC-04) basically interfaces the pilot and copilot grips to the GAD 27 EAU. Both of the sets of trim servos, roll and pitch, as well as the autopilot roll and pitch servos, are shown below. The Garmin servoes, in conjuction with the GAD 27, actually directly control the Velocity-supplied trim servos.

The basic electrical connections for both of the main Garmin G3X display panels are shown in the schematic below (VELO-ELEC-05). In addition, I’ve included the contactor that applies power to the Avionics Bus after the engine has started. The electrical system design actually includes three buses: Main, Aux and Avionics. The Main Bus is normally used to start the engine while the Aux Bus is powering up the electronics. Each bus has its own battery. Once the engine is started, the Avionics Bus is powered up from the Main Bus. That way I not only have backup power to the critical electronics, but I can also power everything up on a separate power source before starting the engine.

This print also includes the aux fuel pump and its control switching.

Finally, VELO-ELEC-06 includes miscellaneous electrical connections for the pitot heat system and the USB charging hubs - one for the front and one for the rear passengers. Gotta be able to charge our devices, of course! The Garmin pitot heat system is a bit more complex than standard pitot heaters since it includes a control box that not only controls the heating element in the pitot but also sends status back to the G3X system.

I realize that these schematics aren’t the clearest when looking at them online. If you are interested in a set of clean prints, please contact me using the form on the home page. Click here to go to that page.

ui© John Trautschold 2018