13 November 2018

Avionics: Minor change in electrical bus topology.

Minor change in my electrical bus topology.  First, a functional explanation of my three buses is in order:

  • Master:  Critical devices for flight such as lights, electric fuel pump, flaps, trim, ELT, alternator field that can also remain powered during engine start.  This bus should always remain on in flight.
  • Avionics 1:  Critical flight instruments such as left side EFIS, AHRS, GTR-200 transceiver, transponder, backup AI and low fuel level indicator.   This bus can be shut off only in VFR flight.
  • Avionics 2: Less critical instruments and devices to include right side EFIS, GTN-650 navigator, capactive fuel indicator, autopilot, GMA-245 intercom and ship's power LEMO.  This bus can be turned off any time to reduce energy demand (it should remain on in IFR to stay legal).
 
With that out-of-the-way, when I installed the canopy camera power, I used the "unassigned" fuse position that was on the Avionics 1 bus.  However, there is no need for the cameras to be on Avionics 1.  And, back when I designed my bus topology, I decided to put the GMA-240 (now a 245) on Avionics 2.  However, I should have kept the intercom on Avionics 1 so I can keep Avionics 2 off (primarily during taxi) and still hear my passenger.  So I decided to swap the two positions:  Intercom and canopy camera.  This required a lot of contorting, cutting of wire ties and losening of screws.  Here is the back side of my fuse block, which I designed (you can learn more about what I did here).  I had to remove a wire from the left and center rows and swap them.


Below is my new fuse legend.


I wish I had put the LEMO power on Avionics 1 so I can maintain power to the headsets with Avionics 2 off.  It isn't practical to change that now and the LEMO versions of my headsets understandably are not provisioned for batteries.

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