Need for two additonal circuit breakers
The Dynon SV-INTERCOM-2S manual calls for a 1A circuit breaker in its supply line. Best practice dictates that the intercom power circuit should NOT be shared with the COM radio circuit. In any case the wiring for the former (including single DB25 pins for each of power and ground) contrasts with the power and ground wiring for the COM radio (where 2 DB25 pins are provided for each of power and ground). So the CB for the COM radio is 3A, excessive for the lighter intercom wiring.
The SV-INTERCOM-2S manual also states:
4.8 Fail-safe Operation
When power is lost or the SV-INTERCOM-2S is powered off, the primary radio is connected directly to the pilot’s headset. If the pilot headset is a stereo headset, radio audio will only be heard in one ear. Intercom conversation and audio from other radios and inputs (including music) will not be heard when in this unpowered fail-safe mode.
which is compatible with the use of separate circuits
So a Klixon 2TC2-1A breaker dubbed "IC" will be added to the essentials bus
Also previously overlooked is the need for a circuit breaker for the AVC1 voltage regulator enable input. This line is fed from the main bus and passes through the firewall. It is best practice to keep this circuit separate from all the other circuits, in the event of a short on this line to (say) the firewall. If this were to occur, and the circuit was shared, then an addtional avionics system would be needlessly taken out. Perhaps however it could be shared with the EFIS circuit, which has its own backup, but the idea seems suboptimal.
A close relation to this is the fact that the EFIS power is also fed to one of the EMS220 voltmeter circuits, as a measurement of the main bus voltage. Two points can be made to justify this: 1) this wire does not pass through the firewall; 2) if a short occurs on this line and the EFIS CB trips then the EFIS will continue to run from its backup; and 3) the EFIS and EMS are closely related systems, the latter does not operate without the former
https://bandc.com/wp-content/uploads/2022/12/AVC1_Technical_Manual_XB100-2-TM_12-8-22.pdf
The AVC1 manual calls for a 1-5A breaker - I will use a Klixon 2TC2-1A. It will be dubbed "REG"
There is just the issue of where to locate these breakers, given the panel has already been made. I have decided to eject the START and USB breakers from the main grouping, replacing these with the IC and REG CBs. The START and USB breakers will be located elsewhere on the panel
The intercom CB will be added to the avionics bus
The regulator enable CB will be added to the main bus
Referring to
the structure will be updated as follows
The main bus will feed the following circuit breakers
- REG - regulator
- LDG - landing lights
- BK CHG - IBBS charge input
- START - start solenoid
- TAXI LT - taxi lights
- LDG LT - landing lights
- AP - autopilot servos
- BOOST - boost pump
- STROBE - strobe lights
- NAV LT - navigation lights
- USB - USB/camera power supplies
The "essential" bus, which can be switched between the main bus and the IBBS battery output, will have multiple breakers:
- EFIS - which then feeds the (main) EFIS toggle switch
- AVNCS - which then feeds the AVNCS toggle switch
- FLAPS - flaps
- CB - cabin light
- TRIM - trim
The switched side of the AVNCS toggle switch will now power the "avionics" bus, on which the following circuit breakers will reside
- COM - com radio
- XPNDR - transponder/ads-b in
- FLARM- flarm
- BK EFIS - backup efis
- HDST -headset
- IC - intercom
There is of course two remaining CBs
- BK OUT - output of IBBS backup
- MAIN BUS - feed to main bus from firewall forward
Author
Review of structure of avionics and essential bus
This post is from Adam Dickson