Further thoughts on circuit breaker arrangement

Previous posts

Electrical circuit breaker planning 2, with Klixon breakers - We Build Planes

Finalise electrics - whether to have a separate "avionics" bus - We Build Planes

The above posts are combined, taking into account there is a new TCW backup battery, and I want "avionics" items to be able to be switched across to a separate backup battery bus.

The backup battery is connected to the main bus, via two separate breakers, one 5A for charge and one 10A for pass through. The backup battery has its own 10A fuse at the output

I have also added a separate power line (20AWG cable) for LEMO powered headsets, with its own breaker, downstream of the radio switch

Maximum continuous load on from backup battery is 8A

Repeating and modifying the table from the first link

On separate "avionics" bus

• Controlled by DT switch which can be set to off, connect to main bus, connect to backup battery bus

"Radio" switch with two separate downstream breakers:

20AWG 7.5A overridden by Dynon schematic 5A => Klixon 2TC2-5

• Com Radio control panel
• Com Radio

20 AWG 7.5A limited to 3A => Klixon 2TC2-3

• LEMO headsets

Since these breakers can be pulled, the LEMO circuit can be disabled without forcing the radio circuit to be disabled

"Transponder" switch with separate breaker 22AWG 5A overridden by Dynon schematic 5A => Klixon 2TC2-5

• Transponder
• ADS-B receiver

"Flarm" switch with separate breaker 22AWG 5A overridden by Flarm manual 3A => Klixon 2TC2-3

• Flarm fusion
• Flarm trafficView80

"EFIS" switch with separate breaker - 2x22AWG ~ 20 AWG 7.5A overridden by Dynon schematic 5A => Klixon 2TC2-5

"EFIS backup" switch with separate breaker - 20AWG 7.5A overridden by Dynon notes 5A => Klixon 2TC2-5

"Elevator Servo" switch 20AWG lines (7.5A) with 22AWG at the motor (5A) => Klixon 2TC2-5

"Aileron Servo" switch 20AWG lines (7.5A) with 22AWG at the motor (5A) => Klixon 2TC2-5

"Trim" breaker 22AWG - 5A Klixon => 2TC2-5

"Flaps" switch with separate breaker 20AWG 7.5A => Klixon 2TC2-7.5

So in the event of a main bus failure, the autopilot in particular remains fully operational, including trim. The EFIS operation can also be extended beyond its own backup battery life. The normal position for the "avionics source" switch is "main". If the IBBS output fuse blows, the "avionics source" switch is returned to "main bus"

NOTE: consider moving autopilot onto main bus, but check that trim system can remain powered

NOTE: not sure if this will work, given the 8A limit

The following are connected directly to the main bus

"USB" switch with separate breaker - 18AWG 10A => Klixon 2TC2-10

"Interior" switch with separate breaker - 22AWG 5A => Klixon 2TC2-5

"Landing Lights" switch (with 3rd position for wig-wag) 16AWG 15A overridden by Deutsche DT connect limit of 13A => Klixon 2TC2-10

"Taxi Lights" switch with separate breaker 16AWG 15A overridden by Deutsche DT connect limit of 13A => Klixon 2TC2-10

"Nav/Strobe Lights" switch with separate breaker 18AWG 10A => Klixon 2TC2-10

"Fuel pump" switch with integral breaker - 3A => TE W31-X2M1G-3

Backup battery via

• 5A Klixon 2TC2-5
• 10A Klixon 2TC2-10

Upstream of the main bus

"Master" switch with integral breaker - 25A => TE W31-X2M1G-25

"Alternator" breaker 12AWG - 25A Klixon 2TC2-25

I note the only 16 AWG wires are the taxi and landing lights - these will call for blue ring terminals, #6 on the power switches (3 per switch, 1 on the live side, and 2 on the dead side), and #8 on the breakers (2 per breaker). This assumes the switches are downstream of the breakers

All the other wires are 18AWG or greater - these can use the red ring terminals, #6 on the power switches (2, sometimes 3, per switch), and #8 on the circuit breakers (2 per breaker).

For flexibility at this stage, assume 3 #6 lugs on each switch and 3 #8 lugs on each breaker. This will allow placing the breakers downstream of the switches.

Each breaker (or switch) is connected to a positive bus bar, another #8 lug

The negative of each wire and shield of each jacketed wire is connected to a negative (or shield) busbar. That is two #8 lugs per shielded cable

With 20 breakers, about 20 switches, overall roughly 6 #8 lugs per breaker, roughly 3 #6 lugs per switch

2 breakers or so are 16AWG 12 blue #8, 6 blue #6

the rest are 18AWG or thinner 108 red #8, 54 red #6

Purchase 150 red #8, 100 red #6

Purchase 50 blue #8, 30 blue #6