When I was working on my commercial licence I met a guy who flew the Screaming Whippet and one of the things I remember him saying about the aircraft was that it had a very complicated electrical system. I was looking forward to meeting this beast, but we were warned in ground school not to pre-read about it in the manual, because there were many options and modifications and that we'd get confused if we did. So it was unveiled on I believe the morning of the second day of class.
It's not so bad. Yeah, it has DC power and three different flavours of AC power, but I can understand the circuitry. There are two 24V lead acid batteries, two 28V starter-generators, and capacity to accept ground power (max 1000A), which can power electrical systems and/or charge the batteries. I've done this enough time that those are pretty standard numbers. The batteries each have their own relay connecting them to the system, then an additional relay connecting the combination, plus the GPU if connected to the battery bus. The battery bus is power distribution central on this airplane. It's located in a junction box behind the left pilot seat, and everything connects to it. Each starter-generator connects to it through a generator relay and a 325A current limiter. The DC battery bus provides power to the left and right essential buses, through 225A current limiters and also to a non-essential bus, through a 150A circuit breaker. The current limiters and circuit breaker are all located in the junction box. Each of those three DC buses described also has a bus tie switch. They are on the circuit breaker panels, under the windows on the left and right sides of the cockpit.
Most of the services are quite predictable, with the left side of the airplane being on the left bus and the right side on the right bus. There are also nine or ten (the tenth is optional) transferable items that can be switched from the left to the right DC bus in the event of a left DC bus failure. They are the turn and bank indicator, the fuel crossflow valve, the valves controlling wing and tail deicing, the windshield heat, the valve controlling left inlet anti-ice, the valve controlling right inlet anti-ice, the flap and gear position indicators, the valves controlling landing gear operation, the solenoid that applies vaccum to open the dump valve and (optionally) the pilot-side DC cockpit instruments. Flaps, nosewheel steering and all exterior lights, including landing lights are on the non-essential bus.
Each essential DC bus has one inverter, and each inverter is connected to 26V AC bus and a 115V AC bus, so four AC buses in total. The L and R 115V buses are connected together through a circuit breaker, as are the two 26V buses, so that with one inverter online, all four buses are powered. Only one inverter can be online at a time. The fuel pressure, oil pressure and some cockpit instruments are on the 26V AC bus. The fuel quantity gauge takes 115V AC. The cockpit edge lighting is powered from the 115V bus, but stepped down to 6V. Other instruments may be on one or the other depending on the airplane, you need to check the CB panels to see.
My brain is full. Remember this two weeks worth of system spam you've been receiving was a three day blitz for me. And I have SOPs and limitations to learn on top of this. I think I'll go jump on the treadmill for an hour. There's too much snow outside to go running, but it's too slushy to go skiing.
Today is Pi Day. You should celebrate by eating pie. You may heat it in an electric, gas or wood-burning, dung-burning or solar powered oven. Or another sort if you have one I didn't think of.
P.S. I got on the scale after jumping off the treadmill. Target weight minus five hundred grams. Booyah! No sugar, no alcohol and get some damned exercise. It works, people. Girl's got legs and she knows how to use 'em. Now to keep it off.