I'm still in the very early stages of figuring out how I want to do the electrical system in my future RV-10. This will be for IFR cross-country flying with the family, so I want plenty of redundancy. And not just safety-of-flight redundancy, but also "you don't have to cancel your trip" redundancy. For this reason, I'm almost certainly going with 2x alternators and 2x batteries, plus a G5 with its own battery. The engine will have dual pMags and therefore the engine will not be electrically dependent.
I'm currently debating between two core architectures. As an engineer, I am trying to balance between over-engineering something and keeping it simple for a future partner in the airplane. Am I missing any pros or cons or have I missed anything else obvious here? There are some weight and cost differences but from what I can tell neither of those are substantial.
Option A: TCW IBBS
In this architecture, I would have one main electrical bus with the main battery and two alternators (one running at a time). The IBBS would charge from the main bus and it would power my essential bus. Three switches: master, backup, and alt1/2.
Pros: simple and seems pretty standard. Very little (if any) electrical design required (e.g. diodes, etc).
Cons: limited backup power will require a pretty streamlined essential bus, catastrophic failure of the IBBS could cause essential bus to fail (but with dual power inputs to most Garmin avionics that may not be an issue?), issue with primary battery would prevent starting the engine
Option B1: Two separate systems
In this architecture, I would divide the entire electrical system into two parts with two full batteries. Bus 1 would have Bat 1+Alt 1 and roughly half of the other items. Bus 2 would have Bat 2+Alt 2 and the other half of the items. The busses would be completely separate. Would be able to safely complete flight with either bus, although with some limitations. For example, one G3X Touch screen on each bus, on ADAHRS on each bus, one radio on each bus, one pMag on each bus, etc. Four switches: Battery 1, Battery 2, Alternator 1, Alternator 2.
Pros: a catastrophic failure (high voltage, short to ground) on one bus should not affect the other bus, more reserve power with two full batteries.
Cons: if one battery fails you'll lose some components (e.g. flaps might only be on Bus 1 and the GPS Navigator might only be on Bus 2), less standard setup
Option B2: Two separate systems w/ crossover
This is exactly the same as Option B1, but now there is a contactor that can connect Bus 1 and Bus 2. This contactor is normally open so the busses are normally separate just like in Option B1. But you can flip a switch and connect the two busses together (you'd need to figure out a way to make sure both alternators don't keep running).
Pros: could allow the use of both batteries to start the engine (if one battery is low or dead or if it is really cold outside), could allow full normal flight to continue even if one battery and/or alternator is dead
Cons: even more complex and non-standard, needs a fifth switch for "crossover", and possibly additional failure modes that might make things less redundant
For the last con above, my concern is when/how you would use such a crossover switch. If one of your busses goes bad during flight, it could be for a variety of reasons: dead battery, short to ground, overvoltage, etc. The only time crossing over would be helpful would be for a dead battery (presumably caused by a bad alternator). But what if there was overvoltage or as short to ground in the bad bus? If you cross the busses together, now you possibly take out the other bus as well.
I'm currently debating between two core architectures. As an engineer, I am trying to balance between over-engineering something and keeping it simple for a future partner in the airplane. Am I missing any pros or cons or have I missed anything else obvious here? There are some weight and cost differences but from what I can tell neither of those are substantial.
Option A: TCW IBBS
In this architecture, I would have one main electrical bus with the main battery and two alternators (one running at a time). The IBBS would charge from the main bus and it would power my essential bus. Three switches: master, backup, and alt1/2.
Pros: simple and seems pretty standard. Very little (if any) electrical design required (e.g. diodes, etc).
Cons: limited backup power will require a pretty streamlined essential bus, catastrophic failure of the IBBS could cause essential bus to fail (but with dual power inputs to most Garmin avionics that may not be an issue?), issue with primary battery would prevent starting the engine
Option B1: Two separate systems
In this architecture, I would divide the entire electrical system into two parts with two full batteries. Bus 1 would have Bat 1+Alt 1 and roughly half of the other items. Bus 2 would have Bat 2+Alt 2 and the other half of the items. The busses would be completely separate. Would be able to safely complete flight with either bus, although with some limitations. For example, one G3X Touch screen on each bus, on ADAHRS on each bus, one radio on each bus, one pMag on each bus, etc. Four switches: Battery 1, Battery 2, Alternator 1, Alternator 2.
Pros: a catastrophic failure (high voltage, short to ground) on one bus should not affect the other bus, more reserve power with two full batteries.
Cons: if one battery fails you'll lose some components (e.g. flaps might only be on Bus 1 and the GPS Navigator might only be on Bus 2), less standard setup
Option B2: Two separate systems w/ crossover
This is exactly the same as Option B1, but now there is a contactor that can connect Bus 1 and Bus 2. This contactor is normally open so the busses are normally separate just like in Option B1. But you can flip a switch and connect the two busses together (you'd need to figure out a way to make sure both alternators don't keep running).
Pros: could allow the use of both batteries to start the engine (if one battery is low or dead or if it is really cold outside), could allow full normal flight to continue even if one battery and/or alternator is dead
Cons: even more complex and non-standard, needs a fifth switch for "crossover", and possibly additional failure modes that might make things less redundant
For the last con above, my concern is when/how you would use such a crossover switch. If one of your busses goes bad during flight, it could be for a variety of reasons: dead battery, short to ground, overvoltage, etc. The only time crossing over would be helpful would be for a dead battery (presumably caused by a bad alternator). But what if there was overvoltage or as short to ground in the bad bus? If you cross the busses together, now you possibly take out the other bus as well.
