Please Critique My Electrical Plan

[lr172]

Originally Posted by RV7ForMe

Hey, No pro at this but the way I read your schematic, you have all the the avionic on the avionics master. If I understand it correctly that you wont be able to start the engine and see oil pressure come up unless you start the engine with everything powered up. I read somewhere in the G3x manual to just put the gea24, ADHARS and one PFD on while the engine starts and to start the rest once the fires are lit. What do you think?

everyone talks about this, however, the likelihood of your engine having good oil pressure at the last shutdown and NOT having good oil pressure on the next startup are pretty remote. Losing an oil pump or developing a catastrophic oil leak are not typically things that happen when the engine is not running.

Yes, this is critical for a first start after major engine work and possibly an oil change if you are prone to forgetting to refill the oil or put on a new filter.

Just food for thought and one man's opinion.

Larry

[mfleming]

Originally Posted by lr172

everyone talks about this, however, the likelihood of your engine having good oil pressure at the last shutdown and NOT having good oil pressure on the next startup are pretty remote. Losing an oil pump or developing a catastrophic oil leak are not typically things that happen when the engine is not running.

Yes, this is critical for a first start after major engine work and possibly an oil change if you are prone to forgetting to refill the oil or put on a new filter.

Just food for thought and one man's opinion.

Larry

If you give my electrical architecture a good look, you'll see that the Primary EFIS comes on with the main bus as well as the clearance delivery bus. So no worries about not seeing the oil pressure.

So, here's my latest attempt: DWG F105

[johnbright]

Originally Posted by mfleming

...here's my latest attempt: DWG F105[/b][/url][/size]

My thoughts:

• You don't need a battery bus except in case you want to add items in the future.
• The battery bus does not need an ANL or fuse in its feeder because the feeder is short.
• A MIDI 23 is more robust than the downstream fuses on the engine bus.
• The SureFly is redundant to the magneto.
• Z-101 shows feeds to battery bus and engine bus unprotected because they are short.
• Z-101 shows the feed from battery to CL bus switched with a relay to meet FAR 23.1361. Bob Nuckolls uses a relay in cases where the feeder's fuse is over 7.5A.
• Surefly will be your engine start magneto. Conventionally on the left. Surefly retards timing for start and provides high energy spark.
• Assuming your magneto is not impulse coupled, consider locking it out for start as described in options A, B, and C here.

[DanH]

John's comments all valid. May I add a practical note regarding short wire runs eliminating the need for circuit protection, here an ANL for the battery bus?

ANL or no ANL obviously depends on the installed bus location. If the battery bus feeds under-cowl loads only, then installing it next to the battery with no ANL makes sense. Each load extending from it will need circuit protection, so the next choice is what form it will take. I'd suggest either a fuse panel with weather cover, or fusible links, as the under-cowl environment doesn't strike me as a great place for CB's.

However, battery bus feeds generally run all kinds of things. in which case I'd suggest the physical bus be located in the cockpit, in a manner similar to all the other circuit protection devices. If the battery and master contactor are firewall forward and the bus is in the cockpit, the connecting cable needs an ANL, or link, or some other kind of circuit protection, even if less than six inches. Fire, crash, abuse, age, or vibration can short the cable where it passes through the firewall, in particular when given some poor routing, or mixing Bowdens with electrical.

[mfleming]

Originally Posted by johnbright

My thoughts:

• You don't need a battery bus except in case you want to add items in the future.
• The battery bus does not need an ANL or fuse in its feeder because the feeder is short.
• A MIDI 23 is more robust than the downstream fuses on the engine bus.
• The SureFly is redundant to the magneto.
• Z-101 shows feeds to battery bus and engine bus unprotected because they are short.
• Z-101 shows the feed from battery to CL bus switched with a relay to meet FAR 23.1361. Bob Nuckolls uses a relay in cases where the feeder's fuse is over 7.5A.
• Surefly will be your engine start magneto. Conventionally on the left. Surefly retards timing for start and provides high energy spark.
• Assuming your magneto is not impulse coupled, consider locking it out for start as described in options A, B, and C here.

Originally Posted by DanH

John's comments all valid. May I add a practical note regarding short wire runs eliminating the need for circuit protection, here an ANL for the battery bus?

ANL or no ANL obviously depends on the installed bus location. If the battery bus feeds under-cowl loads only, then installing it next to the battery with no ANL makes sense. Each load extending from it will need circuit protection, so the next choice is what form it will take. I'd suggest either a fuse panel with weather cover, or fusible links, as the under-cowl environment doesn't strike me as a great place for CB's.

However, battery bus feeds generally run all kinds of things. in which case I'd suggest the physical bus be located in the cockpit, in a manner similar to all the other circuit protection devices. If the battery and master contactor are firewall forward and the bus is in the cockpit, the connecting cable needs an ANL, or link, or some other kind of circuit protection, even if less than six inches. Fire, crash, abuse, age, or vibration can short the cable where it passes through the firewall, in particular when given some poor routing, or mixing Bowdens with electrical.

My Final iteration DWG F105 ends up not having a battery bus.

Somewhere along the line Bob N. suggested a I put an inline fuse for the clearance delivery bus since it drew 3.2 amps. My thinking on the CD bus relay was similar. Since the CD bus amp draw was so low....simplify.

The SureFly will indeed be on the left side...I'll change that on the drawing. And thank you for the B.N. article on mag switches.

[gmcjetpilot]

Originally Posted by mfleming

If you give my electrical architecture a good look, you'll see that the Primary EFIS comes on with the main bus as well as the clearance delivery bus. So no worries about not seeing the oil pressure.

So, here's my latest attempt: DWG F105

I like it a lot better than original. Much more smple, lighter better operationally. But you could do better.

I don't have an issue with clearance delivery switch or avionics switch but Why? It's not necessary and adds two switches and a diode. You can just turn the master master on, start engine, get ATIS and clearance with engine running. Unless clearance void time that takes 1 minute. You are not a Jet at JFK with a pushback time or frequency to monitor before engine start. Avionics can be in during engine start.

However if you want to use com radio w/o starting turn master on get you info, turn master off. The battery can take 1 minute energizing the master relay an bus. I have a handheld battery powered transceiver or smart phone with flight planning software to get weather, make and file a flight plan.

No commercial jet I have flown has clearance delivery or avionics switches. It's more switches and wiring nodes to fail and adds weight, This all could be eliminated. If you want to shed load turn individual items off, or have a non essential bus with CB you can manually pull/trip that would do it.

It takes e switches to power your plane up. Also switches are single point failure items.

[mfleming]

Originally Posted by gmcjetpilot

I like it a lot better than original. Much more smple, lighter better operationally. But you could do better.

I don't have an issue with clearance delivery switch or avionics switch but Why? It's not necessary and adds two switches and a diode. You can just turn the master master on, start engine, get ATIS and clearance with engine running. Unless clearance void time that takes 1 minute. You are not a Jet at JFK with a pushback time or frequency to monitor before engine start. Avionics can be in during engine start.

However if you want to use com radio w/o starting turn master on get you info, turn master off. The battery can take 1 minute energizing the master relay an bus. I have a handheld battery powered transceiver or smart phone with flight planning software to get weather, make and file a flight plan.

No commercial jet I have flown has clearance delivery or avionics switches. It's more switches and wiring nodes to fail and adds weight, This all could be eliminated. If you want to shed load turn individual items off, or have a non essential bus with CB you can manually pull/trip that would do it.

It takes e switches to power your plane up. Also switches are single point failure items.

I hear you

I've spent a lot of time thinking about the want/need for the clearance delivery bus as well as the avionics bus. Really, there's no need for either. I guess it comes down to want.

My thinking with CD bus is the ability to sit there drawing only 3.2 amps while I fiddle with the EFIS and GPS downloading or making up flight plans and not worrying about draining the battery. I'm not a professional pilot (anymore) and It's been my experience in a club plane with a GTN 650 that I aways feel rushed with the engine running and trying to make up a flight plan. Now that being said, one could make a good argument that if I get all my fiddling done using the CD bus, I should be ready to go by the time I flip the master and start the engine and this would eliminate the need for the avionics bus. Someone else said if I eliminate the avionics bus, a future owner might be confused on what avionics were on what bus (not sure that's a valid concern).

The other reason I rationalized the avionics bus is it keeps 5 amps off the system for engine start, more juice for starting. Also, with the avionics bus gone, I would want to feed the #2 MFD with stay alive power from the GAD-27 to prevent possible reboots during engine starts. The rest are fed by the TCW IBBS and won't reboot.

As far as single points of failure go, I plan on flying IFR just not much IMC and there is so much more redundancy built into this system compared to the old days I'm not worried about a switch failure. If a CD switch fails, no consequences as CD bus fed from main bus. If an avionics switch fails, primary EFIS, comm and GPS fed from the CD and main bus, plus IBBS feeds most LRUs. Plenty of time to get on the ground.

Having no clearance delivery or avionics bus is definitely simpler, lighter and doable.

Just not sure that's what I want.

PS-the big boys don't have a CD bus BUT they are tied into shore power and don't worry about battery depletion

[Waiex-guy]

Both of your GSU-25?s are sitting next to each other on behind multiple switches and a little circuit breaker. What is your plan when there is a short on that bus that pops that breaker or damages that switch?

[mfleming]

Originally Posted by Waiex-guy

Both of your GSU-25?s are sitting next to each other on behind multiple switches and a little circuit breaker. What is your plan when there is a short on that bus that pops that breaker or damages that switch?

The #1 GSU-25 is also fed from the TCW IBBS backup battery.

• If the fuse feeding the #1 GSU-25 pops, its now on battery power and the #2 GSU-25 carries on.
  
• If the avionics switch goes bad, the #1 GSU-25 is on battery power and carries on and the #2 GSU-25 is off line.

Of the LRUs on the avionics bus, the GMU-11 magnetometer, #1 MFD, #1 GSU-25, the GAD-29 GPS interface and both GSA-28 autopilot servos are on battery power if the avionics switch goes south.

[Waiex-guy]

Good answer.