Please Critique My Electrical Plan
 

A PDF of my electrical plan can be found here. (Hit refresh until it loads if it say's forbidden)

This is my first pass at the basic electrical architecture for my -7.
The mission is Day VFR, IFR, very little IMC, maybe pass through a marine layer.

This electrical schematic is a variation of one being developed on the Aeroelectric list.

This is a single battery, dual alternator system with a clearance delivery feature.

My version uses a B&C BC410-H 20A back up alternator with their back up regulator. The back up alternator also comes in on the battery side of the master contractor.

Does the main alternator stop outputting when "field" voltage to is is cut?

Finn

Yes, that?s my understanding from B&C.

What is the reason for running the alternator output to the battery side of the master instead of the load side?

I offer that a fault on the alternator output cable (that nice big fat one) is not isolable in your diagram. For smoke in the cabin it would be a good idea to have such things isolated by opening the master(s).

Side note - if you fly IFR I suggest you add the standard manufacture EFIS backup batteries. You will loose your radio and transponder but at least your will keep the wings level.

If you want to fly IFR with more confidence send me a note with your email address and I?ll provide some ideas.

Carl

He does have a fusible link in the wire to the alternator.
In case of main contactor failure, battery will still be charged and can power essential bus.

However, in case of rectifier diodes in alternator partially shorts, the alternator will discharge the battery. A high-amp diode in series with the alternator B+ wire would prevent that. But then he'll need a electrolytic capacitor or small battery on the alternator side to smooth out noise to provide good regulation (if not already provided by regulator).

Finn

The key reason would be keeping the battery bus and navcom bus alive after opening the master contactor, without depleting the battery. It also keeps the standby alternator ballasted with the battery, which although not essential, is generally a good thing.

EDIT...I see Finn already got there.

This seems to be a -7, so the standby alternator, contactor, and battery are all forward of the firewall...they can't make smoke in the cabin. A ground fault in the standby's B-lead would open the circuit protection anyway. The CP is drawn in right above the master contactor.

It does need additional circuit protection of some sort in the wire to the battery bus, as that wire does pass through the firewall and into the panel area. I'd suggest an ANL or similar with post terminals, as the terminals would provide secure junctions where the plan is currently marked "fat wire tie point".

If possible, the battery bus and its feed, as well as the feed to the navcom bus, should be physically located away from other wiring and buses. Like with coronavirus, physical separation increases the odds of survival.

I know B&C shows a backup alternator field switch in their drawings, but I don't know why. The special regulator for backup has a 13V setpoint; it doesn't turn on until the primary alternator goes offline, and then it turns on automatically. The switch doesn't hurt, but on the other hand, parts not on the airplane never give trouble.

Pretty sure you want to move the backup alternator's field supply to the battery bus, so it can regulate with the master contactor open.

Main Alternator B+ is going where?

Assume you don't plan on paralleling both MAIN and AUX alternator and have a way to kill the main alternator, like pull CB.

Do you need a clearance delivery, just turn the master on. However I assume this has secondary advantage of a way to isolate an "essential bus" or clearance delivery bus with BAT master off in flight.

Hot battery bus has a lot on it, lights, clocks. There is a chance of draining the battery. I like the idea the MASTER turns everything off.

There are so many ways to wire a plane. Keep it as simple and "standard" and intuitive to operate as you can, not more complex.

Contactor on the engine side of the firewall, so no smoke.

+1 on the back-up battery.

• Yes, a -7
  
• What is an ANL?
  
• Aux Alt field switch does come off battery bus. I guess B&C shows a field switch in their drawings to isolate the aux alt in the unlikely event one had a double alt problem.

• Aux alt parallels the main alt but the aux alt regulator keeps it offline until the voltage drops below a selected value then gets excited and comes online...no input from the pilot. There are indicator lights on the panel to alert the pilot of the switch.
  
• The battery bus is a artifact of copy and paste...no Hobbs, clock or dome light.

A big fuse.

https://bandc.com/product/anl-curren...base-standard/

https://bandc.com/product/anl-curren...-through-130a/

Ahh yes, brain fart. Main bus tap is a low volt sense, regulator terminals 3 and 5. Probably should move that tap to the battery bus, as page 4 of the installation manual says "If terminal 3 is not connected to power, the SB1B will not work". An open battery contactor could mean no power on the main bus.

Perhaps it has some small power draw when parked, or won't shut down with power present. I dunno. I just like to know why things should be installed.

Maybe it would make more sense to have the MAIN alt operated by a switch and the AUX on a CB only. This way one could turn the MAIN alt off during preflight and check the AUX alt operates OK..

Main alternator is switched in the drawing, one of those progressive toggles allowing BATT or BATT+ALT.

Hey Mike, if you ask B&C why the ALT is switched, let us know too.

My feeling is that you are overthinking this. You have a lot of components here, all of which will take time and effort to bolt to the plane, and each of which could fail in flight.

As you know, there are two schools of thought - backup alternator and backup battery. I just completed an RV-7A and went with the backup battery plan, which seems substantially simpler to me.

I have backups plugged into my Dynon EFIS. If I lose the alternator, I have more than half an hour of power from the main battery, and then an hour more on each of the displays if need be. It's hard to think of a scenario where I couldn't declare an emergency and get onto the ground in half an hour, even in IMC.

You've also got a clearance delivery switch but no avionics master switch. Maybe I'm missing something, but this looks nonstandard from the perspective of a pilot coming from the certified world, and might be confusing for somebody transitioning into your plane. It's unclear on first look if there is additional avionics on some other switch, or if your clearance delivery is another name for the avionics master.

My primary EFIS turns on when I turn on the master because I need it right away before I turn on any other systems.

You show the avionics ground bus being tied to the main bus with 5x 20 AWG wires. I can't see any reason why you don't want both grounds tied tightly together. Why not make them the same bus? Or if they are physically distant, connect with 8AWG (or two 8AWG if you are concerned about redundancy)?

I don't understand the clearance delivery bus being tied to the main bus via a diode and 18 AWG wire. That looks like you have no way to turn off the clearance delivery bus because of the diode. And you have 18 AWG via the diode, but 14 AWG via the clearance delivery solenoid. I would think you'd want the same wire gauge on both, sized to the maximum current the clearance delivery bus would draw.

For your pMag switch, I can speak from experience that it is wise to choose a switch that is difficult to turn off. Pick one where you have to pull it out to flip down, or put a cage over it. I believe I bumped mine off in turbulence during phase 1 testing, which was one step in a failure chain I'm still diagnosing that led to an off-airport landing.

I'm happy to send you my schematics if they'd be useful.

Enjoy!

David

sorry I missed that.. Personally I would change the switch designation to BAT+ALT or something similar in the 3rd position.

So I talked to B&C today. As far as the switch is concerned, B&C sees it as an option for personal preference as long as there is a pullable breaker installed. So the combinations would be: a regular breaker and a switch, a pullable breaker and a switch or just a pullable breaker. The key seems to be...have a way to disable the ALT. They specifically did not recommend a fuse and a switch combo (I forgot to ask them why).

I agree on the labelling...I just haven't come up with the right verbiage yet.

------------------------------------------------------------------------------------

Re-Done Schematic (click refresh until it loads)

So the original schematic I posted was a variation of a newer version of a Bob knuckolls architecture. After looking at my version Bob recommend I just use the original Z-12 architecture with the clearance delivery feature.

The one I posted originally had a engine bus for fully electrically dependent engines. That's why the AUX ALT was tied in directly to the battery and bypassed the battery contractor. Bob didn't think that I needed that, so the new schematic is almost a straight Z-12.

B&C recommended that I wire it up with two shunts to be able to monitor both alternators. I'm not sure exactly how this works. Bob's Z-12 schematic shows two shunts AND a Hall monitor. I'm going to have to do some more research on that.

My thoughts as a follower of Aeroelectric List / Bob Nuckols
 

My thoughts as a follower of Aeroelectric List / Bob Nuckols:

All wound field externally-regulated alternators stop producing when the field current is removed.

Attaching the backup alternator B lead to the battery is for the smoke in the cockpit scenario to keep a running alternator.

Perhaps the best place for the battery bus is forward of the firewall, and Bob shows one of his * notes on its feed meaning 6" or less. FAR 23.1361 would have 5 A breakers or fuses on wires out of the battery bus but Bob allows 7 A fuses because they are faster than breakers. Similarly, the clearance delivery bus relay should be forward of the firewall; the clearance delivery bus can be aft of the firewall because it is "protected" by the relay.

MIDI fuses ("mini" ANLs) have become available, they are smaller and can be used instead of ANLs. They are faster than ANLs though so take a look at their curves. Bob has blessed MIDIs; the smallet available is 23 A. There are also MANLs (another name for "mini" ANLs) but I personally wonder about the quality because I can't tell who makes them.

B&C regulators use a crew accessible breaker for the field because they have overvoltage protection that is subject to nuisance trips so are worth one try at a reset. When Bob shows a fuse on the field wire there is no OV protection.

Bob, who designed the B&C regulators, says the backup regulator with it's optional hall effect sensor is an unnecessary complication and cost designed for certified aircraft. BTW, if the hall effect sensor is added, it will flash a warning above 20 A despite the "20 A" alternator will deliver 32 A at cruise RPM. You can get the same effect of the alternator coming alive when the voltage drops by having two LR3Cs and turning the voltage down on one of them; I'm thinking 13.8 and 14.4 V. One reason for setting the standby alternator to a lower voltage is in case the battery is run-down you don't want to spend alternator capacity charging the battery versus keeping systems alive.

I believe Z-12 was designed for a certified aircraft. That's why it shows breakers directly on the main bus. Compare to Z-101 and others. (BTW Z-101 shows 12 awg from main bus to main alternator CB where it can be 18 awg.)

Two ammeter shunts are shown on dual alternator Z dwgs but that doesn't mean you have to install both. Voltage is a better indication of whether an alternator is supplying the current you need. Ammeters are good for diagnostics on the ground. Does your EMS support two shunts; maybe not, that's one reason Z-101 shows both B leads passing thru one hall effect sensor.

Alternator field switch: If it's not there and the engine is not running the field will draw current running down the battery and heating the alternator. I don't know exactly but maybe it will draw 2 A for the backup alternator and 4 A for the primary alternator.

Bob has renamed the endurance bus to clearance delivery on Z-101. Endurance bus is a term for systems with one alternator or with a small, 8 A, backup alternator. Bob want's to be able to energize the clearance delivery bus without closing the battery contactor which draws significant current (15 ohm coil). There are battery contactors that draw 1/4 or less the current of a legacy contactor but Bob has not adopted them.

Bob is in the one battery two alternator camp and is working on Z-101 as potential successor to Z-12 and Z-14 for OBAM and with EFI+I in mind.

Good comments John.

Mike's latest diagram moves the ALT B regulator's field, sense, and light connections to the main bus. I don't understand why.

Normal operation has ALT B ready to begin generating if main bus voltage falls below its regulator set point. So far so good.

Ok, enter the "classic smoke in the cockpit" response; open the master contactor. Given the progressive BATT-ALT master switch, the main bus is no longer connected to the battery and the primary alternator's field is open, so it also stops producing power. Main bus voltage drops. So how does that affect the ALT B system? Does it come on line in the very short time period while main bus voltage is falling to zero? Or lacking a field supply, does it just not come on line?

Note if it comes on line, it supplies power to the main bus...which is odd, given that the master contactor was opened for a reason.

Sure seems like the entire ALT B system should be a branch of the battery bus. It would still feed the main bus following ALT A failure, assuming normal ops, i.e. a closed master contactor. With an open contactor, it would be truly independent, powering the battery bus and avionics, all ballasted by the battery.

In which case an ALT-B on the battery bus would need a field switch. As an aside, it would not matter if that switch was on or off in normal flight. If on, ALT B would come on line automatically following ALT A failure or an opened contactor. If off, the pilot could fire it up at any time, as it always has a field power supply.

So is the thought that when there is smoke in the cockpit the AUX ALT stays on during the smoke event or everything off and then bring AUX ALT back on through the battery bus?

So when we think of the battery bus being forward of the firewall, do we mean the fuse block also. (sorry if this is a dumb question)


B&C told me that I didn't need the Hall sensor on the back-up regulator and the cost is the same for the LR3 and SB1B...but really, Bob seems to think a generic Ford regulator would be just fine. I guess it just the flip of a switch instead of the AUX ALT coming on automatically.


Totally missed that Z-12 had breakers instead of fuses...I couldn't see the forest for the trees :confused:
I'm into fuses where appropriate.

My GSE 24 appears to support two shunts but really all I care about is that the AUX ALT comes on line and I have some sort of a indication. The less stuff the better. (say's the man who's stuffing his panel with gadgets :rolleyes:


This I did not know...very important info.

I followed Bob N's Z-12 when I redid the schematic. I understand that with smoke in the cockpit opening the master would kill all energy production. Are we thinking that during a smoke event it would be acceptable to leave the AUX ALT online?

I'm just guessing but I think that opening the master would nix any chance that the AUX ALT coming on line (if tied the the main bus)

Sounds like a question for B&C...Monday. Aren't most AUX ALT tied to the main bus?

Totally agree, I was influenced by Bob N. when he suggested I just used Z-12...which this new design basically is.

So with the AUX ALT totally on the battery bus:

• During smoke event, master and AUX ALT field switches OFF
  
• At shutdown, master OFF and AUX ALT field switch OFF

I'm not sure I understand.
If the AUX ALT was tied to the battery bus AND the AUX ALT field switch was off/closed, isn't it true that the AUX ALT could not come on line if the main ALT failed? No energy to the AUX ALT field means no excitement, ergo no juice or have I just confused myself :confused:

[/quote]

Thanks
Michael

Strongly recommend sticking with the B&C regulators - especially the SB regulator. When stuff happens having the SB alternator automatically pick up the load is well worth it. Less pilot action to fix something is preferred.

Current shunts are a left over from when cars had ammeters instead of voltmeters, but running fat wires to a 1940 instrument In the panel is not a great idea - so we have shunts. Back in the day it was cheap to build and ammeter and voltmeters were expensive. A voltmeter provides better system health information than the ammeter. Having both is a very marginal gain in information - for me it does not justify installing a shunt.

If you want to know current loads, do that with your bench power supply on the ground. The data will not change (or if it does the thing you are testing most likely already failed).

Carl

Like this Mike:



I'd put the battery bus on the cockpit side of the firewall, as shown by the purple line. There are only two high current wires passing through the firewall, one for each bus. If either high current wire or bus shorts to ground, the fault pops the respective ANL. Everything downstream of the battery bus and main bus has its own fault protection at the bus, so it's become real hard to get smoke in the cockpit...but if you do, sure, the safest choice is to switch off everything but the mags, find an airport, and sort it out on the ground.

If you build with physical separation between the main bus and battery bus systems (mostly separate firewall pass-throughs and wire routes), there's a pretty good chance you could inspect, then fly home on one of them.

Assume no shorts and popped ANLs. I'd venture an open contactor, contactor control wire, or master switch is the next most probable failure. With an open contactor, the primary alternator should stay live. If it didn't, ALT B (with switch on) would go live, charging the battery and powering the avionics.

I forgot to add it to the switch panel illustration, but there would be one more breaker for the ALT-B field. Operation is dead simple; normal flight is breakers in, all switches UP.

And I'm with Carl on current shunts. I find ammeters pretty useless in flight.

Z-101
 

I'm a fan of Z-101 because endurance is fuel range (battery capacity is not a factor) and alternator capacity is over 30A with master contactor open (Bob also has an 8A version of Z-101). This is especially important with EFI+I current requirements. I spoke about Z-101 recently on VAF here. If interested, my files are linked in my signature. Full disclosure... Bob Nuckols calls Z-101 Preliminary at this time.

I learned a great deal recently on the AeroElectric List. There are some frustrations with fragmented threads which may be why I didn't have complete success using the search function on the site or Google. After subscribing several months ago I learned a lot in addition to what I have read in Bob's book over the years and recently when Z-101 came out I adopted it for my EFI+I equipped RV-6A (not flying yet). Beware, no love for ECBs on AEL.

I'm following Bob's and FAR 23.1361 advice to keep power distribution wires that don't have a remote switch (relay or contactor) close to the source (battery) fused at 7.5A or less. This has implications in maintenance, smoke in the cockpit, and crash scenarios. Attaching the backup alternator B lead to the battery without a relay violates this... one can either justify this that with vacuum pad alternators the alternator is close to the battery or one can add a B lead relay adjacent the battery. Automotive service manuals say first thing, disconnect the battery minus cable.

When I say battery bus I mean the fuse block; fuse block and bus are synonyms in this case.

The B&C aux alternator controller was designed for TC aircraft and has a light that illuminates if the voltage drops due to primary alternator failure causing the aux alternator to come alive. But modern EMS systems will tell us the voltage has dropped. I found my Bob quote:

"If the bus voltage drops below the AUX controller set point, the AUX alternator wakes up and a SPECIAL
circuity within the controller senses this and illuminates an ALTERNATOR LOADED light. The stand-by versions of the alternator controller are not recommended for simple dual alternator installations where the auto-switch feature is not necessary . . . this was a 'bell-n-whistle' aimed primarily at the
STC market for TC aircraft that were receiving the pad driven, aux alternators.

... Bob"

The 5x20awg wires from the firewall ground bus to the avionics ground bus are described in Chapter 18 of Aeroelectric Connection. Note 23 in the appendix, which is called out on the dwg adjacent the avionics ground bus, points to Chapter 18. In Bobspeak the (instrument) panel ground bus is the forest of tabs on the aft side of the firewall and the avionics ground bus is on the IP subpanel.

In a smoke in the cockpit situation the progressive switch for the main bus and alternator makes sense because to de-power the main bus you need to de-power the main alternator. If the aux alternator is on the main bus and switched on I image it would come alive in time to keep itself powered but don't quote me on that but it doesn't matter because your gonna want it off because you want the main bus cold. Keep in mind Z-101 puts the aux alternator on the battery.

With Z-101 I plan to keep the aux alternator on in flight; if the main alt fails I will get an EMS message; if I open the master contactor I won't have to remember to turn the aux alternator on. If using the Ford aux regulator I'm not sure what's wrong with keeping it on but I believe there are low-cost adjustable automotive regulators. I plan on a B&C "primary" regulator set at 13.8V for the aux alternator because I'm not being as frugal as Bob and I like the OV protection.

Yes the aux alternator will come alive with Z-12 or Z-101 if it is switched on after the main alternator fails because the battery is there to energize the field; I the case of Z-12 the master contactor is still closed so the main bus sees the battery; in the case of Z-101 the the aux alternator field is connected to the battery bus so it will come alive even with the battery contactor open.

Keep in mind the AeroElectric Connection book is not updated as often as the drawings at http://www.aeroelectric.com/PPS/Adob...itecture_Pdfs/

Changes I made to Z-101:

• Renamed clearance delivery bus to avionics bus and fed it from opposite ends from battery bus and main bus versus using a single post on the bus.
• Put com 1 on the engine bus with the idea if you kill both the main and avionics busses, you?ll still have a radio.
• Added electronic fuel injection and ignition components.
• Added Crowbar Test buttons to main and battery regulators for annual.
• Used B&C LR3C regulator for battery alternator versus generic Ford.
• Alternator B leads: Used MIDI current limiters versus fuselinks.
• Aux alternator switch is progressive.
• I show an optional aux bus B lead relay.
• Battery contactor is a low coil current version.
• Diodes are schottky.

Even Bob doesn't follow that advice. Z101 attaches the backup alternator's 10 AWG B-lead to the battery, using a 14AWG fusible link for circuit protection.



It is electrically the same as this:



Note that Z101 uses the generic Ford regulator, not the nice B&C with OV protection. The sense terminal is simply jumpered to the field terminal (S to A), so sense and field see the same voltage, taken from the battery bus. Mike's earlier drawings incorporated a B&C regulator, and took sense (and a light) from the main bus while taking field from the battery bus. That won't work with the main contactor open. So, move the sense/light source to the battery bus, same as the field. While there, arrange the ANL so it provides circuit protection for both the alternator B-lead and the battery bus feed through the firewall. It's the same as Z101, but allows the use of the fancy regulator.

Previous post...


Slightly different subject...the addition of circuit protection between the contactor and the main bus. There's none in Z101. The argument seems to be that it's protected by the presence of the master contactor...just open the contactor if that supply wire or the main bus is shorted to ground.

Yep, old school, and it works...but it goes against human nature. When the spit hits the fan, I submit that most GA pilots go all deer-in-the-headlights, and hesitate to open the master. It's a natural aversion to turning off important things in flight. With circuit protection, a shorted bus is shut down automatically, no pilot participation required...and with this system it doesn't shortchange anything to do so. The avionics remain live, the ignitions still ignite, etc.

BTW, for purposes of diagramming at this level, I don't care if I draw in an ANL, a MIDI, a fusible link, or a paper clip, as long as the final choice is reliable in normal use, and burns open at the right amps when things go abnormal.

Thanks for the great response John.

Thanks for the clarification on the battery bus...got it.

So it looks like Bob doesn't think the B&C standby regulator is necessary on a non TC aircraft.
You mentioned using the LR3C as a back up regulator and adjusting the set point a little lower so it will bring on the AUX ALT automatically. Is there a reason not to use the B&C SB1B standby regulator? Same price...

Just a technical point (excuse my ignorance). If voltage indication to the EMS is all we need (I'm OK with that). How does that voltage info get to the EMS? (I'm sure this is a head slapper)

I went back and re-read chapter 18 about the avionics ground bus being a female D-sub connector. This info didn't sink in on the first read but it's brilliant! I've already pencilled this in.


Thanks again for helping me get through this steep learning curve.

Great thoughts on the ANL to protect the main and battery buses. How would one size them? Now that I know what an ANL is :rolleyes:, I've spent some time looking at ANL holders at B&C.

Thanks for all the help

The LR3C:

• Flashes a light, if you install the light, if the voltage falls to "typically between 12.5 and 13 volts".
• The light would not illuminate if the standby alternator was online because the voltage would not fall that far.
• Has provision for a battery temperature sensor that is not used if the battery is in the engine or passenger compartment.
• Has provision for a crowbar OV test button.

The SB1B:

• Illuminates a light, if you install the light, if the bus voltage falls and the standby alternator comes alive.
• The light flashes above 20A if you install the optional hall effect current sensor but you may not want this to happen since the smaller "20A" B&C alternator puts out a little over 30A at cruise RPM.

Now that I think of it, it seems nice to have the SB1B with its "Standy Alt On" panel light feature since we don't need the battery temperature sensor feature of the LR3C.

P.S. The installation manuals say not to use an LED for the light but if you want to you can do this.

P.P.S. Bob Nuckolls says the standby alternator should be set higher than the 13.0V B&C mentions in the install manual. Bob suggests 13.5 V.

Any EMS would have a voltmeter input. I'm using Dynon Skyview; it has two voltmeters. In the Skyview installation manual the key words to search for are:

• "Voltmeter Inputs" where it tells you what pins to connect to.
• "Manual EMS Sensor Settings", then the example happens to be a voltmeter.

The usual. Max expected current plus some, protecting a wire which will carry a little more.

Made a sloppy error on the previous drawing. This one corrected. Eliminates the fusible link in the primary alternator B lead, at the start contactor in Z101. Which is not to say I have something against fusible links. I don't; they are compact and reliable, and particularly useful in small wires as an inline fuse. For larger amps, I'd rather have the ANL or similar, and the post mounting base is real handy for large junction terminations.



Primary power block diagram. It's a simple system really. Make a short-and-open list for the numbered wiring, check for critical failure modes.

Z-12 is at rev N dated 05/03/2020
 

I'm still a fan of Z-101 but FYI Z-12 was revised to rev N on 05/03/2020. Find it here.

Compared to rev M:

• Clearance delivery bus is remotely switched and fed by a fuselink versus a 7.5A fuse.
• Dual alternator B lead shunts are replaced with a single hall effect sensor.
• Main alternator ANL is replaced with a fusible link.
• No CBs on the main bus.
• Mag and EI are not shown.

Battery bus and clearance delivery bus are optional, that's why they are in color.
You can delete the hall effect sensor for the aux alternator regulator.
Well, you can do anything you want!
.
.
.

Simplify-Simplify And Standardize
 

This has been a real learning experience coming up with an electrical architecture for my -7.

Here are some of the things that have driven me to this current design.

1. It dawned on me - I have a 6ah back-up battery for the important stuff
   
2. I don't like the expense, weight and complexity of the AUX ALT
   
3. I like the idea of a clearance delivery bus.
   
4. I respect the idea...but I like an avionics bus :D
   
5. I rediscovered the adage - build it for you ;)

So, here's my latest attempt: DWG F103

PS: I forgot the ANL to the battery bus but it will be there.

What is the function of the 10amp breaker feeding the avionics bus? This places a breaker in series with the the avionics load breakers risking a single fault on the avionics buss taking down the entire buss. If you are worried about a unprotected wire run (which you have many), consider bumping this 10amp breaker to 20 or 25. That way you have some confidence the downstream breakers will pop first on a fault.

The battery bus should be ?the last line of defense? while flying. For example external power depended ignitions and such. Strobes and boost pumps do not meet that criteria. For pMags and standard fuel systems (carb or fuel injected) there is no need for a battery bus.

Now consider two avionics busses - this provides for your clearance deliver objective and well as capability to isolate a fault and still have half of your panel (as in Comm1 + EFIS 1, Comm 2 + EFIS 2). Power these busses from the output of the master relay, not from the main buss. I note your TCW backup battery. You could use that to power one of the avionics busses for your clearance deliver function. It would also be a good way to verify it really works before you have a hard need when flying.

The #6 wire feeding your main buss is way too big for those loads. Save some weight.
Carl

I long for the day, two relays (Bat/Start), one Alt, one battery, one buss. Most Piper and Cessna and Beech are flying like this IFR everyday. Of course they have vacuum pumps for flight instruments and mags.

Simplify is my suggestion..... mine is base-line, dirt-simple, standard AC electrical... The electronic ignition has it's own back up bat, as does the EFIS. I feel pretty safe.... On a real long trip I might carry a spare ND IR alternator to change on the ground...

I'm glad you brought up the 10A breaker for the avionics bus. I have seen this on others wiring architecture but was unsure if I needed it.


The battery bus has the pmag on there because I may change that to a Surefly/Lycoming electronic ignition (only one). I am unsure of the AUX fuel pump location. Having it on the battery bus seemed correct but...

The clearance delivery bus is shown as Bob Nuckolls has designed it. My desire for it, is to be able to fire up the Primary EFIS and GPS navigator to download flight plans. All before starting the engine. I suppose in practice if the devices that are on the clearance delivery bus were on the main buss and the rest of the GDUs/LRUs were on the avionics bus, there would be about the same current draw with the master on compared to the clearance delivery bus...What I'm trying to say is with a avionics bus...maybe I don't need the clearance delivery bus :eek:

I think I just convinced myself to move everything from the clearance delivery bus to the main bus. Because really, what's drawing power on the main bus, not much when all the switches are off (although I understand the ALT field does draw a bit)

I do like the idea of maybe having the TCW IBBS battery power up the items originally on the clearance delivery bus, we'll have to see about that. The comm has only one power in pin as far as I can see.

The 6AWG wire to the main bus was a leftover from the original Z-12 drawing I started from. After you're mentioning it, I looked at the conductor chart from 43.13 and I can downsize it significantly.

Isn't that the truth :rolleyes:

I remember launching into the soup out of Sitka, Alaska in a C-180 back in the day. Absolutely basic electrical/vacuum system, basic IFR configuration. Wow have things changed :D

If you go with the Surefly your design, in my opinion, falls short. While other may be ok with a ship power dependent ignition and a mag, I'm not. I would require a dedicated power source for that ignition.

Carl (800+ happy hours flying behind dual pMags)

When I spoke to the Surefly rep, I think he told me that on the certified aircraft, one Surefly did not require a redundant electrical system but two Surefly's did.

I definitely don't what to introduce the complexity of a redundant electrical system.

New Version
 

So, here's my latest version: DWG F104

EDIT: Unfortunately I overwrote my last version in post #28. Fixed thanks to John Bright.

This version is close to finished.

I replaced the avionics relay with an appropriately rated switch (5A draw).

The rest was cleaning up the drawing and adding all the fuses.

All comments welcome, either or

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?

So this Clearance Delivery Bus has the Primary EFIS, Com and GPS on it.

You can use the clearance delivery bus to listen to ADIS, load flight plan, get a IFR clearance etc... The advantage is, this bus has only a 3.2 amp draw, so saves the battery.

But if you don't want/need to use the CD bus, close the master, the Clearance Delivery Bus is powered through the diode.

The bottom line is anytime the main bus is powered up, so is the Clearance delivery Bus...sot he primary EFIS is on anytime the main bus has juice.

The DC power switches are grouped together to simplify shutting down...Shut down protocol, ALL DC POWER SWITCHES OFF.

When the BATT BUS blows the MIDI fuse for some reason, you would need to backfeed the BATT BUS through the CD switch to feed your Surefly.

Great catch

In Bob Nuckolls recently released Z101A drawing (where the idea for the CD buss came from) he separates the battery bus from the CD bus. The only reason I have a battery bus is to feed the SureFly ignition.

(20 minutes later ;)) I just spoke to SureFly and they said the way to wire their mag is to come directly off the battery with an inline fuse to the mag.

I'm going to eliminate the battery bus and feed the CD bus through an inline 15A fuse. and feed the CD bus though a separate inline fuse.

So, here's my latest attempt: DWG F105