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Show me your Wiring Diagrams

Scott - thanks for transforming my horrible line diagram into something far better.

Some thoughts:
- As Scott discusses, adding the two Engine Busses addressed ship electrical power dependent engines. N/A for pMags.
- Scott reflects the prime function of the standby generator/alternator - that of mitigating the loss of the primary alternator. This is why is it connected in parallel with the primary alternator. Loss of the primary alternator is the most likely failure we have, but not (by far) the biggest risk to flight IF you have a known electrical reserve capacity (more than 2 hours). Depending on mission, some builders my not install it. I am running the very nice Monkwokz 30 amp vacuum pad generator on my RV-8 for the main reason to not get stranded someplace if my B&C primary alternator goes south - my flying is mostly long cross country. 30 amps is more than adequate to run everything I have.
If you want “belts and suspenders”, you could wire the standby alternator via isolation diodes to the left and right vital busses. This would add a mitigation for a fault on the non-vital buss as the non-vital buss would be off at that point (part of the POH to isolate electrial faults). I did that on my RV-10 and it worked as designed. For electrically dependent engines this may not be the best option.

Reminder, this design if for an all up round IFR bird - as in dual EFIS, dual comms and such (the driving reason for left and right vital busses). While overkill for a day VFR plane, I suggest a dual battery design along these lines is required for any plane with a ship power dependent engine.

Carl
 
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.......
Some thoughts:
- As Scott discusses, adding the two Engine Busses addressed ship electrical power dependent engines. N/A for pMags.....
IIRC you utilize mechanical fuel injection. You'd still need something similar for EFI regardless of Ignition type.
 
I'm analyzing failure modes of the design. Starting with the premise that a reliable system should be able to tolerate the failure of any single component, I like the Left & Right Master solenoids. The probability that both will fail at the same time is infinitely small. But I'm not sure that repeating that logic 2 more times enhances reliability. I see added complexity but little gain in reliability.
So some questions:

1. The common theme of this design seems to be that any given bus can be connected to either battery. That's OK but how is either Vital bus any more reliable than the Non-Vital bus?

2. Seems like a lot of busses. I'd like to see which appliances are connected to each bus. What is the advantage of Left & Right Vitals?

3. Does your engine have 2 ECUs?

4. I'd like to see a schematic of the Inj. Diode Bridge.
 
I'm analyzing failure modes…

I’m planning Z101 but a couple generic points.

  • A single connection to the engine or injector bus in an SPOF.
    I’m planning a Bussmann 15600 engine bus modified with dual feeds. Easy mod, ref photos https://photos.app.goo.gl/ZKjbqnU3DfkUKNex2
    and note 2 on my top level schematic: "The engine bus is fed at opposite ends from before and after the battery contactor per FMEA, loose stud at engine bus. Bussmann 15600 blade-type fuse panels are easily modified for the 2nd stud; snap the cap off, remove the bus strip, find the 2nd hex hole in the base for the stud head, notch the cap for the 2nd stud you add, reassemble.".
  • If using wound-field primary and vacuum pad alternators, engine ground is an SPOF for both alternators. I install two engine grounds, it’s a benign failure not detectable at preflight so it goes on the periodic inspection list. Monkworkz has a separate ground but it shouldn’t be shared with the engine ground point, especially if you have a belt-driven alternator also.
 
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My block diagram for a Dual G3x system with connector numbers and buses. Still need to look over if I really need/want all the backup data paths in the G3x install manual. Took a lot of reading of G3x, GTX 650/750xi, G5, GMA 245, GSB 15, PPS, VPX, GTX 45R, GDL 51R manuals to work it all out. Block diagram is good for data bus stuff. Power distribution is a bit tricky but not shown here.

View attachment Bus Diagram.pdf
 
I'm analyzing failure modes of the design. Starting with the premise that a reliable system should be able to tolerate the failure of any single component, I like the Left & Right Master solenoids. The probability that both will fail at the same time is infinitely small. But I'm not sure that repeating that logic 2 more times enhances reliability. I see added complexity but little gain in reliability.
So some questions:

1. The common theme of this design seems to be that any given bus can be connected to either battery. That's OK but how is either Vital bus any more reliable than the Non-Vital bus?

2. Seems like a lot of busses. I'd like to see which appliances are connected to each bus. What is the advantage of Left & Right Vitals?

3. Does your engine have 2 ECUs?

4. I'd like to see a schematic of the Inj. Diode Bridge.

I assume this was related to my Church of Froehlich schematic/post. Keep in mind, the builder gets to do what ever they wish. There's a lot of ways to do it. I'm willing to learn but have no desire to debate. Here are some brief itemized answers.

1 - It goes beyond just reliability. Simplicity for off-nominal situations will be more important than most will imagine. Loss of any supply device or connection does not require immediate operator action. Also, the ability to isolate systems, sub-systems, etc. would be important in the off-chance of a real electrical emergency. I've seen a lot of schematics that were very (too IMO) dependent upon diodes. When everything was working correctly, it was thought free. Smoke in the cockpit would have been extremely challenging to safe the electrical system if even possible. Answer 1.2 = the non-vital would only be utilized when an alternator was supplying watts. If neither is or an off-nominal condition occurs, the masters would supply that isolation. Vital buses can get power from basically any source as/if required even if alts are isolated, battery capacity being your friend.

2. answer 2.2 = Pilot workload. The vitals could be combined, sources diode "isolated" or whatever/any combo. Would the pilot intuitively know a failure source? Relying on dedicated instrumentation has it's limits especially if a system is (overly) dependent on diode iso. The odds of loosing a whole panel and/or vital systems because of a power source failure are greatly reduced. Answer 2.1 = EFISs, ADAHARs, etc. are the most obvious to me. Then coms, other navs etc. since the convenient redundancy is already there. Someone will chime in that they can manage any situation via manually sheading load. Good for them. I trained partial panel years ago with six pack steam gages. I still have zero desire to test those skills in a real world situation.

3. Two redundant ECUs, two (serial to ECU) coils, one set of injectors. Coils get power from ECU, injectors from either hence the (only) planned diodes. If I can make myself knowledgeable and comfortable with the related injector power failure mode of the ECUs, the diodes may not be required.

4. see above

My approach makes sense to me. Build what you want. There are a lot of safe viable approaches. Whatever you end up with, I would encourage you to fully understand the architecture, nominal and off-nominal operations, etc. It's not enough to just know procedures in some cases.

To your general comments:
"I like the Left & Right Master solenoids. The probability that both will fail at the same time is infinitely small." - and if they do, there's enough planned battery capacity keep the aircraft flying for a long time and the non-vital systems are automatically "shed".

"Seems like a lot of buses." Not really but others will argue. I assume people's minds tend to drift to bus bars and a multitude related switches, circuit protection, etc. but really just differently controlled/sourced. Each level of redundant switching (contactors and masters) will fit on the panels I've connected to fronts of the small PC680 battery boxes (reference pic but no contactors installed yet) connected with a few inches of wire each.

The related planned bus switch positions will be: down = off, center = nominal, up = off-nominal/cross feed.

~ different subject but I haven't found any bus manager type devices that would do a better job; some I wouldn't trust at all.

Again, build what you want. If there's a better approach, I'm ready to learn. This path I'm on fits my linear, serial thinking process; both from a build and operations perspective.
 

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4. And, the most significant difference: In the up position (probably upside down, as drawn, but no matter) the P lead is killed (grounded) but the Pmag has +12v power when the (maint) switch is closed. Mine can't do this. This is the part I don't understand. Why do you need this ability? It's because I don't understand how the Pmag works.

...

Thanks for the kind words, and apologies for the delay in responding. I somehow missed this post.

My "maintenance" switch applies 12v to the PMAGS in order to enter setup mode. My normal switches for each pmag support the three positions:

top: 12v + ungrounded (mag active), mag power from aircraft battery/alternator
middle: 0v + ungrounded (mag active), mag power from internal pmag generator
bottom: 0v + grounded (mag inactive)

In order to get into setup mode, the pmag must be grounded (mag inactive) and have 12v applied. This needed an additional switch the way I wired things.

Hope that clarifies my design, which by the way after 170 flight hours, I'm still happy with. To keep things simple, all switches up will get and keep the aircraft flying. All switches down puts everything to sleep.

Smoke? Turn off master switch. Still smoking? Turn off backup battery. Still smoking? Punch!

BTW, the Maintenance LED is only lit when I have that switch on.
 
My "maintenance" switch applies 12v to the PMAGS in order to enter setup mode. My normal switches for each pmag support the three positions:

top: 12v + ungrounded (mag active), mag power from aircraft battery/alternator
middle: 0v + ungrounded (mag active), mag power from internal pmag generator
bottom: 0v + grounded (mag inactive)

In order to get into setup mode, the pmag must be grounded (mag inactive) and have 12v applied. This needed an additional switch the way I wired things.

While there are multiple ways to skin the cat, I tried to simplify the operation and setup of the Pmag and went with what I think is intuitive and less switches.

A pull-able circuit breaker that powers (thru master switch) the Pmag and simple 2 position on-off switch to ground the Pmag. Circuit breaker only gets pulled for the occasional internal generator test.

YMMV, but an alternative that is a little cleaner IMHO.

Fitz
 

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While there are multiple ways to skin the cat, I tried to simplify the operation and setup of the Pmag and went with what I think is intuitive and less switches.

A pull-able circuit breaker that powers (thru master switch) the Pmag and simple 2 position on-off switch to ground the Pmag. Circuit breaker only gets pulled for the occasional internal generator test.

YMMV, but an alternative that is a little cleaner IMHO.

Fitz

I like your diagram, especially the CAN bus layout.

What is the reasoning for having a 20 Amp Circuit Breaker switch (as opposed to just a switch) for the Avionics Bus? It may be obvious, but I'm still a little new to schematics.
 
Thanks!

I think it was just protection for the wiring. All the avionics components are protected by their individual fuse or CB.

Fitz
 
Power System Diagram - RV14

After many hours of reviewing diagrams from The AeroElectric Connection, I have arrived at the following "Initial Concept" for my RV14A project.
I am not experienced in airplane electrical design so any help with poor design or possible safety concerns is appreciated.
Basic design features:
-B&C primary and stby alternators
*Pri alternator will connect to battery contactor output side.
*Stby alternator will connect to battery contactor input side. In the event of Pri Alt failure, this will enable load shedding if needed by placing Bat/Esntl switch to Esntl position. If stby alt can handle amp load then no need to load shed and Bat/Esntl switch will stay in Batt position.
*Pri and Stby Alts are controlled by a 3-pos switch (On-Off-On). Stby Alt will only be selected on when Pri Alt fails.
*Hot Battery Bus -This bus is hot anytime battery is connected. It is located in the avionics sub-panel which is which is easily accessible on pre-flight, but not during flight. Initially for a couple items, but more added because I ran out of space on main CB panel. All but one item on this bus is switched.
*Two TCW-IBBS-12v-6ah batteries. One provides b/u power for PFD1 and associated items. The second is for the GTN650Xi. Because the GTN650 does not have pins for a b/u power source, I moved it to its own bus. if needed, that bus will be powered by its own b/u batt.
*Ignitions - One Surefly and one slick Mag.
Thanks for your inputs.
Diagram of primary power system attached below. REV 02/04/23
 

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re N144EF electrical power schematic rev 01/30/2023

After many hours of reviewing diagrams from The AeroElectric Connection, I have arrived at the following "Initial Concept" for my RV14A project.
I am not experienced in airplane electrical design so any help with poor design or possible safety concerns is appreciated.
Basic design features:
-B&C primary and stby alternators
*Pri alternator will connect to battery contactor output side.
*Stby alternator will connect to battery contactor input side. In the event of Pri Alt failure, this will enable load shedding if needed by placing Bat/Esntl switch to Esntl position. If stby alt can handle amp load then no need to load shed and Bat/Esntl switch will stay in Batt position.
*Pri and Stby Alts are controlled by a 3-pos switch (On-Off-On). Stby Alt will only be selected on when Pri Alt fails.
*Hot Battery Bus -This bus is hot anytime battery is connected. It is located in the avionics sub-panel which is which is easily accessible on pre-flight, but not during flight. Initially for a couple items, but more added because I ran out of space on main CB panel. All but one item on this bus is switched.
*Two TCW-IBBS-12v-6ah batteries. One provides b/u power for PFD1 and associated items. The second is for the GTN650Xi. Because the GTN650 does not have pins for a b/u power source, I moved it to its own bus. if needed, that bus will be powered by its own b/u batt.
*Ignitions - One Surefly and one slick Mag.
Thanks for your inputs.

Are you aware of the Monkworkz vacuum pad alternator? It's PM versus wound field so it starts with no battery present. It makes 30A at 1,800 and up Lycoming RPM.
Be aware the latest Z schematics are not in the Aeroelectric Connection book. I made some notes here.
You'll get lots of help if you post on the Aeroelectric List. I see a number of improvement opportunities IMO.
.
 
Auto or switch ?

*Pri and Stby Alts are controlled by a 3-pos switch (On-Off-On). Stby Alt will only be selected on when Pri Alt fails.

What is the downside setting the Stby Alt regulator 0.3 v below the primary and let it auto engage? An amp draw warning can be added to the EFIS to let you know when the PRI fails and Stby starts.
 
Are you aware of the Monkworkz vacuum pad alternator? It's PM versus wound field so it starts with no battery present. It makes 30A at 1,800 and up Lycoming RPM.
Be aware the latest Z schematics are not in the Aeroelectric Connection book. I made some notes here.
You'll get lots of help if you post on the Aeroelectric List. I see a number of improvement opportunities IMO.
.

Thanks John. I wasn't aware of the Monkworkz alternator. Nice that it doesn't require electricity to come on line and puts out 30a at 1,800 rpm. Looks like a well designed piece of equipment. I already have the B&C Pri and Stdby in the shop and have the external regulators mounted.
I have reviewed most of your info during my design process and used the links you put together. Very helpful and informative. As you suggested, I will post my diagram on the Aeroelectric List to get more ideas.
 
*Pri and Stby Alts are controlled by a 3-pos switch (On-Off-On). Stby Alt will only be selected on when Pri Alt fails.

What is the downside setting the Stby Alt regulator 0.3 v below the primary and let it auto engage? An amp draw warning can be added to the EFIS to let you know when the PRI fails and Stby starts.

Thanks dmattmul. When doing research for this part of my project I, like most I'm guessing, mostly referenced The AeroElectric Connection and Aircraft Wiring Guide. I know most builders follow the direction from AeroElectric regarding alt switching. Like this I believe?.. pri alt is armed when the master switch is turned on, same switch. The stby alt, separate switch, is also switched on and ready to pick up the load. Definitely a proven concept there. The idea presented in the Aircraft Wiring Guide is to switch pri alt on **after start**. If pri alt fails during flight..take a minute (I might try and figure out why it failed..maybe load shed?), and then switch on stby alt.
Also, like you mentioned, I will have a "low volt" CAS msg from the G3X. Additionally, I will have a "low volt" red annunciator on the panel.
Hope this method works for me.
At this point, I haven't run any wires for the pri electrical system so nothing set in stone. Although, my panel is cut and labeled so kind of set in my ways with that.. Thanks again!
 
After many hours of reviewing diagrams from The AeroElectric Connection, I have arrived at the following "Initial Concept" for my RV14A project.

...

Thanks for your inputs.
1. I’m not a Garmin customer, so I can’t comment on some of the nuances of powering Garmin avionics. At least one of my comments below may be incorrect as a result. I will say, however, that I hope your design allows for the engine analyzer and at least one display to be energized by the battery when you start the engine so you can monitor oil pressure and RPM on initial startup. And if the main battery is depleted such that the minimum input voltage of those electronics is not met while the starter is cranking, I hope the TCW-IBBS-12v-6ah kicks in.
2. It is difficult to comment on the circuit breaker rating choices unless the wire gauge is identified for each circuit, or a note stating that “Unless otherwise stated, the wire gauge is XX AWG.”
3. Looking at the Hot Battery bus, this design appears to be for an airplane that must be able to land at night after the Battery Contactor and Essential Bus contactor have been turned off for some reason, while maintaining operational position lights (but not anticollision lights) to comply with 14 CFR Section 91.209(a) (but not Section 91.209(b), unless you invoke the safety provision). And the design seems to also assume that any condensation can be wiped off the front of the windscreen if this scenario happens to occur. And maybe you’re going to navigate by Foreflight in this scenario (USB outlet).
4. Circuit breakers should be sized to protect the wire, per Table 11-3 of AC 43.13-1B. You can always go down in circuit breaker current (at the risk of nuisance trips) or up in wire gauge as appropriate for the load and distance of the wire run. Stating a circuit breaker rating implies a maximum wire size to this commenter.
5. I see lots of circuit breakers but not many switches. Maybe switches are implied, or in the case of avionics, included in the boxes. This is not the case for things like lighting and pitot heat, though. Per AC 43.13-1B Section 11-51, circuit breakers are not recommended to be used as switches.
6. Current limiting devices such as fusible links, fuses, circuit breakers, and ANL devices should be placed as close as possible to the source of the current, to protect the wire downstream of the current source. The diagram implies that some of them are placed near the load, not the source, e.g. the alternator ANLs and the Starter Engaged Light fuse or FLW.
7. I don’t know what kind of landing lights draw only 5A of current and provide the kind of lighting capability that is required by the risk-averse philosophy implied in (3) above. Moreover, a 5A circuit breaker implies a 22 AWG wire going out to the landing lights, which could mean excessive voltage drop—or a nuisance trip on short final if a larger wire gauge is to be used but the circuit breaker is sized to be just adequate for the load.
8. The Starter Contactor is missing a diode across the coil, with the anode connected to ground and the cathode connected to the ‘S’ terminal. See Marc Ausman’s Aircraft Wiring Guide, p. 37, Section 5.3, or the upper right hand corner of Bob Knuckolls’ Figure Z-12.
9. I don’t understand why the design doesn’t follow Bob Knuckolls’ Figure Z-12 and the B&C instructions for the SB1B-14 regulator, which allow both the primary and backup alternators to be running at the same time, with the SB1B-14 deciding when it needs to pick up the load if the primary alternator output voltage drops too far.
10. I see no need for a diode in the feed to the GTN 650 XI bus, because there is only one thing feeding that bus. Diodes (preferably Schottky diodes, which have a different symbol from ordinary switching diodes) are used when there are two power sources for a single bus or load, and the diode is put in series with the backup source. In your diagram, the Avionics Relay is a backup for the Essential Relay for the Avionics/Essential Bus when both relays are on, which makes sense.
11. I don't see any provisions for ground power. You might want to make such a provision to get you through the avionics test and learning phases, even if you don't provide an external connector that would allow an external power source capable of cranking the engine to be plugged in. This could be important if you accidently leave something on that's connected to the Hot Battery Bus. Like, for example, the Hobbs meter, which appears to be powered straight off the battery, or the AV-30, or certain lights.
12. Thanks for sharing your diagram; it has been thought-provoking. I’m going to try to get together with a buddy who is building another RV and is a Garmin customer to see what other comments we might want to make.
 
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Thanks

CF86301,
Thank you for the thorough review of my wire diagram. I know that took some time on your part, but it's exactly the information I need.
I did post an updated diagram this morning which covers a couple things you mentioned. I will continue to update as I get smarter on the subject.
(I can't reply to your comments right now, but will add this place holder and get to it when I get some time.)
Thanks again.

1. The left display (PFD1) and other Garmin devices required for engine instruments during start are not on the Main Power Bus. Therefore, they will not be powered at all from ships battery during start with BAT/ESNTL switch in the BAT position and Avionics switch off. During start, with the STBY BATT for PFD 1 "on", these devices should be fully powered by STBY BATT 1 to enable all necessary engine gauges. The right display (PFD2) is on the Main Power Bus so it will also be powered for start (it may or may not brown out). I didn't really want PFD 2 on the main power bus but wanted to reduce amps from the Avionics/Essential Bus. After engine start, Avionics switch (and Pri Alt switch) will be placed on, and the b/u batt will no longer be providing power and go into charge mode.
(Note: I attached STBY Batteries wire diagram for review)
2. Good point. To clarify my diagram I need to show wire sizing used for each device to justify the C.B sizes listed. I have that information in other diagrams and will add when I get a chance.
3. The Hot Battery bus. Started simple enough. Primarily needed to free up some space on the main C.B. panel. First added a couple interior convenience lights, then thought it would be a good place for the AV-30, etc. It wasn't really designed for the requirement of landing at night with BATT/ESSNTL switch off as you interpreted. I know it kind of looks that way. If it gets to that point I'm having a really bad day, ..and yes as you mentioned, I will be using the Av-30 to keep the greasy side down and the IPAD to navigate. All the items on this bus will be controlled by Honeywell AML 34 rocker switches. (except the hobbs which, after further review, will probably need to move back to Main Power Bus). Yes. The devices on this bus will run the battery down if the switches are left on. That's what checklists are for, and hopefully I will see the Nav and landing Lts on during postflight. :)
4. Yes. CB sizes will be based on wire size. Wire size will be based on loads, length, etc. If it's close, I round up on wire size and down on CB size.
5. Yes. Other than the avionics, all devices will be controlled by Honeywell AML34 rocker switches. I will try and add a picture of my layout.
6. I moved the FLWs close to current source as you suggested. Some FLWs I removed and changed to CBs. Regarding ANL placements; I placed (not physically yet) the ANLs close to the contactors based on what I observed from the diagrams in the AeroElectric Connection. As an example, diagram Z-12 shows ANL placement for the Main Alt near the start contactor with note that states 6" or less. Also a reference to note 10 which says "consider installing a current limiter as close as possible to the starter contactor and wired per the Z-figures". I could be interpreting this incorrectly. My current design has the current limiters connected to the battery and start contactors using copper bars. This can be revised if needed.
7. I have 2 of these per wing. 14awg supply wires currently in place. Data sheet shows 1 amp/light. May have nuisance trips on the 5amp CB. https://flywat.com/products/7168501?_pos=1&_sid=bec4bb4e5&_ss=r
8. Updated diagram (post 61) to add diode...your pushing the limit of my autocad skills now. :) Those diodes come "pre-made" with the RV14. You just have to put them on the correct studs on the contactor. Mine are installed. Good catch!
9. My proposed setup of of leaving the Stby Alt switched OFF until needed seems to be getting mostly negative reviews. Most ask why not just have it switched on and ready to pick up the load in case of Pri Alt failure. Here's my thoughts (for the moment)..I'm flying along, I get a Low Volt CAS msg on the G3X display and my panel mounted annunciator light, I verify the low voltage, take a minute..maybe two, and see if there's an obvious reason it failed..smoke? circuit breaker panel glowing?..a thud and I see the Pri Alt belt across the leading edge of the wing?, etc, I check amp loading to verify within STBY Alt limits, if not maybe load shed..in my set up BATT/ESNTL switch to ESNTL would be the quickest way to accomplish that, and finally..PRI ALT/STBY ALT switch to STBY ALT - ON.
A couple things I'm not sure of: If system amp load is 25 amps (I'm guessing here), how much battery juice gets sucked out during my 1-2 minute troubleshooting. Will it cause too much initial load on the stby alt when I switch it on? I need to do the math on that...when I figure out how to do the math. :) I'm sure there are other negative issues that I'm not considering and I'd like to hear them. Probably some issues with having the Stby Alt activate automatically too though.
10. Regarding the diode. I wanted to have the GTN650 on it's own STBY Batt (STBY BATT 2). It has Com, Nav, GPS capabilities. It doesn't have b/u power input pins like some of the other garmin devices (see devices on STBY BATT 1), I opted to put it on its own bus and have the stby bat feed that bus. The IBBS does have a function, I think called "pass through power", that would possibly work. However, after an email with garmin, it seemed a better approach would be to feed the buss the GTN is on. Garmin had nothing to do with the design I arrived at, and I could have mis-interpreted their email, so further research is required before I go to production. Back to the diode you mentioned.. , the diode is there so STBY Batt 2 only powers the GTN650Xi. Probably giving me around 45 mins of power. Again, I could be missing the big picture here and would like to hear other opinions on this set up. (UPDATE 2/7/22: My interconnect wiring between STBY BATT 2 and the GTN650 is not correct. After consulting TCW, they have advised me of the preferred connection method. I will be updating my diagram and re-post when it is corrected.)
All this seems like I'm aiming for several layers of redundancy, that's not really my intention. I don't "plan" (most pilots don't) on flying in situations where there is no Plan B. However, I feel I need to design a system for that one night I make the decision to descend from VFR into a layer, lets say 4 thousand ft thick, and shoot an approach to my personal minimums. Halfway through the layer, the cabin starts filling with smoke (smells electrical). To me, the fastest way to possibly stop the smoke is switch alternator switch - off (with my setup that's one switch:)), and battery switch - off. At that point both my STBY Batts activate and I finish the approach. If smoke continues, STBY Bat 1 and 2 switches are switched off, and I'm left with AV-30 and Ipad. Wish me luck.
11. Current plan is to use this https://www.audioauthority.com/blog/16 I will need to decide which side of the battery contactor to make the connection. Seems like pros and cons to each option.
12.Thank you for your inputs!
STBY Batteries interconnect diagram attached below. REV 02/03/23 (REMOVED UNTIL DIAGRAM IS CORRECTED)
 
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Never enough light

My advice on landing lights is to have enough light on the runway to allow you to go around or stop before you run into the deer (or here in AZ, the javelina) lurking on the runway. I will always remember (until dementia sets in) doing night TO and landing practice at Montgomery County Airpark (KGAI) some years ago, and on my final landing, having a premonition that something bad might be about to happen. I taxied up Rwy 14 toward the turnoff v.e.r.y. s.l.o.w.l.y, and suddenly spotted a deer in the headlights not 30' in front of me through the crazed and scratchy C-172 windscreen. And farther up the runway, there were two or three more. Now that I'm over 65, I like to have double the lumens.
 
Changes

I'm attaching the latest drawings for my Primary Power System and Stby Batteries for review and suggestions. Nothing at this point has been mounted and no wires have been run so I can easily change plans if needed.
Here's some details for what prompted the changes shown in these updated drawings. This mostly deals with Stby Batt 2 interconnects with the GTN650. This GTN is GPS/Nav/Com.
The GTN650 does not have provisions/pins for a b/u power source like the garmin devices on Stby Batt 1. Garmin advised the GTN would need to be on its own bus with the Stby batt powering only that bus. My first drawings showed the GTN650 on its own bus with Stby Batt 2 powering that bus as Garmin recommend. However, after consulting with TCW I was told my plan would not work due to the setup of the IBBS Batt. I would need to use the "pass-thru" power connections [pins 6,7, 8] to allow the stby batt to operate properly.
I realize with this setup, the GTN is powered solely by the pass-thru and output wiring of the IBBS (three 20awg wires in parallel). The output wires are protected by a single 10amp mini fuse located on the enclosure of the stby battery (not accessible during flight).
The power draw (total all connectors) of the GTN650Xi published by Garmin is 2.65A Typical, 7.72A max. I placed the pass thru wires on a 7.5 cb off the Avionics/Essential Bus. My thought was I would prefer this CB to open before the 10A mini fuse located on the stby battery. That would allow possible reset if the 650 was absolutely needed and I felt the popped CB was a result of radio transmission. I could use com 2 for the remainder of that flight. The max current of 7.72A (probably during radio transmission) would possibly exceed the 7.5 cb, but maybe not enough to pop the CB. I may not find out for sure until test flights. If it does pop, and I would obviously need to re-think this configuration.

Attached, black boxes below, are the latest revisions of the Primary Power System and Stby Batteries drawings.
 

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Mudfly,

As a suggestion, you can save people a lot of time (and eye strain) by showing your design in a block diagram instead of the typical spaghetti chart. As you are looking for feedback on the design this approach may prove beneficial.

For that matter, carry over the block diagram to your POH. For pin to pin wiring documentation a standard Word document is far superior when it comes time for maintenance, modifications, panel updates and such.

But - some quick observations:
- You are using a current shunt on your standby alternator. Not needed - just use the same shunt as the primary. The other option is no shunt at all. You can verify load currents during testing. Buss voltage is your best indication of system health.
- You are using two backup batteries. Curious as to this decision. You could get better backup capacity using a second PC-680. This would simplify maintenance and provide redundancy options not available in your design (and be less expensive).
- Your “Essential” and Avionics” busses are (in practical terms) the same buss. Why add the complexity?
- A #10 wire feeding an always hot battery buss? Suggest you reconsider. If you must have an always hot buss, then the loads should be very minimal. I’ve never had an alway hot buss and never missed it. If you have smoke in the cockpit how do you isolate this 30 amp feed?
- In general it seems your wire gauge choices tend to be too big. Primary alternator output should be ~#6, standby alternator output ~#10, the feed to your primary buss at most should be #10, etc.

I’d guess your panel, with everything on other than pitot heat and landing lights will draw less than 15 amps steady state.

Carl
 
Mudfly,

As a suggestion, you can save people a lot of time (and eye strain) by showing your design in a block diagram instead of the typical spaghetti chart. As you are looking for feedback on the design this approach may prove beneficial.

For that matter, carry over the block diagram to your POH. For pin to pin wiring documentation a standard Word document is far superior when it comes time for maintenance, modifications, panel updates and such.

But - some quick observations:
- You are using a current shunt on your standby alternator. Not needed - just use the same shunt as the primary. The other option is no shunt at all. You can verify load currents during testing. Buss voltage is your best indication of system health.
- You are using two backup batteries. Curious as to this decision. You could get better backup capacity using a second PC-680. This would simplify maintenance and provide redundancy options not available in your design (and be less expensive).
- Your “Essential” and Avionics” busses are (in practical terms) the same buss. Why add the complexity?
- A #10 wire feeding an always hot battery buss? Suggest you reconsider. If you must have an always hot buss, then the loads should be very minimal. I’ve never had an alway hot buss and never missed it. If you have smoke in the cockpit how do you isolate this 30 amp feed?
- In general it seems your wire gauge choices tend to be too big. Primary alternator output should be ~#6, standby alternator output ~#10, the feed to your primary buss at most should be #10, etc.

I’d guess your panel, with everything on other than pitot heat and landing lights will draw less than 15 amps steady state.

Carl

Thanks for your observations Carl!
I only have a minute so can't comment on all right now. However. the one that caught my eye was; "If you have smoke in the cockpit how do you isolate this 30 amp feed?") That's a good question:)
It finally dawned on me that there could be a issue with the fuse holder itself that could cause smoke/fumes, but not enough to blow 30A current limiter. There would be no way to stop it.
I may not be able to get rid of my Hot Bat Bus altogether, but will definitely look real hard at moving it to fwd side of firewall. Also, I will probably remove the move landing and nav lights and put them on the main power bus. I was trying to keep my main power bus CB panel at 25 CBs so I would have a 5x5 setup. Seemed easier and cleaner when installing copper bus strips. I will cross that bridge later.
Thanks again!

Feb 17 reply:
Carl, Thanks for your suggestions. Sorry for the spaghetti charts. Right now that's the easiest/fastest way for me to plan the primary power system. I do have all the other sub-systems in block diagrams using ExpressSCH. Unfortunately, I switched mid-stream to Autocad because my daughter and neighbor are users and they got me hooked. I'm using Autocad LT and, after some practice, I find it much easier than ExpresssSCH.
My replies to your observations:
* Current shunt on stby alternator - It looks like, in my setup..and I could be incorrect, if I only use one shunt for both alternators the shunt would also act as a butt splice. My Pri Alt goes to the output side of the bat contactor, and the Stby Alt goes to the input side. If I switched to a Hall Effect Sensor, looks like I could run both alternator b-leads through one sensor. Maybe not a bad idea.

* Two backup batteries. No good answer there. It's just the path I started down a few years ago when I started planning the electrical system. I bought equipment, had panel cut and labeled based on that planning. Regarding two b/u batts.. I researched on what I might want on b/u batts. It came down to; (1)staying upright, (2)navigation with approach capabilities, and (3)talking to ATC. Stayin upright is covered by the garmin displays (with req'd LRUs) and further by the AV-30. This equipment is powered by stby batt1. Navigation and approach capabilities and talking to ATC is covered by the GT650Xi. This is powered by stby batt 2. The stby batts will also play a part in ground ops; atis, clnc, and keep alive during start requirements. Quick flight scenario: pri alt fails, stby alt will be switched on "manually" (load shed if necessary to reduce amps by switching pwr switch to esntl) and land as soon as practical. Long shot, but now stby alt fails- pwr switch to essntl, and equipment continues to operate until volts drop low enough to automatically activate stby batts 1 and 2. Now should should have another hour at least but, (dark stormy night) would land as soon as possible. Also, for smoke/fire/fume issue (suspected electrical)- I would switch batt switch and alternator switch to off positions. Stby batts 1 and 2 will come online. If smoke/fire/fumes continues, stby bat 1 and 2 switches - off. I'm on Av-30 and Ipad at this point.

* Essential and avionics busses - Essential not really essential. Combined to match switchology. My main power switch is Batt On/Off/Esntl On(On-Off-On). Avionics switch used to secure some equipment during start..although some will be operating on stby batt power. Esntl can be used for ground ops, but mainly for quick load shedding of main power bus if required for stby alt, or no alt operations. Can also be used for smoke/fire/fumes discussed above. Also, Avionics/Essential bus is dual fed and, if needed can be fed by stby alt with main bus secured.

*A #10 wire feeding an always hot battery buss?- Thanks to your review of my diagram I have, for the most part, removed the hot battery bus.

* Large wire gauge choices - Again, you are probably correct. I will review my wire sizes and adjust accordingly.
Please feel free to keep the suggestions coming.
Thanks again for your help!
 
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Updated Diagram (sorry Carl, it's still an eye test)

In todays episode of my Primary Power System design I have moved the Hot
Battery Bus FWF, and created the new Main Power Bus B (it's actually the old
HBB).
My question is the power feed to the new Main Power Bus B.
(Wire length approx. 2.5 ft from MPBA to MPBB)
The attached drawing shows it fed from MPBA through a 10A CB and 18AWG wire. Is this acceptable or would direct run to battery contactor
be preferred? Currently, there will be approx. 7.5A on MPBB.
The main reason for MPBB is to reduce CBs on
MPBA. I would prefer to keep the CB number on MPBA and Avionics/
Essential Busses combined to 25. Just seems easier/cleaner for 5x5 rows of
copper bus bars.
I'm still deciding on the wire protection for the HBB now located FWF. I only
plan on two items on that bus. Right now I'm leaning towards using some
type of in-line fuse holders. Plan B would be mounting a four place
fuse holder.
Sorry for the spaghetti chart and small print. I know it's hard on the eyes. It's just the quickest way for me right now to do this planning.
Attached below is Main Power System Diagram Feb 17
Thanks
 

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Thanks Dan, I think the group needed a break from my eye charts anyway. I'm heading out to work for days so wont be able to post my "daily updates". I probably could use a few days to gather my thoughts:). Feel free to pick up my slack.
I'll have to look for your post. I'll probably learn something.
Shawn
 
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RV-10 Electrical and Avionics Diagrams

Long time lurker, first time poster. I'm about halfway through my RV-10 build and I'm finalizing the electrical and avionics schematics so I'd appreciate any comments or feedback.

Below are links to the avionics bus architecture, the schematic, and an electrical block diagram. For the electrical architecture, in addition to doing a ton of reading and research, I analyzed the following examples:
  • Aeroelectric Z-11, Z-12, Z-13/8, Z-14, Z-101, etc.
  • Cirrus SR20, SR22 (Perspective and non-Perspective)
  • Cessna 172/182 w/G1000 cockpit
  • Beech G36
  • Diamond DA 40, 50
  • Piper PA-28

I selected a dual-battery / dual alternator architecture (essentially Z-14) as the best trade-off for fault tolerance, and reliability for me. I think I've read every VAF post on electrical architecture so I'm not interested in defending this choice but I'd be happy to answer questions on my specific design. Yes, there are simpler architectures but I do a fair amount of aerospace systems design at my day job (including design for fault tolerance) so I find this interesting. I placed certain LRUs on both buses and kept others on separate buses to distribute the load between buses and minimize the effects of rare events like a bus short or an over-voltage scenario. I plan to do a fair amount of flying in IMC so this design meets my personal comfort level. I'm particularly interested in any errors with the G3X system wiring as well as any design issues with the power system.

Thanks in advance,
-Bob Watzlavick
 

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Some more details on the design:
  1. I chose the Monkworkz MZ-30L as the aux alternator because the B&C vacuum pad alternator likely won't do much at idle. My load analysis shows night idle with either A/C or pitot heat on as the most stressing condition.
  2. I'm using a Surefly SIM-6L on the left side and a regular magneto on the right side. I didn't want any hot battery runs across the spar in a forced landing so I'm dual-feeding the Surefly via separate rear-mounted relays and diodes from each bus. I really wanted to go with a PMAG but the Surefly doesn't require annual removal, doesn't require cooling, has a PLD vs. hand coded software, and has significantly more testing per DO-160. I'm sure the PMAG would have worked, I just chose the Surefly for now. I'm not interested in tweaking ignition timing just yet.
  3. Since I have two identical main batteries, I didn't see a need to add any TCW style backup batteries. The loss of either the main or aux bus (even if shorted) won't prevent continued flight and at least one display (PFD or G5) will be available to the pilot. For a smoke-in-the-cockpit scenario, turn off both masters and the G5 will run on its battery. For an alternator failure, close the crossfeed and load shed as needed when time permits.
  4. I'm still working on the panel lighting, I'm leaning toward FCOB LED strips for the backlit panels. I had originally planned to use EL backlights but the FCOB strips have a very high density so with proper placement, they look really good behind an engraved plastic overlay. You just have to arrange the text and artwork to be over the center of the LED strips.
  5. The A/C system is from South Florida Sport Aviation. The selling point for me was the easy integration with the overhead console and interior.
  6. Landing and Nav/Strobe lights are from from Flyleds
  7. I've cut my fingers too many times on tabbed connectors so there are none on my airplane. For grounding, I'm using mil-style terminal junction blocks mounted to a copper ground bar which is then redundantly grounded to the firewall.
  8. I'm using the airframe for the battery returns but otherwise, all LRUs will have power returns back to the ground block.
  9. The main and aux bus feeds are each sourced back from their respective battery to minimize the chance of brownout during engine start. If that doesn't work out, I'll take advantage of the GAD 27 voltage stabilizer. Each of those bus runs has a MIDI fuse on it to protect the long fat run from the rear. The EarthX batteries provide short circuit protection but it will attempt to re-enable itself a few minutes later which I didn't like. I spent a lot of time comparing trip curves of various fuses/breakers and found some interesting observations. The Cirrus forums had a few posts where both an LRU breaker and the associated upstream bus feeder fuse both tripped. After overlaying the range of trip curves of CBs vs. the MIDI fuses they use, it's clear that you need a much higher MIDI fuse for a given downstream breaker size if you don't want the published curves to overlap. I believe the SR22 has a design error with their bus feeder fuses.
  10. I chose the ETX900-VNT for both weight and the protection capabilities of the BMS. I would have no problem recharging one of them (to 100%) and then taking off after a complete discharge because the BMS shuts off the battery before damage. I don't buy the arguments about "I want my battery to give up it's life so I can have 5 more minutes" because you probably got more usable A-h out of the EarthX anyway and you can reuse it after a deep discharge. Yes, the BMS can in rare cases decide to disconnect itself, but the probability of both of them doing that in the same flight is very low, especially if the crossfeed is open.
  11. For O2, I'm provisioning for 2 Inogen G5 oxygen concentrators, if I can find them used, it will be less than half the cost of an installed MH system and provide unlimited O2 up to reasonable altitudes.

-Bob
 
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Long time lurker, first time poster. I'm about halfway through my RV-10 build and I'm finalizing the electrical and avionics schematics so I'd appreciate any comments or feedback.

Some quick questions (not criticisms of your choices) =

- Why the amplocs on the battery side of the masters vs alt side/what is your intended primary use for these indications?
- It appears your crossfeed is intended to always be always closed vs only for upset conditions? If always closed, I would think it would be a candidate for diodes (though I'm not always a fan/prefer more isolation options)
- Kind of related to the above, why the back-up gen tied into the opposite bus from the primary alt? Is it intended to be redundant power vs back-up power?

Some quick thoughts/questions,
 
Some quick thoughts.

What are you POH Emergency Action for “smoke in the cabin” - as in an electrical fault? After you take those actions what is left with power on the panel?

I note your Cross Feed Solenoid seems to be “normally shut” for standard operations. As such, the MonkWorz generator, in backup mode, will provide power to both of your busses. More than enough capacity to do everything you need. But - if your electrical fault is on the buss being feed by that generator you have no way of isolating it from the buss. The MonkWorz can be turned on/off with a switch, but you have that control connected to your Aux Battery master solenoid switch. I suggest a separate on/off switches for the MonkWorz and Aux Battery as a better option.

The #4 wire to your the top buss I overkill.

Before you put that big honker ground jumper in, ask RV builders that have this how often it has been used to jump the battery. While having a “shore power” connection is great for hangar flying and to top off a battery if needed, it can also be used to charge the battery(s) if you run them flat. This is the preferred option for flat battery(s) as doing a jump start then launching with at damaged or at least depleted battery is perhaps an unnecessary risk, especially as you have a ship power depended ignition. I use a #14 jumper wire from the panel and a 30 amp regulated power supply for hangar flying.

Carl
 
Some quick questions (not criticisms of your choices) =

- Why the amplocs on the battery side of the masters vs alt side/what is your intended primary use for these indications?
- It appears your crossfeed is intended to always be always closed vs only for upset conditions? If always closed, I would think it would be a candidate for diodes (though I'm not always a fan/prefer more isolation options)
- Kind of related to the above, why the back-up gen tied into the opposite bus from the primary alt? Is it intended to be redundant power vs back-up power?

Some quick thoughts/questions,

I thought it would be interesting to see batt charge/discharge as well as alternator charge and the GEA 24 has enough inputs for all 4 sensors. It will over-range during start but shouldn't damage the sensor.

The crossfeed is intended to be open unless: 1) if the main batt is low during start, and 2) loss of an alternator in flight. The LRUs are distributed across the buses so that there is sufficient equipment on either single bus for continued flight. But with appropriate load shedding, you can tie the two buses together and keep most of the equipment running.

I'm not a big fan of diode fed buses in general. Per-component is fine but the worst case scenario is a shorted diode so you have to be willing to lose that component. For example, if one of the diodes powering my Surefly fails shorted, you could end up feeding the opposite bus through that shorted diode which would likely blow both fuses one at a time, removing power from the Surefly (which is why I'm keeping a regular mag). A mitigation is to use 2 diodes in series but then you have double the failure chances of an open diode. And it makes it harder to test whether you have a latent failure of one of the two diodes. I'm told the spacecraft guys use a 4-diode arrangement, 2 in series and 2 in parallel. But in general, the shorted diode failure mode mentioned above is what led me away from the simpler architectures. Z-14 is fairly simple in concept and in my opinion easier to analyze for fault tolerance because there are fewer sneak paths.

-Bob
 
Some quick thoughts.

What are you POH Emergency Action for “smoke in the cabin” - as in an electrical fault? After you take those actions what is left with power on the panel?

I note your Cross Feed Solenoid seems to be “normally shut” for standard operations. As such, the MonkWorz generator, in backup mode, will provide power to both of your busses. More than enough capacity to do everything you need. But - if your electrical fault is on the buss being feed by that generator you have no way of isolating it from the buss. The MonkWorz can be turned on/off with a switch, but you have that control connected to your Aux Battery master solenoid switch. I suggest a separate on/off switches for the MonkWorz and Aux Battery as a better option.

The #4 wire to your the top buss I overkill.

Before you put that big honker ground jumper in, ask RV builders that have this how often it has been used to jump the battery. While having a “shore power” connection is great for hangar flying and to top off a battery if needed, it can also be used to charge the battery(s) if you run them flat. This is the preferred option for flat battery(s) as doing a jump start then launching with at damaged or at least depleted battery is perhaps an unnecessary risk, especially as you have a ship power depended ignition. I use a #14 jumper wire from the panel and a 30 amp regulated power supply for hangar flying.

Carl

POH action for smoke in the cockpit will be to turn off both master switches, the G5 and the Surefly will stay running. Having a backup battery bus doesn't protect against smoke as an LRU on the backup bus is equally likely to let the smoke out.

The crossfeed is intended to be open by default - I'll check the schematic, maybe there is a mistake there.

The #4 wire to the top bus is to keep the 100A MIDI fuse on the main bus feeder from tripping before the 20A CB for pitot heat. I forgot to update the block diagram to show the feeder fuses but the detailed schematic shows them. If I ditch the bus feeder fuses, I agree a smaller gauge would be acceptable.

I've already installed the ground power connector so I'm stuck with that. The normal use case is running the avionics and charging the battery but it is also sized for a rare case if I needed a jump start. I tend to agree that is a bad idea as the alternators will be stressed for a while afterwards. Charging the battery to 100% from a GPU would definitely be preferred. But the run is short enough (1 foot) so there's no disadvantage of keeping the fat wire. And lots of FBOs will have that style of GPU connector.

-Bob
 
POH action for smoke in the cockpit will be to turn off both master switches, the G5 and the Surefly will stay running. Having a backup battery bus doesn't protect against smoke as an LRU on the backup bus is equally likely to let the smoke out.SNIP

I assume the G5 stays running on its backup battery - correct?

Where does the SureFly get power after you open both masters? I could not find the feed on your diagrams.

Yep - backup batteries feeding the same buss is an Achilles Heel.

Carl
 
I assume the G5 stays running on its backup battery - correct?

Where does the SureFly get power after you open both masters? I could not find the feed on your diagrams.

Yep - backup batteries feeding the same buss is an Achilles Heel.

Carl

I'm using the battery backup option on the G5. The details of the Surefly are only on the detailed diagram (I forgot to update the block diagram) but it has direct battery connections through relays and diodes.

Just to clarify about the crossfeed behavior - it is intended to be open during normal operation so each bus is fed by the alternator and battery on that side. Even though the PFD, MFD and G5 have dual power inputs, I placed the PFD on the aux bus, the MFD on the main bus, and the G5 on the main bus. The associated AHRS units are also paired that way. That provides protection against something crazy on a bus (overvoltage that isn't mitigated) and still gives the pilot one display (either the PFD or G5). The radios are similar with the GTN 750Xi (COM1) on the main bus and the GTR 20 (COM 2) on the aux bus. The GMA 245 audio panel is on the aux bus so if the aux bus goes down, the failsafe audio pass-thru capability will still keep COM 1 alive for the pilot only. Same with trim and A/P power - they're on separate buses intentionally. In normal operation, the GSA 28 servos provide trim power but if you lose the A/P, then you still have manual trim from the other bus. The complete loss of a bus due to a short would be very unlikely but with a bit of judicious assignment of LRUs to buses, you can improve the capability to the pilot.

For the smoke-in-the-cockpit scenario where all I have left is the G5 (and Surefly), I'll have the iPad and handheld radio to get me out of IMC.

-Bob
 
I thought it would be interesting to see batt charge/discharge as well as alternator charge and the GEA 24 has enough inputs for all 4 sensors. It will over-range during start but shouldn't damage the sensor.

The crossfeed is intended to be open unless: 1) if the main batt is low during start, and 2) loss of an alternator in flight. The LRUs are distributed across the buses so that there is sufficient equipment on either single bus for continued flight. But with appropriate load shedding, you can tie the two buses together and keep most of the equipment running.

I'm not a big fan of diode fed buses in general. Per-component is fine but the worst case scenario is a shorted diode so you have to be willing to lose that component. For example, if one of the diodes powering my Surefly fails shorted, you could end up feeding the opposite bus through that shorted diode which would likely blow both fuses one at a time, removing power from the Surefly (which is why I'm keeping a regular mag). A mitigation is to use 2 diodes in series but then you have double the failure chances of an open diode. And it makes it harder to test whether you have a latent failure of one of the two diodes. I'm told the spacecraft guys use a 4-diode arrangement, 2 in series and 2 in parallel. But in general, the shorted diode failure mode mentioned above is what led me away from the simpler architectures. Z-14 is fairly simple in concept and in my opinion easier to analyze for fault tolerance because there are fewer sneak paths.

-Bob
You're only depicting three amplocs vs four mentioned. I'm not a fan of Diodes either where they can be avoided.

OK. If the crossfeed is NO, the MWz is a redundant generator vs. a back-up per your schematic. Your build, your choice.

I would at least consider the following:

Place your most critical 30 amps on the top bus, everything else on the bottom bus; dual LRU feeds remain the same. Tie the MWz directly to "other" side of the crossfeed (primary alt side). I'd personally choose the lower V, back-up setting on the MWz controller but if not, it can be pilot controlled like a back-up regardless of V setting. The crossfeed then has a lower criticality. The expensive and relatively short-lifed G3 backup battery is not required IMO with three wattage sources available (crossfeed being NO).

You'll have enough electrical system health monitoring to safely determine any threats to the top bus.

Once again; your build, choice.
 
You're only depicting three amplocs vs four mentioned. I'm not a fan of Diodes either where they can be avoided.

OK. If the crossfeed is NO, the MWz is a redundant generator vs. a back-up per your schematic. Your build, your choice.

I would at least consider the following:

Place your most critical 30 amps on the top bus, everything else on the bottom bus; dual LRU feeds remain the same. Tie the MWz directly to "other" side of the crossfeed (primary alt side). I'd personally choose the lower V, back-up setting on the MWz controller but if not, it can be pilot controlled like a back-up regardless of V setting. The crossfeed then has a lower criticality. The expensive and relatively short-lifed G3 backup battery is not required IMO with three wattage sources available (crossfeed being NO).

You'll have enough electrical system health monitoring to safely determine any threats to the top bus.

Once again; your build, choice.

I appreciate the feedback and suggestions. The MZ-30L has a voltage output proportional to current so another Amploc isn't neeed. The MZ-30L is intended to be a full-time power source for the aux bus, not just for backup.

-Bob
 
Limo and shunt/Amploc

I appreciate the feedback and suggestions. The MZ-30L has a voltage output proportional to current so another Amploc isn't neeed. The MZ-30L is intended to be a full-time power source for the aux bus, not just for backup.

-Bob

I’m traveling and all I have is a IPhone so a little difficult to read the prints. It appears you are not using Limo plugs? Love mine.

I’ve always used shunts to since current and appear more robust than a Amploc but my experience is limited to 3 airframes. Any input on users that are more experienced than me? The Amplocs just seem to be a “weak design”.
 
Nice 1st post

Very nicely drawn, and clearly a lot of thought here.

Some more details on the design:
  1. I chose the Monkworkz MZ-30L as the aux alternator because the B&C vacuum pad alternator likely won't do much at idle. My load analysis shows night idle with either A/C or pitot heat on as the most stressing condition.

My setup is very close to yours, except I did the vacuum pad alternator for Bus 2. You are right, doesn't really give you enough amps, even loading Bus 1 with the big draws, I only have a few amps to play with at 1000 RPM on BUS 2. The challenge was the night taxi (No A/C), and I did have to move a few CBs around to avoid using the bus tie at night, or pulling the battery down a bit. (I like independent). That now resolved, I really like flying it and its nice and simple to explain to pilots new to the plane.

I also think that in most cases, I would not bus tie. Certainly you will be in no rush to make the decision what to do next since you have a very flyable set of screens and radios even if one side has failed with G5 / MFD combo or the PFD / G5 (on Battery).

I like the distribution of devices on Bus 1 and 2 and don't see any cross failures. e.g Audio Panel is on Bus 2, and its failsafe to COM 1 which is on Bus 1. GAD29 on same buss as GTN, etc. I like that critical items are powered from one bus only.

You did however connect the GTN serial to the PFD which is Bus 2, not sure what you lose if you fail the PFD and the GTN is only talking to the G3X system through the GAD29 in the scenario where Bus 2 is failed. I'd consider running the GTN serials through the MFD to avoid finding out.

I'll echo the ground power comments. I just put two SAE connectors connected with an inline fuse to the batteries on the baggage firewall. Gives me a path to send enough amps to get me going in an hour or so, and a convenient way to power hangar testing time.

Derek
 
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I’m traveling and all I have is a IPhone so a little difficult to read the prints. It appears you are not using Limo plugs? Love mine.

I’ve always used shunts to since current and appear more robust than a Amploc but my experience is limited to 3 airframes. Any input on users that are more experienced than me? The Amplocs just seem to be a “weak design”.

Support the wires and they do fine and they are lighter. Sample set of 2, problem free 30 year old installs. Shunts have more connections, and need fusible links or fuses. I suspect as a system they are pretty close from a reliability perspective.

Derek
 
You did however connect the GTN serial to the PFD which is Bus 2, not sure what you lose if you fail the PFD and the GTN is only talking to the G3X system through the GAD29 in the scenario where Bus 2 is failed. I'd consider running the GTN serials through the MFD to avoid finding out.

Derek

Thanks for noticing the GTN to PFD connection, I hadn't considered what would happen there if I lose the PFD. My notes say MAPMX2 provides position, altitude, velocity, navigation, and radio tuning from the GTN to a GDU and G5. I think all of that except for the radio also goes over the A429 bus but I'm not 100% sure. CONNEXT2 is used for flight plan transfer to/from the GDU so I'd lose that if the PFD were to fail. But, if I wire it to the MFD and it goes down, then I'm in the same situation. If I'm on an IFR flight plan, I'd have to load approaches on the GTN anyway so I don't see a big loss there, other than that the GDU supposedly stores the waypoints in an approach if you lose the GTN. I've done some limited bench integration of the PFD, MFD, GAD 27, and GEA 24 but I haven't done any prototyping with the GTN yet. Figuring out these kinds of issues is part of the fun for me.

This might be a good question for G3Xpert - is it better to connect the GTN MAPMX2 and CONNEXT2 to the PFD or MFD and why? The G3X manual says to connect MAPMX to the PFD or MFD but to connect CONNEXT to PFD1 only.

-Bob
 
… The #4 wire to the top bus is to keep the 100A MIDI fuse on the main bus feeder from tripping before the 20A CB for pitot heat. I forgot to update the block diagram to show the feeder fuses but the detailed schematic shows them. If I ditch the bus feeder fuses, I agree a smaller gauge would be acceptable…

-Bob

My thoughts:
  • If you’re saying 4 awg is required because of the 100A fuse I would say that is not true.
    • The feeder only needs to be large enough it will not overheat when everything on the bus is turned on and that’s gonna be less than the 54A 10C rise rating of a 6 awg wire and that 54A number is conservative.
    • Also witness if a 4 awg wire was protected by a fuselink it would be 8 awg which melts at 473A.
    • Another example is the commonly used 6 awg B lead from a 60A alternator. The 6 awg wire is rated 54A by the 10C rise criteria but this is conservative and once the alternator is hot it won’t deliver much over 60A. The B lead and battery are protected by an ANL current limiter (located as close to the contactor as possible) placarded 60A. This current limiter opens at maybe 120A.
  • I mention 6 awg because it is Bob Nuckolls’ minimum size suggestion for Fat wires.
  • I collect quotes from the Aeroelectric List:
 
My thoughts:
  • If you’re saying 4 awg is required because of the 100A fuse I would say that is not true.
    • The feeder only needs to be large enough it will not overheat when everything on the bus is turned on and that’s gonna be less than the 54A 10C rise rating of a 6 awg wire and that 54A number is conservative.
    • Also witness if a 4 awg wire was protected by a fuselink it would be 8 awg which melts at 473A.
    • Another example is the commonly used 6 awg B lead from a 60A alternator. The 6 awg wire is rated 54A by the 10C rise criteria but this is conservative and once the alternator is hot it won’t deliver much over 60A. The B lead and battery are protected by an ANL current limiter (located as close to the contactor as possible) placarded 60A. This current limiter opens at maybe 120A.
  • I mention 6 awg because it is Bob Nuckolls’ minimum size suggestion for Fat wires.
  • I collect quotes from the Aeroelectric List:

John - Thanks for your comments. I need to look more closely at the temperature rise vs. trip curve to see what is a reasonable wire size. Here is a transient wire heating calculator that I used to compare the temperature rise vs. the worst-case trip time for the bus feeders:
https://watzlavick.com/robert/rv10/electrical/Transient_Wire_Heating_Calculator.xls

Here's a spreadsheet I created that shows my attempt to compare the various trip curves of common fuses and circuit breakers:
http://watzlavick.com/robert/rv10/electrical/CB-Fuse.xls
It does not take into account temperature effects but at nominal conditions, I had to bump up the rating of a MIDI fuse to 100 A to keep it from overlapping with only a 20 A Klixon 7277 CB. At low fuse ratings, say a 50 A MIDI, there is significant overlap between the 50 A fuse and 20 A CB so you risk blowing the bus feeder before the 20 A fuse trips. This shows why CBs and fuses in series is a bad idea in general and why I think the Cirrus SR22 has a design error - they use 50 A MIDI feeder fuses for 20 A CBs. I read a few reports where both an LRU CB tripped and the associated upstream bus feeder fuse blew and took down the whole bus. If I was willing to spend the $ for a Klixon 6752 CB, then I would only need a 50 A CB because the CBs are matched to each other (typically it's ok to put them in series if the upstream CB has 2X the rating). Then I could use a smaller wire for the bus feeders.

I've been back and forth on the need for bus feeder protection. I've read the same Aeroelectric threads you mention but I have to disagree that TC aircraft don't normally have it. That may have been the case in the past but all the modern designs I reviewed (C172 G1000, DA-40, SR22, Beech G36, PA-28) have some sort of protection between the power sources and buses, typically a large fuse or CB. The question is whether it's worth it and what does it protect against. I came across an FAA paper where they looked at the effectiveness of arc fault vs. traditional CBs. They discovered "ticking faults" that tend to cause fires don't necessarily trip traditional CBs. The EarthX battery has short-circuit current protection in it (as shown in my spreadsheet) but it will re-attempt the connection in a few minutes. If I've crashed and the BMS disconnected the battery due to a hard short, the last thing I want is to "try it again" every few minutes. I'm not 100% committed on the bus feeder fuses but it does protect against hard shorts that don't easily clear with burning away the material. I would also agree that good construction practices can minimize the chances of that kind of fault.

Speaking of reliability, all this electrical stuff is interesting but a more likely scenario in my opinion is a common software fault in the displays or AHRS that takes everything down (ref. Ariane 5 first launch). Airliners have had entire cockpits go dark and I've personally debugged similar issues in an avionics lab where "never supposed to happen" faults still occurred. The G5 is supposed to be independently coded so that mitigates the risk somewhat.

-Bob
 
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I double-checked my numbers and I believe my bus feeder wire sizes are correct, if my fuse chart and wire heating calculator are also correct. For a bus with a maximum Klixon 7277 rating of 20 A, if you want to use a MIDI fuse to protect it upstream, then that fuse needs to be at least 100 A to guarantee the min/max trip curves don't overlap and the CB trips first. Then, if you have a 100 A MIDI fuse, the associated wire size needs to be 4 AWG or larger. The steady-state load requirement is much smaller, it's the fuse opening time that dominates. For example, if there is a 200% load on the wire due to a hard short, the Littelfuse datasheet says a 100 A MIDI fuse will open between 3 and 100 seconds (that's a huge variability). Using transient wire heating analysis with 6 AWG, 200 A, a starting temp of 41 degC (a hot day), and 150 degC wire, the wire will reach max temp in 78 seconds. At 100 seconds (the worst case fuse opening time), the wire will reach 189 degC. Note that this transient analysis assumes no heat transfer so it is more conservative as the time increases. So assuming this is the protection scheme, 4 AWG is required. For a 15 foot run, the weight difference between 4 AWG and 6 AWG is 0.9 lb, not insignificant.

You could argue that within with 60 seconds or so, you'd surely notice the sag in bus voltage but if I'm in IMC, I don't want to be in a rush to do anything related to reconfiguring the electrical system.

Throwing a bit of money at it, a large CB instead of the MIDI fuse allows a more reasonable feeder size. Assuming 100% output from a 60 A alternator, AC.43.13-1B suggests AWG 6. A Klixon 6752-100-80 ($250) will provide plenty of trip margin for the downstream 20 A CB. The CB is 0.25 lb so the weight delta is Is 0.65 pounds. Is that worth $250? Maybe, will have to think about that.

-Bob
 
I've been back and forth on the need for bus feeder protection.
-Bob

Bob,

I'll wade in with my layout based decision and thinking.

I opted against bus feeder protection on the primary bus since I needed to run the #2 for the starter unprotected the length of the airplane anyway, which has basically the same mechanical exposure the #4 will have, and similar impacts should it decide to ground on something.

Then I fed the Bus 1 off the live side of the starter contactor, and saved one thick wire from the back to the front. ( I assume here both your batteries are in the back). I still put the feeder protection on BUS2, which is admittedly not entirely consistent thinking but it made me feel better. (I also use the feeder protection to act as the fuse for an alternator short on bus2, so didn't actually add component count which helped me justify it )

Derek
 
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Bob,

I'll wade in with my layout based decision and thinking.

I opted against bus feeder protection on the primary bus since I needed to run the #2 for the starter unprotected the length of the airplane anyway, which has basically the same mechanical exposure the #4 will have, and similar impacts should it decide to ground on something.

Then I fed the Bus 1 off the live side of the starter contactor, and saved one thick wire from the back to the front. ( I assume here both your batteries are in the back). I still put the feeder protection on BUS2, which is admittedly not entirely consistent thinking but it made me feel better. (I also use the feeder protection to act as the fuse for an alternator short on bus2, so didn't actually add component count which helped me justify it )

Derek

That's a really good point and exactly why I wanted to post the design for comments. After staring at the diagrams for long enough, I tend to get confirmation bias and overlook things like that. Yeah, why bother to protect the feeder when the starter wire is also unprotected. You could mitigate that by placing the starter contactor near the batteries in the back. The DA 40 has a rear main battery and I think the starter contact is nearby but I can't tell for sure from the diagram. All the other aircraft I looked at had their batteries on the firewall so I guess it made sense to protect the feeders. Somehow I feel there is a higher chance of a short behind the panel than on the firewall just because there's more "stuff" going on behind the panel. Good wire support and separation should help.

I wanted to run the main bus feeder from the rear to try and keep the avionics on the main bus up during engine start. I did a voltage drop analysis between the battery and starter and if you assume each of the 11 joints is 2.5 milliohms plus the 2 AWG wire, the voltage drop at 200 A is 7.7V. That's only 6.3 V at the starter with a 14 V battery so that doesn't seem correct. I assumed the ETX900 had an internal resistance of 4 milliohms but that's a WAG.

For your bus 2 protection, is it located on the engine side of the firewall or behind the panel near the bus?

-Bob
 
I wanted to run the main bus feeder from the rear to try and keep the avionics on the main bus up during engine start. I did a voltage drop analysis between the battery and starter and if you assume each of the 11 joints is 2.5 milliohms plus the 2 AWG wire, the voltage drop at 200 A is 7.7V. That's only 6.3 V at the starter with a 14 V battery so that doesn't seem correct. I assumed the ETX900 had an internal resistance of 4 milliohms but that's a WAG.

-Bob

It's pretty hard to keep the voltage over 9 even with the battery on the firewall. The EarthX has a pretty low internal resistance, so might be possible but i never ran the math. I put the GAD27 on bus1 only and used its keep alive to address the sag.


For your bus 2 protection, is it located on the engine side of the firewall or behind the panel near the bus?

-Bob

It's at the back close to the battery since the battery is the source of the big amps.
 
… Note that this transient analysis assumes no heat transfer so it is more conservative as the time increases…

-Bob

I'll practice my amateur spec reading skills and hope I get it right.

Have a look at MIL-W-5088 (I found rev L on everyspec), Wiring, Aerospace Vehicle, Figure 3 about free air current rating of a single copper wire (it consists of two pages and is deep in the document after Paragraph 6 and before Appendix A). Paragraph 6.7.1.a explains how to use Figure 3.

For example, let's say we're on the ground on a hot day. 6 awg copper wire with 150C insulation, environment is 40C, wire is rated 147A.

Then we go to FL200 and keep the cabin at 25C. Figure 5 speaks to altitude derating. Now the rating is 156 x 0.907 = 141A.

So we see how conservative the 10C rise rating of 54A is. It tends to keep us out of trouble with voltage drop though.
.
 
I'll practice my amateur spec reading skills and hope I get it right.

Have a look at MIL-W-5088 (I found rev L on everyspec), Wiring, Aerospace Vehicle, Figure 3 about free air current rating of a single copper wire (it consists of two pages and is deep in the document after Paragraph 6 and before Appendix A). Paragraph 6.7.1.a explains how to use Figure 3.

For example, let's say we're on the ground on a hot day. 6 awg copper wire with 150C insulation, environment is 40C, wire is rated 147A.

Then we go to FL200 and keep the cabin at 25C. Figure 5 speaks to altitude derating. Now the rating is 156 x 0.907 = 141A.

So we see how conservative the 10C rise rating of 54A is. It tends to keep us out of trouble with voltage drop though.
.

Good discussion. I agree with your assertion that in free air, a 6 AWG wire rated at 150 degC could carry 147 A given a 40 degC environment. About half of my run will be in Van's corrugated conduit so some derating would need to be applied. Table 11-9 in AC 43.13-1B says "in bundles, groups, harnesses, or conduits" but I'm interested in a single wire in a conduit so I think that table is a bit too conservative. The ABYC Ampacity rating table, http://assets.bluesea.com/files/resources/reference/21731.pdf, has data for "up to 3 conductors in a sheath, conduit, or bundle) which is probably a closer match. It appears to shows a derating factor of around 0.7 so 147 * 0.7 = 103 A at sea level. My conduit run is fairly short (5 feet or so) but a paper I found said when the conduit length is greater than 20D, you assume the entire run is in conduit. I'd assume having the wire run behind upholstery in the side walls would be a similar situation.

But, the time I'm talking about is not steady state, only the time it takes the bus feeder fuse to blow in an overload situation so that's where I was trying to use a transient analysls. At 150 A, the fuse could take up to 3600 sec to blow so I'm pretty sure the wire would overheat in that amount of time. Surely I'd recognize the situation within an hour if the instrumentation was working. At 200 A, it could take up to 100 sec to trip and I think the wire would get too hot in 100 sec.

Using the ABYC derating, a 4 AWG wire in a conduit should be good to 205 A (free air) * 0.7 (conduit derating) = 144 A. My transient calculator says a 4 AWG wire will reach 150 degC in 381 sec so that seems like more margin for my use case. If I delete the bus feeders, a 6 AWG wire should be more than adequate for the main bus feed.

I was thinking more about the location of the starter contactor and if I'm going to run the main bus feeder from the battery to prevent voltage sags during start, I don't see a disadvantage of having it near the batteries instead of on the firewall. It would certainly be in a cooler location. If you had to replace the engine side portion of that cable, having a disconnect fwd of the firewall would be more convenient but that would increase the voltage drop by one more connection.

-Bob
 
I was thinking more about the location of the starter contactor and if I'm going to run the main bus feeder from the battery to prevent voltage sags during start, I don't see a disadvantage of having it near the batteries instead of on the firewall. It would certainly be in a cooler location. If you had to replace the engine side portion of that cable, having a disconnect fwd of the firewall would be more convenient but that would increase the voltage drop by one more connection.

-Bob

Ok I thought of a good reason not to place the starter contactor in the rear. If I put it near the batteries, and I also run a separate fused bus feeder from the rear, then where is the alternator going to connect? The lowest weight solution is to connect it directly to the bus behind the panel. Since the 60 A alternator would have a 60 A ANL on the firewall to protect against an alternator short, there is now a potential issue of losing the entire main bus. An alternator short could potentially blow the 100 A main bus feeder MIDI before the 60 A ANL because the fuse curves overlap.

I'm leaning towards my original design of keeping the starter contactor on the firewall, having a well-protected 2 AWG wire for it, then a fused bus feeder as previously discussed.

-Bob
 
Three thoughts:
- Panel brown out during start. I do not have this problem. I run two batteries (PC-625) normally in parallel with two master solenoids. The panel runs off separate relays going directly to the battery(s). The left side of the panel gets power before engine start (one EFIS, one Comm, etc.). Both batteries are used for engine start. The right side of the panel comes up after the engine is running.
- Starter solenoid at the battery. I do not recommend this as it adds unnecessary complexity and for aft mounted batteries you essentially double the big wire runs. The protection for the power going from the master to the starter solenoid is the pilot taking action to open the master solenoid(s) for an electrical fault. Having the panel powered via the small relays directly to the batteries provides for a backup mode (continued IFR flight) if the master solenoids are opened.
- For those running electrically dependent engines, this process of direct power from each battery (e.g. one for each EI) is repeated. Again relays to do this are mounted at each battery.

The side benefits of all this are:
- Able to run either side of the panel from either battery (ie normal and alternative power).
- Testing the various backup modes provides hard data on what the plane can do if there is an electrical casualty.
- Elimination of plethora of “backup” batteries that are being put into planes.
- A simple “replace one battery every three years” provides some assurance on the available reserve battery capacity. My six year old PC-625s then gone on for more years of service in lawn tractors, John Deers and such around the airpark. I wonder how many people are flying around with weak backup batteries. I’ve found one dual ship power EI flying RV with a “per install instructions” backup battery with less than 2vdc across the terminals. I told the owner to go buy a lottery ticket.

Carl
 
Contactor

Long time lurker, first time poster. I'm about halfway through my RV-10 build and I'm finalizing the electrical and avionics schematics so I'd appreciate any comments or feedback.

Below are links to the avionics bus architecture, the schematic, and an electrical block diagram. For the electrical architecture, in addition to doing a ton of reading and research, I analyzed the following examples:

-Bob Watzlavick

If you are interested in going with Gigavac (your part number indicates, you are) order early mine was back ordered for 6 months, and it is a more common contactor.
 

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