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Recent Power Loss to Avionics Bus

Dugaru

Well Known Member
[reposted from general discussion]:

For once, I have a relevant data point to add in an electrical discussion! Although I wish I could have skipped the whole thing...

Apologies in advance for my ignorance, since I'm not the builder and know very little about electrical systems. Although I'm learning more.

Last week, on a night flight on an IFR plan, fortunately in gorgeous VMC, I smelled a brief plastic-y burning smell and then everything on my avionics bus went dark. Except for my battery powered G5, for which I developed an even greater appreciation at that moment.

I later determined that I had blown the 15 amp fuse upstream of my diode.

When this happened, I flipped the ebus switch. Everything came back up, which made me happy, and then... everything on the avionics bus promptly died again.

Because I had now blown the 15 amp fuse upstream of the ebus switch.

I've rooted around under the panel since then, and everything is now working with the fuses replaced. I'm planning my next moves to keep this from happening again. But already I have some key lessons:

1. If installing a G5, pay the extra $ for the battery backup.

2. ATC is good at diagnosing electrical failures. Apparently losing comms and transponder simultaneously is a clear sign.....

3. Check the battery on your handheld before flying. Note that even if you do so, and even if the battery indicator is at "half," that handheld, which you have carried FOR YEARS for JUST SUCH AN EMERGENCY, might still go dead when you push the transmit button.

4. The principal problem with losing all comms at night is that it's hard to turn on the lights at airports. This never occurred to me during instrument training regarding lost comms.

5. Airports are extremely dark at night without runway lights. The green/white beacon can be readily identified but doesn't give you enough light to see.

6. ATC can turn on the lights for you, even at a non-towered field with pilot-controlled lighting! I somehow never realized this. Or at least they could at W96, maybe it has to be close to a big transmitter (which W96 presumably is). Can't tell you how grateful I was for that assistance.

7. ATC, for its part, is very grateful when you call PROMPTLY after ending a no-radio IFR flight. Proud to say that I managed to check that box.

8. An RV-9 can of course be readily landed with no flaps, even when it's still trimmed for 150 knots....

9. If instrument rated, always file an instrument flight plan for night flight, even in VMC. That way, if you lose comms, somebody will know that you need the lights turned on.

10. Flying and navigating in an RV at night with just a G5, and an iPad with Foreflight, is no major problem. Did I mention that the battery backup option for the G5 is a good value?
 
[reposted from general discussion]:

8. An RV-9 can of course be readily landed with no flaps, even when it's still trimmed for 150 knots....

In the previous thread, you said that you initially blew the 15A fuse for the *avionics* buss, then the 15A fuse for the E-buss. Do you have flaps and/or trim on either of these busses?

I think a schematic would help understand what happened here, if you can post one.
 
I wish I had a schematic!

I’ve written the builder to see if he has a schematic.

Flaps and trim appear to be on the avionics bus. The “ebus” switch appears to turn on the entire avionics bus.

Again, I’m still learning this stuff, so apologies for any idiotic statements. I suspect I have the ability to perplex/infuriate knowledgeable people with my ignorance. :)

In the previous thread, you said that you initially blew the 15A fuse for the *avionics* buss, then the 15A fuse for the E-buss. Do you have flaps and/or trim on either of these busses?

I think a schematic would help understand what happened here, if you can post one.
 
A 15A fuse might have been sufficient for the avionics buss when the plane was first built, but the addition of new or different avionics might very well now be trying to pull greater than 15A, particularly when the radio or transponder are transmitting.
 
New avionics

I suspect you?re right. It?s worked fine for 18 months in this configuration, BUT the autopilot (which I had added) was working extra hard in big up and down drafts, and I was charging two gadgets on the USB port (which I also had added).

Maybe there was a reason the builder didn?t originally have any accessory plugs or USB charging ports....

I?m not really sure what the easiest fix is. I do at least know I?m not supposed to just put in a bigger fuse. :)




A 15A fuse might have been sufficient for the avionics buss when the plane was first built, but the addition of new or different avionics might very well now be trying to pull greater than 15A, particularly when the radio or transponder are transmitting.
 
This is an example of why two fuses should not be connected in series. You never know which one (or both) will blow. If two fuses must be wired in series, then the main fuse should be several times larger than the smaller fuse. For instance, if the load fuse is 5 amps, use a 30 amp or bigger for the main fuse. Or consider using a fuselink in place of the main fuse.
 
I’m not really sure what the easiest fix is. I do at least know I’m not supposed to just put in a bigger fuse. :)
You can if the wire is sized for it. If not, it should be pretty easy to rewire with larger gauge. It's just two wires: one from main bus to avbus switch, the second from avbus switch to avbus.

FWIW, I put my AP servos on my main bus when I upgraded a few weeks ago for precisely this reason. I put my avbus on a 20A fuse when I first built the plane but have since added enough that I couldn't give 5A to the servos off the avbus. Eventually I'll go from the 14AWG I have now up to 12AWG and that should give me plenty for a 30A fuse to the avbus.
 
diagram needed

...
I?m not really sure what the easiest fix is. I do at least know I?m not supposed to just put in a bigger fuse. :)
My recommendation would be to first do an analysis of what you have today - reverse-engineer a good wiring diagram. From that, the best way to proceed will become very clear.

Even though I firmly believe electricity is the closest thing in the world to magic, there is no magic to wiring our aircraft - make sure that the wires are sized right, the fuses are sized right, and the parts providing power (alternator and battery) are sized and working right, and it will just keep working.

Another plug for spending some time reading Bob's excellent book and website:

http://www.aeroelectric.com/Book/AEC_R12A.pdf

http://www.aeroelectric.com/
 
I see this as a clear example of the limitations of single E buss and single battery design in today?s power hungry glass world.

Carl
 
I see this as a clear example of the limitations of single E buss and single battery design in today’s power hungry glass world.

Carl

Nah.... it's an indication of the need to truly decide what is "essential" to get on the ground safely, and to perform a load analysis.

In this case, remove the autopilot and USB ports from the avionics buss and add them to the "normal" buss and all would have been OK...:)

Agreed though that if you are not the builder, having a good schematic, or even a reverse engineered list of what is connected to what buss, is really a very good idea.

Another thought though - should there even have been a separate avionics bus as opposed to an essential/endurance buss? Perhaps the labeling of the two buses made the problem worse?
 
I guess I don't understand what the debate is about. If there's a major short on the essential bus, both feeds blow fuses, then they're doing their intended jobs, which is to prevent an electrical fire. My guess here is the wrong size of fuse is present on a single item, and that fuse is/was rated higher than 15A. If an errant wrench or screwdriver drops onto the e-bus in flight, then yes both 15A fuses should blow.

The only way around the possibility of blowing both feeds is to physically spread out loads to another bus, to at least have some physical redundancy. So for example if you have two comms, one comm goes on one bus and the other on the other.

For the things that are singular, ie, an iPad, a nav receiver, or a transponder and they are essential for safety in an IFR flight, then those items could be fed from both busses via schottky diodes and two fuses, one from each bus.

Or one can simplify and be careful to size fuses appropriately and not worry about the fringe cases like this one.
 
Another thought.

In this case the feeds should be on breakers, not fuses. The checklist in this case would be to turn off individual items, reset the breaker, and turn things back on one at a time to isolate the fault.

If the breaker trips before anything is turned back on, then go to the alt feed switch.
 
Many thanks for all the comments and insights

I really appreciate the help and patience. It's painfully clear to me that, prior to this incident, I didn't have a sufficient understanding of my electrical system. Not even close. I'm planning to remedy that.

I've now got a copy of the Aeroelectric book, so that's a help.

Three thoughts/questions so far:

1. Moving the autopilot and accessory plug to the main bus seems like a straightforward approach. But I think I really need to put together a schematic first (reverse engineering it if necessary), to make sure I'm not going to overload that bus.

2. If I had understood my electrical system correctly, it might have dawned on me to shed some load (maybe everything but a radio and the transponder) before throwing the ebus switch. Presumably they'd both be well below my 15 amp budget. A working radio and transponder would have made the whole scenario pretty much of a non-issue. Alternatively, the ebus could be configured to be truly "essential." :)

3. The idea of using breakers rather than feeder fuses is intriguing. I can see the upside. Is there a downside?
 
Good to hear that you intend to fully understand your plane's electrical architecture before venturing out again.

It really does sound like you unknowingly added excessive load to the E-bus. Certainly not the fault of the bus, or the design; it's a fault of not understanding the system, and adding too much load to that bus.

Using breakers sounds nice, but wouldn't have really helped. They still would have blown, and if you'd been able to reset them, you could have easily become distracted enough to be a smoking hole right now, instead of calmly moving to backup and flying the plane. That actually happened to an airline crew and their passengers; 'troubleshooting' in the air instead of flying the plane. (BTW, that is a fundamental principle in the AEC book: to make any single event have a easy to implement backup plan, and troubleshoot on the ground.)

Another potential downside to breakers may arise depending on how the plane is wired. If it has fuse blocks, that makes it harder to wire in a breaker in the instrument panel. Reason is that the feeder to the breaker is now unprotected.
 
Breakers can and do fail - that's the only down-side. Then again, fuses also do fail, although the moder ATO or ATM fuses seem to be nearly bullet-proof.

The earlier advice to reverse-engineer the system is a "must do". Without a drawing of the electrical system you're troubleshooting in the dark. When doing this reverse engineering take the time to find where EVERY electrical load sources its power. I've been caught by "quickie" mods done to airplanes that resulted in power being pulled from very dangerous places, simply because that dangerous place was easily accessible to quickly source power.

How about the guy who connected his Garmin 496 power cord to the switched side of the nav lights? The only time his 496 got aircraft power was when the nav lights were turned on! Yup, the nav light circuit breaker was dead simple to access by a weekend hack trying to jam a portable GPS in with minimum effort. This kind of gotcha can sometimes make troubleshooting a real head-scratcher.

As Bob mentioned, split up your loads between those that are essential and those that are not. In my case much of the avionics is considered non-essential (audio panel, 2nd nav/com, autopilot, transponder) so they live on the avionics bus. The essential avionics (EFIS & GNS navigator with its built-in comm radio) are on the essential bus. If I lose the main electrical system I'll still have both navigation and communication ability.

One thing that's important in the instance of an electrical system failure or degradation is to alert ATC that you are on reserve battery power and will strictly limit VHF transmissions, including acknowledgements of their communications. That VHF transmitter sucks back battery power in huge hungry gulps!
 
Some of those USB ports can draw more than 2.4 amps EACH...

Yes, but that is at the 5 volt output. If my old Navy electronics training is still working, that would mean 1 amp at the 12volt input.
P=I x E. 2.4amps x 5 volts = 12 watts output which would mean an input of:
I=P / E. 12 watts / 12 volts = 1 amp.
 
Using breakers sounds nice, but wouldn't have really helped. They still would have blown, and if you'd been able to reset them, you could have easily become distracted enough to be a smoking hole right now, instead of calmly moving to backup and flying the plane.

A breaker would have helped in this case. Turn everything on the e-bus off, reset the breaker, then turn individual items back on while checking the feed breaker. If there was an inappropriately rated fuse on the faulty device, the breaker would trip again and you would know in very short order the faulty device. Reset again, continue powering up other devices and move on. With a fuse in the feed there is no opportunity to fix the problem. This could be done in 30 seconds or less.
 
I smelled a brief plastic-y burning smell and then everything on my avionics bus went dark.

I have never smelled burning plastic from a blown fuse. Maybe others can post their experience. I would strongly advise looking for something that has failed before officially chalking this up to an undersized fuse. Better safe than sorry.

Larry
 
Yes, but that is at the 5 volt output. If my old Navy electronics training is still working, that would mean 1 amp at the 12volt input.
P=I x E. 2.4amps x 5 volts = 12 watts output which would mean an input of:
I=P / E. 12 watts / 12 volts = 1 amp.

No correction for less than perfect efficiency, assuming a 'switcher' voltage converter. Could be anywhere from 95% (highly unlikely) to 50-60%.

And no guarantee it's a switcher; some of the 'super quiet' versions being sold for lots of money use linear regulators, which will consume *more* than the rated consumption of the device.

Charlie
 
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Good point.

This seems like very wise advice.

I did find two blown 15 amp fuses, one where the visible wire was simply "broken," while the other one (the first one to blow) had brown discoloration as if it had heated up.

Everything now works okay (apparently) with those two fuses replaced. And I've rooted around under the panel and on the firewall quite a bit and spotted no apparent damage. But better safe than sorry, indeed. Any ideas about how to prioritize the search -- i.e., any usual or likely suspects?

I have never smelled burning plastic from a blown fuse. Maybe others can post their experience. I would strongly advise looking for something that has failed before officially chalking this up to an undersized fuse. Better safe than sorry.

Larry
 
edit: I realized I didn't answer your question. If nothing looks like it could have touched the bus, and you can turn on and operate everything on the bus without blowing any fuses, do any of the feeders *leaving* that bus have fuses that are bigger than 7 amps or so? It's possible but unlikely that you had a hard fault in one of the wires leaving the bus that cleared itself. But it's pretty odd to blow two different 15A feeder fuses and not have a downstream fuse blow as well, unless it's really close to the feeder value. Did you check to be sure that nothing is fed directly off that bus that *doesn't* have a fuse on the bus? Meaning a 3rd wire on the bus's power input terminal. BTW, where are those two 15A feeder fuses? Are they in two other fuse blocks somewhere?

If you added stuff to that bus (or even if you didn't, since you don't have a wiring diagram), you need to do a careful evaluation of all the loads that are fed from that bus. Look at worst-case current draw from each device. Anything that has an electric motor, any incandescent lights, etc can have a *much* higher inrush current than the spec on the device. Add up all those worst-case currents, and if that number is more than around 8 amps, something needs to go, even if you hadn't had your current (pardon the pun) incident.

You can always upsize the feeders and protection, but you need to decide on the actual purpose of that bus. If you want it to be your ace in the hole after alternator failure, you need to do a load analysis vs battery energy capacity to see how much load exist, and still have a safe (convenient) conclusion of flight. As you discovered, you don't need a transponder (or even a comm) to get back down safely. But I'd want my flight instruments available, and since I'm an un-IFR-rated sissy, I'd want my autopilot, if it were possible. But all those decisions are yours to make. Just make the choices fit the purpose of the bus. BTW, a 17 Amp-Hour battery (typical Odyssey size) won't last anywhere near an hour with a 17 amp load. It'll probably closer to 20-30 minutes. Load vs time is not a straight line with our batteries.

Ain't this fun? (Read the 'Book'.)
 
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My bad...

Yes, but that is at the 5 volt output. If my old Navy electronics training is still working, that would mean 1 amp at the 12volt input.
P=I x E. 2.4amps x 5 volts = 12 watts output which would mean an input of:
I=P / E. 12 watts / 12 volts = 1 amp.

You are quite correct...my bad.:eek:
 
This seems like very wise advice.

I did find two blown 15 amp fuses, one where the visible wire was simply "broken," while the other one (the first one to blow) had brown discoloration as if it had heated up.

Everything now works okay (apparently) with those two fuses replaced. And I've rooted around under the panel and on the firewall quite a bit and spotted no apparent damage. But better safe than sorry, indeed. Any ideas about how to prioritize the search -- i.e., any usual or likely suspects?

If the fuse plastic looks like it melted some, that could be the source of your smell. When electronic components toast themselves, the smell is pretty distinct and not really similar to plastic, so that may be your source. Charlie has good advice and it would seem that if it is working now, it is not a wiring issue and if all the components work, it probably isn't a component. Do you have other fuses on these busses or is the 15 amp the only fuse?

burning insulation could smell like plastic, but I have never smelled Tefzel when it is melting, only PVC, which could be loosely defined as "plasticy." It would be good to get eyeballs on the wiring downstream of the fuse if you can.

Larry
 
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A lot of great advice so far. Something I would like to add though is that per Bob Nuckoll's designs for E-Bus architecture, the feed from Main bus to Diode to E-Bus is not protected by a fuse or breaker. The following is from Z 13/8 but his other designs are similar in this respect:
IMG_1497 by Ed Fleming, on Flickr

I believe Bobs philosophy here is that these wires are (or should be) so short and so unlikely to experience a hard fault that there is no need for protection.

Another important wire that has no circuit protection on almost any airplane, including type certified, is the Main bus feeder. One of the reasons for this is that an open breaker on this line would remove power from the entire electrical system. Placing all essential items on a separate bus, then putting a fuse on the feed to that bus, kind of negates this philosophy.

Not protecting certain wires is alway going to be a controversial subject, but a guy like Bob Nuckolls really knows what he is doing. Tinkering with his designs in even small ways can lead to unintended consequences.
 
Some builders connect many more loads to the E-Bus than what Bob N had envisioned. Those builders should increase the E-Bus fuse to 30 amps or replace it with a 20AWG fuselink.
There is lots of good troubleshooting advice above. But hindsight is better than foresight. A pilot experiencing a dark panel is better off flying the plane and saving troubleshooting for when safely on the ground.
 
Next steps

Although everything appears to be working with the fuses replaced, I'm going to spend some real quality time with the electrical system, putting together a schematic and scoping everything out, before returning the aircraft to service.

And given the seriousness of losing electrical power on an IFR flight, which must not happen again, I'm going to enlist the assistance of an A&P in the troubleshooting process. It's plain to me that I don't have the expertise necessary. At least not yet.

As with many things in life, if you're incompetent, it's extremely important to KNOW that you're incompetent. :) I am at least starting to drink from the firehose with the Aeroelectric book.

I'll be back with more info. Thanks again for all the help and insights.
 
Additional details

edit: I realized I didn't answer your question. If nothing looks like it could have touched the bus, and you can turn on and operate everything on the bus without blowing any fuses, do any of the feeders *leaving* that bus have fuses that are bigger than 7 amps or so? It's possible but unlikely that you had a hard fault in one of the wires leaving the bus that cleared itself. But it's pretty odd to blow two different 15A feeder fuses and not have a downstream fuse blow as well, unless it's really close to the feeder value. Did you check to be sure that nothing is fed directly off that bus that *doesn't* have a fuse on the bus? Meaning a 3rd wire on the bus's power input terminal. BTW, where are those two 15A feeder fuses? Are they in two other fuse blocks somewhere?

I'll check. I haven't found any fuses blown other than the 15A feeder fuses. But I'm still looking.

I have a dropdown fuse panel separated into two areas, one for the main bus and one for the avionics bus. If I remember correctly, the blown 15A fuse upstream of the diode (and thus upstream of the avionics bus) is on the main bus portion of the dropdown fuse panel. The blown 15A fuse upstream of the ebus switch is in an entirely separate fuse block, rather than anywhere on the dropdown panel.

If you added stuff to that bus (or even if you didn't, since you don't have a wiring diagram), you need to do a careful evaluation of all the loads that are fed from that bus. Look at worst-case current draw from each device. Anything that has an electric motor, any incandescent lights, etc can have a *much* higher inrush current than the spec on the device. Add up all those worst-case currents, and if that number is more than around 8 amps, something needs to go, even if you hadn't had your current (pardon the pun) incident.

My current theory (pardon the pun!) is that the reason everything went haywire, after 18 months of normal operation after adding the autopilot and USB port, is that I was in a new condition: I was in very significant updrafts and downdrafts. The pitch servo was doing a ton of work, and possibly had a high inrush current that overloaded the system. For what it's worth, the autopilot has a 5 amp breaker on the panel that did NOT pop. I may have been adding to the problem by charging my iPad from the USB port at the time. I could be wrong about all of this.

You can always upsize the feeders and protection, but you need to decide on the actual purpose of that bus. If you want it to be your ace in the hole after alternator failure, you need to do a load analysis vs battery energy capacity to see how much load exist, and still have a safe (convenient) conclusion of flight. As you discovered, you don't need a transponder (or even a comm) to get back down safely. But I'd want my flight instruments available, and since I'm an un-IFR-rated sissy, I'd want my autopilot, if it were possible. But all those decisions are yours to make. Just make the choices fit the purpose of the bus. BTW, a 17 Amp-Hour battery (typical Odyssey size) won't last anywhere near an hour with a 17 amp load. It'll probably closer to 20-30 minutes. Load vs time is not a straight line with our batteries.

This is an important project that I need to undertake. And it's yet another reason to get the G5 with the internal backup battery. :)

With respect to those decisions, I learned quite a bit from this experience. Sitting in the cockpit on an instrument clearance at night, and with my avionics bus kaput, I discovered that what I really wanted powered from the aircraft was:

- at least one radio (the 430W if possible, the SL40 if not)
- the transponder,
- the GRT EIS for engine info, albeit monochrome :), and
- a landing light.

With that gear -- along with a headset flashlight, the G5 running on its own battery power for four hours, and an iPad with georeferenced plates and its own GPS -- I could have faked basically anything at that point, reasonably safely and with minimal disruption to ATC.

If I had been in actual IMC, the autopilot would also have been very nice to have. I discovered that a kerfuffle like this, which could easily involve navigating to an airport that wasn't originally your destination, is a high workload event. If you're a sissy for wanting an autopilot at a moment like that, so am I -- nobody appreciates them as much as instrument-rated pilots!! :)

Ain't this fun? (Read the 'Book'.)

I guess I'll go with "educational." I do really appreciate all the education I've gotten here.

From what I can tell, this aircraft was originally set up to be a night VFR bird. The second owner got halfway through an IFR upgrade, without rethinking the electrical architecture. I then completed that project, including by adding an autopilot, also without rethinking the electrical architecture. Time for some thinking.
 
If I had been in actual IMC, the autopilot would also have been very nice to have. I discovered that a kerfuffle like this, which could easily involve navigating to an airport that wasn't originally your destination, is a high workload event. If you're a sissy for wanting an autopilot at a moment like that, so am I -- nobody appreciates them as much as instrument-rated pilots!! :)

Bear in mind that the autopilot has to have something to drive it, unless it's self-contained wrt AHRS. An EFIS either on the E-buss or with backup battery should suffice, but if there's no source to send it course guidance or altitude info, if it doesn't have its own attitude control info, it won't do you much good in IMC.
 
True

I think I?ve got that covered. I?ve got a Garmin G5, 307, and GSA28 servos. Although it occurs to me that if I have enough power to run the autopilot for an appreciable period of time in the event of alternator failure, I?ll be powering that whole system, including the G5, so I won?t need the G5 running on battery backup in that case.

Bear in mind that the autopilot has to have something to drive it, unless it's self-contained wrt AHRS. An EFIS either on the E-buss or with backup battery should suffice, but if there's no source to send it course guidance or altitude info, if it doesn't have its own attitude control info, it won't do you much good in IMC.
 
I have been taught for many years to NEVER reset a popped CB in flight. Some troubleshooting procedures might have you pull, and then reset, but we never reset a popped breaker in flight.

I would rather be flying a glider, than a roman candle.
 
Do what you can . . .

re-commission the system (test) on the ground. Even though I had a schematic, worked with Stein to build the panel and installed the panel, once the plane was ready to fly, I hooked up an external power supply with amp readout and progressively activated each piece of equipment and feature while activating each fuse/breaker to know what would happen and how many amps were being demanded. The external input amps were compared to the panel amp indicator. You can do this without knowing the schematic and determine if the implemented design is close to it's limits. You will know positively if you are operating at 14 amps with a 15 amp fuse.

As for the AP - just do the ground check and provide some cycling resistance to the servos. Bring an iPad with low battery and play a video. Test it all.

It is testing you can do and get a good understanding of how close to the limits you are without another surprise.
 
Load Analysis

I'm surprised no-one seems to have ementioned this before, but each plane should have an electrical load analysis done. This is especially important if you are contemplating aEndurance Bus or any sort of partial back-up system.

It's not dificult to do, and an exmaple spreadsheet is here - http://www.vansairforce.com/community/showpost.php?p=92650&postcount=4

This simple spreadheet would have prevented the OP's bus overload.
 
Nah.... it's an indication of the need to truly decide what is "essential" to get on the ground safely, and to perform a load analysis.

Another thought though - should there even have been a separate avionics bus as opposed to an essential/endurance buss? Perhaps the labeling of the two buses made the problem worse?

True Gil, tho I agree with your second statement, and Carls.....wrt glass IFR flying, I dont see the need for an E bus, but the need for two full up busses with redundancy distributed among them.....and as the OP notes, a batt backup EFIS which can be made independent of either buss.....

VFR world, yeah, I see the Ebuss need, or even just your batt BU Efis is your "Ebuss" (magnetos assumed).....

Just my .02 tho.
 
True Gil, tho I agree with your second statement, and Carls.....wrt glass IFR flying, I dont see the need for an E bus, but the need for two full up busses with redundancy distributed among them.....and as the OP notes, a batt backup EFIS which can be made independent of either buss.....

VFR world, yeah, I see the Ebuss need, or even just your batt BU Efis is your "Ebuss" (magnetos assumed).....

Just my .02 tho.

My statement was meant to be more generic....:)

Whatever system youy use beyond a simple bus needs a load analysis (really just a listing) to document how many amps are connnected to what bus in a normal and in an emergency/failed condition. This analysis can also allow for those devices, now becoming much more common, that have their own indepenedent internal back-up batteries.

Fill out the sreadsheet, modifying it to suit your own architecture.
 
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Update with exciting new discoveries

So I finally got enough time to do some additional troubleshooting (really annoying how work gets in the way of airplane time....).

I've confirmed the only fuses blown were the 15A feeder fuses.

To recap, one of those blown 15A feeder fuses is upstream of the diode, which is in turn upstream of the essential bus. The essential bus in my RV basically has avionics (including autopilot) along with flaps and trim.

The other blown 15A feeder fuse is also upstream of the essential bus. It protects the circuit that gets juice when I flip the "essential bus" switch to ON.

The next piece of important information: my flap motor appears to be toast. Possibly literally. I disconnected it, hauled out my trusty multimeter, and determined that the wires to the flap motor are getting power when the switch is engaged, but the motor does nada.

Current theory (pardon the expression): What I smelled was my flap motor dying. It was drawing enough power to blow the feeder fuses (first the one upstream of the diode, then, when I flipped on the essential bus without shedding any load, it killed that 15A fuse just as readily). The flap motor was not, however, drawing enough power to blow its own 7.5A fuse. So the flap motor gulping current at less than 7.5 amps, and the autopilot working hard, and all the avionics fired up was too much--indicating too much load on the bus.

Or, possibly, too big of a fuse on the flap motor. I've read in old threads here that 5A is the specified fuse for the flap motor, but that people (apparently including my builder) put 7.5A fuses on due to the 5A occasionally blowing when the motor is huffing and puffing.

Now, the observant among you (who haven't fallen asleep yet, or been driven insane by my electronic ignorance), are probably wondering why my flap motor would have died during cruise flight. I have a theory for that too.

My builder put the flap switch on the stick. It's spring loaded such that it won't stay in down position, but it will stay in up position. That makes sense to me. However, its position on the stick is such that it can be inadvertently bumped up. On at least two occasions I can think of, I have discovered in cruise flight that my flap motor was running, with the switch in up position.

I think that during this flight, I could have had the flap motor running "up," at the stops, for as long as 40 minutes (!). Probably more than sufficient to kill a motor that already had 360 trouble-free hours. I can't be sure of this, because I was sufficiently focused on flying during this event that I just didn't notice the position of the flap switch, and can't recall if I turned it off.

It was an exciting time, and it was pretty dark.

So, conclusions so far:

1. New flap motor. I may have acted too quickly there. I sourced a Pittman 9234S004 from a servo company pretty cheap, but it now occurs to me that the Vans version has a worm gear on it that probably needs to come from the original equipment supplier.

2. Load analysis on the essential bus needed, very possibly resulting in some re-wiring.

3. A "flaps in transit" light seems like a good idea, assuming I don't go with something more exotic like a limit switch.

4. In retrospect, the manual flaps in my old Warrior seem pretty brilliant. :)

5. The -9 flies just great without flaps, and still isn't even remotely hard to land, even when the trim setting is out of whack for your landing speed.

So much to love about this airplane.

Thanks again for all the help
Doug
 
.....
So, conclusions so far:

1. New flap motor. I may have acted too quickly there. I sourced a Pittman 9234S004 from a servo company pretty cheap, but it now occurs to me that the Vans version has a worm gear on it that probably needs to come from the original equipment supplier.

2. Load analysis on the essential bus needed, very possibly resulting in some re-wiring.

3. A "flaps in transit" light seems like a good idea, assuming I don't go with something more exotic like a limit switch.

4. In retrospect, the manual flaps in my old Warrior seem pretty brilliant. :)

5. The -9 flies just great without flaps, and still isn't even remotely hard to land, even when the trim setting is out of whack for your landing speed.

So much to love about this airplane.

Thanks again for all the help
Doug

OR... move the flap switch away from the stick, just like most planes out there...:)
 
Or keep the flap switch on the stick but consider:
- Install a micoswitch that turns off the flap motor when the flap is all the way up.
- Install the nice Flap Postioning Systems sold by Van?s. I installed this on two planes and it is going in the new project as well. It turns off the flap motor at each flap preposition point.

Carl
 
Sounds like in addition to doing a load analysis, you need to do a deep dive into the basic 'philosophy' of the plane's electrical architecture. If the plane has an E-bus (meaning Endurance, Essential, etc, intended to allow continued operation to the destination on reduced alternator power or battery-alone power after primary alternator failure), There is no reason to have the flaps (or landing lights, or...etc) on that bus in a plane like an RV. The whole point of an E-bus, at least in the Aeroelectric Connection universe, is to give the pilot a very quick/simple low-workload method of shedding all nonessential loads when the primary alternator goes south.

And as has been pointed out, you don't want to fuse a bus at less than the total potential draw on that bus (load analysis). That's almost certainly what bit you when you blew those fuses.
 
Bob N's intent for the "E" in E-Bus stands for Endurance, not emergency and not essential. In fact, putting all essential loads on a separate bus that is not as robust as the main power bus could eventually result in an emergency. In case of an alternator failure, it is desired to reduce the load on the battery so that it will last long enough to get safely on the ground. Having an Endurance bus reduces pilot work load in a stressful situation. Instead of having to decide which switches to shut off and which ones to leave on, that job can be predetermined. All the pilot has to do is turn on the Endurance bus and shut off the master switch. This might be a good feature in an airplane with many switches. For an aircraft with not many switches, there is not much benefit in having an Endurance bus. Color coding switches would make it easy to decide which ones to shut off. Putting all electrical loads on the main power bus keeps the electrical system simple with less to go wrong. If it is not installed, it can not fail. Some might argue that there should be a backup in case the battery contactor fails in flight (a rarity). Actually the battery does not supply electrical power to an airplane. The alternator does. Many alternators, once running, will keep producing power after the battery is disconnected. However, the battery does provide voltage stability. Even so, an alternator will likely supply suitable power without a battery long enough to make a safe landing. For those who must have a backup, a second contactor could be wired in parallel with the battery contactor. Or a heavy duty relay (disabled during engine cranking) could be wired in parallel with the battery contactor.
 
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