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03-07-2017, 10:54 AM
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Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,435
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I'm pretty sure that no single wiring failure will kill the engine but there's one that might come close -- if I have this correctly. Kindly let me know. If I'm wrong, well, it was fun thinking about it and I'd like to learn from my error.
The only wires which could influence both ignitions and pumps are above the green boxes. The ones above the battery controller (I think that's what it is) can only kill the left-hand green box and then only if the battery controller doesn't have a diode set up like the one just above the right green box, and that's probably unlikely. But even if it didn't, that would only affect the left green box.
However, if there was no diode in the battery controller (or between the left battery and the diode over the right box), a failure to ground of the wire between the diode that's shown and the right green box would kill the right side box. It would also short out the left side battery, and cause the fusible link that's between the controller and the right box's diode to blow. Depending on a few things like the relative current available to the left side equipment and the speed that the fusible link blows, that might cause the engine to shut down; after the link blows it could be restarted. If the pilot knows that particular failure occurred and attempts a restart.
An architecture improvement might be to move the right diode inside the right green box and put a preemptive diode in the left green box. That would eliminate this particular failure.
So would an engine-driven pump and independently-self-powered ignitions, but then we wouldn't have this fun game because these systems wouldn't be powered by the ship's electrical power system, and some complexity would be avoided.
The somewhat subtle nature of this type of failure suggests that troubleshooting would be unlikely while still in the air. Sure be nice to have some sort of failure annunciation system, wouldn't it? Worth mentioning is that depending on the characteristics of the battery controller, the alternator may or may not remain on line, and perhaps might not be able to be placed back on line. So the failure annunciation system ought to have its own backup battery, perhaps a 9 v one that you can replace on the condition inspection. It would run something like an Arduino that would drive a small display briefly identifying the failure. While this system itself would not be redundant, it wouldn't need to be, given our acceptance of the need only to be one-failure tolerant.
Dave
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03-07-2017, 11:07 AM
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Join Date: Jul 2005
Location: Denver, CO
Posts: 295
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Quote:
Originally Posted by David Paule
a failure to ground of the wire between the diode that's shown and the right green box would kill the right side box. It would also short out the left side battery, and cause the fusible link that's between the controller and the right box's diode to blow.
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Here's what I came up with:
From the right battery's perspective, this failure is an open wire which simply prevents charging current from the alternator reaching the battery. The right side of the dual batt/EFI bus would contine to work normally on battery power.
The fuse would certainly trip due to current from the Alt, isolating the grounded wire. Hopefully this happened fast enough, if it does then both the Alt and left battery might be just fine and continue to operate as normal.
I'd *assume* the EFI controller/etc would use the higher voltage source (the left side), basically leaving the right side in reserve until the Alt was disabled or shut down.
__________________
// corey crawford
// rv-7a (sold)
// denver, co @ KBJC
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03-07-2017, 01:04 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by David Paule
The only wires which could influence both ignitions and pumps are above the green boxes. The ones above the battery controller (I think that's what it is) ....
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"BATT CONT" is an ordinary continuous duty battery contactor.
Quote:
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...can only kill the left-hand green box and then only if the battery controller doesn't have a diode set up like the one just above the right green box, and that's probably unlikely. But even if it didn't, that would only affect the left green box.
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See posts 46 and 48.
Quote:
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...a failure to ground of the wire between the diode that's shown and the right green box would kill the right side box.
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Yes, it might kill the right EFI/EI....if that wire actually existed. It's only on the drawing because I couldn't draw the diode's cathode on top of the fusible link junction. Well, I could, but it looks messy:
The real thing would connect the diode at the junction, either directly or via a very short wire. Please note that your point was entirely valid for the first version of this drawing. I picked it up the problem when I reviewed it, and moved the diode. See the last sentence and illustration in post 58.
BTW, the green rectangles are not physical boxes. They just highlight each independent bus.
Quote:
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It would also short out the left side battery, and cause the fusible link that's between the controller and the right box's diode to blow.
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...leaving the left side EFI/EI operational. Conduct a little experiment. Splice a short length of 22 ga wire (a fusible link for 5 amps) into the middle of a much larger cable. Connect the ends across a battery and see how long it takes to pop the small wire. Go ahead, it's fun! We're guys. We like to blow things up.
Note the locations where I've drawn fusible links may require, or can accept, another kind of circuit protection...and most of them can be tailored for the speed at which they open. For example, see those ANL current limiters in the alternator and main bus feeds? At 500 amps (a battery short) an 80 AMP ANL opens in just a fuzz more than a tenth of a second.
http://www.cooperindustries.com/cont...S_2024_ANL.pdf
Look here, engineer bait....many data sheets  :
http://www.cooperindustries.com/cont...eets.html.html
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 03-07-2017 at 01:16 PM.
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03-07-2017, 02:58 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Quote:
Originally Posted by rv7charlie
2 hrs of full load battery is *heavy*. Smartest/lightest is dual identical alts, but hard to do on a typical a/c engine.
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I never specified full load. I established the requirement of two hours of continued IFR flight if the alternator is lost. Two very different conditions.
Carl
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03-07-2017, 03:19 PM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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So, you mean needle/ball/airspeed & vectors on your handheld comm with carb & mags?
Why worry? No electrons needed....
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03-07-2017, 03:24 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Quote:
Originally Posted by rv7charlie
So, you mean needle/ball/airspeed & vectors on your handheld comm with carb & mags?
Why worry? No electrons needed....
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No. I mean:
- Dual EFIS (with all the bells and whistles)
- Auto Pilot
- Transponder
- Primary and backup NAV/Comm
This is not all that hard. This setup has been flying in three RV-8 and and an RV-10 for years.
Carl
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03-07-2017, 03:35 PM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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No, it's not hard, but you do need to specify actual loads; not just a list of avioncs types. And these days, type of engine control, as well.
How many continuous amps? How many intermittent amps, and for how long?
Without defined energy requirements, you can't define, well, energy requirements.
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03-12-2017, 02:14 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by Bill Palmer
In many of your past posts on other topics, you have offered positive solutions. How about doing that with respect to aircraft electrical system architectures, particularly in support of redundancy and safety? How about the glass is half full; not half empty?
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Fair enough.
So far I've demonstrated one way to analyze failure modes, used the method to demonstrate that a Bus Manager has a long list of them, offered a simple alternative, and asked everyone to try finding its flaws using the same.
Admittedly the alternative might be too simple for some airplanes. For sure it's a good approach to powering dual ignition only, where following the KIS principle is a fine path. However, an IFR airplane with EFI fuel delivery and heavy overall electrical demands might be well served with a dual alternator, dual battery, split bus system. With multiple sources of power, it can make sense to use a single bus dedicated to injection, ignition, and pumps, and develop multiple ways to feed it.
Here's a dual feed built with one relay and a pair of contactors, or three relays, the difference mostly being how much current you want to handle. Going forward, I anticipate all three positions will be solid state relays. The EFI/EI bus is a branch of the main system dedicated to those things alone. I've shown it hooked to split bus airframe architecture, but it wouldn't be any different hooked to any dual source of power. It is an auto-switching feed which normally sends power to the EFI bus via the primary path on the left, but automatically brings the other path on line if the first is interrupted. There are two switches for control, and operation is intuitive; simply turn on both to fly, or one at a time for test.
I've done a wire-by-wire for failure modes, but peer review is welcome.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 03-12-2017 at 07:51 PM.
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03-12-2017, 06:50 PM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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Here is another schematic for your entertainment:
VIEW PDF Click down arrow to download. 
__________________
Joe Gores
RV-12 Flying
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03-13-2017, 08:10 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Joe, I'm going to assume the e-bus in your diagram powers all the engine electronics (dual ECUs, coils, etc), as that's the context here. If it's just a brownout and backup bus for an EFIS, well....
As a critical engine electronics power bus, it has issues, three to be precise. As drawn, with all switches in flight position:
Corrections are not difficult. First think about what can be removed, not what can be added; parts not installed never cause a failure.
Here I could not see much value in the hot lead and start disconnect relay between the main contactor and the e-bus, wires 1, 2, and 3 above. The backup battery will charge and loads can be carried via the diode path from the main bus. The #6 wire problem can be corrected by simply moving the diode. If a single diode bothers you, run another diode feed in parallel. The bus remains effective against brownout.
Ok, so with the elimination of a few wires and the diode moved to the e-bus junction, we have:
Must do the homework. A fella can stare at a whole diagram a long time, and never see the shark swimming below the surface. Go wire by wire, and think about each.
PS: Add circuit protection (ANL, fuse, CB, fusible link) between wire #3 and the main bus, and the pilot won't be required to open the main contactor to cure fault 3-shorted.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 03-13-2017 at 08:33 AM.
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