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RV-14 Electrical Diagram

mulde35d

Well Known Member
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With all the discussion on lighting and electrical noise I thought I would post the primary power and G3X pinout diagram that I created over the course of about 6 weeks of sitting in hotel rooms bored out of my mind. This is still under revision as I actually build it, but while the pictures are only JPEG I would be happy to email the full working Visio product or a read only PDF to anyone who is interested (PM me with your email address and specify which file type you would like). I created this from scratch while referencing an electrical drawing that was produced by a professional company to give me some ideas on how to lay things out in a clear manner. Hence why it may look like a paid for product, but is purely an original creation. The wire numbering scheme is also original and has a decoding method to the madness that should help me identify wires quickly in the aircraft should I find problems once in flight.

I am also open to any input from any electrical guru's in the house as most of this was self learning from the baseline installation documents with a couple calls to Garmin for some detailed pinout instructions. Have fun on the eye chart if you so desire. Of note, I am now up to revision 3 based on everyone's inputs and help

Electrical-v2.jpg


Electrical-v1.jpg
 
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A quick review yields some thoughts:
- #8 wire from the battery to the master solenoid, and then to the starter motor? These should be #2.
- While you went to great strides to document wiring details I note that you have several single point failure points in the power distribution.
- As I have posted on the past, a basic two battery - single alternator scheme provides more redundancy than a single battery, two alternaor scheme. The second alternator mitigates one risk only, the loss of the primary alternator.

Carl
 
Diagram

Good catch on the cable size. I have heard a lot of arguments on dual battery vs dual alternator and went with the dual alternator based on my plan to fly a lot of hard IFR. Battery is time limited while the backup alternator is indefinite. Can't get rid of all single point failures.

Question: How many amps does the typical starter pull?
 
A quick review yields some thoughts:
- #8 wire from the battery to the master solenoid, and then to the starter motor? These should be #2.
- While you went to great strides to document wiring details I note that you have several single point failure points in the power distribution.
- As I have posted on the past, a basic two battery - single alternator scheme provides more redundancy than a single battery, two alternaor scheme. The second alternator mitigates one risk only, the loss of the primary alternator.

Carl

MY FWF kit included #2 for the cables you mention.
 
Jon, I?d like to review the Visio file.
I?ve got the same system going on my -10, but my layout is like 20 pages. Gotta love the eye chart!

Sending PM with email.

Garmin connector kits arrive this weekend to start the harnesses.
 
Good catch on the cable size. I have heard a lot of arguments on dual battery vs dual alternator and went with the dual alternator based on my plan to fly a lot of hard IFR. Battery is time limited while the backup alternator is indefinite. Can't get rid of all single point failures.

Question: How many amps does the typical starter pull?

Sorry - have to disagree. While you can?t eliminate all single point failures you need not add to them.

PM me if you want to see another approach.

Carl
 
Sorry - have to disagree. While you can?t eliminate all single point failures you need not add to them.

PM me if you want to see another approach.

Carl

Carl, I believe your system adds quite a bit of complexity to help avoid the single point failure, in its place you've added many more failure points.

Just as an example, the link below is to a recent electrical power system failure on a Boeing 773, even with some of the brightest engineers designing the systems and all the redundant stuff it still can happen. The RAT and backup battery appeared to have saved the day.
http://avherald.com/h?article=4c1cc3f6

Personally I'm a fan of really simple electrical systems, single bat and 2 alternators is what I run, (I've never had to use the backup alt but nice to know its there if I need it).
 
Other Options

Carl, I would love to look over some other possible methods of wiring the primary power system. I do think others who read the forum would also appreciate the look though if you are able to post it to the forum in a similar manner. Luckily I, and many others, am early enough in the build phase that I could easily make changes to the system. So far I have had around 9 people ask for the visio product that I posted, which makes me believe we are really educating each other with this discussion.

As Walt mentioned, I am trying to keep it simple and relatively low cost (not that anything Garmin is low cost) while still having backups in place during IFR flight. I don't have much electrical engineering background and think many of us can benefit from at least seeing different ways of wiring the aircraft. Thanks for the input and I look forward to any drawings you may be able to post.
 
* You'll be spending a reasonable amount of time updating databases over the life of the plane. I wish my G3X system used the second power input on the display screens and GTN as a separate bus (on the ground) for programming, so I wouldn't have to pull a zillion circuit breakers to keep the battery draw down. And with a toggle switch, the second power inputs could be alternatively used for backup bus, whatever;
* The pin numbers for the serial buses, CANbus etc are overkill (I think that's what's in the diagram). Much more useful in the real world is a tabulation, not a diagram, of Serial Out 1 from XXX goes to Serial In 3 of YYY. It's easy enough to look at the pin numbers later on if you need them, but your approach makes it hard to see which port is which. This information is important because each of those serial ports has to be configured with the right protocol, baud rate, phase of the moon, etc.
* Yes, diagrams are cool, but for my money, tabulations of avionics interconnects are much easier to use. Your mileage may vary.
* When time comes to build, group your circuit breakers in a logical way so that you can find them easily in a hurry. Trim and autopilot especially.

Ed
 
G3X system updates

That's an interesting idea I hadn't thought about it in regards to system updates. It would be too easy to run a parallel power wire from a dedicated hot CB/Switch to one of the many power inputs on the GTN 650 and GDU 460. It could normally be left open, and then turned on / closed to provide power for updates without having to touch the master. I like the idea, just have to locate it so it doesn't accidentally get flipped as it would essentially be its own hot bus. This is why I like sharing these things on this forum.
 
That's an interesting idea I hadn't thought about it in regards to system updates. It would be too easy to run a parallel power wire from a dedicated hot CB/Switch to one of the many power inputs on the GTN 650 and GDU 460. It could normally be left open, and then turned on / closed to provide power for updates without having to touch the master. I like the idea, just have to locate it so it doesn't accidentally get flipped as it would essentially be its own hot bus. This is why I like sharing these things on this forum.

The G3X manual details backup battery inputs, pretty standard stuff.
The GTN power requirments are such that multiple HD pins are tied together, they are not meant to be used as seperate power inputs.
 
Good point Walt, forgot the HD pins can only handle about 3 amps each. Should still be simple enough to run a hot battery wire through a breaker/switch as if it were a backup battery. I am thinking locate it above the circuit breakers away from all other switches or next to the USB extension plug above the GDU460. I know I haven?t posted a panel layout yet, but it is coming.
 
Is a separate avionics bus required? If it is, consider 2 feeds as if either the switch or relay fails then all on that bus are lost.
Pete
 
Great question on the avionics bus. I used one primarily to protect the avionics during startup and provide a fast method of load shedding. However, based on what I have read, I don’t believe the Garmin products need the protection. Maybe a Garmin rep can pipe in on the topic.
 
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Garmin Support

I spoke with a Garmin rep this morning in regards to the GAD 27 "Keep Alive Power". He mentioned it is primarily designed for power throughput from a second battery / backup battery source to power critical components during engine start while the starter pulls off the main battery. Since I don't have a backup or second battery it would be pointless to run anything through those pins.

Also, he stated that none of the G3X suite or other modern Garmin products need the stable voltage during start. No damage will be done due to voltage changes. Now if the battery voltage from the main battery drops too low during start then they may turn-off / reset, but won't do any damage.

Your guys input is sending me down additional research paths. I like it, getting smarter every day. Thanks
 
I spoke with a Garmin rep this morning in regards to the GAD 27 "Keep Alive Power". He mentioned it is primarily designed for power throughput from a second battery / backup battery source ...

Was the Garmin rep one of the G3xperts? This doesn't sound right. Here is a blurb straight from Garmin.

Voltage Stabilizer for Consistent Power

For light aircraft that may not have a redundant power source, the GAD 27 adapter can be used as a voltage stabilizer to maintain a consistent power bus output of 12 V, preventing high-draw situations such as engine startup from dropping your avionics off-line. Your G3X Touch display stays lit, your engine monitoring reference stays powered up, and you?re able to maintain a stable, continuous power flow during momentary high current draw situations.


From memory, I believe it provides enough stabilizing current at 12v for the PFD, the engine monitor and the GAD 27 itself, which is all you need.

I have a GAD 27 installed but I also have a redundant power source. Never the less, I have the GAD 27 wired to the main bus per the above. It works fine if the aux bus is off during startup.
 
No matter what Garmin says, I would not crank the engine with power to the GTN-650. In my planes I do not crank the engine with any avionics on line.

You decide what you want to do.

Carl
 
Many points of failure between B+ & avionics bus, and only one source of power.

Start circuit is unconventional; norm is to supply power to the start contactor coil from a 'fused' line through the switch, with the other end of the coil grounded.

Same with the avionics control circuit. Not saying it's wrong, but it's not the typical technique, and could cause a bit of confusion if a non-owner is trying to troubleshoot it.

You mentioned electrical noise, but it's difficult to see in the 'eye charts' what you're doing to mitigate it. You may well have dealt with it, but if not, be aware that most (nearly all?) noise issues are caused by ground issues. Where, what and how you ground matters a lot.

I'm another who has to disagree with Carl on the dual bat vs dual alt issue. I hear his argument, but dual bats doubles up on the most reliable accessory in the plane, and still results in finite (and variable with age) capacity. Alternators, on the other hand, have limited and very unpredictable lifespans. It's an even bigger issue with the current trend to electrically dependent engines, which often require quite a bit of electrical energy. Everyone should go with their (intelligently researched) comfort zone; mine is dual identical alternators (I have the luxury of mounting two).

Charlie
 
Garmin discussion

In regards to the GAD 27, I was speaking with a member of the G3X team who was knowledgable on the products. There is always the possibility that I mis-interpreted the conversation, but I am sitting back trying to think of how the GAD 27 could provide 12V power from a single battery if the battery itself is being drawn below 12V. The only method I can think is that the GAD27 would have an internal capacitor. This would stabilize power fluctuations and provide full 12V power for a very limited time should the battery drop below 12V. I guess that would have to be it if their is no backup power source, but I don't know the internals of the GAD 27 and I don't know anyone willing to open up a $500 component to see what's inside.

In response to Charlie's post, I appreciate the input on the start circuit. I originally had a fuse in line but after some conversations with a couple aircraft electrical engineers at work I pulled it since they convinced me it was pointless. I don't remember the conversation real well, but I am pretty sure it centered around the CB protects the wire from overheating due to pulling too much voltage. In the case of the 22 AWG starter wire if it were to accidentally ground out (the only time it would pull any voltage) then the bigger problem would be the active starter and not the 22 AWG wire heat. Hence no CB. Similar with the avionics relay, if the avionics master wire were to ground out it would simply close the relay, a pretty normal state. Hence no CB

I am curious, based on the comment about multiple failure points between the battery and avionics bus, how would one reduce those failure points while maintaining functionality and limiting complexity. Or is that simply the reality of the setup.
 
but I am sitting back trying to think of how the GAD 27 could provide 12V power from a single battery if the battery itself is being drawn below 12V.

Modern voltage regulators can handle this quite easily within limits. They will all have some dropout voltage below which they can't raise the voltage and there will also be limits on the amperage they can deliver.

In our case, the devices used will just draw more amperage at the lower voltage to deliver the target voltage and amperage. Not accounting for losses, here is a simplistic example. 2 amps at 12 volts is 24 watts. If you use a device that can deliver 2 amps of 12 volts from an input of 8 volts, it will draw 3 amps - or 24 watts - from the battery. Of course there is no free lunch as the conversion will not be perfectly efficient. The device will draw more than 3 amps and produce waste heat in this example.
 
SNIP

I'm another who has to disagree with Carl on the dual bat vs dual alt issue. I hear his argument, but dual bats doubles up on the most reliable accessory in the plane, and still results in finite (and variable with age) capacity. Alternators, on the other hand, have limited and very unpredictable lifespans. It's an even bigger issue with the current trend to electrically dependent engines, which often require quite a bit of electrical energy. Everyone should go with their (intelligently researched) comfort zone; mine is dual identical alternators (I have the luxury of mounting two).

Charlie

It seems I?ve failed to communicate. The battery is the most reliable element in your electrical system (assuming you have not abused it). It is the other stuff you add to it that adds all the potential single point failures.

The second battery is not solely for capacity - and is not simply two batteries running in parallel in lieu of a single, larger battery. The second battery and thoughtful design is to get independent power to the panel when some other component, junction or whatever fails.

Stuff breaks. Recognize this and design for ?graceful degradation? and power restoration options, not for a dark panel.

I stand by my assessment; thoughtful dual batteries and single alternaor designs provide superior redundancy compared to single battery, dual alternator schemes. In most cases the weight penalty is small to none, especially if the risk mitigation is adding a bunch of avionic or engine backup batteries that spend most of their life just along for the ride. Adding a standby alternator is perfectly acceptable.

So - eyeball the single master relay, the single avionics relay, the single ground wire to the battery, etc. and figure out what happens if any of them fail.

All my comments assume the builder plans on flying IFR, and/or flying with an electrically dependent engine.

Carl
 
Failure modes

So - eyeball the single master relay, the single avionics relay, the single ground wire to the battery, etc. and figure out what happens if any of them fail.

Carl

Excellent, thank you for pointing out the failure points I keep hearing about. Now the fun part. Let?s divide these up into a couple categories and please correct me if I am wrong since these are great talking points.

Master relay failure. If it fails to off prior to engine start then no power is available. If it fails to off after the alternators are online then the alternators continue to power everything and no battery backup exists. If it fails in the on position then you can?t shutoff power. None of these failures seem to be a threat to life even in IFR. Compound failures of the master and alternators would be required for this to likely be a problem.

Single avionics relay failure. If it fails in the off position then you loose the avionics bus (partial panel situation). If it fails in the on position then everything still works until the Master and alternator are turned off. No threat to life in IFR as long as the main bus has the critical IFR instruments still available (G5 and magnetometer or compass as a minimum).

Single ground wire failure. The only way I could think this would fail is if it became disconnected from the battery or firewall. So check on preflight to minimize the risk. But if it does fail then revert to a battery powered G5 to maintain aircraft control if IFR. Possible threat to life, but very unlikely given a descent preflight and proper torque on the bolts.

My OPINION, and I emphasize opinion is that all of these degraded modes are acceptable since the risk is unlikely and some graceful degredation is built in to the setup.

My thought process was to maintain the essential IFR equipment on the main bus with equipment that could be shed quickly on the avionics bus. The backup alternator provides an unlimited supply of 30 amp power should the most likely failure occur (which I believe to be a primary alternator failure). If the primary and alternate failed in flight then I could turn off the avionics bus and communicate the problem to ATC over the remaining comm radio while continuing to control the aircraft on a partial panel. Should the main batter then run out of power then the G5 backup battery would provide basic pitch, roll, yaw, airspeed, and altitude information to control the aircraft for an additional 30 minutes. That seems like a lot of redundancy to me already.

Please don?t take this as criticism on your points since I really like thinking through and talking through failure modes. I think it makes everyone smarter on electrical which seems to be a complicated topic in experimental setups. Fortunately the basic electrical principles apply to everything. If anyone has additional failure point they see in the diagram let?s bring them up and we can discuss their possible effects.
 
.....

All my comments assume the builder plans on flying IFR, and/or flying with an electrically dependent engine.

Carl

I think that is one of the biggest risk items.

If the last part of your sentence is not true by having a magneto then a lot of the rest of the system can be made simpler...:)
 
Back to the Avionics buss.
Kinda like talking primer.
You will find that many including myself are not using an avionics buss or switch. I follow the thought that the modern stuff can handle it.
I do have a IBBS 6ah back up battery to keep the PFD from rebooting and as short period back up to the main battery.
Most of my panel will stay alive during a start unless prolonged then only the PFD stays alive.
Saves a few points of failure.
I guess I am a bit of a maverick since I also use fuses instead of breakers.
 
I think that is one of the biggest risk items.

If the last part of your sentence is not true by having a magneto then a lot of the rest of the system can be made simpler...:)

Gil, I am curious about your comment on the magneto. After researching the new P-Mags I was under the impression they run off aircraft power, but also have a built in alternator to power themselves should the aircraft power fail. Hence what the test switch is checking during run up. Wouldn?t that work just as well in a dual Pmag setup without the need for a magneto?
 
Gil, I am curious about your comment on the magneto. After researching the new P-Mags I was under the impression they run off aircraft power, but also have a built in alternator to power themselves should the aircraft power fail. Hence what the test switch is checking during run up. Wouldn?t that work just as well in a dual Pmag setup without the need for a magneto?

The Pmags run on aircraft's power up until about 800 rpm then the internal power takes over until rpms fall below 800 presumably at shutdown. Test switches remove aircraft power from the Pmag so you can see if it's self powering is working above 800rpm. In the run up block above 800rpm, his the switch and if the Pmag dies, then something is wrong internally. Otherwise you have no way to know if the internal power in working properly.
 
Jon,

Good thought process. Please take it a few steps further and also consider:

- High resistance contacts (in my simple example the battery ground). They work until they don’t - or melt on over current, and vibration is a contributor. This is the single failure mode of a somewhat recent twin (two alternators) going dark at night from a common buss bar connection failing. If you must do an avionics master at least consider using two - one for each side of the panel.

- While partial panel is a good last line of defense, I would not consider it acceptable as a planned prolonged mode for IFR. In this case I’d view the G5 as the instrument to keep the wings level as you restore power to the rest of the panel by throwing a switch to power from the other battery. In my plane one EFIS and one Nav/Comm retain power if one side is lost. The other side can be restored by a single pilot action.

- I would never consider running an alternator without a battery as acceptable. If you plan on this as a backup mode, please do a lot of testing.

- Look beyond component (switch, relay, etc.) as the only failure points. Wire junctions will bite you.

- Using procedures to mitigate design shortfalls seems to be the popular thing of late. I offer that any single fault should not prevent continued IFR flight with no pilot action. Panel restoration should be achievable with minor pilot action. Remember the pilot pucker factor needs to be considered.

At this point it seems you already made your decisions so I’ll step off my soapbox. I’m hopeful my comments will provide other readers some areas to examine as they consider their design objectives.

Carl
 
Gil, I am curious about your comment on the magneto. After researching the new P-Mags I was under the impression they run off aircraft power, but also have a built in alternator to power themselves should the aircraft power fail. Hence what the test switch is checking during run up. Wouldn’t that work just as well in a dual Pmag setup without the need for a magneto?

Yes, but I would vote for a single magneto based on less (no :) ) software involved.

Similar theory to not using a small Dynon unit as a back-up to a large unit if they are both running the same software.

IIRC the Pmags had a similar problem with a early design iteration.

I have seen different estimates of the gain of the second EI system and it is not that significant. A single system that gives variable timing over the fixed timing of a magneto is a big deal though
 
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In response to Charlie's post, I appreciate the input on the start circuit. I originally had a fuse in line but after some conversations with a couple aircraft electrical engineers at work I pulled it since they convinced me it was pointless. I don't remember the conversation real well, but I am pretty sure it centered around the CB protects the wire from overheating due to pulling too much voltage. In the case of the 22 AWG starter wire if it were to accidentally ground out (the only time it would pull any voltage) then the bigger problem would be the active starter and not the 22 AWG wire heat. Hence no CB. Similar with the avionics relay, if the avionics master wire were to ground out it would simply close the relay, a pretty normal state. Hence no CB

I am curious, based on the comment about multiple failure points between the battery and avionics bus, how would one reduce those failure points while maintaining functionality and limiting complexity. Or is that simply the reality of the setup.

I hear you on the start circuit. I didn't mean to imply that it's actually wrong, but it is an 'unconventional' method of controlling the start circuit.

Sorry; I didn't study all the items on the main bus. My comment about the avionics bus assumed that it had all the critical avionics on it, so would need an alternate power feed. If the avionics bus is non-critical, then it's a non-issue.

On 2bat vs 2alt, I have only an engine bus and an airframe bus. Airframe bus is conventionally powered via the master contactor; the engine bus via a high current switch. Another high current switch is a cross-tie between the two buses. One alt feeds each bus. Adding a second battery to the 2alt system would be only slightly more complex, but add 15 lbs (or $400, if we're talking Lithium).

Charlie
 
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