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Please critique my electrical diagram

KiloWhiskey1

Well Known Member
I'd like to get some feedback on a wiring diagram that I'm trying to finalize.

Full disclosure: this is for my Panther LSA build and not for an RV, but I do think it would be applicable to anyone that is at this stage in their RV build. If it helps, I have built two RV7s, partnered in an 8, and helped friends with two RV-10 builds. I also try to add value when I can here on VAF. And, for what it’s worth my engine for this build came off an RV-4 that I bought from a fellow VAF member, so my Panther is sorta-kinda RVish. If the moderators still think this is an out of bounds post, then please take it down.

So here is where I am so far. I have taken the Aeroelectric Z-11 diagram and changed it to include a B&C alternator w/ B&C external voltage regulator. I've also changed to dual PMags and a push button start switch.

The questions that I have are:

Do you see any mistakes or issues?

Would you take any of the components that I currently have on the endurance bus off and move them to the main bus? Rationale would help for learning purposes.

How do I figure out the best wire and fuse size for the wire that goes from the battery bus to the ebus switch (that wire will be less than 12” inches in my application)? Aeroelectric shows a 7amp fuse with a 16AWG wire, but my equipment list for the ebus is different, so the amp draw will be different vs the original Z-11 drawing.

Here is the link to my diagram:

https://i.imgur.com/UWrWLs3.jpg

Thanks for the help!

Keith
 
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You might consider moving the landing light to the Ess Bus. You can always decide not to use it if you're running out of electrons, but it might be nice to spend your last few amps on lighting the runway.
 
Keith,

I wired my Europa back in early 2000's in a very similar manner to what you have drawn.

Today I really question having independent Main Bus and Endurance Bus. Back then some avionics drew significant current but not so much today. Everything you show on the main bus has or requires it's own On Off switch, so you can turn off all that stuff pretty easily and quickly especially if you group the switches.

So my vote would be to have just one bus and eliminate the Endurance Bus.

You don't show toggle switches, but I'm sure you know that the GRT units do not have them built in, they are external supplied by you.

A small backup battery for EFIS and EIS will permit engine start without the EFIS rebooting. Although since I switched to a EarthX lithium my GRT stays up during engine start.

For the E Bus wire size, add up the amps and use the wire sizing chart in Aeroelectric. Remember to use the transmit amps on the comm.

Jim Butcher
 
The P-mags each need a normally closed test button on the power wires. Also, only one mag is used to provide tach signal.

I use a Battery Buss, Main Buss, and Avionics Buss system. No Essential Bus. I just turn stuff off if necessary.

I have my flaps and GPS on the Battery Buss. I like to be able to raise and lower flaps while working on the plane without powering up. I prefer to have the option to power up the GPS and enter routes before powering up.
 
Today I really question having independent Main Bus and Endurance Bus.

For VFR, me too.

What started as an essential bus, a tool for rapid load shedding, became an endurance bus after folks decided everything up to and including their electric toothbrush was "essential".

KIS.
 
I would look at the Z-10 diagram for the P-Mags and Push-to-Start features and at a minimum, incorporate the brownout battery circuit. Z-10 also splits the L&R P-Mags to the Main Bus and Battery Bus.

John Salak
RV-12 N896HS
 
If I'm reading this correctly, it looks like the USB chargers and map lights are always hot?

If that were me, sooner or later I'd take off before sunup, forget that light was on, park it for a few days and come back to a dead ships battery.
 
ditto on the items on the hot buss the onlything I have on a hot buss is my EI's. also, the alternate endurance bus feed going through a 7A fuse. with the loads on your endurance bus, it will possibly blow. look at your loads with the comm transmitting, adsb running ect. add up all the load, add a safety margin and size everything to handle that. when you are down to your last way to power things, the last thing you want is for it to go dark because you hit the trim switch at the wrong time.

if this is a VFR bird, I would not go through the trouble of multiple busses. main buss, split if you want an avionics buss and be done with it.

bob burns
RV-4 N82RB
 
Thread drift question - Keith - What software did you use to draw your electrical diagram? I need to convert my scribbles to real drawings and don?t want to draw everything from scratch. Something with a symbol library would be great.
 
Thread drift question - Keith - What software did you use to draw your electrical diagram? I need to convert my scribbles to real drawings and don?t want to draw everything from scratch. Something with a symbol library would be great.

My way was not the most elegant. I started by downloading the AeroElectric pdf of the figures from their website. From there I copied and pasted Z-11 into Excel. I then pasted blank text boxes over the areas that I wanted to ultimately change. I then copied parts of other figures from the AeroElectric pdf that I wanted to add (ie. small symbols, pmags, and the B&C voltage regulator). After I had everything the way I wanted it, I exported it back to adobe and created the pdf that?s in this thread. I?m pretty proficient with Excel, so it worked okay for me. I didn?t really want to learn a new Cad program, which seems to be how others have created theirs, so this was my way of avoiding that step.
 
electrical schematic software

Thread drift question - Keith - What software did you use to draw your electrical diagram? I need to convert my scribbles to real drawings and don?t want to draw everything from scratch. Something with a symbol library would be great.

I'm quite happy with Eagle, which is free from Autodesk. I might estimate a 20 hour learning curve. I can share symbol files for anyone who wants.
 
You might consider moving the landing light to the Ess Bus. You can always decide not to use it if you're running out of electrons, but it might be nice to spend your last few amps on lighting the runway.

Thanks for the tip. Makes perfect sense.
 
Keith,

I wired my Europa back in early 2000's in a very similar manner to what you have drawn.

Today I really question having independent Main Bus and Endurance Bus. Back then some avionics drew significant current but not so much today. Everything you show on the main bus has or requires it's own On Off switch, so you can turn off all that stuff pretty easily and quickly especially if you group the switches.

So my vote would be to have just one bus and eliminate the Endurance Bus.

You don't show toggle switches, but I'm sure you know that the GRT units do not have them built in, they are external supplied by you.

A small backup battery for EFIS and EIS will permit engine start without the EFIS rebooting. Although since I switched to a EarthX lithium my GRT stays up during engine start.

For the E Bus wire size, add up the amps and use the wire sizing chart in Aeroelectric. Remember to use the transmit amps on the comm.

Jim Butcher

Thanks for the feedback. I'm still trying to decide if I want to do an avionics master and do away with the ebus.

Regarding sizing the ebus wire and fuse. I calculate my loads to require a 25amp fuse at max potential draw plus a little margin and a 14AWG wire to the switch. Much larger than Z-11s 7amp fuse which is displayed with roughly 30amps worth of fuses. I figure the Z-11 example ebus equipment list might actually draw 20amps max, which makes me wonder why he just suggests a 7amp fuse. I need to learn more on that piece.

Thanks again for the reply!

Keith
 
I would look at the Z-10 diagram for the P-Mags and Push-to-Start features and at a minimum, incorporate the brownout battery circuit. Z-10 also splits the L&R P-Mags to the Main Bus and Battery Bus.

John Salak
RV-12 N896HS

Thanks for pointing that out. I'll take a look at Z-10.
 
If I'm reading this correctly, it looks like the USB chargers and map lights are always hot?

If that were me, sooner or later I'd take off before sunup, forget that light was on, park it for a few days and come back to a dead ships battery.

Great point. I have moved both off the battery bus. Thanks!
 
ditto on the items on the hot buss the onlything I have on a hot buss is my EI's. also, the alternate endurance bus feed going through a 7A fuse. with the loads on your endurance bus, it will possibly blow. look at your loads with the comm transmitting, adsb running ect. add up all the load, add a safety margin and size everything to handle that. when you are down to your last way to power things, the last thing you want is for it to go dark because you hit the trim switch at the wrong time.

if this is a VFR bird, I would not go through the trouble of multiple busses. main buss, split if you want an avionics buss and be done with it.

bob burns
RV-4 N82RB

Thanks Bob. It is going to be strictly a VFR craft, so the ebus may be overkill. If I go with a main buss and avionics master, would a switch be adequate or is a relay needed? I'll have a max draw on that switch of roughly 13amps. on the other end of the switch, I would be running all the avionics through blade fuses on a separate distribution block.
 
An avionics switch is an unnecessary single point of failure.
Read Bob Nuckolls' ARTICLE.

Thanks. I’ve read The AeroElectric book and the article and I think, while not perfect, a parallel circuit would give some redundant protection. Using one DPST switch to activate both circuits to the avionics bus would keep it to one switch and add a second path.

My first RV build had three EFIS screens that went back to their manufacturer multiple times for issues that could have been surge related. I don’t know for sure what the culprit was, but I am a little paranoid about cranking with expensive avionics already powered up (even though modern avionics are supposed to be immune). I also like that an avionics bus switch allows the master to be turned on without booting up all the avionics every time. This allows maintenance and trouble shooting on the non-avionics equipment without drawing the battery down as much.

I’m a big believer in Bob Nuckolls and his design philosophies, but I’m trying to marry my needs with his know how to come up with what I like. And, I’m still in the design phase and might stick with the ebus anyway. Still thinking it through...
 
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An avionics switch is an unnecessary single point of failure.
Read Bob Nuckolls' ARTICLE.

Yeah, Bob has declared them unnecessary for some time. That said, we either figure out how to turn all the avionics on and off as a group, or do them all individually.

Per Bob's "failure tolerance" philosophy, assume the avionics master will fail eventually, then decide if it would be a problem in flight. If yes, plan for mitigation. If no, install the avionics master and enjoy the convenience.
 
:D
Yeah, Bob has declared them unnecessary for some time. That said, we either figure out how to turn all the avionics on and off as a group, or do them all individually.

Per Bob's "failure tolerance" philosophy, assume the avionics master will fail eventually, then decide if it would be a problem in flight. If yes, plan for mitigation. If no, install the avionics master and enjoy the convenience.

I agree Dan. And the fact that all my avionics are either remotely mounted or have no off switches, leaves me wanting the avionics master for that alone. Not that I want to add failure points, but my primary design goal is to have a sturdy electrical system that limits the risk of catastrophic issues like runaway alternators, smoking wires, and fires.

Ultimately it?s going to be a simple LSA machine with a VFR only mission. And I?ve always got my iPad, iPhone, and piece of yarn on the windscreen to keep me in line :p
 
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And the fact that all my avionics are either remotely mounted or have no off switches, leaves me wanting the avionics master for that alone.

Easy way to improve avionics master switch life is to reduce load. See what you might move to the main bus. Leave low draw things on the avionics bus; radio, xponder, etc. Nothing motor driven.

Might consider a dedicated EFIS/EIS battery pack for the second +input. They come on with the master but don't brown out while cranking, and of course they stay on if you open the master in flight.

The EIS requires some additional connections. One approach is to use a junction block and incorporate the necessary resistors and diodes.

Junction%20Block.jpg


Junction%20Block%20Diagram.jpg
 
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...The EIS requires some additional connections. One approach is to use a junction block and incorporate the necessary resistors and diodes.

Junction%20Block.jpg


Junction%20Block%20Diagram.jpg
Hi Dan, I like the way you pulled this together in one unit. Very clean and easy to visualize what's happening. GRT should include this in their diagrams, or even create a little box.
 
Dan,

Thanks for the pics. Quick question: what is the MAP POWER SUPPLY in your drawing? Is that coming from the avionics master switch?

Also, how did you wire up your backup battery switch? Z-10/8 uses two relays: one for the starter button and the other for the alternate feed to the ebus. Do you know of a less complex way to accomplish backup battery power to the EFIS and EIS that isolates them during startup? Is that what the two black diodes are used for in your picture?

Thanks! Keith


Easy way to improve avionics master switch life is to reduce load. See what you might move to the main bus. Leave low draw things on the avionics bus; radio, xponder, etc. Nothing motor driven.

Might consider a dedicated EFIS/EIS battery pack for the second +input. They come on with the master but don't brown out while cranking, and of course they stay on if you open the master in flight.

The EIS requires some additional connections. One approach is to use a junction block and incorporate the necessary resistors and diodes.

Junction%20Block.jpg


Junction%20Block%20Diagram.jpg
 
Quick question: what is the MAP POWER SUPPLY in your drawing? Is that coming from the avionics master switch?

No, that's power TO the MAP sensor. Backup battery and main bus feed both the EIS and the MAP sensor via the diodes.

Also, how did you wire up your backup battery switch? Z-10/8 uses two relays: one for the starter button and the other for the alternate feed to the ebus. Do you know of a less complex way to accomplish backup battery power to the EFIS and EIS that isolates them during startup? Is that what the two black diodes are used for in your picture?

Thanks! Keith

Yes, the diodes here for the EIS, as well as internal diodes in the GRT EFIS dual power inputs. Neither see the oscillating voltage on the main bus while cranking.

The small backup battery pack came from GRT 10 years ago. I don't know if it is still available. Nice little package.

EFIS%20Backup.JPG


Low%20Voltage%20LED.jpg
 
Thanks Dan. That makes sense to me now and is exactly what I needed.

Very much appreciated!

No, that's power TO the MAP sensor. Backup battery and main bus feed both the EIS and the MAP sensor via the diodes.



Yes, the diodes here for the EIS, as well as internal diodes in the GRT EFIS dual power inputs. Neither see the oscillating voltage on the main bus while cranking.

The small backup battery pack came from GRT 10 years ago. I don't know if it is still available. Nice little package.

EFIS%20Backup.JPG


Low%20Voltage%20LED.jpg
 
Thanks Bob. It is going to be strictly a VFR craft, so the ebus may be overkill. If I go with a main buss and avionics master, would a switch be adequate or is a relay needed? I'll have a max draw on that switch of roughly 13amps. on the other end of the switch, I would be running all the avionics through blade fuses on a separate distribution block.

as it is very hard to find a DC rated switch rated for more than 10 amps, you would either have to find one, use a relay, or use a switch breaker.

i like to use a switch breaker, it adds protection from a bus short. I like bobs ideas, except for avionics masters ( I like them) if you are worried about single point failures, simply add a backup avionics switch in parallel.

mine is very simple I used a single buss bar, cut in two pieces, connecting each to each other through the switch breaker. I do not have a backup, I do not fly IFR in mine. but it would be easy to add one in parallel.

when calculating max draw you do not have to add up all the loads to get the max. just the continuous and intermittent that could be used together. however, on a small airplane the total of all loads is usually not that much anyway, and it will only mean a size or two upsize in the wire. not much weight gain in a few inches of wire. I tend to use at least one size bigger than I need anyway. my plane may weigh a couple of ounces more because of it. if you are at 13 amps i would use a 20amp switch breaker/relay and wire sized for that load from the feed to the breaker switch or relay, and up to the avionics buss.

bob burns
RV-4 N82RB
 
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