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battery bus protection question

jcarne

Well Known Member
Patron
Ok the wiring preparation continues. I'm working off of Bob K's Z-11 schematic and he shows that the battery bus wire does not need protected as long as it is less than 6 inches long. I do not want to put my battery bus FWF so my question is would you use a fusible link, inline fuse, or something else? Take a look at the red oval below. I changed the drawing to an inline fuse but would like to see what you all think.

P.S. I only really care about running some cabin lighting but I don't know what else I might want to add. Either way I need to protect this wire coming from the battery.

Capture by Jereme Carne, on Flickr
 
Jereme,

Specific to your question, yes, an "always hot" wire to your courtesy light bus should have some sort of circuit protection. The exact choice of circuit protection isn't critical as long as it is guaranteed to open before the wire gets too hot.

We tend to add things later. For example, you may wish to add a cigar lighter socket to the always hot bus so you can blow up your air mattress at OSH. If so, a 20ga wire and associated circuit protection would be marginal. I'd consider upsizing the supply wire and using something like an ANL, or perhaps just an inline blade fuse.

Now to the drawing as presented. I see an E-bus Alt Feed with a 30 amp fuse feeding from the courtesy light bus. I'm assuming it is an unintended artifact from drawing work in progress. If you do intend such a feed, you'll need to rethink some details.
 
Jereme,

Specific to your question, yes, an "always hot" wire to your courtesy light bus should have some sort of circuit protection. The exact choice of circuit protection isn't critical as long as it is guaranteed to open before the wire gets too hot.

We tend to add things later. For example, you may wish to add a cigar lighter socket to the always hot bus so you can blow up your air mattress at OSH. If so, a 20ga wire and associated circuit protection would be marginal. I'd consider upsizing the supply wire and using something like an ANL, or perhaps just an inline blade fuse.

Now to the drawing as presented. I see an E-bus Alt Feed with a 30 amp fuse feeding from the courtesy light bus. I'm assuming it is an unintended artifact from drawing work in progress. If you do intend such a feed, you'll need to rethink some details.

Dan stellar catch on a couple accounts. Yes the drawing is still a work in progress but I'm glad you pointed some things out. I had forgotten about the cigarette lighter socket, definitely need one of them.

As far as the e-bus feed, I was planning on using one so I will need to upside the wire going from the battery to the battery bus. Good catch. Unless of course you think an e-bus is antiquated in today's EFIS world?
 
Jereme,
What page is this on? I looked and can't find it? Saw the script but not the figure.
 
Jereme,
What page is this on? I looked and can't find it? Saw the script but not the figure.

The diagram in question is in Aeroelectric Connection (back of book) by Bob Knuckolls found here. I am using the CAD version he has on his website which is slightly updated in a couple of areas. (you can also make changes if you know CAD)

It's a great book to read as far as learning electrical stuff.
 
As far as the e-bus feed, I was planning on using one so I will need to upside the wire going from the battery to the battery bus. Good catch. Unless of course you think an e-bus is antiquated in today's EFIS world?

I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair ;)

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.
 
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair ;)

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.

Exactly correct. Essential buss schemes may support vacuum pumps and spinning iron gyros but they fall short of the mark for modern, IFR dual glass installs - even less for aircraft power dependent EI and EFI.

Carl
 
It is usually bad practice to wire fuses in series. Sometimes a short circuit will
blow both fuses, even if one is much larger than the other. An exception is a
current limiter, which is very slow to blow, such as Maxi or ANL. The builder
should compare the danger of arcs and sparks to that of a fuse blowing and
disabling important electrical devices. The chances of a short circuit can be
minimized by good workmanship and double insulation at the firewall penetration.
An alternative is a heavy duty relay to turn on and off power coming from the
battery bus. Post crash fires are often started by electrical sparks. A relay can
shut off power close to the source in case of smoke or fire or imminent forced landing.
 
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair ;)

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.

Exactly correct. Essential buss schemes may support vacuum pumps and spinning iron gyros but they fall short of the mark for modern, IFR dual glass installs - even less for aircraft power dependent EI and EFI.

Carl

What would you suggest then Dan and Carl? The plan is VFR initially but I want to add everything needed to make this bird IFR by adding a GPS and a backup battery. I'm trying to plan for IFR capabilities for the future. Main bus and avionics bus? Just one bus? Something else? I would like to only do my drawing once if possible. haha Thanks for your input, it is put to good use!

It is usually bad practice to wire fuses in series. Sometimes a short circuit will
blow both fuses, even if one is much larger than the other. An exception is a
current limiter, which is very slow to blow, such as Maxi or ANL. The builder
should compare the danger of arcs and sparks to that of a fuse blowing and
disabling important electrical devices. The chances of a short circuit can be
minimized by good workmanship and double insulation at the firewall penetration.
An alternative is a heavy duty relay to turn on and off power coming from the
battery bus. Post crash fires are often started by electrical sparks. A relay can
shut off power close to the source in case of smoke or fire or imminent forced landing.

Mich this inline fuse would be very close to the battery contactor. I'm not a big fan of running unprotected wires. If I lose this fuse and only lose my cabin lights and plug I'm ok with that. (assuming I abandon this e-bus theory) Or did I miss your point entirely?
 
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What would you suggest then Dan and Carl? The plan is VFR initially but I want to add everything needed to make this bird IFR by adding a GPS and a backup battery. I'm trying to plan for IFR capabilities for the future. Main bus and avionics bus? Just one bus? Something else? I would like to only do my drawing once if possible. haha Thanks for your input, it is put to good use!
SNIP

Jereme,

PM me your email address and I?ll provide my power distribution scheme, and design objectives it supports.

Carl
 
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair ;)

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.

Im not following what the criticism of the Nuckoll's E-bus architecture is. Its what I have (Z-13/8), along with P-mags and a two-screen EFIS. Im VFR and using AFP fuel injection (no EFI), and a single battery, dual alternator, although Im not sure what all that has to do with using an E-bus or not. Can you elaborate for a simple minded kind of guy like me?

thanks

Erich
 
Im not following what the criticism of the Nuckoll's E-bus architecture is. Its what I have (Z-13/8), along with P-mags and a two-screen EFIS. Im VFR and using AFP fuel injection (no EFI), and a single battery, dual alternator, although Im not sure what all that has to do with using an E-bus or not. Can you elaborate for a simple minded kind of guy like me?

thanks

Erich

For VFR with pMags this is not as critical. For IFR with dual glass panels these single battery designs typically produce single point failure risks (note - the second alternator mitigates the one risk that is most likely but has a low impact, but not the less likely with higher impact risks).

Many ways to mitigate, like adding a covey of backup batteries (not my preference).

Carl
 
Im not following what the criticism of the Nuckoll's E-bus architecture is.

It's not criticism Erich, at least not by me. I merely think we're moving past it.

Try this. The E-bus is load shedding architecture based on a vacuum pump, single wet battery, and one alternator. Flip a switch, quickly knock off everything but a radio and some basic nav. Gyros to stay upright, analog airspeed, etc.

Today we have battery technology which is improving every day, in both capacity and reduced weight. Alternators are small and light compared to the past monsters, so it's easier to justify two of them.

Aircraft electrical design is migrating to dual independent bus power for EI and/or EFI. It will soon be the standard, even on the certified side. Those are loads we can't shed. And of course everything in the panel is electric, no gyros. Load shedding is no longer a real option, but it doesn't matter. Given the available capacity we can install, there is no real need for it.
 
I don?t think it?s such a problem with fuses in series if you take some precautions. It?s true that in the event of a dead short the current could be much higher that the fuse rating for a short amount of time. Often shorts are not dead shorts though but low impedance shorts.

I think in the situation that you have the worst case you have is a dead short on one of your sub-circuits takes out the upstream fuse. So you lose your interior light or your clock power in that event. Not really a big deal. You could make the wire from the battery larger and use a larger fuse for the feeder fuse. That is probably what I would do. Having an unprotected wire is never a good idea. You could use a time lag fuse for the feeder fuse and that might help too. The alternative of have a hot glowing wire until it melts through in one spot isn?t a good alternative in my mind for a fault condition.
 
IMHO no need for an E-bus. Most avionics have an ON/OFF switch. If necessary add extra dedicated switches for other avionics/components that you may want to load shed if the alternator fails.
Might take an extra second or two to load shed than with an E-bus setup but is that really a problem?

Can?t say I am keen on an Avionics bus and single avionics switch - switch fails and you lose your avionics. I have a single bus with switches on all avionics. Takes a couple of seconds to switch everything ON or OFF but one of the reasons I built a plane is because I love gadgets including switches.:cool:
Fin
9A IFR
Australia.
 
For VFR with pMags this is not as critical. For IFR with dual glass panels these single battery designs typically produce single point failure risks (note - the second alternator mitigates the one risk that is most likely but has a low impact, but not the less likely with higher impact risks).

Many ways to mitigate, like adding a covey of backup batteries (not my preference).

Carl

Thanks for the email Carl, I'm digesting as we speak. Looks like a very redundant system despite many relays.

It's not criticism Erich, at least not by me. I merely think we're moving past it.

Try this. The E-bus is load shedding architecture based on a vacuum pump, single wet battery, and one alternator. Flip a switch, quickly knock off everything but a radio and some basic nav. Gyros to stay upright, analog airspeed, etc.

Today we have battery technology which is improving every day, in both capacity and reduced weight. Alternators are small and light compared to the past monsters, so it's easier to justify two of them.

Aircraft electrical design is migrating to dual independent bus power for EI and/or EFI. It will soon be the standard, even on the certified side. Those are loads we can't shed. And of course everything in the panel is electric, no gyros. Load shedding is no longer a real option, but it doesn't matter. Given the available capacity we can install, there is no real need for it.

Dan would you happen to have any schematics or basic sketches of what the dual independent bus architecture would look like?

I don?t think it?s such a problem with fuses in series if you take some precautions. It?s true that in the event of a dead short the current could be much higher that the fuse rating for a short amount of time. Often shorts are not dead shorts though but low impedance shorts.

I think in the situation that you have the worst case you have is a dead short on one of your sub-circuits takes out the upstream fuse. So you lose your interior light or your clock power in that event. Not really a big deal. You could make the wire from the battery larger and use a larger fuse for the feeder fuse. That is probably what I would do. Having an unprotected wire is never a good idea. You could use a time lag fuse for the feeder fuse and that might help too. The alternative of have a hot glowing wire until it melts through in one spot isn?t a good alternative in my mind for a fault condition.

Thanks for the good feedback and ideas Ray.

IMHO no need for an E-bus. Most avionics have an ON/OFF switch. If necessary add extra dedicated switches for other avionics/components that you may want to load shed if the alternator fails.
Might take an extra second or two to load shed than with an E-bus setup but is that really a problem?

Can?t say I am keen on an Avionics bus and single avionics switch - switch fails and you lose your avionics. I have a single bus with switches on all avionics. Takes a couple of seconds to switch everything ON or OFF but one of the reasons I built a plane is because I love gadgets including switches.:cool:
Fin
9A IFR
Australia.

Interesting approach Fin, thanks for the ideas. I'm now in the process of rethinking my buses.
 
Ok, just throwing ideas out there. I like what Carl has sent me as I sure as heck can't find any single point failure modes. However, does anyone see any in this drawing? This is a modified Z-19 (I still need to add a battery bus but no big deal, mainly seeing if there are any single point failures)

-If you lose your alternator you still have two batteries feeding both buses. (also: alternator I'm going with has it's own overvoltage protection)

-If you lose your main battery and/or contactor you still have alternator and aux battery feeding both buses

-If you lose your aux battery and/or contactor you still have main battery and alternator feeding both buses.

Am I missing something here on a redundancy perspective?

Capture by Jereme Carne, on Flickr
 
Possible smoke alert

If you activate the Bus 2 alternate feed relay without closing either of the battery contactors, you'll be backfeeding Bus 1 through an un-fused 16 awg wire. Not sure that's up to the possible loads. It sure wouldn't carry the starter.

If I remember right, 'Lectric Bob has a diode and a thinner wire where you show the 6 gage interconnect wire in order to feed the E-Buss without backfeeding the main bus. The whole purpose of Bob's alternate feed is to be able to quickly shed the lighting and other heavy loads and to run the E-bus without the ~1A draw of a contactor once the alternator fails. You've already got redundant feeds to both the busses. You don't need a way to smoke a wire by inadvertently throwing switches in the wrong sequence. At the very least, fuse that wire at the battery. Speaking of which, the way it's drawn, you might wind up trying to charge Batt 2 through that 16 gage wire with a certain combination of switch positions.

Ed Holyoke
 
If you activate the Bus 2 alternate feed relay without closing either of the battery contactors, you'll be backfeeding Bus 1 through an un-fused 16 awg wire. Not sure that's up to the possible loads. It sure wouldn't carry the starter.

If I remember right, 'Lectric Bob has a diode and a thinner wire where you show the 6 gage interconnect wire in order to feed the E-Buss without backfeeding the main bus. The whole purpose of Bob's alternate feed is to be able to quickly shed the lighting and other heavy loads and to run the E-bus without the ~1A draw of a contactor once the alternator fails. You've already got redundant feeds to both the busses. You don't need a way to smoke a wire by inadvertently throwing switches in the wrong sequence. At the very least, fuse that wire at the battery. Speaking of which, the way it's drawn, you might wind up trying to charge Batt 2 through that 16 gage wire with a certain combination of switch positions.

Ed Holyoke

Ed, awesome feedback! Your memory is correct, Bob shows a diode with a 16awg wire between the two buses. At this point I'm trying to avoid the E-bus setup as I would rather be able to get power to anything I want. My thinking is, two batteries should give me more than enough juice to get where I need to in an IFR situation (especially considering the EFIS has it's own back up battery) and I can load shed/select what I want manually. I understand workload in a situation like this may be higher but I can't imagine myself turning the landing lights on when I know power is limited. haha

So here is revision 2 based on your feedback. After thinking about what you said it does seem like the bus 2 bypass relay was pointless in my case. I sent a 6awg wire direct to the buses now. I also deleted the copper bar between the two battery contactors since the aux battery will likely be in the cabin of the plane towards the back somewhere (this may change wire gauge but I need to look into that). The only downside I see at this point is that like you said if the alternator fails I will have to have the current draw from the two contactors to keep the batteries online. The only single point failure I see at this point is the wire going from bus 1 to bus 2. However, I would imagine that failure EXTREMELY unlikely especially if I make it out of copper bar. Also, if that connection fails it only takes out bus 2.

Let me know if I am missing something else. Thanks again for all your help everyone, keep it comin!

P.S. Don't pay any attention to anything coming off of the buses. I haven't changed that yet. :)

Capture by Jereme Carne, on Flickr
 
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Jereme,

You're moving things around on existing diagrams without much big picture oversight. Asking folks to vet this diagram is something akin to click bait. We can spend time with it, but to what end?

Start with basics. Will you have engine electrical loads? That would EI, and/or EFI with the required electric pumps.
 
Jereme,

You're moving things around on existing diagrams without much big picture oversight. Asking folks to vet this diagram is something akin to click bait. We can spend time with it, but to what end?

Start with basics. Will you have engine electrical loads? That would EI, and/or EFI with the required electric pumps.

Dan all I'm trying to do at this point is figure out a bus design with redundant power to them (which is why I said don't look at any loads coming off of them in hopes of not wasting anyone's time). I have the stock Van's engine with 2 mags. Future edition of p-mags is a possibility but I have no desire to add EFI.

I am told by some to start with your buses so that's what I was doing. Remember, I haven't done this before and the only drawings I have to go off of all have e-buses and the only one with two batteries one alternator had EFI which I had to delete. :)
 
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The fuse in the aux battery circuit could blow when trying to start the engine using the aux battery.
This will happen someday due to pilot error.
Prevent that by disabling the aux contactor during starting with a start switch interlock.
Since both buses are connected in parallel, they are essentially one bus with unnecessary connections.
Why not have just one bus?
 
An E-Bus isn't really needed. Just arrange the switches with important ones on
the left and not so important ones on the right side. When it is desired to shed
loads quickly, shut off the switches on the right side with one motion of the
hand. Color code the switches if desired. If you need some load turned back on
later, you will not have to think about what bus it is connected to. Just turn that
one switch back on. Keep it simple.
 
The fuse in the aux battery circuit could blow when trying to start the engine using the aux battery.
This will happen someday due to pilot error.
Prevent that by disabling the aux contactor during starting with a start switch interlock.
Since both buses are connected in parallel, they are essentially one bus with unnecessary connections.
Why not have just one bus?

Joe, thanks for the feedback. The fuse on the aux bat will be a large one like an ANL as I would like both batteries for starting.

The buses/fuse blocks I'm going with only hold up to 20 circuits which is why they are separate buses since I will have 2 fuse blocks.

An E-Bus isn't really needed. Just arrange the switches with important ones on
the left and not so important ones on the right side. When it is desired to shed
loads quickly, shut off the switches on the right side with one motion of the
hand. Color code the switches if desired. If you need some load turned back on
later, you will not have to think about what bus it is connected to. Just turn that
one switch back on. Keep it simple.

I believe we are on the same page and that the drawing already accomplishes this by always having power to both buses. I can then load shed with my switches and don't have think about what bus it's on.
 
Jereme,

To answer your question, yes, you are still building in single point failures.

On your ebuss or whatever you want to call it, you can have multiple ways of getting power to it, but you have no way to isolate a fault on the buss - other than loosing your panel all together.

Thinking of an eBuss as a load shed tool, in my opinion, falls short what can be achieved with a dual battery setup. Think ?fault isolation? when something fries. This is the heart of the design I sent you and why I use four small 30 amp relays to feed the two avionics busses, and two master relays.

But shoot fire - if you add enough backup batteries for your displays you will be fine.

Carl
 
Jereme,

To answer your question, yes, you are still building in single point failures.

On your ebuss or whatever you want to call it, you can have multiple ways of getting power to it, but you have no way to isolate a fault on the buss - other than loosing your panel all together.

Carl

Carl could you elaborate on what kind of fault you are talking about? I'm just not understanding what would take out the whole panel. If a device faults it should blow the fuse associated with it in turn isolating it. At the very least can't I turn it off with the switch associated with it? Are you talking about the bus itself developing a problem? Help me understand.
 
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I have the stock Van's engine with 2 mags. Future edition of p-mags is a possibility but I have no desire to add EFI.

Mags, maybe P-mags later, VFR, with a glass panel? Don't re-invent the wheel. Strip down a Z-11 to bare essentials. Add little or nothing.

EFIS has dual power input pins? Install a dedicated EFIS brownout battery.

Drop the low voltage warn. Your EFIS probably includes a low voltage warning. Ditch the hot battery bus. Turning on the master to blow up your air mattress is not a burden.

A Plane Power has an internal regulator with over-voltage protection. A B&C uses an external regulator with OV protection. Pick one, eliminate the extra modules in Z-11. Personally I'd ditch the ammeter and shunt too.

Ask yourself if you need an endurance bus for largely day VFR. If not, eliminate that too. Smoke in the cockpit? Turn off the master. The airplane flies fine, and the EFIS has its own power, remember?

Don't build for "Maybe someday I might do this". Don't make yourself crazy thinking about what-ifs and redundancy. Avoid Optionitis, a critical disease. The most reliable system is usually the least complex, installed with the most care.

An IFR RV-10 with EI/EFI? That's a whole different deal. It's not your deal.
 
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Mags, maybe P-mags later, VFR, with a glass panel? Don't re-invent the wheel. Strip down a Z-11 to bare essentials. Add little or nothing.

Dan, mags initially, P-mag when mags need overhauled, VFR initially but I WILL make it IFR when I can afford the GPS at a later date (I started my instrument training and would like to finish it). Yes to glass, I will have dual dynon HDX screens with backup batteries. I started with a Z-11 initially until I realized a backup battery in an IFR plane is probably a good idea. The Z-11 also has an E-bus at it's core which almost everyone is telling me not to do. See my confusion now?

EFIS has dual power input pins? Install a dedicated EFIS brownout battery.

yes to both

Drop the low voltage warn. Your EFIS probably includes a low voltage warning. Ditch the hot battery bus. Turning on the master to blow up your air mattress is not a burden.

I plan on using the Dynon for low voltage so it is already dropped in my drawing.


A Plane Power has an internal regulator with over-voltage protection. A B&C uses an external regulator with OV protection. Pick one, eliminate the extra modules in Z-11. Personally I'd ditch the ammeter and shunt too.

I'm using B&C with external reg, ammeter and shunt are already on the plane so I'll keep them.

Ask yourself if you need an endurance bus for largely day VFR. If not, eliminate that too. Smoke in the cockpit? Turn off the master. The airplane flies fine, and the EFIS has its own power, remember?

Don't build for "Maybe someday I might do this". Don't make yourself crazy thinking about what-ifs and redundancy. Avoid Optionitis, a critical disease. The most reliable system is usually the least complex agreed, installed with the most care.

An IFR RV-10 with EI/EFI? That's a whole different deal. It's not your deal.

I have answered many of these questions throughout the thread but they are kind of spread out so hopefully this puts them in a more central location. Here is the summary:

-VFR initially but I WILL make it IFR when money allows for a GPS so I would like to design for IFR where all I have to add is the GPS and ARINC-429.

-B&C alternator

-Dual Dynon HDX with Dynon everything (backup batteries, autopilot, 2 axis trim, pitot heat, etc.)

-mags until overhaul, then P-mags

-fuel injected with electric boost of course

-electric flaps


The last drawing I posted is the Z-19 with some things removed. At this point it looks like a Z-11 with the E-bus relay and diode removed with the two buses hooked together and another battery and battery contactor added, that's all I did to it. So my main question is: is that good enough in anyone's mind to be comfortable with in the soup? That's the only goal I have right now, develop a bus architecture that will be okay in IFR conditions. I'm not looking to remove ALL single point failures as we have to take some risks (our engines being the biggest single point) but I would like to feel comfortable with my electrical design.
 
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Sure, draw in the P-mag power supply, and install the wiring to the engine compartment now. Both P-mags can feed from the same main bus, as they provide internal power (above a minimum RPM) when the bus supply is interrupted. Point here is that working P-mags don't need anything beyond a stripped Z-11.

In my opinion, the minimum IFR option is a second battery...really just replacing the EFIS brownout supply with a full size battery for the additional load of GPS, radio, and transponder. The KIS approach would be an avionics bus with dual feeds.

Illustration is crippled today, a server upload problem. Maybe later.
 
So my main question is: is that good enough
Yes, almost.
Add a switch to control the aux battery contactor.
Increase the wire size between the aux battery contactor and the starter contactor.
Make it the same size as on the main contactor.
That ANL fuse will drop voltage going to the starter, slowing it down.
And the fuse adds more potential failure points.
Consider eliminating that ANL fuse. Instead, double insulate the cable
so that there is absolutely no chance of it shorting to ground.
It is not anymore dangerous than the main bus feeder.
Thousands of aircraft are flying with no fuse between the battery and the main bus.
I think that Carl was implying that a ground fault on the main bus or its feeder could
take down the whole system. True, but good workmanship
will reduce the chances of that happening.
 
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Sure, draw in the P-mag power supply, and install the wiring to the engine compartment now. Both P-mags can feed from the same main bus, as they provide internal power (above a minimum RPM) when the bus supply is interrupted. Point here is that working P-mags don't need anything beyond a stripped Z-11.

In my opinion, the minimum IFR option is a second battery...really just replacing the EFIS brownout supply with a full size battery for the additional load of GPS, radio, and transponder. The KIS approach would be an avionics bus with dual feeds.

Illustration is crippled today, a server upload problem. Maybe later.

Thanks for the reply. Looking forward to that illustration when server is back up. One option I have toyed with is just doing the Z-13/8 schematic as well. Basically the Z-11 with an 8 amp aux. alternator. The nice thing about that drawing is it already has the P-mags on it too. Slightly more expensive, yes. Lighter than a dual battery, yes. So many choices...

Yes, almost.
Add a switch to control the aux battery contactor.
Increase the wire size between the aux battery contactor and the starter contactor.
Make it the same size as on the main contactor.
That ANL fuse will drop voltage going to the starter, slowing it down.
And the fuse adds more potential failure points.
Consider eliminating that ANL fuse. Instead, double insulate the cable
so that there is absolutely no chance of it shorting to ground.
It is not anymore dangerous than the main bus feeder.
Thousands of aircraft are flying with no fuse between the battery and the main bus.
I think that Carl was implying that a ground fault on the main bus or its feeder could
take down the whole system. True, but good workmanship
will reduce the chances of that happening.

Joe thanks for the feedback. All great points that I'll take to that drawing if that's the scheme I use.
 
Most builders are better off using one of Bob Nuckolls' designs instead of
designing their own. Z-13/8 is Bob's favorite. Builders get satisfaction by using
their ingenuity to "improve" upon the design. But we do not know what we do
not know. Sometimes a flaw only shows up under certain circumstances, Bob's
architecture included. But his schematics have improved over the years with
flaws having been found and eliminated. Now Bob's architecture is well proven.
Which is better, simplicity with no redundancy or redundancy at the expense of
complexity? Whatever you decide, practice good workmanship. The majority of
electrical failures are due to bad connections. Make good crimps or solder joints
and support wires so that they will not break or short out.
 
Most builders are better off using one of Bob Nuckolls' designs instead of
designing their own. Z-13/8 is Bob's favorite. Builders get satisfaction by using
their ingenuity to "improve" upon the design. But we do not know what we do
not know. Sometimes a flaw only shows up under certain circumstances, Bob's
architecture included. But his schematics have improved over the years with
flaws having been found and eliminated. Now Bob's architecture is well proven.
Which is better, simplicity with no redundancy or redundancy at the expense of
complexity? Whatever you decide, practice good workmanship. The majority of
electrical failures are due to bad connections. Make good crimps or solder joints
and support wires so that they will not break or short out.

Ya at this point I think I'm just going to do up a Z-13/8. It has some redundancy built in with the aux alt. without being overly complex. I have to take a step back and ask myself what is most likely to fail? The answer from my research seems to be alternator virtually anywhere I look. Therefore, this design mitigates that (I have even heard a few tales of battery failure where the SD-8 runs everything just fine). It may not mitigate everything but it does the big ones. Like you said, this design is also proven. I understand people wanting to get past the E-bus mentality but I also don't see anything inherently wrong with it either.

I may not be an electrical designer but I do have experience in wiring so luckily that is on my side when I build it.

Thanks for all your feedback everyone and especially your time. :)
 
Most builders are better off using one of Bob Nuckolls' designs instead of designing their own.

Ya at this point I think I'm just going to do up a Z-13/8.

Good plan. Satisfy your designer itch by reviewing it carefully. There are potential changes; define them on a revised drawing for your airplane.

For example, the P-mag wiring is drawn with fused bus power, which doesn't allow a convenient check of the self-power function. You may wish to revise the drawing with pullable breakers, or the addition of a power switches. Note the S700-2-10 switch as drawn makes no sense; the p-lead is grounded in "BAT". Nor is there a prohibition on switching bus power to "OFF" when the engine is running, as the note seems to state. Personally I'd install individual ignition power and p-lead switches, as it allows self power checks, as well as ignition power OFF with the master ON. A broken p-lead is much more of a hazard with a P-mag than with a standard magneto, as a powered P-mag will fire when rotated forward or backward, at near zero rate.

Before anyone asks, yes, I have found a P-mag with dead internal power during a pre-buy. And every airport has a few broken p-lead horror stories.

As you intend to use a B&C main alternator, redraw for the B&C regulator and eliminate the OV module on that supply.

There may be more, but you get the idea. You're not changing architecture, just component-related detail.

Next consider the physical location of every component. Physical location can sometimes drive a required change. Even if a location doesn't change the diagram, it's best to mentally establish where everything goes before drilling holes or cutting wire.

After drawing in all detail changes, and double-checking your work, I'm sure folks here will be happy to provide review.

I understand people wanting to get past the E-bus mentality but I also don't see anything inherently wrong with it either.

Nothing inherently wrong. Just keep the loads truly essential, the absolutely minimum needed to get on the ground.
 
Good plan. Satisfy your designer itch by reviewing it carefully. There are potential changes; define them on a revised drawing for your airplane.

For example, the P-mag wiring is drawn with fused bus power, which doesn't allow a convenient check of the self-power function. You may wish to revise the drawing with pullable breakers, or the addition of a power switches. Note the S700-2-10 switch as drawn makes no sense; the p-lead is grounded in "BAT". Nor is there a prohibition on switching bus power to "OFF" when the engine is running, as the note seems to state. Personally I'd install individual ignition power and p-lead switches, as it allows self power checks, as well as ignition power OFF with the master ON. A broken p-lead is much more of a hazard with a P-mag than with a standard magneto, as a powered P-mag will fire when rotated forward or backward, at near zero rate.

Before anyone asks, yes, I have found a P-mag with dead internal power during a pre-buy. And every airport has a few broken p-lead horror stories.

As you intend to use a B&C main alternator, redraw for the B&C regulator and eliminate the OV module on that supply.

There may be more, but you get the idea. You're not changing architecture, just component-related detail.

Next consider the physical location of every component. Physical location can sometimes drive a required change. Even if a location doesn't change the diagram, it's best to mentally establish where everything goes before drilling holes or cutting wire.

After drawing in all detail changes, and double-checking your work, I'm sure folks here will be happy to provide review.



Nothing inherently wrong. Just keep the loads truly essential, the absolutely minimum needed to get on the ground.

Thanks for the great reply Dan. I'm in the process already of making many of those changes you specified. The only other thing that is somewhat major is how the power gets to the bus, I have a dual ANL setup that changes slightly how power is routed to the bus but the overall bus architecture is unchanged. Now I see it is somewhat unnecessary but both ANLs are already installed on the plane since I was doing firewall work.
 
Thanks for the great reply Dan. I'm in the process already of making many of those changes you specified. The only other thing that is somewhat major is how the power gets to the bus, I have a dual ANL setup that changes slightly how power is routed to the bus but the overall bus architecture is unchanged. Now I see it is somewhat unnecessary but both ANLs are already installed on the plane since I was doing firewall work.

Ok, so draw in the dual ANL's as well as all other component changes.
 
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