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Nuckolls Z-13, but with a real standby alt vs. SD-8?

N546RV

Well Known Member
My questions will continue until morale improves...

First, for reference, the aforementioned Z-13 schematic, since I'm sure few of us can recall these things on-demand (click for larger image):



I'm planning an IFR-capable airplane with dual SDS CPI2 electronic ignition - so keeping the electrons flowing is something I care about. (side note: the CPI2 and EFISs will have dedicated backup batteries)

One thing I like about the Z-13 setup is that the SD-8 feeds in ahead of the master contactor - so even a failure of that component doesn't force you onto solely battery power. It also provides a quick load-shedding ability without giving up generated power.

Thing is, the SD-8 is a bit on the light side for my backup use. If I want to continue flying without immediately leaning on backup batteries, just one side of the CPI2 and a single EFIS screen puts me over budget on amps. If I immediately lean on backup batteries, then they become the limiting factor of my endurance, and there's hardly any need for a backup alternator then.

So something like a B&C 410-H seems more in line with what I'm looking for; 20 amps gives me a lot more headroom, and I could run one CPI2 side, one Skyview screen, plus enough other things to make continued flight not a huge deal (com radio, xpdr...trim...).

Thing is, I don't think I've seen any proposed schematics with a Z-13 placement of the standby alternator, but using an actual alternator (as opposed to a PM unit like the SD-8). I'm wondering if there's a problem with this idea that's not obvious to me? Or is this just an uncommon idea?

A very simplified example of the layout I'm talking about:

69kSXtkl.png
 
After you turn off MASTER, your E-BUS and MAIN BUS will stay energized until you turn off the PRIMARY ALT.
 
The B&C 20 amp standby alternator is a very nice unit. I recommend wiring it as they discuss in their installation manual.

Specifically:
- A separate breaker for the primary alternator voltage regulator and a separate breaker for the standby alternator breaker.
- No ?alternator field switch? for either. For the rare occasion you want to turn off an alternator just open the breaker. I pulled the primary alternator VR breaker every once in awhile to make sure the standby alternator picks up the load. If you really must have a field switch, replace the voltage regulator pull breaker with a switch breaker - but again one for each regulator. I suspect you will find you normally just leave them in the on position.
- The primary and standby alternator are both always on. Each output can to to the same or different places - as long as in normal operation the standby alternator voltage regulator is seeing the same buss voltage as the primary alternator voltage regulator. The standby alternator is set so that is has zero output unless the primary alternator output (as measured on the buss) fall below the pickup voltage you set - say 12.8 to 13.0 VDC. Setting this pickup voltage does two things, it provides more than adequate current to run everything on just the standby alternator, but the voltage is not so high as to have a battery charging load (assuming you have not abused your battery(s)). You battery just floats along, available if you need it. The big benefit is that there is no pilot action for the loss of the primary alternator. You will know it is gone by buss voltage going from ~14.1vdc to ~13vdc and the nice little yellow light you get with the B&C voltage regulator coming on.

Carl
 
The B&C 20 amp standby alternator is a very nice unit. I recommend wiring it as they discuss in their installation manual.


Carl

Completely agree.
Might want to consider the Z-12 configuration ( with modifications) from Bob Nuckols - especially if you consider using an electronic ignition system such as P Mag that has a built in PMG providing power when the RPM is above 800. The other considerations are simple revertion to conventional magnetos if you have concerns about The P Mag concept and the bigger issue in my mind of having to add mass to the flywheel for the magnets and subsequent harmonic balancing. Tying the availability of the ignition system to the availability of the electrical distribution system for a single engine airplane is difficult without adding a lot of complexity.

KT
 
my thoughts

My thoughts:

The latest Z schematics are at http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/

A wound field alternator will draw a lot of current with engine off and overheat because the regulator sees low voltage and commands full output with no alternator fan.

B&C 410-H and 462-H alternator outputs on a Lycoming with its 1.3 drive ratio per B&C "Quick Facts" documents.
..................................................Amps output @ 14.4 V
Engine RPM.....Vacuum Pad RPM......410-H.....462-H
...1538..................2000.................15..........26
...1923..................2500.................24..........29
...2308..................3000.................29..........32
...2692..................3500.................32..........35​

Bob Nuckolls says modern alternators and regulators will work fine with the battery disconnected, main contactor failure, barring a large inrush load like a hydraulic pump RVs don't have.

Here's what Bob Nuckolls said on Aeroelectric List posting "One battery/two alternators IFR z-diagram":

Dec 20, 2019, poster says: "I also now understand one of the drawbacks of Z-12 architecture is if the battery contactor fails, both alternators go offline."

Bob Says:

"That's generally not true with modern alternators . . . and only a few of the legacy alternators.

It's true that many alternators will not come online without a battery present . . .but once running, they'll hum along oblivious to battery being there or not.

With HEAVY inrush loads like klieg-lights in the wings or hydraulic pump motors. It was theoretically possible to stall an alternator . . . from which recovery would be impossible unless a battery were present.

Bob . . ."​

Jan 08, 2020, poster says: "Need there be a load on a wound field alternator for it to continue working in case of battery disconnect?"

Bob Says:

"No . . . you can 'stall' a free-running alternator by hitting it with a big load, generally larger than it's nameplate rating. If you have and electro-hydraulic gear, then inrush on the PM pump motor may well cause a self-excited alternator to go down . . . but if you remove most if not all loads, they'll generally self excite and come back on line whereupon you can turn some things back on.

Folks used to be fond of dual, 150 watt landing lights . . . turning both of these puppies on at the same time might take down an alternator that's not supported by a battery.

With the advent of led lighting and the relative rarity of retractable gear airplanes, those antagonists are mostly ghosts of yesteryear.

Depending on the regulator design, most alternators will come on line in an orderly fashion with small or no loads . . . they will run in a civilized manner as long as you don't hammer them with a 'start up transient' that exceeds nameplate rating.

Bob . . ."​

Aeroelectric List is a good place to ask your questions. There has been discussion there recently pointing to Z-12 for electrically dependent engines. Bob is working on the next rev, which will be rev N; endurance bus will be deleted because larger alternators, compared to SD-8, are now available; a low-cost standby regulator will be used because low voltage warning from the regulator is now redundant with modern avionics; a cranking brown-out booster is currently shown in rev N but I wonder if it's necessary with modern electronic devices.

In case of electrical fire in the cockpit you should be able to open the master contactor without stopping the engine.

A wire by wire fault analysis is a good idea, if a wire opens or shorts what will happen, what will you do about it, will you know what to do about it, how will it be discovered?

A Gigavac GV-200BA1 dual coil master contactor draws 0.23A (dropout voltage 0.5) versus 1A for a legacy contactor. The GV-200MA-1 PWM contactor draws 0.13A (dropout voltage 6.5).

For SDS CPi2 current draw ref VAF post http://www.vansairforce.com/community/showthread.php?p=1398618#post1398618
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Couple comments here...

The B&C 410 alternator will deliver 32A on a Lycoming with its 1.3 drive ratio at 2,700 engine RPM which is 3,500 alternator RPM; 29A at 2,300 engine rpm.

Absolutely correct, I have the same B&C 410 for my backup (also electrically dependent on my airplane) and it will put out well over the advertised 20-amp rating. I have tested mine extensively and it's good for full IFR night ops in my airplane.

Bob Nuckols says modern alternators and regulators will work fine with the battery disconnted, main contactor failure, barring a large load dump like a hydraulic pump RVs don't have.

Again, correct, I have tested my 410 in this exact scenario. Primary alternator off, standby alternator taking the load - then kill the master to isolate the battery. The standby takes the full load of the airplane and holds steady voltage, with my normal load running between 14 and 18 amps. I can even transmit on the radio without noticeable voltage sag. There have been comments made by people that know more about alternators than I do which indicate that as long as you have "substantial" load on the alternator, the voltage should remain stable without a battery in the circuit. My testing agrees with that.

In case of electrical fire in the cockpit you should be able to open the master contactor without stopping the engine.

And here is where careful thought and design is required - in the scenario I lay out above, with the standby feeding in downstream of the master, you can kill the master and the primary alternator and you have isolated the battery (huge power source) from an electrical fire scenario, but the backup alternator is still pushing power to something that may be failed downstream of the master. If that failure happens to be a "fat wire" dead short causing sparks and fire, then likely the voltage will sag almost instantly and you'll drop the field on the standby alternator taking it offline, and everything goes dark. If it's just a small short and you're smoking the insulation off some wires, it will continue.
 
....SNIP
Again, correct, I have tested my 410 in this exact scenario. Primary alternator off, standby alternator taking the load - then kill the master to isolate the battery. The standby takes the full load of the airplane and holds steady voltage, with my normal load running between 14 and 18 amps. I can even transmit on the radio without noticeable voltage sag. There have been comments made by people that know more about alternators than I do which indicate that as long as you have "substantial" load on the alternator, the voltage should remain stable without a battery in the circuit. My testing agrees with that. SNIP.....

This is a nice to know (and as pointed out - if tested) capability. I caution against designing this as an acceptable backup mode for reasons also pointed out. There are better backup mode design options for electrically dependent RVs.

Carl
 
This is a nice to know (and as pointed out - if tested) capability. I caution against designing this as an acceptable backup mode for reasons also pointed out. There are better backup mode design options for electrically dependent RVs.

Carl

Certainly - I was addressing the failure mode of my EarthX battery BMS taking a dump and dropping my battery off the bus.
 
This thread is relevant to my interests :D as I'm in the same boat regarding electrical architecture and the ever-more-urgent need to commit to one electrical design to complete my build. I've also narrowed the field (...groan...) to 2 alternators and single battery. I just installed the relevant B&C equipment and am probably going vented EarthX in the tailcone. SDS CPi2 is going in currently, and will have a small AGM Pb battery for that as well as a TCW LiFePO4 backup for the avionics. Bendix mechanical injection - so not dependent on electrons for that part.

Z-12 seems a solid place to start. Given a surplus of power from either alternator, I'm not sold on the Carl's elegant use of relays as a means of bypassing the battery contactors to reduce coil draw. If I lose two alternators on a single flight, I'm not pressing on beyond the next airport above minimums regardless of battery endurance.

Someone mentioned added mass on flywheel from installing timing sense magnets... the magnets and set screws Ross provides for the CPi system are perhaps two grams' worth - and spread pretty evenly around the flywheel perimeter. The net imbalance after drill chips is going to be hard to measure - and it's possible that hooking a P mag or magneto to the accessory gear train will introduce more imbalance in the rotating mass than SDS's magnets and set screws. Just speculating, but I'd bet on it.

Enjoying the discussion on this topic and will follow very closely.
 
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True - but on some installs (like an RV-10) it does not fit well (slightly larger form factor). So, check clearances before you get the 462-H.

Carl

Good point. I do know in this case that it fits though through another builder. It has to be clocked in a certain position though which I suspect is because of the field wire harness.
 
410-H versus 462-H

Have you looked at the B&C 462-H? It puts out a bit more than the 410 and fits the same.

Ref edited post #5... I added a table of published output currents for B&C 410-H and 462-H alternators. Greatest benefit of larger alternator is at low rpm.
 
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... There have been comments made by people that know more about alternators than I do which indicate that as long as you have "substantial" load on the alternator, the voltage should remain stable without a battery in the circuit....

Ref edited post #5. I got a response from Bob Nuckolls on Aeroelectric List to my question "Need there be a load on a wound field alternator for it to continue working in case of battery disconnect?". In a word he said "no".
 
SDS says "4 cylinder coil pack and controller draw about 1.2 amps at 2,500 rpm", that's for one coil.

Interesting - I was about to ask you where this came from, but in the process of going to get my reference (the CPI2 installation manual), I found it on the general product page. For my load planning sheet, I was using continuous values of 1 amp per controller and 6 amps per coil, based off wording from the install manual about power provisions.

Regarding the controllers:
Current draw is less than 1 amp on this wire.

And for the coils:
With SDS supplied coilpacks, average current draw is less than 6 amps below 5000 rpms.

(Those numbers are for one board/coil, so I get to double them for my installation)

I suppose the operative words there are "less than," but I still find it overall a bit inconsistent. I suppose I'll bop on over to the electronic ignition forum and ask Ross for a definite answer. It's a pretty huge discrepancy, and 2.4 amps to keep both ignitions running is waaay better than 14...

Thanks for the tidbit here, this may majorly change my planning.
 
This thread is relevant to my interests :D as I'm in the same boat regarding electrical architecture and the ever-more-urgent need to commit to one electrical design to complete my build. I've also narrowed the field (...groan...) to 2 alternators and single battery. I just installed the relevant B&C equipment and am probably going vented EarthX in the tailcone. SDS CPi2 is going in currently, and will have a small AGM Pb battery for that as well as a TCW LiFePO4 backup for the avionics. Bendix mechanical injection - so not dependent on electrons for that part.

Z-12 seems a solid place to start. Given a surplus of power from either alternator, I'm not sold on the Carl's elegant use of relays as a means of bypassing the battery contactors to reduce coil draw. If I lose two alternators on a single flight, I'm not pressing on beyond the next airport above minimums regardless of battery endurance.

Someone mentioned added mass on flywheel from installing timing sense magnets... the magnets and set screws Ross provides for the CPi system are perhaps two grams' worth - and spread pretty evenly around the flywheel perimeter. The net imbalance after drill chips is going to be hard to measure - and it's possible that hooking a P mag or magneto to the accessory gear train will introduce more imbalance in the rotating mass than SDS's magnets and set screws. Just speculating, but I'd bet on it.

Enjoying the discussion on this topic and will follow very closely.

I spent a lot of time working through a lot of different configurations before settling on a variant of the Z-12 configuration. I added a 22,000 micro farad 50 volt capacitor to both the main and endurance busses to provide lower source impedance for the switch mode converters in the HDX displays in the event that the battery goes off line and power is provided only by an alternator.
You may well be right about the added flywheel components being a non issue as far as harmonic effects are concerned. I just prefer to use an approved propeller and flywheel and not make any changes to the flywheel. The effects of mass, inertia and imbalance at the magneto drives are modified by the gear ratio ( by the square of the gear ratio more precisely) but that is already a known quantity. The bigger issue is the need for independent power to the two ignition systems with no single point failures. The P mag solves this problem once the engine is running. The only common mode fault that would be a concern would be an overvoltage that could fail both P mags so solid overvoltage protection is very important. The Z-12 configuration is a good choice if you are using ignition with independent PMG power - maybe not for ignition that is dependent on a full time electrical supply.

KT
 
Someone brought up the possibility of creating a harmonic by adding our triggering magnets to the flywheel. Not sure where this idea came from.

The magnets and set screws weigh around 1 gram per assembly and about 1 gram of aluminum is drilled out to install them. The trigger mags are spaced 180 degrees apart on 4 cylinder engines and 120 degrees on 6 cylinder ones, so these are perfectly balanced. The synch magnet is 30 degrees from the #1 trigger magnet.

Fact- The stock flywheel with ring gear weighs around 6.75 pounds
Fact- We've seen total weight differences of up to 25 grams on factory flywheels of the same type
Fact- We've seen imbalances in factory cast flywheels of up to 6 grams (6X the effect of that one synch magnet)
Fact- The factory and aftermarket offers flywheels with a second sheave to run a/c which adds around .3 pounds to the assembly

There is a 20-65 pound propeller also bolted to the flywheel.

Some folks run flywheels with no belt flange- works fine. Saves about .5 pounds.

Light Speed has run a similar magnet setup on their ignition system for years.

We have over 1000 of our setups in service for hundreds of thousands of hours.

Never heard a single report of any of these things causing a harmonic and logic would dictate that adding something to change the MMOI by .0002% would have no effect on anything...
 
Thanks, Ross!

Now remind us if you would what the coil and controller current draw is for purposes of our battery-only and alternator-only endurance discussion here :)

I know I have those figures in my install documents but they're not at work with me today.
 
\ <snip> The bigger issue is the need for independent power to the two ignition systems with no single point failures. The P mag solves this problem once the engine is running. The only common mode fault that would be a concern would be an overvoltage that could fail both P mags so solid overvoltage protection is very important. The Z-12 configuration is a good choice if you are using ignition with independent PMG power - maybe not for ignition that is dependent on a full time electrical supply.

KT

Keith - I'm trusting that Ross has worked out a reasonable solution with his backup battery system that lets the CPi maintain a small sealed electrolyte lead acid battery that is tapped for ignition power if the main DC system goes dark. With that system backing up a Z-12 running B&C/EarthX hardware, I feel safe enough to go flying.

Just my $.02, of course.
 
Keith - I'm trusting that Ross has worked out a reasonable solution with his backup battery system that lets the CPi maintain a small sealed electrolyte lead acid battery that is tapped for ignition power if the main DC system goes dark. With that system backing up a Z-12 running B&C/EarthX hardware, I feel safe enough to go flying.

Just my $.02, of course.

Bill,
Looks like the issue of adding components to the flywheel got beaten to death but the bigger issue of not having independence from a single point failure in the electrical system for a modified automotive ignition did not. At least it would seem we have reached a common conclusion about using a hydromechanical fuel injection solution as opposed to a modified automotive electronic fuel injection offering. If there were small PMG?s that would fit in the magneto locations and provide the necessary self power for a modified automotive ignition system then in my view the playing field would be more evenly balanced between the competing offerings. For me the installational simplicity of the P mag and the easy retreat back to a magneto based system if I get cold feet made the decision to go with P mag much easier. I also not a fan of having (needing?) a unit in the cab to play with the ignition timing. I want the ignition system to do what is necessary based on having the correct sensors fed to the control unit and be completely out of sight other than to signal it is working or failed. Not saying my way is right just that it works for me.

KT
 
CPI-2 Specific Observations

Relating to the SDS CPI-2 with backup battery, you don't need anything else connected to it and in fact, you shouldn't. You just need electrons present.

The controllers have internal OV protection, voltage sensing for both primary and backup batteries and automatic battery switchover. They also have several strategies available to extend the backup battery life, including reducing coil charge time and even switching off one coil if voltage really drops low.

The point of the extra 6 months of development all this entailed, was to eliminate any external interference, other OV devices which may or may not work, voltage spikes or sags and in fact, discussions like this.

Connect your power and ground wires to the primary and backup batteries and that's it. As long as you have enough battery capacity left to charge the coils and voltage is over 7.5, the engine will keep running. There are no connections from ships main power directly to the backup battery. It is isolated by the controller which monitors and charges it accordingly.

Job 1 is to keep firing the spark plugs no matter what happens to the primary battery or alternator.

The CPI-2 is not designed for automotive use. It was a clean sheet design, specifically for aviation engines.
 
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Relating to the SDS CPI-2 with backup battery, you don't need anything else connected to it and in fact, you shouldn't. You just need electrons present.

The controllers have internal OV protection, voltage sensing for both primary and backup batteries and automatic battery switchover. They also have several strategies available to extend the backup battery life, including reducing coil charge time and even switching off one coil if voltage really drops low.

The point of the extra 6 months of development all this entailed, was to eliminate any external interference, other OV devices which may or may not work, voltage spikes or sags and in fact, discussions like this.

Connect your power and ground wires to the primary and backup batteries and that's it. As long as you have enough battery capacity left to charge the coils and voltage is over 7.5, the engine will keep running. There are no connections from ships main power directly to the backup battery. It is isolated by the controller which monitors and charges it accordingly.

Job 1 is to keep firing the spark plugs no matter what happens to the primary battery or alternator.

It would be interesting to see what a block schematic of this looks like. If the SDS Ignition has a front end that provides a step up from 12 volts to 400 to 600 volts or higher for the charging circuit as many automotive systems have then that would be a constant power demand and the current demand would go up as the supply voltage goes down reflecting a negative impedance. The selection of backup battery characteristics has a big impact on the time available for the ignition to continue working from the time the electrons stop flowing into the backup battery. The battery voltage decline will likely be rapid once the battery capacity is close to exhausted due to the constant power demand characteristic so replacing the backup battery on a regular basis may be necessary to ensure enough time to make a safe landing after a power distribution system failure. If both ignition system backup batteries are sourced from the same supply as in the Z-12 then the common mode failure would likely result in loss of the second ignition within a very short time from the loss of the first. This may be OK if you can reach somewhere suitable to land.
KT
 
....SNIP The selection of backup battery characteristics has a big impact on the time available for the ignition to continue working from the time the electrons stop flowing into the backup battery. The battery voltage decline will likely be rapid once the battery capacity is close to exhausted due to the constant power demand characteristic so replacing the backup battery on a regular basis may be necessary to ensure enough time to make a safe landing after a power distribution system failure......SNIP
KT

+1
This needs to be clearly understood. I?ve seen more than one dual electronic ignition install in RVs (not pMag) with an absolutely dead ignition backup battery (as in 0vdc across the terminals). One builder was not aware on what this meant for keeping the engine running.

- I stress that such backup batteries need to be replaced no less frequently than every two years. This is the only practical way to have confidence in battery endurance. Load testing is only as good as the tester?s ability and considering such batteries are cheap, not worth the effort.
- I also stress that the backup batteries should be sized for at least two hours of flight, better yet continued flight to fuel exhaustion (along with power to the panel to support IFR flight).

If you are struggling to shave off an Amp-hr here and there for an electrically dependent engine, you are in the wrong game. Also assume your primary, backup, backup to the backup alternator may be working just fine, but the fault you have that is making you look for a field now that the fan has stopped may not be any of these alternators.

Sorry for the thread drift, but it seemed the big picture was being lost in the grass.

Carl
 
It would be interesting to see what a block schematic of this looks like. If the SDS Ignition has a front end that provides a step up from 12 volts to 400 to 600 volts or higher for the charging circuit as many automotive systems have then that would be a constant power demand and the current demand would go up as the supply voltage goes down reflecting a negative impedance. The selection of backup battery characteristics has a big impact on the time available for the ignition to continue working from the time the electrons stop flowing into the backup battery. The battery voltage decline will likely be rapid once the battery capacity is close to exhausted due to the constant power demand characteristic so replacing the backup battery on a regular basis may be necessary to ensure enough time to make a safe landing after a power distribution system failure. If both ignition system backup batteries are sourced from the same supply as in the Z-12 then the common mode failure would likely result in loss of the second ignition within a very short time from the loss of the first. This may be OK if you can reach somewhere suitable to land.
KT

SDS uses a straight inductive discharge coil setup as the majority of OEM automotive ignition systems use and runs at a nominal 14V. This is not CDI. There is no 400-600V on the primaries.

As I stated in the previous post, there are no connections to ships power directly to the the backup battery and there SHOULD NOT BE or the system won't work as designed.

As I also stated in the previous post, the controller monitors voltage on both batteries, charges the backup battery and switches to the backup when the primary voltage falls below a programmed value. It also displays both battery voltages and has both visual and aural warnings if anything is amiss. It's about as informational to the pilot, seamless and foolproof as could be reasonably designed.


Green LED indicates controller is on main bus and < or > also indicates which power source is being used on the screen. The red Fault LED is not lit showing everything is nominal.

The controller can also cut coil charge time by about 25% to save even more power and can also shut off one of the 2 coil packs on dual systems to extend run time even longer.

It can also advance timing a programmed amount when operating on one coil to optimize engine power. (only one flame front).

We recommend replacing the BU battery every 3 years or so.

When we were designing the CPI-2, many people told us they didn't want to think too much about backup electrical design and wanted automatic monitoring and backup power switching, so that is what we delivered. They just wanted the engine to keep running no matter what happened to the aircraft primary power system.

If you buy our battery tray, it comes pre-wired and fused as well. Folks wanted a complete engineered solution here as well.
 
+1
This needs to be clearly understood. I?ve seen more than one dual electronic ignition install in RVs (not pMag) with an absolutely dead ignition backup battery (as in 0vdc across the terminals). One builder was not aware on what this meant for keeping the engine running.

Carl

With CPI-2, you'll know right away if you should even start the flight regarding the BU battery condition. We have settings for both Lead Acid and LiFePO4 batteries in the controller for charging and discharge thresholds.
 
Just by way of updating the original question here - after doing some load analysis and rudimentary failure planning, I'm no longer fixated on the need to have a standby alternator that lives ahead of the contactor. This is for a couple reasons - first, as mentioned here and elsewhere, if the contactor fails open in flight it doesn't automatically kill the alternator. Second, even if some major failure takes down the main bus, I have lots of opportunities to load-shed enough to get an easy hour+ of endurance on battery along. (subject to the normal caveats about battery health)

As pointed out here, this is pushing me more towards a Z-12 type architecture, so I'm currently working on a new layout to see how that shapes up.
 
Just by way of updating the original question here - ---<SNIP>----As pointed out here, this is pushing me more towards a Z-12 type architecture, so I'm currently working on a new layout to see how that shapes up.

So how's the progress on the new architecture?
 
Z-101

FYI there has been discussion on Aeroelectric List in recent weeks about a schematic to supersede Z-12 and potentially Z-14 also.

It's called Z101. Find the latest rev at http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/

Like Z12 it is single battery dual alternator.

Like Z13/8, the aux alternator is connected to the battery even if the main master contactor is off. Unlike Z13/8, Z101 uses a wound-field aux alternator of 30+ A capacity.

Recall Z14 is dual battery dual alternator. Bob Nuckolls' intent is Z101 will be equally reliable as Z14.

Z101 key features are:
  • Single battery dual alternator.
  • Clearance delivery bus so comm 1 can be turned on by itself.
  • Optional brown-out booster on the clearance delivery bus. (A suitable brown-out booster remains elusive.)
  • Engine bus for electrically dependent engines. Engine will keep running with main master off. (smoke in the cockpit scenario)
  • Aux alternator connected to battery with no contactor or relay. A battery of diminished capacity will not affect aircraft endurance. Thankfully, for vacuum-pad-mounted alternators this always-hot wire is relatively short if the battery is on the firewall; for battery remote from the engine compartment, an aux alternator B lead relay could be added.
In my implementation the engine bus is powered from both ends so if one connection comes loose the bus is still powered.​
So why hasn't there been a wound field alternator on the battery before now? Here's Bob:

"If an alternator feed is moved to the battery (like 100% of cars) then the regulator supply and voltage sense must also be moved to the battery side of the contactor as well. From a performance perspective, there's nothing wrong with it . . . and it would mitigate the failed contactor scenario. The only down side is that the b-lead is hot all the time. This has post crash safety implications and maintenance implications (be sure to unhook battery(-) before turning wrenches under the cowl just like you do on your car.

Bob..."​
 
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So how's the progress on the new architecture?

It's been a couple months since I did any banging on schematics, but this is the current version of my power distribution sheet (click for full-size image):



Much like Z-12, both alternators live downstream of the master contactor, and are thus dependent on it. Note that there's no dedicated alt field switch; both alternators will be energized when the battery master is on. While most circuit protection will be via fuse blocks, both alt fields will be on pullable circuit breakers, allowing for them to be de-energized if needed for ground testing, etc.

Having both alternators energized at all times, and the backup regulator set lower, means that a failure of the primary requires no action on my part. I'll get an alert on the EFIS (via the backup regulator's warning-light output), and stuff will continue to run. No real load-shedding will be needed in this situation.

If both alternators are lost, almost everything on the main bus can be manually load shed; if the master fails, then that obviously happens without my intervention. All the continuous loads on the e-bus come out to under 15 amps, with the exception of pitot heat; ship's battery-only endurance would work out to ~50 or ~35 minutes in those two cases. At any time I'd have the option of taking the CPIs off ship's power and letting them run on their backup battery; that'd shed another 5 amps. I could also power down the Skyview PFD and run the MFD off its backup battery (this would require that the master contactor be open; I don't think there's a way to force a Skyview screen to ignore ship's power and run on the battery)

All these load-shed options would need to be massaged into a workflow that could be referenced in-flight, but I think they lend themselves to a fairly linear flow: "stage 1" load shed would mean killing the main bus - probably by simply opening the master contactor (assuming it didn't fail). From there, evaluation of landing options could lead to "stage 2" - forcing the CPIs and a Skyview display off ship's power if additional breathing room on flight time was desired.

In the case of major systemic failures, the CPIs have their backup battery so the engine keeps turning, and the Skyviews have their backup batteries so I retain an attitude reference.
 
Phillip,

Good analysis for loss of output on one or both alternators. I note however that your design does not support isolating either alternator from your load buss. The simple example to look at is a fault on a buss (e.g. cabin smoke) and both alternators will feed it until the fault melts away.

You may want to add another master solenoid or two to be able to isolate loads in the event of less probable (but more severe outcome) electrical faults. This will also provide option to isolate an alternator failing and output voltage spiking up. I would not rely on the voltage regulator for this critical function.

For me, two batteries each with a master solenoid, the alternator connected to the output of these master solenoids. On any electrical problem the immediate action is to open both master solenoids. The panel is powered via separate 30 amp relays (or switches) that connect to the battery side of the master solenoids so the full IFR panel is still powered (2-3 hours of capacity).

Carl
 
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