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  #1  
Old 01-06-2020, 11:59 PM
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N546RV N546RV is offline
 
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Default Nuckolls Z-13, but with a real standby alt vs. SD-8?

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:

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  #2  
Old 01-07-2020, 05:50 AM
supik supik is offline
 
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After you turn off MASTER, your E-BUS and MAIN BUS will stay energized until you turn off the PRIMARY ALT.
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  #3  
Old 01-07-2020, 12:47 PM
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Carl Froehlich Carl Froehlich is offline
 
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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
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  #4  
Old 01-07-2020, 02:33 PM
keitht keitht is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
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
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  #5  
Old 01-07-2020, 09:56 PM
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johnbright johnbright is offline
 
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Default my thoughts

My thoughts:

The latest Z schematics are at http://www.aeroelectric.com/PPS/Adob...itecture_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/communit...18#post1398618
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Last edited by johnbright : 01-11-2020 at 07:28 PM. Reason: Add Bob N quotes re alt w/o batt. Add B&C alt currents for 410-H and 462-H. Link to SDS CPi2 current draw thread.
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  #6  
Old 01-08-2020, 08:27 AM
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airguy airguy is offline
 
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Couple comments here...

Quote:
Originally Posted by johnbright View Post

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.

Quote:
Originally Posted by johnbright View Post
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.

Quote:
Originally Posted by johnbright View Post

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.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #7  
Old 01-08-2020, 09:21 AM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by airguy View Post
....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
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  #8  
Old 01-08-2020, 11:44 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
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.
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N16GN flying 900 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #9  
Old 01-08-2020, 12:01 PM
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Bill Boyd Bill Boyd is offline
 
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This thread is relevant to my interests 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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Last edited by Bill Boyd : 01-08-2020 at 12:04 PM.
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  #10  
Old 01-08-2020, 02:27 PM
RandyAB RandyAB is offline
 
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Have you looked at the B&C 462-H? It puts out a bit more than the 410 and fits the same.
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