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

[Carl Froehlich]

Originally Posted by RandyAB

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

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

[RandyAB]

Originally Posted by Carl Froehlich

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.

[johnbright]

Originally Posted by RandyAB

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.

[johnbright]

Originally Posted by airguy

... 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".

[N546RV]

Originally Posted by johnbright

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.

[johnbright]

Originally Posted by N546RV

... 2.4 amps to keep both ignitions running is waaay better than 14...

And you only need one ignition to keep the engine running.

[keitht]

Originally Posted by Bill Boyd

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.

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

[rv6ejguy]

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...

[Bill Boyd]

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.

[Bill Boyd]

Originally Posted by keitht

\ <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.