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Z-14 Modified for VPX and SDS EFI

b727capt

Member
I am getting close to having to commit to an electrical system design and I would like to get some feedback. I am going to have an electrically dependent airplane and would like to keep procedures as simple as possible yet incorporate innovative ideas like the VPX. I plan on normal operation with the cross-feed closed and the Aux voltage regulator set lower than the primary.

Do I use a single switch to control the relays for the Eng/Ess buss or do I use 2 different switches to be able to test and isolate?

Do I use a B&C standby regulator for the Aux Gen or the main regulator?

Any other suggestions?

i-pwXx4zw-M.jpg
 
switches

My opinion on one of your questions -
I'm going with two switches. I've seen pictures of panels that just use one switch for fuel pump and bus selection. But I design safety critical control systems at work and letting a simple thing like a switch be a single point failure is beyond my comfort level.
 
I lost a lot of sleep over this very issue. Don't know if you have a 4 or 6 cylinder engine and a single or dual channel SDS, but they operate differently depending on which setup you have.

If you have a 6 cylinder engine and dual channel SDS, Ross and Barry have come up with an improved design for their injector relay box to allow redundant power sources for the injectors.

I too am using Z-14 and a VPX, but all of the SDS components are powered through CB's and hot battery busses. Dual B&C alternators and external regulators. One PC-680 and one EarthX. Dual independent busses.

I rarely check PM's so mail me if you want to discuss. I'm building an RV-10 and have a dual channel full SDS EFI and ignition.

krea dot ellis at gmail dot com
 
If you have a 6 cylinder engine and dual channel SDS, Ross and Barry have come up with an improved design for their injector relay box to allow redundant power sources for the injectors.

Does that only apply to a 6-cyl? I'm building an RV-14 with a VP-X and was originally planning on a dual-channel full SDS but lack of redundant power for the injection and the complexity of the electrical system made me change my mind. I have since decided to just go with a single CPI-2 and simplify the electrical system. The ability to have redundant power sources for the injection could change my mind again.
 
The 4 cylinder relay box(es) are different from what I understand. Barry was able to modify the 6 cylinder box for redundant power. This was an important upgrade for me.

I suggest you reach out to Ross or Barry or possibly Ross will chime in.
 
I have a 200hp IO360 and plan on having the dual ECU SDS system.

letting a simple thing like a switch be a single point failure is beyond my comfort level.

I thought about that...but the chances of a switch failing if not actuated are very slim. If it turns on before flight there should be no reason to operate that switch until you are back on the ground therefore very little chance of failure.
 
Are you on the Matronics list server or aeroelectic? If not, you should check them out. Bob Nuckolls is putting out new diagrams for electrically dependent engines that are much less complex than Z14. Look in the architecture PDFs under Z101P5.
 
Look in the architecture PDFs under Z101P5.

I don't know how anyone finds what they're looking for on Matronics lists. I'd like to look at those architecture PDFs but all I can ever see is a chronological list of messages; no subforums whatsoever.
 
Agreed

I don't know how anyone finds what they're looking for on Matronics lists. I'd like to look at those architecture PDFs but all I can ever see is a chronological list of messages; no subforums whatsoever.

There is a lot of useful (and some less so) information and it's really difficult to navigate.

Take a look here for the various Z architectures.
 
An alternator is not capable of putting out much more than what it is rated for.
So the alternator output does not need protecting.
But if the alternator or its "B" lead shorts out, the battery and aircraft electrical system need protecting.
So put a current limiter at the battery end of the "B" lead.
The current limiter should be rated at slightly more than the alternator rating to prevent nuisance opening of the circuit.
 
Aeroelectric links

I don't know how anyone finds what they're looking for on Matronics lists. I'd like to look at those architecture PDFs but all I can ever see is a chronological list of messages; no subforums whatsoever.

I feel your pain, that’s why I created a list of links to Bob Nuckolls’ stuff. Doesn’t solve that the Aeroelectric List itself is clunky to say the least but at least the Z templates and more are easy to find. Threads on the Aeroelectric List get fragmented when some respond on the Matronics website and some respond by email. If you subscribe to the Aeroelectric List you’ll learn a lot over time and if you ask a question, Bob Nuckolls and/or other experts usually respond.

When it comes to the culture wars between fuses, CBs, and ECBs, the Aeroelectric List is in the fuse camp except for the alternator field which has a CB due to crowbar nuisance trips.
 
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I couldn't get your circuit to blow up enough to read, so apologies if you have addressed this. Are you sufficiently confident in the reliability of the VPX to trust it to power an electrically dependent engine? You may like to consider a complete bypass circuit to keep the engine running when the VPX barfs. If it were mine one of the ECUs would be powered directly from the battery with one switch selection. Do you really need relays? I have bypassed my battery relay once in 8 years and use a 20A switch to connect the endurance bus to the battery. I rarely test it - perhaps during maintenance as my ground power supply is only 7A. A 10A switch is easy to find - you are unlikely to be pulling much more current most of the time with the landing lights and pitot heat off.

Think about the possible failures and how you will mitigate them. Do it over a week or two to question your first decisions/answers. Although switches are quite reliable having everything dependent on one item is asking for trouble when you're 200 miles from home with a couple of hours to sun set.

Pete
 
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