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Questions as I Design My Circuit Diagram

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markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Fri Dec 13, 2019 2:19 pm Post subject: Questions as I Design My Circuit Diagram

I am building an LSA Carbon Cub which will be electrically dependent. since I will be flying only day VFR, I have followed Bob's advice and I am following the KISS principle and wiring the plane like a C150 using the Z11 schematic as a starting point.



The only things I know about electrical systems is what I have learned reading Bob's book, so I am a total novice at this. As I design my own schematic I realize that I have questions that I cannot answer. They may be dumb, and if so I apologize.



1. I have read that all circuits should have overload protection to protect the wire. When I look at Z11 there doesn't appear to be a fuse or CB on the wire from the Battery Contactor to the Main Bus, nor on the wire from the Main Bus to the Endurance Bus. What is the convention in use here?



2. I have read that alternators only deliver 80% of their rated power, so I am missing 8 amps of power from my 40 amp rated Hartzell X-Drive. My 7 feet of 8AWG wire back to the battery accounts for less than 1 amp of the loss. Where does it go? Is this 80% number really true?



3. I am going to start with a single (big) EarthX battery in my plane. However the battery compartment under the pilot's seat is easily accessible (the seat tilts forward) and another EarthX would fit in nicely. I might want to add another battery at some point in the future when I fly over water or mountains here in the Northwest. 



Bob has published elegant solutions to the 2 battery configuration, and I know that he has forgotten more than I will ever know about aircraft electrics. However I am wondering if there are reasons why I couldn't keep it simple and just wire up a 200 amp Marine battery switch as a simple A/B flip flop to a second battery? There probably are.



Thanks.



Mark

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nuckolls.bob(at)aeroelect
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Posted: Fri Dec 13, 2019 4:08 pm Post subject: Questions as I Design My Circuit Diagram

At 04:19 PM 12/13/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "markfw" <markwheelermd(at)icloud.com>



 I am building an LSA Carbon Cub which will be electrically dependent. since I will be flying only day VFR, I have followed Bob's advice and I am following the KISS principle and wiring the plane like a C150 using the Z11 schematic as a starting point. 	


   What have you changed and why?



 

  	  Quote: 	
		  The only things I know about electrical systems is what I have learned reading Bob's book, so I am a total novice at this. As I design my own schematic I realize that I have questions that I cannot answer. They may be dumb, and if so I apologize.



 1. I have read that all circuits should have overload protection to protect the wire. When I look at Z11 there doesn't appear to be a fuse or CB on the wire from the Battery Contactor to the Main Bus, nor on the wire from the Main Bus to the Endurance Bus. What is the convention in use here? 	


   The only wires needing protection are those

   that feed some accessory from a source capable

   of burning the wire.



   Bus feeders (referred to here on the list as

   'fat wires" are generally not at risk for

   burning . . . there are no probable faults

   'hard' enough to put those wires at risk

   with one exception: Rolling your airplane up

   in a ball on the rocks . . . which is why

   the wire-burning source (battery) is expected

   to be off line (battery master off) before

   you hit the rocks.



   Z11 is correct and complete as published.



  	  Quote: 	
		  2. I have read that alternators only deliver 80% of their rated power, so I am missing 8 amps of power from my 40 amp rated Hartzell X-Drive. My 7 feet of 8AWG wire back to the battery accounts for less than 1 amp of the loss. Where does it go? Is this 80% number really true? 	


   No. The general rule is that maximum

   anticipated running loads for your airplane

   should not be greater than 80% of the

   alternator's ratings. This leaves 20% for

   battery replenishment after takeoff.



   Modern, light weight alternators generally

   have much more snort than required by our

   airplanes. Have you done a load analysis for

   your project?  In TC aircraft designs, this

   is one of the FIRST studies started and

   then maintained through certification. It's

   a critical part of the certification process.



 

  	  Quote: 	
		  3. I am going to start with a single (big) EarthX battery in my plane. However the battery compartment under the pilot's seat is easily accessible (the seat tilts forward) and another EarthX would fit in nicely. I might want to add another battery at some point in the future when I fly over water or mountains here in the Northwest. 	


  What engine is in your airplane?

  	  Quote: 	
		   



 Bob has published elegant solutions to the 2 battery configuration, and I know that he has forgotten more than I will ever know about aircraft electrics. However I am wondering if there are reasons why I couldn't keep it simple and just wire up a 200 amp Marine battery switch as a simple A/B flip flop to a second battery? There probably are. 	


   This has been suggested many times here

   on the List over the years. Given the

   proximity of your battery to the cabin,

   a manual switch is a perfectly acceptable

   substituted for a master contactor. I took

   dual instruction in a Piper TriPacer that

   had manual switches for both the battery

   master and the starter.



 

 

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Fri Dec 13, 2019 7:48 pm Post subject: Re: Questions as I Design My Circuit Diagram

2.  An alternator will deliver 100 percent of its rated power if the load 

demands it.   However, the alternator could overheat if fully loaded unless it is 

adequately cooled.  Amperage is not lost over a length of wire, voltage is 

lost.  Where does it go?  Lost energy is turned into heat that warms the wire.  

8 AWG wire should carry 40 amps with minimal voltage loss.  Loading an 

alternator to 80 percent of its capacity is a rule of thumb to ensure that it 

does not overheat.  Modern avionics in a  VFR Carbon Cub are unlikely to 

draw more 10 amps.

-

3. After engine start, the aircraft electrical system gets its power from the 

alternator, not the battery.  The battery serves as a backup in case the 

alternator fails.  Usually a backup to a backup is not necessary in a VFR aircraft.

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_________________
Joe Gores

markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Sat Dec 14, 2019 11:04 am Post subject: Re: Questions as I Design My Circuit Diagram

Bob,



Thank you for your reply.



I changed Z11 in four ways:

1. I am using an EFI system so I enlarged the Endurance Bus to incorporate all of the EFI component circuits;

2. I added a Lighting Bus with C/B's just to make wiring the panel easier and because I was out of fuse positions on my Port side fuse block;

3. I did not incorporate the E-Bus alternate feed;

4. I used SSR relays rather than contactors.



I assumed that Z11 was correct. I was only asking about the reasoning about when to use fuses for my own education.



Does 8AWG wire qualify as "fat" in this context of circuit protection?



I will have an O-340 from LyCon as my engine.



My load analysis is attached to this e-mail.



Joe, I was not asking about a second battery to backup my primary battery. I was asking about it as a way to extend my flight time in the Alternator Out situation. With my EFI my ALT OUT cruise power consumption is 20A so a 7 pound ETX1200 battery would give me approximately an hour of flight time, which should work for most of my needs. I was just exploring what it would take to add in a second battery for certain higher risk trips over water or mountains so I would not have to carry that extra weight all of the time.



Mark



P.S. Is there any way to respond to replies to an original post individually rather than as a group?

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ceengland7(at)gmail.com
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Posted: Sun Dec 15, 2019 1:44 pm Post subject: Questions as I Design My Circuit Diagram

On Sun, Dec 15, 2019 at 3:18 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 01:04 PM 12/14/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "markfw" <markwheelermd(at)icloud.com (markwheelermd(at)icloud.com)>



 Bob,



 Thank you for your reply.



 I changed Z11 in four ways:

 1. I am using an EFI system so I enlarged the Endurance Bus to incorporate all of the EFI component circuits 	


    Okay, in the 'endurance mode' what are your

    design goals for battery only operations? The

    E-bus plus Battery bus loads generally define

    alternator-out loads. Not real clear from

    the load analysis narrative.



  	  Quote: 	
		  2. I added a Lighting Bus with C/B's just to make wiring the panel easier and because I was out of fuse positions on my Port side fuse block; 	


    added cbs?  Why not another small fuse

    block?



  	  Quote: 	
		  3. I did not incorporate the E-Bus alternate feed; 	


    then you don't have an e-bus . . . it's just

    an extension of the main bus.



  	  Quote: 	
		  4. I used SSR relays rather than contactors. 	


    Z-11 doesn't care what kind of contactor.

    The Z drawings are about architecture and

    failure mode effects mitigation.



  	  Quote: 	
		  I assumed that Z11 was correct. I was only asking about the reasoning about when to use fuses for my own education. 	


    Very good.



 

  	  Quote: 	
		  Does 8AWG wire qualify as "fat" in this context of circuit protection? 	


    yes



 

  	  Quote: 	
		  I will have an O-340 from LyCon as my engine. 	


    Do you have an otherwise unused vacuum pump

    pad? Why not a second alternator?



 

  	  Quote: 	
		  My load analysis is attached to this e-mail. 	


    Do your injectors really draw 1.5A average or

    6A for the suite of injectors? 



 

  	  Quote: 	
		  Joe, I was not asking about a second battery to backup my primary battery. I was asking about it as a way to extend my flight time in the Alternator Out situation. With my EFI my ALT OUT cruise power consumption is 20A so a 7 pound ETX1200 battery would give me approximately an hour of flight time, which should work for most of my needs. I was just exploring what it would take to add in a second battery for certain higher risk trips over water or mountains so I would not have to carry that extra weight all of the time. 	


   An pad-driven alternator would easily carry

   your anticipated system loads, have a lower

   cost of ownership than a second battery. The

   'e bus' goes away. Would recommend a battery

   bus that would support all vital engine functions

   so that the panel could be made 'max dark' without

   killing the engine.



   We would sure like to see a schematic

   of this system. Schematics are the fundamental

   language for FFA (Function and Failure Analysis).

   It appears that you have a 50A b-lead breaker

   on the panel? That hasn't been done on most TC

   aircraft in decades . . . it's not illustrated

   on any z-figure.



   You speak to an 'essential bus' but with

   no narrative or schematic as to how this

   bus gets isolated for energy management

   in an alternator-out condition?



   



 

   Bob . . .

	




Bob,

I can't directly address your Q about individual injector current draw. They tend to 'peak' at each trigger, but duty cycle varies wildly, and how they're operated varies wildly among control techniques (true timed injection which is rare in a/c vs 'batch fire' vs 'semi-sequential' vs ??).  But the alt engine guys have been flying auto-style electronic engine control for a lot longer than the Lyc guys, and common numbers by numerous guys flying this type of *system* for a high pressure fuel pump, injectors, igniters, and computer would be 12-15 amps; likely leaning toward the high side of that spread. I have a friend who's a retired P-W engineer who tested his system in flight for battery-only operation. With a healthy PC680, IIRC he flew for ~40 minutes  before seeing  voltage drop to near 'discharge state' before bringing the alternator back on line. I don't recall what power setting he was using for the test. Obviously, operating at higher power levels requires more energy for the various electronic bits.

Charlie

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markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Sun Dec 15, 2019 3:23 pm Post subject: Re: Questions as I Design My Circuit Diagram

Bob,



My design goals for Alt Out operations are approximately 1 hour of flight time to get on the ground while continuing use of my EFI, EFIS, EIS 1 radio and the transponder.



As an overarching design constraint, I am LSA so I am weight sensitive in all of my decisions.



I am using surface mounted fuse blocks on the cockpit quarter panels where I can see if there has been a blown fuse because an LED lights up. No I don't intend to change them in flight, but I want to know. I have a space constraint for mounting another fuse block, so I decided to use C/B's. However, I will say that I went back and forth on this and this morning I actually moved them onto the existing fuse block rather than keeping some spare circuits. Weight is about a wash either way.



It's clear that I don't understand the difference between an E-Bus and an Endurance Bus. What I am calling an E-Bus is a bus fed by the battery that can power my essential electrical needs (approximately 20 amps) for an hour. My main Bus is on a switch so I can dump all of my non-essential loads easily. The Alt Field is on a separate switch, so I would also turn that off.



I have attached my current schematic which is A WORK IN PROGRESS (wire gauges are wrong, no grounds, no sheet for the EFI itself, etc). I do plan to submit it here when I am happy with it. However it certainly is tough for you to give me advice without any idea at all about what I am up to.



Since I am very weight conscious I decided early on that I would use the light weight ECI accessory pad which does not provide a vacuum or prop governor. This saves 1.5 pounds. The B&C SD-20 spine driven alternator is 5.75 pounds, plus creates space issues for me under the cowl. I thought that I would rather spend that 7.25 pounds on a spare battery if my mission needed it.



The injectors draw 1.5 - 2.0 amps each depending on load. The vendor recommends 5 amp fuses.



The 50 amp b-lead breaker is simply copied from what Cubcrafters does on their certified Carbon Cubs. What is the right answer? An ANL fuse somewhere?



Mark

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markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Sun Dec 15, 2019 7:35 pm Post subject: Re: Questions as I Design My Circuit Diagram

Bob,



You were right. My spreadsheet numbers (and my memory of the correct numbers) were wrong. 



The range of energy consumption per injection according to their vendor is .5 - 1.5 amps depending on load.



My load (5 gph) is at the bottom of his range.



It doesn’t change my design, but I have to eat humble pie.



Mark

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