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Z-13/8 inquiry

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bcone1381

Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan

Posted: Wed Nov 15, 2017 3:41 am Post subject: Z-13/8 inquiry

In the beginning phase of planning the architecture of my electrical system. I have never done this before, and appreciate your mentoring.  I have two questions for you after reading thru the background for the questions



The 12th edition of the Aero Electric Connection book Chapter 17 is titled Electrical System Reliability.  In this CH, Bob introduces us to a Cessna electrical system, then provides reliability improvements.  Bob expands the Avionics Bus to serve as an Essential Bus, and then replaces the Cessna avionics master with a diode for its normal power feed. 



The alternate power feed from the Battery to the Essential Bus shown in the CH17 example is a simple switch.  This improvement over the Cessna system removes the 1 amp draw of the Batter Contactor.  Thats Great, I love it.



But, when I check out the Z-13/8 diagram, it shows an S704-1 relay....supplied by B&C.  



Questions:  

1) Why don't we use a switch as discussed in Ch 17?  

2) What is the amp draw of this Relay?  Maybe thats a Q. for B&C

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_________________
Brooks Cone
Bearhawk Patrol Kit Build

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Wed Nov 15, 2017 5:55 am Post subject: Re: Z-13/8 inquiry

A relay can be used for remote control.  That allows the circuit to be shut off near the battery without running always-hot wires into the cockpit.  Shutting off power near the source is important in case of smoke in the cockpit or in case of an imminent forced landing.

A small switch can control a relay.  A relay can control a larger current.

The relay manufacturer's data sheet will state the current draw.  I think that the current will be less than 1/10 amp.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 15, 2017 8:32 am Post subject: Z-13/8 inquiry

At 05:41 AM 11/15/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com>



 In the beginning phase of planning the architecture of my electrical system. I have never done this before, and appreciate your mentoring.  I have two questions for you after reading thru the background for the questions



 The 12th edition of the Aero Electric Connection book Chapter 17 is titled Electrical System Reliability.  In this CH, Bob introduces us to a Cessna electrical system, then provides reliability improvements.  Bob expands the Avionics Bus to serve as an Essential Bus, and then replaces the Cessna avionics master with a diode for its normal power feed. 



 The alternate power feed from the Battery to the Essential Bus shown in the CH17 example is a simple switch.  This improvement over the Cessna system removes the 1 amp draw of the Batter Contactor.  Thats Great, I love it.



 But, when I check out the Z-13/8 diagram, it shows an S704-1 relay....supplied by B&C.  



 Questions:  

 1) Why don't we use a switch as discussed in Ch 17?  

 2) What is the amp draw of this Relay?  Maybe thats a Q. for B&C 	


    The e-bus was, as far as I can remember, first

    installed on a LongEz about 1985. I was talking

    with a reader one night on the phone. He was in

    California if memory serves. His engine driven power

    source was the SD8 alternator . . . 



    We were discussing his load analysis



  http://tinyurl.com/9rt6ymn



  http://tinyurl.com/7jqypwj



    While running through the list of electro-

    whizzies needed for comfortable continuation

    of flight. battery only, to intended destination,

    a major component of electrical loads was

    the battery contactor . . . it's current

    draw after warm up and at battery only voltages

    was on the order of 0.6A.



  http://tinyurl.com/mpcgp3t



  http://tinyurl.com/k6bwdqo



    Contactor power would not be available to run endurance

    loads during battery only operations.



    During that conversation, we crafted what

    started out as an 'essential' bus but later

    corrected to 'endurance' bus. The goal

    during that conversation was to craft a system

    whereby a long distance flight would NOT be

    limited not by battery capacity but by fuel

    aboard.



    As I recall, his endurance loads were finally

    pared down to about 2.2 amps. His design goal

    for battery only ops was 4 hours. This meant

    that a battery at end of service life had to

    support his 2.2A load for 4 hours. If end

    of service life was 75% of new capacity, then

    a new battery needed to support 2.2A for 

    at least 5.5 hours.



    I don't recall what constellation of battery products

    were in popular consideration back then but let

    us suppose that same conversation was today and

    the Hawker PC680 was one of several candidates

    under consideration.



 [img]cid:.0[/img]



 

   Here we see that a 2.2A load on a new battery is good for

   5 hours . . . barely adequate to the design goal. Leaving

   a 0.6A battery contactor load in the mix would have dropped

   new battery endurance to 4 hours.



   The endurance bus with dual feed paths was birthed that

   evening. The 2.2A endurance load could be tapped directly

   from the battery bus through a fuse of 7.5 amps or less.



   This brings up another design goal for making direct

   connections to batteries. The legacy design conventions

   in type certified aircraft called for always hot feeders to

   be protected at no more than 5A. The idea was to limit

   the battery's ability to start fires in the event of

   a landing that was really hard to walk away from.



   TC designs for taking power away from the battery at

   greater current levels had to be crew controlled

   like the battery contactor. As our OBAM aircraft

   evolved, some design goals called for e-bus loads

   exceeding that which could be carried on 7.5A fuse

   (we adopted 7A over the 5A figure because fuses

   are MANY times faster than breakers).



   So you see, there is no cookie-cutter answer to

   your question. Using an e-bus alternate feed

   relay is a decision driven by (1) establishment

   of design goals for flight in the endurance

   mode (2) selection hardware you're going to run

   in the endurance mode, (3) selecting battery

   capacity to meet the goal and (4) PERIODIC MAINTENANCE

   checks to MAINTAIN the battery at the required

   capacity.



   This conversation took place years before Z13/8 . . .

   a time when vacuum pumps were being installed

   on large numbers of OBAM aircraft.  As the such-n-blow

   instruments began to disappear from the panels, the

   vacuum pump pad became the ideal real estate for

   installing a SECOND engine driven power source and

   the SD8 was an obvious choice.



   Z13/8 was crafted to exploit that real estate

   and allow the builder to craft an e-bus load

   value on the order of 8A. Battery capacity was

   no longer the primary consideration for endurance

   after loss of main alternator.



   Hence the development of Z32 which installs a relay

   to serve as a kind of mini-battery contactor that

   gives the crew direct control over that feeder

   AT THE BATTERY protected by a 10A fuse.



   It follows that the relay (which draws about 0.1A)

   is only needed if e-bus loads exceed 5A or so in

   the ENDURANCE mode . . . in the case of Z13/8,

   maximum endurance load without taxing the battery

   is 8A and the feeder is a bit fatter wire. So

   the e-bus alternate feed relay became a permanent

   feature in Z13/8 revision T. 



 

   Bob . . .

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bcone1381

Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan

Posted: Wed Nov 15, 2017 9:31 am Post subject: Re: Z-13/8 inquiry

I feel like I am starting to dissect an onion....so many layers.  Your explanation of the TC design goals makes clear the need for the contractor.  



The Load analysis information you just shared must be my next path to start exploring.  This will be ton of fun to figure out. 



Thanks so much.  

I know of nowhere that an aircraft builder can get clear answers to questions based on truth and principle and void of opinion and heresy.

_________________
Brooks Cone
Bearhawk Patrol Kit Build

bcone1381

Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan

Posted: Mon Feb 05, 2018 6:07 pm Post subject: Re: Z-13/8 inquiry

More Questions.



I took a screen shot of a small part of the Z-10/8 wiring diagram.  Focus with me on the bus tie between the Main Power Bus and the Endurance Bus.  The Endurance Bus gets its primary feed from the Main Power bus thru the Diode, and its typical of the diagrams in AEC.



This circuit is unprotected....no fuse, no circuit breaker, no current limiter, no fuse link.  I guess thats ok., but seems abnormal.  Can I have some feedback?  



I argue with myself that its because we want a reliable E-bus feed.  Then I see that the diagrams in AEC fuse the Alternate Feed from the Hot Battery Bus.

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Brooks Cone
Bearhawk Patrol Kit Build

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 06, 2018 8:05 am Post subject: Z-13/8 inquiry

At 08:07 PM 2/5/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964(at)gmail.com>



 More Questions.



 I took a screen shot of a small part of the Z-10/8 wiring diagram.  Focus with me on the bus tie between the Main Power Bus and the Endurance Bus.  The Endurance Bus gets its primary feed from the Main Power bus thru the Diode, and its typical of the diagrams in AEC.



 This circuit is unprotected....no fuse, no circuit breaker, no current limiter, no fuse link.  I guess thats ok., but seems abnormal.  Can I have some feedback?  	


   The e-bus and main bus should be located close to each

   other. The wires that connect the normal feedpath diode

   are short. Risk to those wires is nil. No protection

   warranted.



 

  	  Quote: 	
		  I argue with myself that its because we want a reliable E-bus feed. 	


   You have two feed paths . . . loss of one is unlikely,

   loss of both is exceedingly unlikely. 



  	  Quote: 	
		    Then I see that the diagrams in AEC fuse the Alternate Feed from the Hot Battery Bus. 	


   That's a long feeder that's not so free of risk.



 

   Bob . . .

mmcelrea

Joined: 05 Nov 2017
Posts: 10

Posted: Fri Feb 23, 2018 7:03 pm Post subject: Re: Z-13/8 inquiry

Why is there no protection on the feed wire to the main bus from the battery contactor? Assuming the contactor is on the firewall fwd and the main bus is on a sub panel in front of the main panel it’s going to be a wire of potentially a couple of feet long. Same thing could apply to the battery bus.

Also why are the amp outputs monitored from both alternators? If the main alternator fails and the amps in/out of the battery is monitored instead of the sd8 output then load sharing might be easier? If you knew that the battery was being discharged would you have an idea what endurance you might have?

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sat Feb 24, 2018 8:20 am Post subject: Re: Z-13/8 inquiry

Most aircraft are wired without protection on the main bus feeder.

  The theory is that if the feeder shorts to sheet metal, then the sheet 

metal will burn away before the feeder burns in two.  The most likely 

place for the feeder to short out is where it passes through the firewall.  

If properly installed, then that will not happen.

  As for a battery bus, adding a fuse is likely to cause a problem, 

not eliminate one.

  There are 3 possible locations for an ammeter: alternator output, 

battery current, or aircraft load.  Each location has its advantages 

and disadvantages.  There has been much debate about which 

location is best.  It is a matter of personal preference.  No matter 

which location is chosen, the important thing is for the pilot to 

understand what the ammeter is displaying.  For example, suppose 

the builder installs the ammeter to measure aircraft load.  The aircraft 

is then sold.  While on a cross country trip, the new owner notices that 

the voltage is low.  He is not concerned because the ammeter is showing 

normal current.  He does not realize that the alternator has failed and 

the battery is running down.  Actually an ammeter is not a necessity.  

A voltmeter will tell the condition of the electrical system.  If the voltage 

drops much below 14, something is wrong.  Do the troubleshooting on 

the ground.

_________________
Joe Gores

speedy11

Joined: 29 Jun 2015
Posts: 62
Location: Port Orange, FL

Posted: Sun Feb 25, 2018 4:50 pm Post subject: Z-13/8 inquiry

Joe,

 Can one assume that a Hall Effect would be installed on one of the three places an ammeter would be installed?

 It seems logical that a Hall Effect would be placed on the lead from the alternator.  Thus, it would correlate with the activation of the low voltage light.

 How about a shunt?  Same locations as ammeter?

 Suppose you have two batteries.  Hall Effect on the alternator lead and shunt on the second battery + lead?

 Stan

 

  Subject: Re: Z-13/8 inquiry

 From: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 

 Most aircraft are wired without protection on the main bus feeder.

   The theory is that if the feeder shorts to sheet metal, then the sheet 

 metal will burn away before the feeder burns in two.  The most likely 

 place for the feeder to short out is where it passes through the firewall.  

 If properly installed, then that will not happen.

   As for a battery bus, adding a fuse is likely to cause a problem, 

 not eliminate one.

   There are 3 possible locations for an ammeter: alternator output, 

 battery current, or aircraft load.  Each location has its advantages 

 and disadvantages.  There has been much debate about which 

 location is best.  It is a matter of personal preference.  No matter 

 which location is chosen, the important thing is for the pilot to 

 understand what the ammeter is displaying.  For example, suppose 

 the builder installs the ammeter to measure aircraft load.  The aircraft 

 is then sold.  While on a cross country trip, the new owner notices that 

 the voltage is low.  He is not concerned because the ammeter is showing 

 normal current.  He does not realize that the alternator has failed and 

 the battery is running down.  Actually an ammeter is not a necessity.  

 A voltmeter will tell the condition of the electrical system.  If the voltage 

 drops much below 14, something is wrong.  Do the troubleshooting on 

 the ground.

 

 --------

 Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Mon Feb 26, 2018 6:18 am Post subject: Re: Z-13/8 inquiry

Stan,

It is up to the aircraft builder to decide how many and where to locate current sensors.  It does not matter if the sensors are shunt or hall effect type, as long as each is compatible with its display.  Some EFISs have inputs for more than one current sensor.  If a display only has one input, a selector switch can choose which sensor to connect to the display.  Your plan to use one hall effect sensor and one shunt sensor will work, provided that the sensors are compatible with the display(s).

_________________
Joe Gores

bcone1381

Joined: 25 Apr 2017
Posts: 42
Location: Southeast Michigan

Posted: Fri Jul 19, 2019 9:12 am Post subject: Re: Z-13/8 inquiry

[quote="nuckolls.bob(at)aeroelect"]At 05:41 AM 11/15/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "bcone1381" <bcone1964>



 

   This brings up another design goal for making direct

   connections to batteries. The legacy design conventions

   in type certified aircraft called for always hot feeders to

   be protected at no more than 5A. The idea was to limit

   the battery's ability to start fires in the event of

   a landing that was really hard to walk away from.



   Bob . . . 	




My Load Analysis looks like the electrical system will have less than 10A draw.  4.5A continuous, 9.5A when the Fuel Pump is on. So, simplification, reliability and weight reduction would demand dual buses with equal loads, and ditching the Battery Master Relay.  Is that unconventional idea a bad idea?  What am i not seeing?

_________________
Brooks Cone
Bearhawk Patrol Kit Build

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Fri Jul 19, 2019 11:27 am Post subject: Re: Z-13/8 inquiry

The pilot needs a way to quickly shut off all sources of electrical power at the source.

This is important in case of smoke or fire or an imminent forced landing.  A battery contactor will fulfill that need.

A battery contactor can also be shut off if the starter contactor welds itself shut.

Each circuit should have its own fuse.  If a fuse blows, only one load will quit working.

 Dual buses are more complicated than a single bus

_________________
Joe Gores

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Fri Jul 19, 2019 11:53 am Post subject: Z-13/8 inquiry

A battery contactor allows for easy connection to a battery charger, whereby the battery charging current is limited to the battery, without powering the bus/systems. It also allows for easy connection to a ground power source to power the bus/systems, without subjecting the battery to the ground power.



On Fri, Jul 19, 2019 at 11:37 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 The pilot needs a way to quickly shut off all sources of electrical power at the source.

 This is important in case of smoke or fire or an imminent forced landing.  A battery contactor will fulfill that need.

 A battery contactor can also be shut off if the starter contactor welds itself shut.

 Each circuit should have its own fuse.  If a fuse blows, only one load will quit working.

  Dual buses are more complicated than a single bus

 

 --------

 Joe Gores

 

 

 

 

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