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DaveG601XL
Joined: 27 Oct 2006
Posts: 351
Location: Cincinnati, Oh
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 Posted: Thu Oct 25, 2007 1:52 pm Post subject: Electrical Drawing Critisism Wanted |
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Here is the drawing I have generated so far based on what I hope I have learned from this group and Bob's book. I am building a Jabiru 3300 powered Zenith 601XL. I am trying to make it a fairly simple day/night VFR machine. Electrical items planned include Dynon FlightDek 180, Garmin 296, Com, Xponder, Trutrack wing leveler, intercom, fuel boost pump and nav/landing/cockpit lights. If anybody here has a few minutes, please shoot holes in my overall electrical schematic. It is a combination of a few different Z diagrams and other builder's sites, like Matt's zodiacxl.com.
You may debate my choice of instruments if you wish, but I am mainly trying to make sure I didn't do anything stupid with the electrons and get to the point of passing the smoke test. I started this exercise knowing virtually nothing so I guess this is a final exam of sorts. Now fire away.
Thanks,
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| Description: |
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Download |
| Filename: |
My Drawing_01.pdf |
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362 Time(s) |
_________________
David Gallagher
Cincinnati, OH area |
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nuckolls.bob(at)cox.net
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| Posted: Fri Oct 26, 2007 4:03 am Post subject: Electrical Drawing Critisism Wanted |
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At 02:52 PM 10/25/2007 -0700, you wrote:
| Quote: |
<david.m.gallagher(at)ge.com>
Here is the drawing I have generated so far based on what I hope I have
learned from this group and Bob's book. I am building a Jabiru 3300
powered Zenith 601XL. I am trying to make it a fairly simple day/night
VFR machine. Electrical items planned include Dynon FlightDek 180, Garmin
296, Com, Xponder, Trutrack wing leveler, intercom, fuel boost pump and
nav/landing/cockpit lights. If anybody here has a few minutes, please
shoot holes in my overall electrical schematic. It is a combination of a
few different Z diagrams and other builder's sites, like Matt's zodiacxl.com.
You may debate my choice of instruments if you wish, but I am mainly
trying to make sure I didn't do anything stupid with the electrons and get
to the point of passing the smoke test. I started this exercise knowing
virtually nothing so I guess this is a final exam of sorts. Now fire away.
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I'd recommend that you use the OV protection
relay to open the AC output from the alternator
by having it break one of the two blue leads.
This philosophy is illustrated in
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z16M.pdf
Bob . . .
----------------------------------------
( "Problems are the price of progress. )
( Don't bring me anything but trouble. )
( Good news weakens me." )
( -Charles F. Kettering- )
----------------------------------------
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kuffel(at)cyberport.net
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| Posted: Fri Oct 26, 2007 9:05 am Post subject: Electrical Drawing Critisism Wanted |
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David,
Am of the opinion the use of the Dynon D-180, or any other EFIS
with internal battery backup, justifies a simplification to Bob's
method of feeding the Endurance Bus. In your diagram, remove the
Note 12 diode, remove the Avionics Master Switch and connect the
14AWG wire which fed the diode from the Main Bus to the unused
contact on the 1-3 E-Bus Alt Feed Switch.
This results in fewer parts and eliminates the voltage drop
across the diode along with the heat the diode generates. While
Bob specifies a very robust unit, the heat sensitive diode is
still a weak link compared to the other components in the path.
Now, come an electrical emergency (fire, trim runaway, A/P
failure, alternator runaway, etc.), you have one and only one
consistent action to take.. turn off the battery master.
Continue to fly the plane with the EFIS (and your GPS as backup).
At your leisure: 1) tell the EFIS and GPS you want them to
continue to operate on their internal battery power 2) turn off
everything fed by the Endurance Bus 3) switch the Endurance Bus
Alternate Feed to Battery Direct and 4) turn on each E-Bus load
one at a time and verify the item doesn't contribute to the problem.
Would also suggest the use of combined circuit breaker-switches
instead of the acres of breakers and separate switches of most
aircraft.
Fewer components, simpler procedures. Bob, what are the
negatives to this approach?
Tom Kuffel, AL7AU, CFI
Whitefish, MT
Building Sportsman
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nuckolls.bob(at)cox.net
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| Posted: Mon Oct 29, 2007 5:48 am Post subject: Electrical Drawing Critisism Wanted |
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At 11:03 AM 10/26/2007 -0600, you wrote:
| Quote: |
David,
Am of the opinion the use of the Dynon D-180, or any other EFIS with
internal battery backup, justifies a simplification to Bob's method of
feeding the Endurance Bus. In your diagram, remove the Note 12 diode,
remove the Avionics Master Switch and connect the 14AWG wire which fed the
diode from the Main Bus to the unused contact on the 1-3 E-Bus Alt Feed Switch.
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. . . which makes the alternate feed switch a single point
of failure for both feeds to the ebus.
| Quote: | This results in fewer parts and eliminates the voltage drop across the
diode along with the heat the diode generates. While Bob specifies a very
robust unit, the heat sensitive diode is still a weak link compared to the
other components in the path.
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But I've never seen one fail. Just how "heat sensitive"
is it? Can you quantify these assertions against the
components published capabilities and limits?
| Quote: | Now, come an electrical emergency (fire, trim runaway, A/P failure,
alternator runaway, etc.), you have one and only one consistent action to
take.. turn off the battery master. Continue to fly the plane with the
EFIS (and your GPS as backup). At your leisure: 1) tell the EFIS and GPS
you want them to continue to operate on their internal battery power 2)
turn off everything fed by the Endurance Bus 3) switch the Endurance Bus
Alternate Feed to Battery Direct and 4) turn on each E-Bus load one at a
time and verify the item doesn't contribute to the problem.
Would also suggest the use of combined circuit breaker-switches instead of
the acres of breakers and separate switches of most aircraft.
Fewer components, simpler procedures. Bob, what are the negatives to this
approach?
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Breaker-switches are mechanically complex devices,
expensive and require that you build "the bus" right
on the back of a row of switches in addition to
other busses along the backs of breakers that are not
switches.
http://www.aeroelectric.com/Pictures/Breakers/W31_1.jpg
We used about 80,000 of this breaker/switch
in Beech products over the past 40 years or
so. They would not be my first choice for
today's elegant design . . . like helicopters,
waayyyy to many moving parts going in different
directions.
The short path to Nirvana are the fuseblocks.
The busses are already fabricated, they're mounted
out of the way in minutes and do not encroach on
panel space.
I'll remind readers that the architectures
depicted in the z-figures offer specific features
for operation and failure mitigation. When
modifying an architectural feature of the drawings
for the purpose of some customization, be
aware that you may be tossing out some
salient feature.
While in Houston this weekend for a seminar,
I received a direct e-mail with several
attachments from a reader who likes the
book and thought the z-figures were really
helpful. He then offers up his own vision
of how he would like to wire the airplane
hoping for a few hours of my time to do
critical design review.
What he proposes will offer precisely
the functionality he is striving for but
ignores the thought processes that go into
minimum parts count, low cost of ownership,
optimum performance design based on the
histories for failures and their potential
consequences.
It's much more useful application of
your and my time to ask first how some
potentially ignored failure mode or missing
operational feature can be handled with a
modification to a z-figure.
One the all eggs are broken and scrambled,
the recipe is now yours to cook and savor
with all it's new features. In these
situations, it goes to individual taste
at the expense of the science and logic.
I'm not suggesting for a minute that
changes are bad or that the z-figures
are "golden". I'm only saying that
these recipes for success are refined
over years of consideration at the
operations and fabrication level. Proposed
change may well be the next step forward but
these are best accomplished incrementally.
One step at a time and with lots of eyes
and gray-matter pondering the consequences
both intended and unintended.
I hope that none of you feels that you've
waded into the tar pit and that years of
experience would save you from potential
hazards. Know that some of my customers
with decades of experience are doing the
same thing. Seems that everyone with a
voltmeter and a screwdriver in hand believes
that little tweaks to a design are
intellectually satisfying or bureaucratically
prudent while offering up little risk or cost.
'Tis not so.
I'm struggling with a "simple" design
change mandated by what appears to be an
ill-informed, upper level manager that
seriously impacts failure modes, installation
effort/risk and increases costs of ownership
by $thousands$ per ship-set.
As soon as first-articles are delivered and the
consequences of their decisions become
apparent on the iron-bird, I'm going to
suggest that my services might best
be utilized elsewhere.
These experiences reinforce an observation
by one of my heros who accurately noted
that one may know a great deal and still
understand nothing.
Bob . . .
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kuffel(at)cyberport.net
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| Posted: Mon Oct 29, 2007 4:03 pm Post subject: Electrical Drawing Critisism Wanted |
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Much of what Bob said is valid. But in this case must gently
disagree because:
Me: << remove the Note 12 diode, remove the Avionics Master Switch >>
Bob: << which makes the alternate feed switch a single point
of failure for both feeds to the ebus. >>
Disagree this is a fatal flaw. 1) The failure rate of a robust
switch, occasionally switching zero current (in my scenario), is
vanishingly small. 2) Even if the switch fails, the Dynon and
GPS continue to run, giving me time to land. 3) If I ever intend
to be in the clouds for more than "oops, do a 180 back to not in
the clouds" then I have a 2nd Nav/Com and Xpndr on the main bus.
This gives me the ability to stay upright, navigate and,
perhaps with ATC help, land in hard IFR.
Me: << eliminates the voltage drop across the diode along with
the heat the diode generates. .. robust unit, the heat sensitive
diode is still a weak link compared to the other components >>
Bob: << But I've never seen one fail. Just how "heat sensitive"
is it? Can you quantify these assertions >>
I've managed to fry many a semiconductor device in my career.
The crossover diode is a semiconductor device and thus "heat
sensitive" compared to wires, connectors, even switches, etc.
This is what I said. Robust but weak compared to other
components. Don't have numbers but have no doubt if I short out
the E-bus, the diode will melt. Do admit my aversion to the
voltage drop and power loss of the diode is a personal prejudice.
Me: << combined circuit breaker-switches instead of the acres of
breakers and separate switches >>
Bob: << Breaker-switches are mechanically complex devices,
expensive and require that you build "the bus" right
on the back of a row of switches in addition to
other busses along the backs of breakers that are not
switches. >>
The AIRPAX R11 series of circuit breaker/switches I mentioned in
my 9/29/07 post have many advantages over separate circuit
breakers and switches. They are hydraulic-magnetically tripped.
This gives a more stable trip point than the thermal types we
often use. Not only are the same components (without the trip
coil) sold as a switch, they are also rated for use in life
critical medical equipment. They are mechanically simpler than
the breaker in W31_1.jpg. At $11.05 from OnlineComponents.com
they are certainly less expensive than a separate switch and
circuit breaker. Don't see how it is more onerous to build a bus
behind the row of CB/Switches than it is to build a several row
bus behind the (usually far away) CB panel and run a dozen or
more wires over to the switches. In fact, my IFR capable
Sportman has so few pure circuit breakers (5) they all fit in the
left hand subpanel, along with the master switch, ignition sw,
E-bus crossover sw, etc. This puts all my bus wiring in one
local area, the same situation as a CB panel.
My aversion to fuse blocks is an even stronger prejudice. As a
control freak, I can envision failure modes (pitch trim or fuel
transfer overload for example) where I want to deliberately
override, if only for a short while, the condition causing the
trip. This is impossible with remote access fuse blocks.
Hope it is clear I am not saying there is anything wrong with
Bob's diagrams. Was trying to tell David my reasoning for
preferring an alternate approach given an internal battery backup
EFIS and GPS.
Tom Kuffel
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nuckolls.bob(at)cox.net
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| Posted: Mon Oct 29, 2007 7:18 pm Post subject: Electrical Drawing Critisism Wanted |
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At 06:03 PM 10/29/2007 -0600, you wrote:
| Quote: |
Much of what Bob said is valid. But in this case must gently disagree
because:
Me: << remove the Note 12 diode, remove the Avionics Master Switch >>
Bob: << which makes the alternate feed switch a single point
of failure for both feeds to the ebus. >>
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<snip>
| Quote: | Hope it is clear I am not saying there is anything wrong with Bob's
diagrams. Was trying to tell David my reasoning for preferring an
alternate approach given an internal battery backup EFIS and GPS.
Tom Kuffel
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Nobody here should be upset if you act upon
your own perceptions in the manner you see
fit. I certainly won't. I was asked and I
answered. There are many chefs with their
own recipes for success . . . some of whom
gather a clientele, others who may not.
I was only suggesting that alternatives
should be gauged against design goals that
strive for the desired functionality with
the minimum of $time$ in design, procurement,
fabrication, failure tolerance and cost of
ownership. Without a doubt, there are folks
who offer exceedingly robust products with
names like Airpax, TI, Cutler-Hammer, etc.
But even the mighty Potter-Brumfield came
very close to causing an expensive,
fleet-wide AD for a simple design deficiency
in the switch-breaker I cited.
My goal is to craft architectures that require
no special consideration for robustnes of
components . . . I.e, it shouldn't matter
if one buys switches at the hardware store.
We've had these discussions on different
topics . . . there'a a following of factory
fresh Nipon-Denso alternators who have
suggested it is not necessary to have absolute
control -OR- O.V. protection. Faith in these
products just might be justified. I
have no personal knowledge or experience
to reinforce those notions but I have strong
anecdotal information that suggests the faith
is unfounded. Nor do I want to recommend
that all my readers go out and buy factory
fresh, ND, Airpax, TI, or any other brand.
My design goals strive to craft a system
that is failure-tolerant for components
that may not have the robustness of those
upper-crust devices that some folks choose
to champion and recommend.
I fully understand the creative juices
that flow when one launches into so grand
a dream as crafting one's own airplane.
They're called "experimental" and they
can and should be viewed in this light.
This isn't about people my friend, it's
about ideas. It has been suggested that
diodes are somehow fragile and switches
are perhaps sufficiently robust to
offset a diode's shortcomings.
I'd be pleased to know the simple
ideas that support these assertions.
Bob . . .
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kuffel(at)cyberport.net
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| Posted: Mon Oct 29, 2007 9:45 pm Post subject: Electrical Drawing Critisism Wanted |
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Bob,
<< alternate approach given an internal battery backup EFIS and
GPS. >>
<< alternatives
should be gauged against design goals that
strive for the desired functionality with
the minimum of $time$ in design, procurement,
fabrication, failure tolerance and cost of
ownership. >>
And fewer components don't address these goals?
<< My goal is to craft architectures that require
no special consideration for robustnes of
components >>
And the crossover diode doesn't have to be robust compared to
regular diodes?
<< It has been suggested that
diodes are somehow fragile and switches
are perhaps sufficiently robust to
offset a diode's shortcomings.
I'd be pleased to know the simple
ideas that support these assertions. >>
No, I am suggesting no diode at all is more robust than any diode
and its attendant wiring. Would agree the single point failure
of the suggested change would be unacceptable if it weren't for
the internal batteries on the EFIS and GPS. But given the
premise, don't see how the change violates the goals of less
cost, simpler design, simpler installation, less maintenance and
reasonable fault tolerance (if you do have to shut down the main
bus your exposure to single point failure is the same with either
setup, perhaps less since the rare but additional possibility of
a shorted diode doesn't exist when it's omitted).
Tom Kuffel
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