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deej(at)deej.net
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 Posted: Wed Jan 08, 2014 8:58 am Post subject: Proposed new Z diagram? |
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Bob, I think I am getting a glimmer of understanding of the underlying
message you've been trying to communicate. I've been looking at this as
a top-down approach, and I presented a draft in roughly step 3 of my
design process and you've been asking about things back in step 1 that
I've attempted to communicate, but have failed to do so successfully.
You've also been asking about things in step 5, but we aren't there
yet... 
In rough terms, my "steps" are along the lines of:
1) List features and design goals.
2) Draft a circuit to reflect step 1. Note this is to illustrate a
functional representation, and is not intended as a implementation
diagram, thus specific values for components are not indicated at this time.
3) Review the circuit and verify functionality, checking for undesired
behaviour, etc. (This is where I submitted my first post to the mailing
list asking for peer review)
4) Spec each individual load and determine the appropriate location for
each load in the circuit. Examples would be to finalize the list of
which devices would be on the redundant bus, which would be on the main
bus, etc.
5) Fill in specific values for components in the circuit diagram and
draft an implementation diagram.
6) Review, verify, finalize.
7) Build the circuit and test, test, test.
Here is my list of features and design goals:
1) There are devices that are considered critical to the safe operation
of the aircraft. These devices should be able to draw power from two
completely independent power buses and battery sources. This shall be
known as the "redundant" bus.
2) When everything is on, devices on the redundant bus should be able to
automatically draw power from either source, with no user intervention
required. Ie, if one of the bus/batteries fails or is turned off, the
devices on the redundant bus will remain powered on using the other source.
3) Bonus feature if alternator-only mode can be optionally supported.
4) Minimize "always-hot" wires.
5) No parasitic loads on the battery when everything is "off" (ie,
clocks, etc.).
6) Each battery and associated bus should be able to be switched "off"
and isolated from the rest of the circuit.
7) With special regard to the engine ignition, the ability to switch off
independently of the other devices for pre-flight equivalent of "mag
checks".
Notes:
The EFIS has three built-in diode isolated power inputs. This implies
that it can be wired directly to the primary and secondary power buses
directly using two of those inputs.
Devices having only one power input and that are considered critical are
wired to the redundant bus. Other non-critical devices will be wired to
the primary bus.
The aircraft will initially have one mag and one Electronic Ignition
(EI). Eventually the second mag will likely be replaced with a second
Electronic Ignition. Based on discussions that we've had so far on the
list, I've already realized a change to be made from my initial drawing
with regards to how the ECU is connected. There will be one switch for
the mag, and one switch for the EI (versus the two switches for the
single EI as shown currently). When the mag is swapped for the second
EI, the switch will be swapped as well, leaving one switch for each EI,
allowing them to be switched on and off independently.
Physical layout:
My panel is laid out such that the engine switches are separate from the
rest. The three will be laid out as Mag (or 1st EI), 2nd EI, Starter.
Electrical would be Primary Power, Alternator, Secondary Power, followed
by the switches for the lights, etc.
Operations:
Normal operations are Primary, Alternator, and Secondary switches in the
on position before engine start, and until engine shutdown.
In the event of "smoke", Primary and Alternator would be turned off by
hitting the two leftmost switches. This cuts power to all but the
flight critical devices and has the highest chance of cutting power to
whatever is "smoking". If "smoke" continues, turn on Primary power and
turn off Secondary. If "smoke" still continues, get on the ground ASAP
- one or the other power bus must remain on to power the engine and EFIS.
Note there is a good argument to be made to replace the two separate
Alternator and Primary power switches with a combined three position
switch. This would reduce the total DC power switch count to 2, and
slightly reduce operations complexity while only giving up
alternator-only mode, which has dubious value in a two redundant bus
arrangement. After further thought, I am going to make this change in
my diagram.
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
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deej(at)deej.net
Guest
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| Posted: Wed Jan 08, 2014 11:54 am Post subject: Proposed new Z diagram? |
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Updated "Z-redundant-B" diagram at
http://deej.net/glastar/pics/electrical/Z-redundant-B.jpg
Changes:
Removed alternator-only operation by combining the separate Alt and
Primary bus switches into a single three position switch (Off, Bat,
Bat+Alt).
Reduced operational complexity by removing separate Alt switch. Now has
2 DC power switches (Primary/Alt and Secondary) versus 3. In the event
of "smoke", turn the left most switch (Primary/Alt) off. This cuts
power to all but the flight critical devices and has the highest chance
of cutting power to whatever is "smoking".
Reflects two EI ECUs with independent switching to allow pre-flight
equivalent of "mag checks"
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
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livingjw(at)earthlink.net
Guest
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| Posted: Wed Jan 08, 2014 1:57 pm Post subject: Proposed new Z diagram? |
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How do you know that each feed going into your diodes is working?
On 1/8/2014 2:53 PM, Dj Merrill wrote:
| Quote: |
Updated "Z-redundant-B" diagram at
http://deej.net/glastar/pics/electrical/Z-redundant-B.jpg
Changes:
Removed alternator-only operation by combining the separate Alt and
Primary bus switches into a single three position switch (Off, Bat,
Bat+Alt).
Reduced operational complexity by removing separate Alt switch. Now has
2 DC power switches (Primary/Alt and Secondary) versus 3. In the event
of "smoke", turn the left most switch (Primary/Alt) off. This cuts
power to all but the flight critical devices and has the highest chance
of cutting power to whatever is "smoking".
Reflects two EI ECUs with independent switching to allow pre-flight
equivalent of "mag checks"
-Dj
|
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jan 08, 2014 2:28 pm Post subject: Proposed new Z diagram? |
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| Quote: |
In rough terms, my "steps" are along the lines of:
1) List features and design goals.
|
Let's concentrate on this step. Take the Z-figure
that comes closest to what you want. Describe which
features do not address a design goal and articulate
what you would do different . . . speak to the design
goal either in terms of (1) a perceived risk that is
mitigated by a proposed change or (2) "just because."
There is no wrong motivation . . . but features
in the 1-bucket can be evaluated against legacy
lessons-learned and technical/economic trade-offs;
stuff in the 2-bucket are not technically debatable.
The feature offers functionality that is easily confirmed
by looking at the diagram and no sifting of
simple-ideas is needed. The change is justified
"just because".
This is an important exercise . . . if there are
compelling revelations of shortcoming in any of
the Z-figures, I'm intently interested in knowing
what they are. At the same time I am reluctant
to publish pretty-variations-on-a-theme that offer
no demonstrable increase in utility or reduction
of risk.
I just received a drawing from another reader
who has crafted a one-battery, two-alternator
configuration loosely based on Z-12 but with a
avionics master switch and some errors in
functionality. My question to him will be similar,
"How does Z-12 fall short of your expectations
for risk management and what information do you
have indicating that an avionics master is useful/
necessary?"
Bob . . .
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deej(at)deej.net
Guest
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| Posted: Wed Jan 08, 2014 5:16 pm Post subject: Proposed new Z diagram? |
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On 1/8/2014 4:56 PM, John W Livingston wrote:
| Quote: |
<livingjw(at)earthlink.net>
How do you know that each feed going into your diodes is working?
|
Hi John,
Excellent question. The GRT HX EFIS monitors each power input, and
will notify you if either of the two power inputs lose power. This will
verify that the Primary and Secondary buses are getting power.
I do not have any monitoring in the diagram to tell if each of the
diodes is working, however, a pre-flight check turning off each of the
buses before enabling the alternator could be an option. If any of the
critical devices power down, one of the diodes has failed (or some other
issue).
-Dj
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
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jluckey(at)pacbell.net
Guest
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| Posted: Wed Jan 08, 2014 6:10 pm Post subject: Proposed new Z diagram? |
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Dj, I cannot find your latest drawing. Can you send a link or attach it?
thx
From: Dj Merrill <deej(at)deej.net>
To: aeroelectric-list(at)matronics.com
Sent: Wednesday, January 8, 2014 5:15 PM
Subject: Re: Re: Proposed new Z diagram?
--> AeroElectric-List message posted by: Dj Merrill <deej(at)deej.net (deej(at)deej.net)>
On 1/8/2014 4:56 PM, John W Livingston wrote:
| Quote: | --> AeroElectric-List message posted by: John W Livingston <livingjw(at)earthlink.net (livingjw(at)earthlink.net)>
How do you know that each feed going into your diodes is working?
|
Hi John,
Excellent question. The GRT HX EFIS monitors each power input, and will notify you if either of the two power inputs lose power. This will verify that the Primary and Secondary buses are getting power.
I do not have any monitoring in the diagram to tell if each of the diodes is working, however, a pre-flight check turning off each of the buses before enabling the alternator could be an option. If any of the critical devices power down, one of the diodes has failed (or some other issue).
-Dj
-- Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.nnbsp; * The Builder's Bookstore [url=http://www.bu HomebuiltHELP www.mypilotstore.com[/url]
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deej(at)deej.net
Guest
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| Posted: Wed Jan 08, 2014 6:17 pm Post subject: Proposed new Z diagram? |
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On 1/8/2014 3:11 PM, Robert L. Nuckolls, III wrote:
| Quote: | > 1) List features and design goals.
Let's concentrate on this step. Take the Z-figure
that comes closest to what you want. Describe which
features do not address a design goal and articulate
what you would do different . . . speak to the design
goal either in terms of (1) a perceived risk that is
mitigated by a proposed change or (2) "just because."
|
The closest from the Connection is Z-19.
Using my list of features/design goals from the previous email (for
reference they are included at the end of this email) and comparing to Z-19:
1) For avionics, Z-19 offers power from two separate batteries, but it
does not offer it from two independent power buses. However, it DOES
have both of these features in the engine section of the circuit.
(Because if we can do it with the critical EI, it makes sense to also do
it with other equally critical devices. Non-critical devices in
Z-redundant-B are on the Primary bus just like Z-19)
2) Z-19 offers this feature with regards to the batteries.
3) No alternator-only mode, but since I've also removed this from
Z-redundant-B this is a null.
4) Z-19 does not minimize "always hot" wiring. (Because I don't like it,
and it is easy to create a circuit that does minimize "always hot"
wiring. I have nothing in my plane that requires "always hot" power
other than the contactors.)
5) Z-19 has parasitic loads. (Because I don't like my battery being
drained between flights, and I have nothing in the plane that requires a
constant power source. The GRT EFIS will sync its time via the GPS
signal after power-up.)
6) Z-19 does not offer this feature. (This is a cross between "just
because I want to" and safety. In general bus wiring is "safe", with
the common cause of failure being installation error as we've discussed
on the list. I'm not perfect, and could inadvertently crimp a bad
connection or make a bad solder joint. Additionally, being able to
switch off and isolate the two separate buses allows me to easily turn
off all non-critical devices with a single switch if there are issues in
flight)
7) As written, Z-19 supports a single EI which can be turned off, but
requires modification to support two EIs that can be turned off
independently. (This is a safety feature to ensure both ignitions are
working correctly during the pre-flight checks)
What I would do different (ie, what I did) was take the features
that I liked from the Z-19 diagram and use it as a basis to create
Z-redundant-B. You can see many of the features of Z-19 in the
Z-redundant diagram, with emphasis on the redundant engine bus concept
in Z-19 extended to support flight critical devices.
As an exercise, let's flip this around. Suppose hypothetically
Z-redundant-B had been around for awhile, and someone proposed Z-19.
Why would you choose to use Z-19 over Z-redundant-B? What
features/design goals exist in Z-19 that you desire compared to
Z-redundant-B?
-Dj
| Quote: | Here is my list of features and design goals:
1) There are devices that are considered critical to the safe operation
of the aircraft. These devices should be able to draw power from two
completely independent power buses and battery sources. This shall be
known as the "redundant" bus.
2) When everything is on, devices on the redundant bus should be able to
automatically draw power from either source, with no user intervention
required. Ie, if one of the bus/batteries fails or is turned off, the
devices on the redundant bus will remain powered on using the other source.
3) Bonus feature if alternator-only mode can be optionally supported.
4) Minimize "always-hot" wires.
5) No parasitic loads on the battery when everything is "off" (ie,
clocks, etc.).
6) Each battery and associated bus should be able to be switched "off"
and isolated from the rest of the circuit.
7) With special regard to the engine ignition, the ability to switch off
independently of the other devices for pre-flight equivalent of "mag
checks".
|
--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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deej(at)deej.net
Guest
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| Posted: Wed Jan 08, 2014 6:18 pm Post subject: Proposed new Z diagram? |
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On 1/8/2014 9:09 PM, Jeff Luckey wrote:
| Quote: | Dj, I cannot find your latest drawing. Can you send a link or attach it?
|
Hi Jeff,
It can be found at:
http://deej.net/glastar/pics/electrical/Z-redundant-B.jpg
-Dj
[quote]--
Dj Merrill - N1JOV - VP EAA Chapter 87
Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Glastar Flyer N866RH - http://deej.net/glastar/
[b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Thu Jan 09, 2014 7:11 am Post subject: Proposed new Z diagram? |
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At 03:56 PM 1/8/2014, you wrote:
| Quote: |
<livingjw(at)earthlink.net>
How do you know that each feed going into your diodes is working?
|
A cogent question. Any feature added to a
system intended to mitigate risk due to some
failure needs to be 'monitored' for functionality.
This can be a pre-flight test procedure, a
data acquisition system that watches for
anomalous conditions, a periodic investigation
during 100 hr inspections, etc. etc.
The thrust of John's question may not be
obvious . . . it's important that 'failed
features' not be allowed to persist
as latent failures.
The inability to detect such failures has
a tendency to negate their benefits.
Bob . . .
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