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aarongleixner(at)sbcgloba
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 Posted: Sun Apr 29, 2007 12:48 pm Post subject: Z-13/20 Questions |
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I'm planning the electrical system for my RV-10, and really like the layout of the Z-13/8 system, but want the extra power of the SD-20. I originally was looking at the Z-12 layout, but didn't like 1) Single point failure of battery contactor leaves you running endurance bus on battery only, and 2) in the event of main alternator failure, I want to quickly switch to a large endurance bus and not have to start turning off loads individually on the main bus if I'm over 20 Amps.
My question is why can't I use the Z-13/8 layout, and simply increase the size of the e-bus fuse on the main battery bus to 20 amps, and us an e-bus alternate feed switch that could handle 20 maps. The alternator field for the backup alternator could be run from the e-bus. It eliminates the S701-1 e-bus contactor which adds a lot of wire runs for the RV-10 with battery in the tail. Seems like a simple solution, what am I missing?
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Mon Apr 30, 2007 4:59 am Post subject: Z-13/20 Questions |
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At 01:46 PM 4/29/2007 -0700, you wrote:
| Quote: | I'm planning the electrical system for my RV-10, and really like the
layout of the Z-13/8 system, but want the extra power of the SD-20. I
originally was looking at the Z-12 layout, but didn't like 1) Single point
failure of battery contactor leaves you running endurance bus on battery
only, and 2) in the event of main alternator failure, I want to quickly
switch to a large endurance bus and not have to start turning off loads
individually on the main bus if I'm over 20 Amps.
My question is why can't I use the Z-13/8 layout, and simply increase the
size of the e-bus fuse on the main battery bus to 20 amps, and us an e-bus
alternate feed switch that could handle 20 maps. The alternator field for
the backup alternator could be run from the e-bus. It eliminates the
S701-1 e-bus contactor which adds a lot of wire runs for the RV-10 with
battery in the tail. Seems like a simple solution, what am I missing?
|
Under what conditions to you expect to exploit the
capability of so robust a standby system? And what
is the probability of experiencing such an event?
There are hundreds of thousand of airplanes flying
wired per Figure 17-1. If I were to choose to venture
into IMC with a rented airplane, what I see is what
I get. It's all "certified" and and not one pilot
I know has ever opined that he/she would never file
to go into the clouds because the airplane offered
weak, if any options for plan-b. The airplane
might still be fitted with a flooded battery that
only gets replaced when it fails to crank and engine.
The alternator is a descendant of the best-we-knew-
how-to-do in 1965 and are technological junk by
today's standards.
Given the proven track record of modern alternators,
RG batteries, and preventative maintenance philosophies
that insure minimal battery capacity, if you were still
wired per C-172, your electrical system offers a quantum
jump in reliability.
Now comes an opportunity to add still more capability
for avoiding a bad day with the wife and kids aboard.
Converting the avionics bus to a dual feed endurance
bus along with a load shedding plan that may well
offer battery only endurance that exceeds duration
of fuel aboard.
Then we have the prevalence of all electric panel
hardware that offers a rational way to get rid
of the weight and complexity of a vacuum system
that leaves a vacuum pump pad open. This is
an opportunity to support an 8A endurance bus
indefinitely and save 100% of a well maintained
battery for approach and landing.
You've said you "want" the extra power of the
SD-20 . . . under what conditions would you
expect to "need" that much endurance power? Finally,
given the demonstrated performance of modern
alternators, batteries and e-bus structures,
what is the perceived return on investment for
adding weight and complexity to a system that
is pretty close to "golden".
What you propose to do can be done. There
are many variations on a theme that can be
considered and installed in your project. My
advice is to first deduce circumstances and put
numbers to the situation that makes Z-13/8
fall short of your reliability needs. I.e,
do the failure mode effects analysis.
Recall that 99.99% of all breakers installed
on all aircraft are never called upon to do
their job but they take up space and offer
no small cost-of-ownership. If there's
something "missing" in your proposal for
a more robust endurance supply, it's for not
expressing numbers and logic that offer a
compelling argument for doing so. There
are a gazillion things all those buttons
do on my VCR, TV and cable remotes that I
would just as happy with if they were not
there. I'm always hitting the wrong button
in the dark. What you need to do is properly
convince yourself that the proposed change
is a good thing. At the moment, I can
perceive no conditions of operation that
make the SD-20 attractive, perhaps you
have some ideas that have not been considered
here on the List. But take care lest you're
simply jacking up cost-of-ownership for your
project by adding "breakers that never need
to work" and "buttons that are a pain-in-the-
arse in the dark."
In fact, I've convinced myself that Z-13/20
architecture needs to come out of the next
revision. The next step up from Z-13/8 should
be Z-14 and I'd judge that very few, perhaps
1% of OBAM aircraft projects would make good
use of a Z-14 installation. Is there a better
place to invest the cash and fuel?
Bob . . .
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aarongleixner(at)sbcgloba
Guest
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| Posted: Sun May 06, 2007 9:54 am Post subject: Z-13/20 Questions |
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Bob,
Thanks for the response. After having alternators fail on 3 of my last 4 cars at relatively low time, I'm working on the assumption that the main alternator will fail at some point. Considering Murphy's Law, I know it will happen in heavy IFR with the entire family on board. Also, with the EFIS, I won't have a vacuum system to keep me straight and level, when the alternator fails, unlike some of the older planes you mention below. The minimum equipment list I developed is as follows:
Garmin 430W - Having a hard time finding exact power usage, but most people seem to be using 3 Amps for the Nav and 1 Amp for the Comm (+6A more when transmitting)
Garmin 330 Transponder - 2A
Digiflight Autopilot - 0.5 A Base load + 2 Amps intermittent for Servos
Grand Rapids EFIS - 2A (Two Screens) + 0.2 A for AHRS
Interior Lights + Bose Headsets - 0.4 A
Electric Trim - 0.3A + 1.2A intermittent for servos
Backup ADI - 0.5A
This gives a continuous load of 9.9A going intermittently to 13.1A. This loading seems to be in excess of what you would like for the SD-8, and even reducing the EFIS to 1 screen still seems like too much. So this drove me to look at the SD-20. When looking at the differential from the SD-8 to SD-20, I am estimating a $250 price difference (OV regulator included) and 2 pound weight increase. With the ability of the SD-20 to carry all the loads, even during landing, having a healthy battery becomes less critical. With my battery at $150, being able to extend replacements by even 1 year, rapidly pays off the $250 alternator difference, to the point where the larger alternator could have the lower life cycle cost. For me the two pounds is insignificant, and my lower stress levels when the main alternator fails would be a significant plus for the SD-20.
So this brings me back to the desire to have the optimal single battery, dual alternator setup using the SD-20. The Z-12 diagram comes close, but failure of the master contactor would really ruin my day especially without a well maintained battery. It also only allows for 7A or less on the endurance buss. Z-14 seems like overkill, with plenty of extra components to maintain, along with the second battery. Z-13/8 seems like the optimal setup, assuming I could upsize to the SD-20, and enlarge the endurance buss and alternate feed to handle 20 Amps. The Z-13/20 setup adds the 2nd contactor, which now causes lots of wire run problems with the battery in the tail.
Bob, what am I missing? Do you see any issues with using the Z-13/8 setup and replacing the 7A fuse on the battery bus with a 20A fuse, upsizing the wire to handle 20A, getting an e-bus diode that can handle 20A, and picking an e-bus switch good for 20A. The SD-20 Alt Field would be run off the e-bus to assure it continues to run if the master contactor fails.
Could this be the replacement diagram when you pull Z-13/20 from the book? I guarantee there are other RV-10 builders that are looking for the optimal 1 battery, 2 alternator solution that has the power to run an EFIS/autopilot/transponder/GNS430 or equivalent package when the primary alternator fails.
Aaron
"Robert L. Nuckolls, III" <nuckollsr(at)cox.net> wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
At 01:46 PM 4/29/2007 -0700, you wrote:
| Quote: | I'm planning the electrical system for my RV-10, and really like the
layout of the Z-13/8 system, but want the extra power of the SD-20. I
originally was looking at the Z-12 layout, but didn't like 1) Single point
failure of battery contactor leaves you running endurance bus on battery
only, and 2) in the event of main alternator failure, I want to quickly
switch to a large endurance bus and not have to start turning off loads
individually on the main bus if I'm over 20 Amps.
My question is why can't I use the Z-13/8 layout, and simply increase the
size of the e-bus fuse on the main battery bus to 20 amps, and us an e-bus
alternate feed switch that could handle 20 maps. The alternator field for
the backup alternator could be run from the e-bus. It eliminates the
S701-1 e-bus contactor which adds a lot of wire runs for the RV-10 with
battery in the tail. Seems like a simple solution, what am I missing?
|
Under what conditions to you expect to exploit the
capability of so robust a standby system? And what
is the probability of experiencing such an event?
There are hundreds of thousand of airplanes flying
wired per Figure 17-1. If I were to choose to venture
into IMC with a rented airplane, what I see is what
I get. It's all "certified" and and not one pilot
I know has ever opined that he/she would never file
to go into the clouds because the airplane offered
weak, if any options for plan-b. The airplane
might still be fitted with a flooded battery that
only gets replaced when it fails to crank and engine.
The alternator is a descendant of the best-we-knew-
how-to-do in 1965 and are technological junk by
today's standards.
Given the proven track record of modern alternators,
RG batteries, and preventative maintenance philosophies
that insure minimal battery capacity, if you were still
wired per C-172, your electrical system offers a quantum
jump in reliability.
Now comes an opportunity to add still more capability
for avoiding a bad day with the wife and kids aboard.
Converting the avionics bus to a dual feed endurance
bus along with a load shedding plan that may well
offer battery only endurance that exceeds duration
of fuel aboard.
Then we have the prevalence of all electric panel
hardware that offers a rational way to get rid
of the weight and complexity of a vacuum system
that leaves a vacuum pump pad open. This is
an opportunity to support an 8A endurance bus
indefinitely and save 100% of a well maintained
battery for approach and landing.
You've said you "want" the extra power of the
SD-20 . . . under what conditions would you
expect to "need" that much endurance power? Finally,
given the demonstrated performance of modern
alternators, batteries and e-bus structures,
what is the perceived return on investment for
adding weight and complexity to a system that
is pretty close to "golden".
What you propose to do can be done. There
are many variations on a theme that can be
considered and installed in your project. My
advice is to first deduce circumstances and put
numbers to the situation that makes Z-13/8
fall short of your reliability needs. I.e,
do the failure mode effects analysis.
Recall that 99.99% of all breakers installed
on all aircraft are never called upon to do
their job but they take up space and offer
no small cost-of-ownership. If there's
something "missing" in your proposal for
a more robust endurance supply, it's for not
expressing numbers and logic that offer a
compelling argument for doing so. There
are a gazillion things all those buttons
do on my VCR, TV and cable remotes that I
would just as happy with if they were not
there. I'm always hitting the wrong button
in the dark. What you need to do is properly
convince yourself that the proposed change
is a good thing. At the moment, I can
perceive no conditions of operation that
make the SD-20 attractive, perhaps you
have some ideas that have not been considered
here on the List. But take care lest you're
simply jacking up cost-of-ownership for your
project by adding "breakers that never need
to work" and "buttons that are a pain-in-the-
arse in the dark."
In fact, I've convinced myself that Z-13/20
architecture needs to come out of the next
revision. The next step up from Z-13/8 should
be Z-14 and I'd judge that very few, perhaps
1% of OBAM aircraft projects would make good
use of a Z-14 installation. Is there a better
place to invest the cash and [quote][b]
| | - 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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