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LarryRosen
Joined: 16 Jan 2006
Posts: 415
Location: Medford, NJ
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 Posted: Mon Mar 23, 2015 11:19 am Post subject: Z12 vs Z13-8 |
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I would like some confirmation that my rational for choosing between Z12
(60 & 20 amp alternators)and Z13-8 (60 and 20 amp alternators) is rational.
I am building a Vans RV-10. Based on my current projections, normal
continuous load will range between 20 and 35 amps. Low being day VFR
and high when landing at night. My maximum instantaneous load is 63
amps. This would be if every electrical motor was running, every radio
was transmitting, every light was on, etc. A very unlikely possibility
but a value that nice to have. My endurance bus load is 12 amps with a
maximum instantaneous load of 21 amps. All on a 14 volt system.
I will be using an Odyssey PC925 battery and per their applications
manual (at)25C
(<http://www.odysseybattery.com/documents/US-ODY-AM-001_0406.pdf> page
7) (at)25C the time to 10.02 volts, that I derated to 80% is:
45 min 22.5 amps
1 hr 17.5 amps
2 hr 9.5 amps
3 hr 6.6 amps
4 hr 5.1 amps
If I were to use a single alternator single battery electrical design
with an endurance buss, in an alternator out scenario, running off the
e-bus I would have over an hour of flight time to land before I run out
of electrical power. Not that bad a scenario.
Z13-8 adds the SD8 alternator and at my projected cruse or 2,300 to
2,400 rpm (the alternator would spin at 3,000 rpm) it produces 6.8
amps. My battery would need to make up the additional 5.2 amps
(12-6. . This gives almost 4 hours of endurance. Easily 3 hours with
electrical reserve for the additional electrical load when landing.
Z12 adds a 20 amp alternator (B&C) or 30 amps (plane power). I could
not find specific output data for either alternator. B&C says 20 amps
at 3,500 rpm vs my 3,000 rpm cruse. All plane power says is 30 amps at
cruse for their 14 volt model not their 13.6 volt model. Since my
e-buss load is only 12 amps I could run on the e-bus until my fuel runs
out.
I am finding very little downside to adding the 20/30 amp backup
alternator. It does add about 2 pounds. The cost difference is very
little $200 at the most.
I am currently leaning towards Z12, but I wanted some feedback to
confirm that my evaluation is sound.
Larry Rosen
RV-10 back to building
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Larry Rosen
#40356
N205EN (reserved)
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nuckolls.bob(at)aeroelect
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| Posted: Mon Mar 23, 2015 5:42 pm Post subject: Z12 vs Z13-8 |
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At 14:17 2015-03-23, you wrote:
I would like some confirmation that my rational for choosing between
Z12 (60 & 20 amp alternators)and Z13-8 (60 and 20 amp alternators) is rational.
I am building a Vans RV-10. Based on my current projections, normal
continuous load will range between 20 and 35 amps. Low being day VFR
and high when landing at night. My maximum instantaneous load is 63
amps. This would be if every electrical motor was running, every
radio was transmitting, every light was on, etc. A very unlikely
possibility but a value that nice to have. My endurance bus load is
12 amps with a maximum instantaneous load of 21 amps. All on a 14 volt system.
Thats a pretty broad brush load analysis. Intermittent
loads MAY total a lot of amps but their ENERGY requirements
are generally low and not part of your endurance calculation.
I will be using an Odyssey PC925 battery and per their applications
manual (at)25C
(<http://www.odysseybattery.com/documents/US-ODY-AM-001_0406.pdf>
page 7) (at)25C the time to 10.02 volts, that I derated to 80% is:
45 min 22.5 amps
1 hr 17.5 amps
2 hr 9.5 amps
3 hr 6.6 amps
4 hr 5.1 amps
If I were to use a single alternator single battery electrical design
with an endurance buss, in an alternator out scenario, running off
the e-bus I would have over an hour of flight time to land before I
run out of electrical power. Not that bad a scenario.
Is your e-bus load that high? Nor normal running
loads are not endurance loads. Figure out just what
electro-whizzies are necessary and useful for continued
flight at cruise. The ENDURANCE mode minimizes loads
consistent with capable navigation and aviation.
Z13-8 adds the SD8 alternator and at my projected cruse or 2,300 to
2,400 rpm (the alternator would spin at 3,000 rpm) it produces 6.8
amps. My battery would need to make up the additional 5.2 amps
(12-6.. This gives almost 4 hours of endurance. Easily 3 hours
with electrical reserve for the additional electrical load when landing.
Ideally, your TOTAL endurance loads would be carried
by the 8A s/b alternator thus saving the battery's
stored energy for descent and approach to landing.
Z12 adds a 20 amp alternator (B&C) or 30 amps (plane power). I could
not find specific output data for either alternator. B&C says 20
amps at 3,500 rpm vs my 3,000 rpm cruse. All plane power says is 30
amps at cruse for their 14 volt model not their 13.6 volt
model. Since my e-buss load is only 12 amps I could run on the e-bus
until my fuel runs out.
The Endurance Mode . . . doesn't mean keeping
the coffee pot hot and the stereo running.
It means supporting the minimalist load of
electro-whizzies that will carry you to
airport in sight.
At that time, will ALL of the battery's contents
held in reserve, you can come down final with
klieg lights and coupled autopilot approach
while carrying on conversation with ATC . . . using
BATTERY + S?B alternator to support the load for
the few minutes needed to comfortably terminate
the flight.
Unless you have an electrically dependent engine
with a voracious appetite for Joules, you should
be able to cruise handily on 8A.
I am finding very little downside to adding the 20/30 amp backup
alternator. It does add about 2 pounds. The cost difference is very
little $200 at the most.
I am currently leaning towards Z12, but I wanted some feedback to
confirm that my evaluation is sound.
The downside is mostly dollars. Further, know
that in the not too distant future, the SD-8
is likely to be 'upgraded' . . . don't know
exactly how much but the increase will be
significant.
Get this form from my website
http://www.aeroelectric.com/PPS/Load_Analysis/Blank_Form.pdf
One page for each bus. One equipment item
per line. Fill in steady state operating
for each device categorized by flight
condition. The goal is to get the MAIN ALT
DEAD condition down to 8A or less load.
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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nuckolls.bob(at)aeroelect
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| Posted: Tue Mar 24, 2015 1:55 pm Post subject: Z12 vs Z13-8 |
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At 08:43 2015-03-24, you wrote:
| Quote: |
Choosing the size of the backup alternator is a matter of personal
preference. There is no right or wrong answer.
|
But I think there is an 'elegant' answer . . . based
on design goals and numbers to guide and validate
the final decision.
I missed the 925 selection. THAT IS a beefy battery.
The rough numbers offered suggested that design
goals call for the battery to carry a lot more
loads than I would have expected.
Hence, my suggestion that he back up and sort the
numbers against anticipated flight configurations.
For it is those numbers that show the adequacy of
alternators and batteries being considered.
I'd bet that the stock SD-8 and a PC-680 would get
the job done . . . but that's my perception of 'the
job' which may differ markedly from his. Until
we have the numbers, we're all blow'n smoke.
Bob . . .
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LarryRosen
Joined: 16 Jan 2006
Posts: 415
Location: Medford, NJ
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| Posted: Tue Mar 24, 2015 4:38 pm Post subject: Z12 vs Z13-8 |
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I have gone through a complete analysis of every electric component and
looked at the loads for different flight configurations. For simplicity
I only showed a range for my normal loads and what I had for an
endurance mode. I was looking for a review of my analysis and everyone
has helped me with that.
The endurance design I have is a 'keep the coffee pot warm' design and
not a 'safe for flight' design. My struggle is wanting to make the
alternator out situation a 'non event' with all or most of the
conveniences I will have in the plane. Making the endurance mode a
'safe for flight' mode would drastically cut that loads.
Designing for 'non-event' vs 'safe for flight' is drastically
different. I will need to go back and determine what my design goal is.
Larry
On 3/24/2015 5:53 PM, Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 08:43 2015-03-24, you wrote:
>
>
> Choosing the size of the backup alternator is a matter of personal
> preference. There is no right or wrong answer.
But I think there is an 'elegant' answer . . . based
on design goals and numbers to guide and validate
the final decision.
I missed the 925 selection. THAT IS a beefy battery.
The rough numbers offered suggested that design
goals call for the battery to carry a lot more
loads than I would have expected.
Hence, my suggestion that he back up and sort the
numbers against anticipated flight configurations.
For it is those numbers that show the adequacy of
alternators and batteries being considered.
I'd bet that the stock SD-8 and a PC-680 would get
the job done . . . but that's my perception of 'the
job' which may differ markedly from his. Until
we have the numbers, we're all blow'n smoke.
Bob . . .
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_________________
Larry Rosen
#40356
N205EN (reserved)
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Mar 25, 2015 6:54 am Post subject: Z12 vs Z13-8 |
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At 19:36 2015-03-24, you wrote:
I have gone through a complete analysis of every electric component
and looked at the loads for different flight configurations. For
simplicity I only showed a range for my normal loads and what I had
for an endurance mode. I was looking for a review of my analysis and
everyone has helped me with that.
The endurance design I have is a 'keep the coffee pot warm' design
and not a 'safe for flight' design. My struggle is wanting to make
the alternator out situation a 'non event' with all or most of the
conveniences I will have in the plane. Making the endurance mode a
'safe for flight' mode would drastically cut that loads.
Designing for 'non-event' vs 'safe for flight' is drastically
different. I will need to go back and determine what my design goal is.
Good for you my friend . . . and please
don't feel that any one else's goals
SHOULD be adopted by yourself based on
their 'cultural weight'. Your decision
should be aided by knowledge of the
options re-enforced by an understanding
of their performance.
In the final analysis, what ever goes
into your airplane should be UNDERSTOOD
and architectured such that no single failure
will be any cause for concern beyond,
"Oh fooey . . . is that thing broke . . .
again?"
The elegant solution to your design goals
will offer the lightest weight and lowest
cost of ownership consistent with a benign
FMEA. Within that framework, it matters
to nobody but yourself what parts go into
the design. To the extent that we may assist
in sorting out bits and pieces, we are
at your service.
Bob . . .
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jluckey(at)pacbell.net
Guest
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| Posted: Wed Mar 25, 2015 9:01 am Post subject: Z12 vs Z13-8 |
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Larry,
Have you considered what it would be like to experience an alternator failure in flight?
(or course you have - but follow me down this rabbit hole)
There is lots of talk about having enough electrons in reserve to continue the flight for
a "long time" or until fuel is exhausted. But would most of us actually do that?
If I imagine myself in the cockpit of an airplane in flight and experiencing an electrical
problem, I want to know EXACTLY what's failed, RIGHT NOW! That may not be easy
to determine from the left seat.
I'm gonna land at the first "reasonable" airport to determine exactly what's
wrong - NOT fly on for another hour or two, not knowing what's happening under
the hood.
There are all kinds of possible failure modes: did the belt break?, did a wire break?,
is that broken wire arcing against the airframe?, Is that arcing near a fuel line?, is
the regulator on fire?, (did I bring extra toilet paper?) etc, etc. These questions would
be running thru my mind and give me a high sphincter-factor all the way to touchdown.
We absolutely need to have some reserve built into the system.
But how much reserve is an interesting question because it involves so many factors.
Concerns about safety, personal comfort level, engineering, etc. I think a reserve of
"hours" is probably overkill and would probably not ever be used by prudent pilots
due to the reasons cited above. And, of course, mere minutes of reserve would not
be smart either.
You might give this idea some thought before deciding on a giant battery that
could "keep the coffee pot warm" for a couple of hours.
In a nutshell here are some ideas I use to decide on electrical energy reserves
for battery-only operations:
1. Based upon my airplane's cruise speed & flight planning, I never
plan to be more than 15-20 minutes from a "reasonable*" airport. (in my RV-7
that's probably about 40-50 miles)
2. Add 10 minutes just in case I have to shoot an approach. Of course, we're
hoping for VFR at the "reasonable" airport - but planning for worst case.
3. So that's about 30 minutes. Now double it, just 'cuz.
So my number is 60 minutes.
It turns out that my actual number for my RV-7 with dual batteries (PC-680s), single
alternator system will actually be better than that. (Reserve power is only one factor
in my design decision for having 2 batts. With 2 batts I get things like brown-out
protection on start-up, auto fail-over so EFIS does not re-boot in flight, reserve
starting energy in case I flood the engine, etc.)
Food for thought, your mileage may vary, non-attorney spokesperson.
Thanks for listening,
-Jeff
*reasonable airport is one w/ a good runway, near a town with an auto parts store.
On Wednesday, March 25, 2015 8:12 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 19:36 2015-03-24, you wrote:
--> AeroElectric-List message posted by: Larry Rosen <n205en(at)gmail.com (n205en(at)gmail.com)>
I have gone through a complete analysis of every electric component
and looked at the loads for different flight configurations. For
simplicity I only showed a range for my normal loads and what I had
for an endurance mode. I was looking for a review of my analysis and
everyone has helped me with that.
The endurance design I have is a 'keep the coffee pot warm' design
and not a 'safe for flight' design. My struggle is wanting to make
the alternator out situation a 'non event' with all or most of the
conveniences I will have in the plane. Making the endurance mode a
'safe for flight' mode would drastically cut that loads.
Designing for 'non-event' vs 'safe for flight' is drastically
different. I will need to go back and determine what my design goal is.
Good for you my friend . . . and please
don't feel that any one else's goals
SHOULD be adopted by yourself based on
their 'cultural weight'. Your decision
should be aided by knowledge of the
options re-enforced by an understanding
of their performance.
In the final analysis, what ever goes
into your airplane should be UNDERSTOOD
and architectured such that no single failure
will be any cause for concern beyond,
"Oh fooey . . . is that thing broke . . .
again?"
The elegant solution to your design goals
will offer the lightest weight and lowest
cost of ownership consistent with a benign
FMEA. Within that framework, it matters
to nobody but yourself what parts go into
the design. To the extent that we may assist
in sorting out bits and pieces, we are
at your service.
&nbAeroElectric-List" target="_blank">http://www.matronics.com/Navigator?Aersp; - MATRONICS WEB FORUMS -
= --> http://========================
[quote][b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Mar 25, 2015 11:43 am Post subject: Z12 vs Z13-8 |
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At 12:00 2015-03-25, you wrote:
Larry,
Have you considered what it would be like to experience an alternator
failure in flight?
(of course you have - but follow me down this rabbit hole)
There is lots of talk about having enough electrons in reserve to
continue the flight for
a "long time" or until fuel is exhausted. But would most of us
actually do that?
Just because you CAN does not mean that you
always WILL. Further, it depends on your
understanding and confidence in the options
at the time a failure first manifests.
In a nutshell here are some ideas I use to decide on electrical energy reserves
for battery-only operations:
1. Based upon my airplane's cruise speed & flight planning, I never
plan to be more than 15-20 minutes from a "reasonable*" airport. (in my RV-7
that's probably about 40-50 miles)
Dr. Dee and I are fond of trips to places
like Santa Fe, Flagstaff, Laramie, etc.
Nice places to go with few 'reasonable' airports
along the way . . . even those which are
friendly to my airplane may not have tools and
logistical support for a timely repair.
2. Add 10 minutes just in case I have to shoot an approach. Of course, we're
hoping for VFR at the "reasonable" airport - but planning for worst case.
3. So that's about 30 minutes. Now double it, just 'cuz.
So my number is 60 minutes.
It turns out that my actual number for my RV-7 with dual batteries
(PC-680s), single
alternator system will actually be better than that. (Reserve power
is only one factor
in my design decision for having 2 batts. With 2 batts I get things
like brown-out
protection on start-up, auto fail-over so EFIS does not re-boot in
flight, reserve
starting energy in case I flood the engine, etc.)
Food for thought, your mileage may vary, non-attorney spokesperson.
Thanks for listening,
You have re-enforced the point I made yesterday
about having NUMBERS that add protein to the
constellation of interesting flavors that make
up our personal air travel 'stew'.
In the TC aircraft world, we publish tables
of hard numbers for validated performance with
limits along with holy-watered "emergency procedures".
Like the craftsman who's only tool is a hammer,
the anointed in charge of writing POH
pages striped with red hash marks are not allowed
and in some cases incapable of writing
procedures that are modified 'on the fly'
while airborne or 'improved upon' with modifications
to equipment lists while on the ground.
For these folks, every failure event must be treated
as an emergency. "LAND WHEN PRACTICAL" is a
common phrase in the heavy-iron POH.
I've not powered up a panel mounted VOR or
GPS in decades. My dual hand-held gps receivers
supplemented with a hand-held COM would get
me any place I needed to go with the master
switch OFF.
Were our ol' J3 long-legged enough to be
a travel machine, the recipe for my 'stew'
would not change whether I was headed for
Santa Fe or out for a $100 hamburger.
I once encountered a salesman at Beech who
was recounting his experience with a pilot
who just departed in a brand new A36.
He said he spent a couple hours capped off
with a $400 hamburger at Hutch . . . showing
the new owner how all the neat stuff worked.
I asked if he demonstrated how to operate
the airplane in the "J-3 Mode".
"Say what?"
"Yeah, power everything off and get home."
"Why would I want to do that? He just paid
close to a $million$ for this machine, why
would I even suggest that there was value
knowing such things?"
Why indeed. The red-striped pages have it
all covered. A half dozen approval signatures
on the page attest to that assertion. I
didn't pursue the conversation further,
I needed to work with these guys.
In particular, POH authors would be aghast at
any suggestion for powering down the whole
airplane with continued flight to friendly facilities
using only tools in your flight bag.
Your example, and mine, are validations of
my assertion that the OBAM aircraft and
pilot are not bounded by the red-bordered
pages. They are also encouraged to ignore
'cultural common knowledge' about what
constitutes tense moments in an airplane.
I can't watch most video productions on
aviation past the first couple of times
the script writers get it totally wrong.
The vast majority of problems manifest as
a failure to perform. The thing simply
quits . . . whether by internal failure
or external when a wire comes unhooked.
Certain manifestations encourage us to
extra-ordinary action: Bad smells, wildly
fluctuating voltages . . . while very rare,
those are the things that say, "Power it all
down and get out the flight bag tools . . .
and yes, land as soon as practical."
The properly maintained battery will
always get the engine started. It's not
going to short. If an RG, it's not going
to spout hot-acid even when over charged . . .
and your ov protection system should stall
that off.
So once you have one (or in your case two)
RELIABLE batteries on board plus robust
engine driven power source(s), it's not
unreasonable to PLAN for extended flight
after the failure is detected. For the
pilot with your particular mix of flight
profiles, the e-bus and stand-by alternator
are redundant. For my mix of flight
profiles (always in rented airplanes), I
am not terribly weird for considering the
bulk of the ship's electrical system redundant.
If I can do it in a J3 . . . I can do it in an A36.
If electrical systems were a one size fits
all proposition, then the 'Connection could
be reduced to a couple dozen pages with
one Z-figure . . . and perhaps even an
Appendix E where the pages have red hash-
marks around the edges.
Cookie cutters are for cookies . . . not
The best performing airplanes in the world.
Bob . . .
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