nuckolls.bob(at)aeroelect
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 Posted: Tue Feb 22, 2011 8:05 pm Post subject: a couple questions about Z10/8 diagram |
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At 08:13 PM 2/22/2011, you wrote:
Bob - thanks for taking the time to provide feedback! My responses
are in-line below. Phil
>> (7AH backup) What equipment are you carrying that drives this decision?
Primarily my electronic ignition, EIS and EFIS
How much time to you expect to spend with
your head in the clouds?
>> your worry-bucket seems to be carrying some issues.
It sure is! I only have one teenager and had some excess space in
that bucket 
Understand.
I've experienced the failed alternator in a production airplane and
don't want to be there by my own doing in my homebuilt. The plane I
owned was rented with a flight school and I was at the mercy of their
maintenance as were those who rented it.
Yup, been there, done that. But keep in mind that
the service life of alternators on t/c aircraft is
miserable. Plane power, B&C, and many OBAM aircraft
builders are adapting modern alternators to aircraft
with great results. B&C's return rate is a very small
number of the total fleet. I suspect others are seeing
similar performance.
Keep in mind, that for every dark-n-stormy-night story
about some failure, there are thousands of other non-
stories that you never hear about. The real risks for
tense days in the cockpit due to alternator failure
are a tiny fraction of what your grandpa had to endure
on his Cherokee that keeps breaking certified brackets.
It was stranded twice because of a failed alternator that wasn't
noticed in a timely fashion.
Typical TC aircraft . . . no timely notification of
low voltage. Most dark-n-stormy-night story tellers
say the first notion they had for a failed alternator
was when the panel started going black/silent.
The first sign of a problem was the comm radio no longer
transmitted. Short minutes later the nav would quit. Thankfully the
problem was never more nerve-wracking than having to abort the flight
somewhat short of the intended destination and it never happened
while under IFR. My plan is to have a well thought-out and implemented
By 'implemented' I hope you mean WELL maintained.
Your ship's main battery should not be run until it
no longer cranks the engine. It needs to be replaced
when its MEASURED capacity no longer supports your
design goals for alternator out endurance.
. . electrical system in my RV that will provide the necessary
ability to alert me to an issue then let me continue without any
worries for an hour minimum and up to two hours. That gives me lots
of options to complete the flight to a ho-hum end; most likely at the
intended destination.
Okay, what's your endurance load?
>> (switch in place of the brownout battery relay) What failure mode
do you perceive that loss of the relay would be a pre-cursor to your
own dark-n-stormy-night story?
In hindsight I probably should have left this out. Comparing my auto
industry automation where the relays make and break thousands of
times before failure compared to fact that the switch that was used
to set the machine in motion is actuated one or more orders of
magnitude fewer times isn't 'fair'. I had a relay in my BandC
shopping cart when I left work, I will just order it tomorrow
What electronic ignition(s) are planned?
>> It would be helpful to know more about your equipment list and
the reasons that drive installation of a second battery.
The 'Connection basic list (xponder, nav radio, panel flood, turn
coordinator) plus my electronic ignition and a rear pax light. The
ignition adds 2A to the basic list, though I am debating putting one
on the battery bus and the other on the e-bus which would lighten the
load by 1A to just under 4A.
Okay, it looks like you need 2 hours at a 4A rate.
An exemplar 17 a.h. battery discharged at 4.25A
is good for 3 hours new
http://www.aeroelectric.com/Pictures/Curves/17AH_12V_Capacity_vs_Load.gif
and 2+ hours at end of life.
>> What are your e-bus loads? Do you NEED a heat-sinked normal
feedpath diode? You're building a metal airplane. I suspect the
bare-foot rectifier assembly can be simply bolted to some portion of
the airplane.
I already have the diode on a heat sink because I hadn't planned on
the shelf behind the panel for a small battery. Now that I am going
to have a plate there, the barefoot one would work but I will just
stick with the one on a heatsink. I was wondering about the Schottky
diode and if there was a benefit to the lower voltage losses when
compared to the diode I have already.
No advantage from an energy conservation perspective
(the main alternator is up and running when that diode
is in service). There's an advantage that less heat sink
is needed. The Schottky would most certainly run well
"bare-sinked".
>> (PB/Tyco circuit breakers connected to forest of tabs bus) Too
many parts and joints. Why not use breakers that are bus-bar friendly?
Size, weight and cost. I'll admit I like the way they look and that
I'm not excited about fuse blocks.
But I'm not excited about all the monkey-motion for using
these fast-on terminated devices. Please consider the miniature
screw-terminal devices.
http://aeroelectric.com/Pictures/Breakers/Klixon_1.jpg
>> Maybe I missed the answer to this question in the text ...
I started to ask just one question - the one about the relay - and
then just kept adding more. I miss a lot in the text that I pick up
when I reread sections. I recently updated from v10 to v12a and I
have to start from square two. So much to learn.... Frankly the
adventure of rewiring my airplane has been made tremendously easier
because of your text and website. I've gone from tentatively
engaging to full-on fun with it because of them!
Good. Wiring your airplane ought to be the fun part.
A guy who attended my second or third seminar way back when
wrote to me a couple weeks after the seminar. He had been
sticking electro-whizzies in his LongEz for years. After
the seminar, he went home, ripped it all out and wrote
to tell me it all went back in a couple weekends but with
confidence of understanding.
I'm not convinced that you need two batteries yet . . .
Reducing battery maintenance to two articles will pay
for the better breakers in a few years.
Bob . . .
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