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Z14 architecture

 
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Feb 03, 2020 7:28 am    Post subject: Z14 architecture Reply with quote

At 06:48 AM 2/3/2020, you wrote:
Quote:
The whole reason for the cross-feed contactor
is to PREVENT a 'dire emergency' . . . not
react to one.


I'm not sure I follow this. I assumed the contactor is installed for the possibility
of alternator and battery failure on one bus . . .

Alternator failure only . . . you wouldn't
know if a battery 'failed' in flight and besides,
properly maintained batteries don't fail . . .
they get replaced at some significant point
on their wear-out curve.

Quote:
(or to tie the batteries together for engine start).

True. This was one of the disappointments
in Garmin's 'adaptation' of Z-14 in
their installation manual. They replaced
the cross-feed contactor with a diode.
this PREVENTED exploitation of BOTH
batteries to crank a 6-cyliner engine!

Quote:
I'm not sure exactly how this would happen, given crowbar protection for the
alternator, unless the battery was weak

Substitute 'neglected' for 'weak'

Quote:
or the bus somehow was shorted?

Okay . . . pick any airplane. Any
suite of tools . . . then go in and
'short' any distribution component
to ground. How would you do it? How
would that same even occur spontaneously
in an artfully assembled airplane?

Answer is, they don't. In 45 years of
herding electrons and chasing failure
gremlins in a/c . . . I've never encountered
a 'shorted' anything when it comes to
power distribution hardware. Plenty
of opens, burned up, cracked or simply
crapped out . . . but no faults to
ground precipitating broad, multi-system
failures.

I've not read any accident analysis where
shorted bus distribution hardware initiated
or contributed to a bad day in the
cockpit.

Quote:
If the bus was shorted, then closing the cross-tie would bring the other
side down too . . .

Moot point per assertions above . .

Quote:
I assume. A good preflight should discover a weak battery.

No assumptions warranted . . . good
preventative maintenance replaces
a battery before it becomes un-airworthy.

Quote:
My concern would be bus failure, but after a little education from you here,
it sounds like properly installed busses and their wire feeds generally don't fail.
Point taken and lessen learned if true.

Correct. There are things like
wing struts, prop bolts, propeller blades,
control cables, elevator hinges, etc. etc.
that are simply not part of the design
decisions and operating (plan-b) considerations
for electrical systems. While there are
stories of such failures they are so rare
that any such event is really big news.

. . . and when you do hear of such things,
there are seldom details on the chain
of events that lead up to the ultimate
failure.

Quote:
Okay, failure of WHAT component would prompt closing
the cross-tie? Will failure of that component result
in instant loss of engine?

First question answered (maybe) above. As to the second question -
(assume you are referring to electrical components here) -

Yes

Quote:
. . . failure of the single power source injector bus. Again, starting to learn from you
- I'm going to guess your response will be that it's not a single power source
and if well constructed, the chances of failure of both the alternator AND
battery OR the bus are extremely remote?

Exactly!

Quote:
Batteries which, in my never humble opinion,
only add cost of ownership and offer little
benefit in terms of mission reliability.

If for nothing else, the IBBS battery keeps the screens from rebooting
during start - which I have seen numerous times on my RV-7 (single battery).
Maybe not necessary with dual bus architecture and dual batteries cross-tied
for engine start. Your thoughts?

varies from system to system, a/c to
a/c . . . and we have discussed ways
to fabricate an electrical system
that negates brown-out effects without
adding (ugh!) more batteries.

Quote:
Define 'slightly' and articulate the
sequence of failure events that would
bring that benefit into play.

Lacking a batter explanation, I would say my preference would be to have the
ability to power an injector bus from either main/hot battery bus. That would
be my idea of slightly more redundant.

Z-14 as published already does that,
from either the main or aux busses.
Z-12 has a similar degree of robustness
with a single bus.

I'm not well versed enough to articulate what failures might occur to
require the second power source.

. . . which is a perfectly legitimate
cause for concern. Ignorance is at
least crippling if not dangerous.
Education is neither easy or cheap.
We all have to work at it.


Quote:
I suggest that what we're doing here
has the same goals. Another goal is to
eliminate the word 'emergency' from the
lexicon of electrics-speak . . . we're
just not going to have one.

And I am very grateful to have you and the others on this forum
as a resource to help me through this fun (and sometimes trying) process.

That's what we do here . . . and
we're pleased that you're finding
value in what is offered.


Bob . . .


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