nuckolls.bob(at)aeroelect
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 Posted: Tue Dec 16, 2008 6:35 am Post subject: To Z12 or not to Z12, that is the question. |
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| Quote: | | Comments/Questions: Bob a couple of years ago I emailed you requesting information on the Z-14 for my RV-7. Your response was that it may be "overkill" for my airplane. The airplane has a 60 amp main, belt driven alternator and a 20 amp standby alternator, both from B & C. It has one battery. It'll have back-up batteries for the EFIS, GPS and a TruTrak ADI. Now I'm trying to decide between Z-12 and Z-13/20. As I understand your wiring diagrams, Z-12 basically runs off the main alternator, with the standby ready in case voltage from the main drops below a certain level and then it (the standby) takes over. Whereas Z-13/20 utilizes the standby to power an endurance bus, which in turns runs a series of backup instruments and needed lights, flaps, etc. Am I correct? |
No. ENDURANCE speaks to minimizing loads on a limited
power resource (battery and perhaps battery + 8A
alternator) for the purpose of having an electrical
endurance that is equal to or greater than flight
endurance as established by remaining fuel.
This means the E-bus is configured first with
those items most useful for HOURS of flight while
the airport of intended destination gets closer.
It's NOT an emergency bus . . . it's the bus that
keeps a maintenance item (crapped alternator) from
becoming an emergency. It has a secondary role of
keeping a contactor failure from becoming an
emergency also by offering dual power paths
to e-bus powered equipment.
Z-13/20 was a bad dream. I'm sorry I published
it. It was removed from the website and will be
removed from subsequent print documents. My
recommendation is that you go with Z-12 as
published. With this abundance of secondary
engine-driven power, you don't need much of
a plan-B . . .just start turning things off
until the SD-20 "overload" light goes out.
If you can't make it home on 20A of snort,
you've got too much stuff in your airplane.
The system you describe has back-ups to back-ups
to the extent that it makes a rational failure
mode effects analysis problematic . . . not
necessarily a bad thing . . . just something
of an exercise in feather-chasing. Don't put
flaps on the e-bus. Review the archives for
e-bus discussions. The real value of the e-bus
speaks to battery-only endurance . . . an
instance that is exceedingly unlikely in your
airplane.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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