creightonious
Joined: 10 Mar 2007
Posts: 40
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 Posted: Tue Aug 10, 2010 7:06 am Post subject: Electrically-Dependent Dual Battery, Single Alternator Syst |
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I've posted previously about this and some conceptual progress has been made.
The system is based upon Z-19. It differs principally in that it incorporates two independent, stand-alone EFI systems. There is no commonality beyond the tank selector and neither is a back-up, rather I conceive of them as a Monday and a Tuesday system. Only one system can be used at a time and each is used on alternate flights.
The EFI system draw is approximately 10 amps and as conceived the Engine Battery Bus and the Main Battery Bus are primarily the EFI Bus 1 and 2, respectively. So far so good.
Note that each of these busses is run off the hot (non-switched) side of the respective contactor. (The Bat Bus switch is a race car switch to reduce draw by 1 amp).
The problem enters thus: Each EFI system must be able to be powered by either battery. (1 at a time) Absent a number of switches/relays on the bus feeds there doesn't seem to be an elegant way to isolate the batteries. Back feeding can be handled by heat-sinked schottky diodes (4 of them in this case) The result is effectively a single large (2x) battery when running in an alternator-out situation.
This may not be a bad thing, assuming 2 good batteries, but I am more comfortable with the scenario of running 1 battery down, switching to the other and having a known drop-dead (literally) time upon which to depend. Which, of course, requires the ability to isolate the batteries.
I apologize for the long-winded post, but decisions must be put into tinned copper and tefzel and I plead for some wisdom from the forum.
Many thanks,
Creighton Smith Rotax 912
P.S. I wish I could add a second alternator, but the intake manifold and runners don't leave enough space and the stock alternator is replaced by the ignition hall effect crank sensor and a 50 amp, belt driven IR alternator.
C S
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