Shaun Simpkins wrote:
> ...
> If you would like to see how the big boys do all-electric, check out the SR-22
> Pilot's Operating Handbook on the Cirrus Design website
> http://www.cirrusdesign.com
> Page 3-28 and Page 7-39 et. seq. are very interesting reading and a neat way
> of implementing a dual-alt dual-bat dual-bus system without the need for a
> crossfeed switch.
Approach with caution though! That diode between system #1 and #2
needs to be rated for the max load on system #2, to include charging
its battery plus whatever may have caused the system to fail. The amp
ratings on high-current diodes may be for 1/2-wave AC, and she'll
smoke under DC, requiring considerable derating and likely
heat-sinking in any case. This is especially critical where, as on
the Cirrus, one puts the "essential" items on the secondary
alternator. Lose the secondary system, then cook the interconnecting
diode, and there's no switch to manually connect the essential stuff
to a system #1 that's still working! As in life, everything's a
compromise.
Thanx for pointing out the Cirrus design though. Nothing on its
essential bus is essential for day VFR flight, unlike on the 914 and
its main fuel pump. Using a pair (or 3) of low Vf Schottky diodes on
just that pump, plus if necessary the instrumentation that can show
why one of the electrical systems is in failure, isn't a big power
dissipation problem and means the engine will always run whilst one
sorts things out with no need for panic. On my "to do" list.
Regards,
Fred F.
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