"........ if there's two independent
> sources of power (spelled batteries)......"
Possibly, under the FARs.
JAR-E is more relaxed and only calls for two independent sources of
electrical power; there is nothing that explicitly prohibits one of these
being the engine-driven generator, so long as the electrical system can
allow each to operate independently of the other
Duncan McF.
<fillinger@ameritech.net>
>
> > I am not one bit convinced of the need for a spare
> > battery. The plane carries on flying without a blink if you switch off
> > master and alternator switches!
>
> That's because it's wired as it's supposed to be! It's picking off
> regulator current before fed to the bus, but it's not redundant. If one
> has a battery relay, and the alternator/regulator fails, and the overall
> problem is such the battery must be disconnected, the engine will quit.
> There's no way to wire the 914 pumps to any single electrical system
> which would meet current FAA rules, were this a production A/C. It's
> also interesting to note that this is a relaxation of the rule prior to
> 1965, since way back then one pump must have been engine-driven. Now
> redundant electrical pumps are permitted if there's two independent
> sources of power (spelled batteries).
>
> One partial solution is to wire one pump "off-master" - direct to
> battery. Satisfactory if one will never leave the A/C with it still
> switched on. Not an independent source of power, but redundant if the
> rest of the electrical system has failed and battery still good.
>
> For full compliance the FAA has approved, as a separate independent
> power source, a simple pack of dated alkaline "D" cells. I believe this
> will provide enough alternate power to a pump to get to some nearby
> airport if the main electrical system has smoked.
>
> Not trying to convince; just suggestions for any builder considering
> options.
>
> Fred F.
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