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Date: Sat, 23 Dec 2006 12:49:05 -0500
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Subject: Re: [LML] Re: System level reliability
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From: "John Schroeder" <jschroeder@perigee.net>
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Colyn -

I agree with Mike Easley's commentary. Z-14 is not the Columbia system. Columbia has Z-14 in principle, but degrades it with two other busses and several potential failure points. The ANL fuses of Z-14 protect the DC busses from an alternator problem. There is further protection by the c/b in the regulator/alternator (crowbar overvoltage circuitry). The alternator also can be shut down by taking the field voltage off using the installed switch. I would be more intertested in his assessment of the Z-14 system itself.

Cheers,

John

On Fri, 22 Dec 2006 23:16:49 -0500, colyncase on earthlink <colyncase@earthlink.net> wrote:

> Mike said,
> I think the dual bus, crossfeed setup is excellent.
>
> I reviewed my system with an EE this morning.  This guy is also a pilot and experienced a night IMC total electrical failure in a baron.
> He pointed out a couple negatives to the "columbia" style dual bus with cross-feed.
> 1) if the primary alternator shorts there is no way to run anything on your primary bus because any alternate source will also see the short.
> 2) if anything on the primary bus shorts in such a way that you can't isolate it with a breaker, your xfeed is similarly useless.
> So having an xfeed in some circumstances can lead you to wiping out your backup power source.
>
> He suggested isolating the primary load bus so that it doesn't share the fate of the primary alternator.  One way would be with a switch that
> can choose either power source (primary or backup) at the primary load bus. Another way to would be to diode feed it (with much bigger diodes)
> similarly to how the essential bus is shown on the Columbia.
>
> Colyn
>