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Re: Designing for Failure

Subject: Re: Designing for Failure
From: William S. Stewart <bill@helixsys.com>
Date: Sat, 21 Aug 1999 08:12:52
Your message said in part:

>   Our recommended wiring diagrams for amateur built aircraft
>   show single operator, two pole switches for the DC power
>   master switch and a pullable breaker for the alternator
>   feeding the alternator field. Alternator and battery
>   come ON and OFF together.

I am having a problem applying this statement to the Rotax 914.  There does
not seem to be any way of controlling the alternator field.  I have the
recommended Europa wiring diagram which shows terrminal C of the regulator
connected to positive battery through a 5 amp breaker.  On the other hand
the Rotax wiring diagram shows terminal C connected directly to terminals R
and +B, with the additional caveat "never sever connection between terminal
C and +B of the regulator, e.g by removal of a fuse".

What is the best way of connecting the 914 to obtain the results in your
message?

A second question:

What would be the consequences of eliminating the master relay, and instead
having a master switch that switched power to all systems except the wire
to the starter relay.  The only consequence I could see is that there would
always be battery power to the starter relay, which could result in a
problem if that component failed in the on position.  (a highly unlikely
occurence).

I would like to eliminate this relay, it seems to draw a substantial amount
of power.

Bill Stewart, A098 (N6LB).



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