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>  Being a simple VFR pilot I am overwhelmed by all
> this talk of emergency battery busses, isolation
> diodes, relays, etc.
> BILL HANNAHAN
>
OK - if the LML can stand just ONE last post on this topic from
me....
I've since realized that a diode is not even necessary. The same
DPDT switch that selects between normal and backup power can also
simultaneously connect and disconnect the backup batter from the charging
bus and eliminate the problem of voltage drop.
My backup power system then consists of only two devices...the
backup battery and a single DPDT switch. The backup battery is then directly
connected to the charging bus, same as the primary battery.
I have added one simple refinement - a small digital voltmeter to
display the backup battery's voltage while in use. By operating the backup
power system on the ground to verify running time, one could watch the
battery's voltage decay and learn at what voltage level the first gyro
"flagged off".
Thus, the pilot would have a pretty good visual indication of how
much time remained when in actual use. This is bound to increase "comfort
level", should actual use of backup power ever be required.
Bill Rumburg
N403WR  (Sonic bOOm)



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