rparigor@suffolk.lib.ny.us wrote:
> I have aOdyssey PC545 battery and a
> total los 2200mA NiMh emergency battery. There is also a SD20S with a LR3C
> sitting on the vacuum pad. I also have an E-bus. Thx. for the input.
>
> I too think that if the regulator fails, internal Rotax generator
> will not run a fuel pump.
>
> Anyway, my "what if" is
> when flying with lots of fuel and not too much in the way of
> landing areas I get some severe smoke in cockpit thought to be electrical
> in nature.
Well, with a totally separated dual setup (as you could have as well, as
you also have dual alternators), it is just a matter of finding out the
bad system which should not cost more than two seconds (you do have an
amp-gauge, do you?) , and keeping the healthy system on and running the
associated pump. Any additional complexity will only increase the
failure points.
> Thus my "what if"
> question is can I extend the range of my total loss battery by turning on
> and off the fuel pump?
Sure, there are several things you can do. There is no magic number in
duty cycle here, as it depends on the state of the fuel filters,
altitude, power setting, etc. You can run the pump on a 50%-50% duty
cycle and see what happens, and adjust the duty cycle accordingly.
Better would it be to use a feed-back system, using the return flow as
an indication how much electricity you can safely spare.
You can also make a switched power supply for the fuel pump, and run it
on reduced voltage, again adjusting the fuel pump power related to the
fuel return flow.
But I feel that all this kind of trickery will only increase the chances
of failure.
What's wrong with two totally separated systems, each with its own
alternator, battery and fuel pump? This eliminates every single failure
point. You are already almost there, with two fuel pumps and two
alternators. Just add a second battery (I use two 8Ah batteries, so
essentially I have just split the normal battery into two smaller ones
so I have no weight penalty), and of course a second main power switch.
Once you are there, it is easy to use the additional redundancy
everywhere. I have the CHT's and coolant temperature indicators each on
a separate bus. Just like the NAV and GPS. And the attitude indicator
and turn indicator. Etc. I can loose an entire bus without too much
worries, will always keep at least one fuel pump, some navigation
instruments, and some engine instruments (enough to locate and reach the
nearest landing strip).
It is so easy to set it up like this, once you have two fuel pumps and
two alternators anyway.
Oh, and just in case I experience multiple failures (suddenly fuel pump
A stops, and alternator B dies as well) I have a last card to play: a
cross-over switch between both buses which essentially ties both buses
together. Of course this violates the dual setup approach, so it is only
used in a genuine emergency, if no other options remain. It is a "all or
nothing" last resort.
BTW This is not intended as a "my system is better than yours" but an
invitation to either shoot bullets in my approach, so I can fix any
overlookings and improve my system, or to help you to improve your system.
--
Frans Veldman
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