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mprather(at)spro.net
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 Posted: Wed Oct 10, 2007 11:56 am Post subject: [Probable SPAM] Z-19 E Bus feeder questions - Fuse se |
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As has been discussed, fuses are generally there to protect the wire.
Wire is sized to be electrically adequate (with margin - sometimes large)
and mechanically robust. The sizes of the fuses (and the total sum of the
values of the fuses) are only peripherally related to the total bus draw.
I would say that the size of the fuse feeding the e-bus should be
determined by what the actual loads will be. The wires fed by the e-bus
are already protected by the individual fuses. While 7A for the e-bus
feed might seem small, I question what single engine airplane would need
26A continuous on the endurance bus.
Free anecdotes (worth what you pay for it): My car has a 75A alternator,
but adding up the fuse values shows that the bus capacity is in the realm
of 175A.
Also, Z19 as drawn has a 16g feed. The 10C rise load for 16g is 12.5A -
far short of the 26A fuse load on the bus. That's okay for the reasons
mentioned above.
Regards,
Matt-
[quote]
Mike,
I'll wait for the Bob's definitive answer but this makes no
sense. That would be like adding a 100 am panel to your home and feeding
it off a 20 amp breaker in your main panel.
The lead from the main power bus to the endurance bus should be
a direct feed from the same terminal as the main feed. Between them is a
diode to prevent backflow if the e-bus alternate is used.
Also, I have an issue with the orphaned switch for fuel pump #2.
Why not integrate it with the engine primary and secondary switching?
Note that if fuel pump #1 makes trouble, this diagram provides no way to
isolate it, but rather one method to switch the bus that feeds it. With
switch #2 I can turn it off/on at will which is fine as a backup, but I
want that functionality for #1 also.
--
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mikefapex
Joined: 05 Jul 2007
Posts: 70
Location: Colorado
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| Posted: Wed Oct 10, 2007 1:58 pm Post subject: Re: [Probable SPAM] Z-19 E Bus feeder questions - Fus |
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Matt,
What you say makes sense. But what has me asking the questions is why the large difference between the fuse size of the Main power bus and the listed components on the Endurance Bus. Even if you cut the E-bus in half, amperage load-wise, you still get a 13/7 mix. That just seems askew.
matt wrote: >>
As has been discussed, fuses are generally there to protect the wire.
Wire is sized to be electrically adequate (with margin - sometimes large)
and mechanically robust. The sizes of the fuses (and the total sum of the
values of the fuses) are only peripherally related to the total bus draw.
I would say that the size of the fuse feeding the e-bus should be
determined by what the actual loads will be. The wires fed by the e-bus
are already protected by the individual fuses. While 7A for the e-bus
feed might seem small, I question what single engine airplane would need
26A continuous on the endurance bus.
Free anecdotes (worth what you pay for it): My car has a 75A alternator,
but adding up the fuse values shows that the bus capacity is in the realm
of 175A.
Also, Z19 as drawn has a 16g feed. The 10C rise load for 16g is 12.5A -
far short of the 26A fuse load on the bus. That's okay for the reasons
mentioned above.
<<
Mike
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