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<< Lancair Builders' Mail List >>
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Hamid mentions in a post to the Lancair List tonight that all relays
should
have diodes protecting them. In the main/essential bus system that we both
have in our airplanes that use the small relay for the essential bus, did
you use any diodes with the essential bus relay?<
Yes, I used transorbs on many of the relays that I considered critical.
Hamid is correct that relays will weld shut thus the reason to carefully
size them. Too big and the contact will not self clean, too small and they
eventually weld shut. Transorbs help prevent the contact damage and
welding as the relays are opened especially when the relay is used to turn
off inductive loads.
Did you wire your relay so that the essential bus can be powered via a
rocker switch with the relay coil unenergized? (i.e. if the relay fails in
the NC/unenergized position, the essential bus gets power by turning on a
switch).<
I could not find a small double throw mechanical switch that would handle
the current required for the essential bus and match the looks of my other
switches. So, I used pretty switch that activates a properly rated relay. The essential bus is normally powered by the radio bus. If power to the
radio bus is interrupted either by failure of any number of parts or by me
turning off the radio bus switch the essential bus is not powered. To get
power to the essential bus, I have to switch the emergency bus switch on
which activates a relay and the essential bus is powered directly from the
battery without going through the master relay. A big part of the essential bus is that it can get its power directly from
the battery without any parts inbetween and can be isolated from all the
other buses should there be a fault on any of them. In an emergency, the
essential bus should be able to get power without the master relay on. I
check this prior to every IFR departure. For example, you have electrical
smoke in flight and you turn off the master switch which solves the smoke
problem. Do you have enough to keep flying IFR? Maybe but difficult
without an essential bus that meets the above criteria.
I'll submit the electrical pictorial schematic for my Lancair to Marve for
inclusion in the LNN. I tried to incorporate all the best from the
AeroElectric publication and my own experience for an IFR X-country
machine.
Jim Frantz
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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