Yeah, I am looking at the Z-13/8 drawing. It just doesnt make sense to me why there is even an e-bus alt feed switch \if there is no problem feeding power to the e-bus from both sides at once. If the alt was failed you could just shut off the battery contactor and let it continue to feed from the battery bus side.
... Since the ebus is fed directly from the battery when the switch is closed, the battery will be drained on shutdown unless all devices fed by the ebus are off.
I recall Dan Checkoway saying (way back in the old days. ) he normally ran with the ebus switch closed, since any failure of the main bus circuit would then be automatically backed up. I didn't understand that until I wired mine and looked at Z-11 carefully. Another advantage is, when the ebus switch is closed you eliminate the voltage drop thru the Schottkey diode, which is not insignificant.
I turn the ebus switch on for normal running, and turn it off for normal shutdown just like all the other toggles.
I recently ran across this thread and thought to myself "awesome, i'll just run with my ebus on at all times, that makes sense!" However, I've been doing some more reading and found this in the VPX user manual, which seems to indicate that having the ebus on at all times may not always be very desirable:
"If you have a primary alternator and a secondary (backup) alternator only
one alternator (field wire) should be powered on at a time. Therefore, we
refer to one alternator as the primary and the other as the secondary. If
both are on simultaneously, they do not equally ?contribute? to powering
the loads. The one whose voltage regulator is set to the highest voltage
will draw all the current (sometimes called current hogging), possibly
overloading the alternator"
What does everyone think about the above consideration?
?
Here is a sample Z13/8 with a couple modifications, for reference to ponder these questions: http://n42bu.com/SharedFiles/Z13-8R2-N42BU.png
Looking at your wiring diagram, it seems like you use one switch to control both the E-Bus alternate feed and the Standby Alternator. Is this correct?
You don?t want both alternators running at the same time, unless the voltage regulator for the standby alternator is set to a lower voltage than the one for the main alternator. If the standby alternator?s voltage regulator is set to a higher voltage than the main, it?ll run at full output all the time, and that is probably not good for long life.
Correct, one switch will turn on my ebus feed and also activate the standby alt. Sounds like if I could verify my standby alt (SD-8) is set to lower voltage than the plane power I may be ok to run both, otherwise not.
Electrons behave oddly!