E-Bus alternative feed turned on during normal operations...

[idleup]

What happens if your E-Bus feed switch is turned on during normal operations? In this scenario it looks like power would be coming in from two directions according to Z-13/8...

[Mike S]

All depends on how things are wired, pretty sure if exactly like Nuckols drawings it should be fine.

My plane uses a similar, but different setup, and I always run both aux, and main power switches on when flying. Diode in circuit lets the system select main power if the aux is low.

[idleup]

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.

[Kevin Horton]

Originally Posted by idleup

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.

Wouldn't that have the e-bus fed from the battery, all the time? You'd have to be sure to turn everything powered by the e-bus off after landing. If not, the battery would be dead when you next came out to the hangar to go flying.

[Rupester]

... 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.

[idleup]

It all makes sense now. Thanks guys :-)

[WingsOnWheels]

Originally Posted by Rupester

... 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.

That's a very good point about the diode. I hadn't thought about it that way at all. Something new to add to my operation schema. Thanks

[blahphish]

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?

I have the following thoughts/questions:

1. Assuming a backup alternator was being 'seen' since it had the higher voltage and was overloaded, this would simply mean it couldnt keep up with the demand of the electrical system and therefore the battery would be depleted over time. This would manifest itself as a gradual voltage drop of a running system, correct?

2. Assuming a system with the Nuckols Z13/8 scheme, for example, that means essentially having two nonadjustable voltage regulators in having the "ford regulator" plus the built-in regulator on the plane power alternator, right? I wonder what the expected voltage output of each of these is..

3. There might be an interesting situation where in the Z13/8 the endurance bus would see higher voltage from the backup alternator but perhaps the main bus would see higher voltage from the main alternator due to the diode that exists between the main and endurance bus. Is it possible that two different buses could in fact 'see' two different alternators as described?

Here is a sample Z13/8 with a couple modifications, for reference to ponder these questions: http://n42bu.com/SharedFiles/Z13-8R2-N42BU.png

[N15JB]

Brian,

I don't know anything about the VPX system, but in a non-VPX the secondary alt. is always set less than the primary alt.; typically 0.5V less. IIRC my PlanePower 60A primary is set at 14.2V and the B&C 20A secondary is set at 13.7V. I always fly with both alts. on, but the secondary normally contributes nothing. I did have a primary alt. failure about a year ago, announced by a 0Amps warning. Flew on battery power for a while, till batt. voltage dropped to 13.7V, at which time the secondary alt. came on line. I believe the B&C 20A alt. actually puts out 24-28A at cruise RPMs. In my all glass -10 I can keep everything running except the heated pitot and landing lights.

Jim Berry
RV-10

[Kevin Horton]

Originally Posted by blahphish

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.