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What to monitor in a dual alternator airplane

 
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nuckolls.bob(at)aeroelect
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PostPosted: Mon Sep 24, 2018 4:52 am    Post subject: What to monitor in a dual alternator airplane Reply with quote

At 09:50 PM 9/23/2018, you wrote:
Quote:
Folks,

Over the years that I subscribed to this mailing list, there have been many conversations about monitoring voltage and current in an airplane. I want to approach this from a different perspective and see if I understand correctly.

The basic questions are:
  1. What should I monitor in my airplane?
  2. How do I interpret the indications, especially in flight?

Bus voltage with ACTIVE NOTIFICATION of
LOW VOLTS.

LIGHT OFF, pour another cup of coffee.

LIGHT ON, finish present cup of coffee . . . turn
ON E-bus alternate feed, turn OFF battery master.

If you have a second alternator, turn it ON but
reduce e-bus loads to that which the alternator
supports.

AIRPORT IN SIGHT, turn battery master back on
and terminate flight.

Just because you CAN monitor a lot off stuff
doesn't mean that it's useful for managing
systems during flight. In fact, being able
to take a video game tour through your electrical
system is a DISTRACTION from your duties as
pilot. Be a pilot in the air and a mechanic
on the ground.


Quote:
My own airplane has a 12 volt system with two B&C alternators and voltage regulators. The primary regulator is an LR3C preset to 14.4 volts. The standby regulator is part of an SB1B-14 and is preset to 13.0 volts.

13.5 is better based on the analysis offered
yesterday.


Quote:
Here is what I think that I need to monitor:
  • Voltage (should pretty pretty much the same everywhere so I am just using my EFIS' bus voltage indicator)

Yup, you can stop there . . . everything else is
superfluous to your comfortable termination of the
flight. Save those machinations as to cause/effect
until on the ground . . . especially when the troops
here on the List are available to help.


Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Sep 24, 2018 7:38 am    Post subject: What to monitor in a dual alternator airplane Reply with quote

Quote:
Barry - Why would you have the second Alt. set to ANYTHING less than the charging voltage?
13.0 VDC is NOT a Charging Voltage.

Correct. There are TWO choices in the B&C product
line for selection of an AUX alternator controller.
The SB/LS series regulators were tailored for Z-12
style installations in TC aircraft where the AUX
alternator is paralleled to the main bus and turned
ON during normal phases of flight. The AUX controller
is set for come level slightly below the MAIN
controller so that under normal ops, it completely
relaxes but in a condition ready to go to work
should the bus voltage drop.

The AUX alternator was never intended to charge
batteries . . . only hold the bus at some level
above the battery's discharge voltage such that
battery energy is held in reserve for decent/approach
phases of flight.

If the bus voltage drops below the AUX controller
set point, the AUX alternator wakes up and a SPECIAL
circuity within the controller senses this and illuminates
an ALTERNATOR LOADED light.

The stand-by versions of the alternator controller
are not recommended for simple dual alternator installations
where the auto-switch feature is not necessary . . .
this was a 'bell-n-whistle' aimed primarily at the
STC market for TC aircraft that were receiving the
pad driven, aux alternators.

Yeah, 13.0 is a bit too low . . . 13.5 is better.
Will talk with B&C about this. Further, if one is
flying a lithium battery, the set-point for the
SB/LS regulators becomes still more critical.
There will probably be a reassessment of design
philosophy for alternator controllers to bring
them into better alignment with the new
technologies.

. . . but know that there is a reason for
the '13.0 madness' . . .

Bottom line is that there is no good reason
to monitor/worry/fuss over any condition other
that to know that bus voltage is above 14.0V. It can
never be that high except that the alternator
is carrying present system loads. If that
condition changes, then you call in the cavalry
and bring the bus back up to 13.5 or higher
depending on the second system installed.

ALL other currents, voltages, humidity and
phases of the moon are irrelevant to the primary
goal of supporting needed electro-whizzies
through all phases of the flight.




Bob . . .


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BMC_Dave



Joined: 04 Jul 2018
Posts: 22

PostPosted: Wed Sep 26, 2018 11:03 am    Post subject: Re: What to monitor in a dual alternator airplane Reply with quote

[quote="nuckolls.bob(at)aeroelect"]
Quote:


The stand-by versions of the alternator controller
are not recommended for simple dual alternator installations
where the auto-switch feature is not necessary . . .


Glad I just happened across this then as it's not immediately apparent. Basing my design off Z-12 I had assumed the AUX ALT field was open until needed. The standby regulator document does explain this though, leave it closed in normal ops.

I'm curious as to the need for a breaker for the alternator field if it's already on a switch? Are those still necessary?


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