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What to monitor in a dual alternator airplane

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 24, 2018 4:52 am Post subject: What to monitor in a dual alternator airplane

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:  What should I monitor in my airplane? 
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
Guest

Posted: Mon Sep 24, 2018 7:38 am Post subject: What to monitor in a dual alternator airplane

 	  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: 40

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

[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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