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Why have a switch on ALT Field?
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harley(at)AgelessWings.co
Guest

Posted: Mon Sep 28, 2009 9:15 am Post subject: Why have a switch on ALT Field?

 	  Quote: 	
		      	  Quote: 	
		      I'm sorry if my words are too much for you.

    When I wear my teacher-hat, the answers

    I offer are intended to lead to understanding of

    the foundation upon which the answer is based.

    It's my belief that once understanding is

    achieved, the student then becomes a teacher

    on the same discussion. Perhaps I presume too

    much . . . that everyone here on the List is

    as enthusiastic about understanding as I  . . . 	
 	
 Don't stop, Bob...that's the way I always try to explain things, figuring that most people don't believe me or want to know the reason why and need a more detailed explanation or an understanding for themselves...that was from my working days as well, when I had to train the mechanics after I had installed one of the new automated systems. 

 

 Of course they all usually fall asleep ...<G>

 

 Harley

    [quote][b]

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Mon Sep 28, 2009 10:26 am Post subject: Re: Why have a switch on ALT Field?

Bob N.



Please to not take my request for a simpler answer the wrong way, I am enthusiastic about learning, I was just not getting it.  When I was asked about teaching as in instructor pilot in the Air Force, I always said what made a good instructor was being able to give the same information many different ways until the student got it.  We all learn different ways and at a different pace.  My email to you was meant to communicate that I was not getting it, please tell me a different way.  In radio jargon "I did not copy say again".



To everyone on this thread, my knowledge of how the alternator and regulator and field work has increased ten fold and that is what my ultimate goal was, I never want to stop learning.



I will put in the field switch after all is said and done for the following reasons not in any particular priority.



1. CBs don't' make good switches

2. Convenience

3.  There might be something I did not get and don't want to add a switch later

4. It has always been done that way   



Thank you again to all who posted I hope I am not the only one who gained from this thread.

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 28, 2009 8:52 pm Post subject: Why have a switch on ALT Field?

 	  Quote: 	
		  

To everyone on this thread, my knowledge of how the alternator and 

regulator and field work has increased ten fold and that is what my 

ultimate goal was, I never want to stop learning.


	


    Great!

 	  Quote: 	
		  I will put in the field switch after all is said and done for the 

following reasons not in any particular priority.



1. CBs don't' make good switches

2. Convenience

3.  There might be something I did not get and don't want to add a 

switch later

4. It had always been done that way  [Laughing]


	


    All those things are true so even if the

    explanations offered seem arcane, the

    benefits for having the switch will be

    secured.



 	  Quote: 	
		  Thank you again to all who posted I hope I am not the only one who 

gained from this thread.


	


    At last count, subscribers to this List numbered

    over 1800. If you look at the posting stats on

    Matronics, this list is one of the busiest on

    Matt's service. I have to believe the goals

    for sharing are being realized.



    Thank you for participating.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

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ianxbrown

Joined: 16 May 2009
Posts: 80

Posted: Sat Oct 10, 2009 9:34 am Post subject: Why have a switch on ALT Field?

Hi Bob,

 It's an internally regulated alternator from Aero Sport Power in BC.  It switches off and ceases to charge when I remove the 12V "IGN" input.  It took me a while to get to the airport and check it.   

 

 Ian

 

 On Sun, 2009-09-27 at 09:29 -0400, bakerocb(at)cox.net wrote:  	  Quote: 	
		    	  Quote: 	
		  

--> AeroElectric-List message posted by: <bakerocb(at)cox.net (bakerocb(at)cox.net)>



9/27/209



Hello Ian, Thanks for reading my post and responding. Please let me make an 

attempt at reducing your confusion. You wrote:



1) "As I understand it, the switch is on the alternator field low-current 

12V line (called IGN on my alternator) ........"



Can you both turn ON (activate) and turn OFF (deactivate) your alternator's 

electrical output with this alternator field switch?** This is generally 

considered a desireable design goal.



There are some internally regulated alternators that, once activated, draw 

their field current from inside the alternator and it is not possible to 

deactivate those alternator's electrical output by turning OFF an external 

field switch. While this subject has been hotly debated several times on the 

aeroelectric list it is generally considered that the feature of not being 

able to shut down the alternator's electrical output with an external field 

switch is an undesirable design goal.



2) "..........the circuit breaker protects the output side (B lead)."



The primary purpose of a CB or fuse in the B lead is to protect the wiring 

in the B lead. This wiring normally goes from the positive terminal of the 

battery to a main battery contactor and then onto the B output terminal of 

the alternator. If this wiring should encounter a short to ground the 

BATTERY could dump a huge amount of amperage into the wiring and cause a 

fire. Therefore the primary  purpose of the CB or fuse in the B lead wiring 

is to protect the wiring from BATTERY electrical output.



But since there are alternators that could "run away" and not be shut down 

by a switch in the circuit providing electricity to the alternator's field 

some people who have those kinds of alternators look upon the CB in the B 

lead as a means of cutting off the excess electrical flow from the 

alternator.



Depending upon the manual pulling of a circuit breaker in the B lead as the 

only means of terminating an over voltage situation or a "run away" 

alternator is generally not considered a desirable design goal.



Does this help?



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



**PS: I'd be interested in knowing how your alternator field switch does 

work and if you have an externally or internally regulated alternator?



=======================================================



Time: 10:45:24 AM PST US

Subject: Re: Why have a switch on ALT Field?

From: Ian <ixb(at)videotron.ca (ixb(at)videotron.ca)>



OK, now here's one more vote for "confused".   I thought the circuit

breaker was supposed to be rated at the output amperage of the

alternator because it's that current that one wants to limit.   My 40A

circuit breaker would do nothing for me on the alternator field circuit.



As I understand it, the switch is on the alternator field low-current

12V line (called IGN on my alternator) and the circuit breaker protects

the output side (B lead).   Mine is wired this way because it made

sense.



Ian Brown,

RV-9A, Bromont, QC

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 10, 2009 10:24 am Post subject: Why have a switch on ALT Field?

At 12:28 PM 10/10/2009, you wrote:

 	  Quote: 	
		  Hi Bob,

It's an internally regulated alternator from Aero Sport Power in 

BC.  It switches off and ceases to charge when I remove the 12V 

"IGN" input.  It took me a while to get to the airport and check it.


	


   Okay, the IGN input to your internally regulated alternator

   is a simple, low-current "alternator-enable" signal that goes

   to the regulator circuit. It is NOT the alternator's field

   supply. See:



http://aeroelectric.com/Pictures/Schematics/Internal_Regulator.jpg



   This is why the IGN input doesn't need to be supplied/

   protected by a very large source. A 1A fuse would be

   fine. This figure also serves to illustrate the fact

   that there are electronics DOWNSTREAM of the IGN input

   signal that can mis-behave and give one reasons to

   want the alternator off line.



   Without having direct control over the field supply

   circuit, other provisions are necessary if one's

   design goals include any time, any conditions,

   On/Off control of the alternator.



        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

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