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Why CB on regulator field supply?

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Voyager

Joined: 30 Jun 2020
Posts: 77

Posted: Sun Jan 16, 2022 1:25 pm Post subject: Why CB on regulator field supply?

I have two questions I have yet to find an answer to either through searches here or in the AeroElectric Connection.



1. I follow Bob’s logic on using fuses rather than breakers and am planning that for my RANS S-21.  However, his one exception seems to be on the supply for the regulator (alternator field).  I am assuming a CB is specified here either to make testing the OC crowbar easier as the test is then nondestructive or because of the time to trip characteristic of a CB compared to a fuse.  Can someone enlighten me as to the reason?



2. Peripherally related is the question as to why the FAA recommends higher rated CBs than fuses on many conductor sizes in table 11-3 in AC43.13-1B?  Anyone explain that?



I assume both of those are explained somewhere, but I’ve yet to stumble on the explanations.



Thanks,

Matt

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Sun Jan 16, 2022 3:11 pm Post subject: Why CB on regulator field supply?

On Sun, Jan 16, 2022 at 3:31 PM Voyager <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Voyager" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 

 I have two questions I have yet to find an answer to either through searches here or in the AeroElectric Connection.

 

 1. I follow Bob’s logic on using fuses rather than breakers and am planning that for my RANS S-21.  However, his one exception seems to be on the supply for the regulator (alternator field).  I am assuming a CB is specified here either to make testing the OC crowbar easier as the test is then nondestructive or because of the time to trip characteristic of a CB compared to a fuse.  Can someone enlighten me as to the reason?

 

 2. Peripherally related is the question as to why the FAA recommends higher rated CBs than fuses on many conductor sizes in table 11-3 in AC43.13-1B?  Anyone explain that?

 

 I assume both of those are explained somewhere, but I’ve yet to stumble on the explanations.

 

 Thanks,

 Matt

 

 	
I'd have to wonder if the AC43 table issue is tied to the 'conditions':

 

[img]cid:ii_kyhv81nr0[/img]



Wild guess, but perhaps the fuse milspec is for some slow-blow fuse. A 'generic' breaker will typically open much slower than a 'generic' fuse. (Note the quotes....)

My understanding is that the roots of using a pullable breaker for the field are (at least) two-fold: It gives the pilot a way to manually disable a problem alternator, and it allows recovering from a 'nuisance trip' for instance, a momentary 'spike' in voltage due to a load dump may cause the OV protection to trip. A breaker gives you a chance to be sure that the OV issue is real, and not a nuisance trip.

Charlie

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Charlie

Voyager

Joined: 30 Jun 2020
Posts: 77

Posted: Wed Jan 19, 2022 6:36 am Post subject: Re: Why CB on regulator field supply?

 	  Ceengland wrote: 	
		  On Sun, Jan 16, 2022 at 3:31 PM Voyager <m> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Voyager" <m>

 

 I have two questions I have yet to find an answer to either through searches here or in the AeroElectric Connection.

 

 1. I follow Bob’s logic on using fuses rather than breakers and am planning that for my RANS S-21.  However, his one exception seems to be on the supply for the regulator (alternator field).  I am assuming a CB is specified here either to make testing the OC crowbar easier as the test is then nondestructive or because of the time to trip characteristic of a CB compared to a fuse.  Can someone enlighten me as to the reason?

 

 2. Peripherally related is the question as to why the FAA recommends higher rated CBs than fuses on many conductor sizes in table 11-3 in AC43.13-1B?  Anyone explain that?

 

 I assume both of those are explained somewhere, but I’ve yet to stumble on the explanations.

 

 Thanks,

 Matt

 

 	
I'd have to wonder if the AC43 table issue is tied to the 'conditions':

 

[img]cid:ii_kyhv81nr0[/img]



Wild guess, but perhaps the fuse milspec is for some slow-blow fuse. A 'generic' breaker will typically open much slower than a 'generic' fuse. (Note the quotes....)

My understanding is that the roots of using a pullable breaker for the field are (at least) two-fold: It gives the pilot a way to manually disable a problem alternator, and it allows recovering from a 'nuisance trip' for instance, a momentary 'spike' in voltage due to a load dump may cause the OV protection to trip. A breaker gives you a chance to be sure that the OV issue is real, and not a nuisance trip.

Charlie 	




The characteristics of fuses vs. CB and nuisance trips were my guesses also, but I was hoping someone had more than a guess.  Since the alternator supply is on a switch, I am not sure using a CB to manually turn off the alternator is needed as you can just turn off the alternator switch.

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Wed Jan 19, 2022 8:07 am Post subject: Why CB on regulator field supply?

On Wed, Jan 19, 2022, 8:56 AM Voyager <m.whiting(at)frontier.com (m.whiting(at)frontier.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Voyager" <m.whiting(at)frontier.com (m.whiting(at)frontier.com)>

 

 

 Ceengland wrote:

 > On Sun, Jan 16, 2022 at 3:31 PM Voyager  wrote:

 > 

 > 

 > > --> AeroElectric-List message posted by: "Voyager" 

 > >  

 > >  I have two questions I have yet to find an answer to either through searches here or in the AeroElectric Connection.

 > >  

 > >  1. I follow Bob’s logic on using fuses rather than breakers and am planning that for my RANS S-21.  However, his one exception seems to be on the supply for the regulator (alternator field).  I am assuming a CB is specified here either to make testing the OC crowbar easier as the test is then nondestructive or because of the time to trip characteristic of a CB compared to a fuse.  Can someone enlighten me as to the reason?

 > >  

 > >  2. Peripherally related is the question as to why the FAA recommends higher rated CBs than fuses on many conductor sizes in table 11-3 in AC43.13-1B?  Anyone explain that?

 > >  

 > >  I assume both of those are explained somewhere, but I’ve yet to stumble on the explanations.

 > >  

 > >  Thanks,

 > >  Matt

 > >  

 > >  

 > I'd have to wonder if the AC43 table issue is tied to the 'conditions':

 >  

 > [img]cid:ii_kyhv81nr0[/img]

 > 

 > Wild guess, but perhaps the fuse milspec is for some slow-blow fuse. A 'generic' breaker will typically open much slower than a 'generic' fuse. (Note the quotes....)

 > 

 > 

 > My understanding is that the roots of using a pullable breaker for the field are (at least) two-fold: It gives the pilot a way to manually disable a problem alternator, and it allows recovering from a 'nuisance trip' for instance, a momentary 'spike' in voltage due to a load dump may cause the OV protection to trip. A breaker gives you a chance to be sure that the OV issue is real, and not a nuisance trip.

 > 

 > 

 > Charlie

 

 

 The characteristics of fuses vs. CB and nuisance trips were my guesses also, but I was hoping someone had more than a guess.  Since the alternator supply is on a switch, I am not sure using a CB to manually turn off the alternator is needed as you can just turn off the alternator switch.



The gotcha is the OV protection; if it 'nuisance trips, with a fuse there's no recovery. With a breaker, you can reset it.

_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 20, 2022 8:57 am Post subject: Why CB on regulator field supply?

 	  Quote: 	
		  

 The characteristics of fuses vs. CB and nuisance trips were my guesses also, but I was hoping someone had more than a guess.  Since the alternator supply is on a switch, I am not sure using a CB to manually turn off the alternator is needed as you can just turn off the alternator switch. 	


    ASSUMING elects to incorporate crowbar ov

    protection in their project, then to mitigate

    possible but RARE nuisance trips of the OV

    system, a crew accessible circuit breaker is

    the field supply protection of choice. In

    the event of an OV trip event, the pilot has

    an opportunity to reset the breaker ONE time

    to confirm the existence of failure in the

    alternator's regulator.



    ADDITIONALLY, if one chooses to use a DPST

    battery master switch, battery and alternator come

    ON-OFF together, the a pullable field supply

    breaker is handy for disabling the alternator

    for battery only ground operations thus elininating

    an energy wasting, full-field drain on the battery.



    NOTE. When picking a breaker for upstream management

    of field supply in the crowbar system, it is a

    really good idea to pick a breaker that is (1)

    qualified to function as designed after a substantial

    number of hard-fault trips. (2) actuates really

    fast under the typical 50 to 200A current pulse

    that an OV event impresses on the device. This style of breaker

    is highly recommended for this application:



  http://aeroelectric.com/Pictures/Breakers/circuitbreakers.jpg



    This is one of many breakers NOT suited for service

    upstream of a crowbar ov management device:



  http://aeroelectric.com/Pictures/Breakers/Breaker_Failure_1a.jpg

 

    Note also that all wound-field, alternator controllers

    from B&C feature built-in crowbar ov management systems.

    Incorporation of the recommended breaker applies to

    these products. I've had a few readers over the years

    who elected to protect their field supply with a fuse . . .

    this is no more hazardous than a host of other

    alternator failures . . . but pretty inconvenient

    if that fuse resides in the recommended out-of-sight-

    out-of-mind location in the airplane.



    



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Thu Jan 27, 2022 11:59 am Post subject: Why CB on regulator field supply?

Bob,  This discussion poses a (probably dumb) question.  My system consists of a L40 alternator, LR3C-14 regulator and the 2 circuit breakers and lamp that come with B&C's installation kit.  Also have the standard split rocker switch for batt and alt.   The question is what is the appropriate action- in flight- to take if one of the breakers should pop or the light illuminates.   While I'm sure I could muddle through it, it would be nice to have a clear course of action.  If the 5A breaker pops does that mean there was an overvoltage situation.  If I reset it one time and it pops again, does that mean there is a problem with the regulator?  What about a warning lite and the breakers don't pop.  Does that mean that maybe the alternator is not producing power?

  Also, for me at least, being primarily VFR neither situation would be considered an emergency.

Thanks, Steve

On Thu, Jan 20, 2022 at 12:03 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		     	  Quote: 	
		  

 The characteristics of fuses vs. CB and nuisance trips were my guesses also, but I was hoping someone had more than a guess.  Since the alternator supply is on a switch, I am not sure using a CB to manually turn off the alternator is needed as you can just turn off the alternator switch. 	


    ASSUMING elects to incorporate crowbar ov

    protection in their project, then to mitigate

    possible but RARE nuisance trips of the OV

    system, a crew accessible circuit breaker is

    the field supply protection of choice. In

    the event of an OV trip event, the pilot has

    an opportunity to reset the breaker ONE time

    to confirm the existence of failure in the

    alternator's regulator.



    ADDITIONALLY, if one chooses to use a DPST

    battery master switch, battery and alternator come

    ON-OFF together, the a pullable field supply

    breaker is handy for disabling the alternator

    for battery only ground operations thus elininating

    an energy wasting, full-field drain on the battery.



    NOTE. When picking a breaker for upstream management

    of field supply in the crowbar system, it is a

    really good idea to pick a breaker that is (1)

    qualified to function as designed after a substantial

    number of hard-fault trips. (2) actuates really

    fast under the typical 50 to 200A current pulse

    that an OV event impresses on the device. This style of breaker

    is highly recommended for this application:



  http://aeroelectric.com/Pictures/Breakers/circuitbreakers.jpg



    This is one of many breakers NOT suited for service

    upstream of a crowbar ov management device:



  http://aeroelectric.com/Pictures/Breakers/Breaker_Failure_1a.jpg

 

    Note also that all wound-field, alternator controllers

    from B&C feature built-in crowbar ov management systems.

    Incorporation of the recommended breaker applies to

    these products. I've had a few readers over the years

    who elected to protect their field supply with a fuse . . .

    this is no more hazardous than a host of other

    alternator failures . . . but pretty inconvenient

    if that fuse resides in the recommended out-of-sight-

    out-of-mind location in the airplane.



    



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

_________________
Steve

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Thu Jan 27, 2022 4:34 pm Post subject: Re: Why CB on regulator field supply?

Whenever any circuit breaker pops, it is best to wait until safely on the ground before resetting or troubleshooting.

  Circuit breakers can trip due to over current, or short circuits, or from loose wire terminals that make heat.

 The best indicator of charging system failure is a voltmeter showing low voltage (less than 13.5VDC).

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 28, 2022 9:55 pm Post subject: Why CB on regulator field supply?

At 06:34 PM 1/27/2022, you wrote:

 --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Whenever any circuit breaker pops, it is best to wait until safely on the ground before resetting or troubleshooting.



   yeahhhh . . . mostly . . .



 Circuit breakers can trip due to over current



  (soft fault)



 or short circuits



  (hard fault)



 or from loose wire terminals that make heat . . 



  (terminal on the breaker itself? probably

   not . . . you'd have to conduct a LOT of

   loose-joint, heat-energy into the breaker

   to trip it's bi-metal current sense mechanism)



 The best indicator of charging system failure is a voltmeter

 showing low voltage (less than 13.5VDC).



   Yes, but this discussion was about the SPECIAL

   CASE for a DELIBERATE hard fault generated

   by a crowbar ov management system. In this

   case, it's possible that the ov trip was

   a nuisance event so resetting this breaker

   ONE time is called for. A short interval

   re-trip is probable cause that the ov

   condition is real.



   The last generation of crowbar ov modules

   were much more resistant to the dv/dt

   transient . . . a number of my readers

   have reported satisfactory operations with

   just a fuse on the alternator field supply

   feeder. If I resurrect this product, it will

   probably be 100% immune to such stimuli.



 



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Mon Jan 31, 2022 7:33 am Post subject: Re: Why CB on regulator field supply?

 	  Quote: 	
		  or from loose wire terminals that make heat . .



(terminal on the breaker itself? probably

not . . . you'd have to conduct a LOT of

loose-joint, heat-energy into the breaker

to trip it's bi-metal current sense mechanism) 	


I was speaking in general when I gave 3 causes for breakers tripping, not specifically the alternator field circuit.

I worked in an industrial electrical setting.  On more than one occasion I found circuit breakers tripped due to heat caused by their screws being loose.  Of course those circuit were probably carrying 15 amps or more.  The whole electrical system in my RV-12 uses less than 15 amps.  

Speaking of loose screws, it seems that the vast majority of electrical problems are caused by loose connections.

_________________
Joe Gores

Voyager

Joined: 30 Jun 2020
Posts: 77

Posted: Sun Feb 13, 2022 5:58 am Post subject: Re: Why CB on regulator field supply?

Bob,  thanks for your explanation.  What you said is what I was guessing, but it is good to hear it from the source.  I plan to use a CB on the alternator and fuses everywhere else as I think the alternator field is the only circuit where you consistently use a CB in your architectural diagrams.  Please let me know if there are other areas where you consider a CB a better solution.



Regards,

Matt

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