Today's Message Index:
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1. 06:37 AM - Re: Why CB on regulator field supply? (Voyager)
2. 08:07 AM - Re: Re: Why CB on regulator field supply? (Charlie England)
Message 1
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| Subject: | Re: Why CB on regulator field supply? |
Ceengland wrote:
> On Sun, Jan 16, 2022 at 3:31 PM Voyager wrote:
>
>
> >
> > I have two questions I have yet to find an answer to either through searches
here or in the AeroElectric Connection.
> >
> > 1. I follow Bobs 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 Ive 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.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=505743#505743
Message 2
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| Subject: | Re: Why CB on regulator field supply? |
On Wed, Jan 19, 2022, 8:56 AM Voyager <m.whiting@frontier.com> wrote:
m
> >
>
>
> Ceengland wrote:
> > On Sun, Jan 16, 2022 at 3:31 PM Voyager wrote:
> >
> >
> > >
> > > 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=99s logic on using fuses rather than breakers
and am
> planning that for my RANS S-21. However, his one exception seems to be o
n
> 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 i
s
> 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=99ve 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 disab
le
> 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 O
V
> 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 alternat
or
> 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.
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