---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 01/19/22: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 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 _____________________________________ Time: 06:37:38 AM PST US Subject: AeroElectric-List: Re: Why CB on regulator field supply? From: "Voyager" 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 _____________________________________ Time: 08:07:15 AM PST US From: Charlie England Subject: Re: AeroElectric-List: Re: Why CB on regulator field supply? On Wed, Jan 19, 2022, 8:56 AM Voyager 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. ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.