AeroElectric-List Digest Archive

Sun 04/04/10


Total Messages Posted: 10



Today's Message Index:
----------------------
 
     1. 05:34 AM - Re: Re: Fusible links vs fuses (James Kilford)
     2. 05:59 AM - Alternator protection ANL-40 rating (James Kilford)
     3. 06:51 AM - Re: Alternator protection ANL-40 rating (Robert L. Nuckolls, III)
     4. 06:54 AM - Re: Re: Fusible links vs fuses (Robert L. Nuckolls, III)
     5. 07:01 AM - ANL-40 mounting (James Kilford)
     6. 07:27 AM - Re: Fusible links vs fuses (rckol)
     7. 07:34 AM - Re: Re: Fusible links vs fuses (James Kilford)
     8. 09:24 AM - Re: Re: Fusible links vs fuses (Robert L. Nuckolls, III)
     9. 12:17 PM - Re: Re: Fusible links vs fuses (Robert L. Nuckolls, III)
    10. 02:41 PM - Re: Radio mounting (Jae Chang)
 
 
 


Message 1


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    Time: 05:34:17 AM PST US
    Subject: Re: Fusible links vs fuses
    From: James Kilford <james@etravel.org>
    Thanks for that rck. So the fusible link is just intended to be a worst-case-scenario, probably-won't-ever-blow fuse. Makes sense as it reduces joints. What Bob wrote about the alternator is interesting, and makes me think of another question, which I'll post separately. James On Fri, Apr 2, 2010 at 9:55 PM, rckol <rckol@kaehlers.com> wrote: > > James, > > The fuseable link is to protect the wire between the bus and the breaker. The breaker is there as part of the overvoltage protection circuit. If you get an overvoltage event, you want the resetable breaker to trip, not the proposed fuse to blow, hence the sturdier fuseable link. > > -------- > rck > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=292811#292811 > >


    Message 2


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    Time: 05:59:00 AM PST US
    Subject: Alternator protection ANL-40 rating
    From: James Kilford <james@etravel.org>
    Bob, Interesting what you said about the B-lead protection. I had thought that my (planned) ANL-40 is going to protect the B-lead wire from the battery. It's interesting to read about this over-current scenario that could end up blowing the ANL-40 in a "normal" situation, i.e. something designed to protect has introduced a new failure mode. However, I read on the B&C Specialty web site that the ANL-40 can handle 80% more current than its rated capacity on a continuous basis. It sounds as though this is going to stand anything extra the alternator can put out. Is this assertion correct? Thanks in anticipation, James On Sat, Apr 3, 2010 at 5:07 AM, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com> wrote: > <nuckolls.bob@aeroelectric.com> > > At 10:14 PM 4/2/2010, you wrote: >> >> >> James, >> >> The 5 amp breaker in the line controlling the regulator is for overvoltage >> protection, assuming you are using a B&C or PlanePower regulator for an >> externally regulated alternator or are using a PlanePower internally >> regulated alternator with built in OV protection (or an OVM-14 module). >> >> Your overcurrent protection would be in the form of a big breaker or fuse >> (40+ amps) on the B lead (output) of the alternator. > > Very close except that alternators don't require over-current > protection like their older cousins, the generator. > > Alternators are magnetically limited in their ability > to deliver current . . . so as the load on an alternator > goes up, there comes a time about 10-20% over nameplate > rating where the critter wont deliver any more and the > output sags. > > Maximum output from the alternator happens when the > machine is cold. On rare occasions (cold morning, > jump start dead battery, battery is relatively > new and will accept lots of recharge current) > one can get a nuisance trip of the 60A breaker > in an airplane fitted with a 60A alternator. > This is because total ship's electrical loads > plus battery recharge current will be what ever > the alternator will deliver . . . which may be > greater than the 60A breaker rating on the > panel. > > This happened to me once . . . the second of > only two times I've had a breaker open in flight. > This is why we select b-lead protection well above the > name-plate rating for the alternator so that the > breaker doesn't nuisance trip. It's also why I > call the 60A breaker on most Cessnas and Pipers > the "breaker designed to nuisance trip". > > In any case, the b-lead breaker is to protect > the rest of the system if you get shorted diodes > in the alternator (very rare). The fusible link > in most cares serves the same purpose. > > Bob . . . > >


    Message 3


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    Time: 06:51:50 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Alternator protection ANL-40 rating
    At 07:55 AM 4/4/2010, you wrote: > >Bob, > >Interesting what you said about the B-lead protection. > >I had thought that my (planned) ANL-40 is going to protect the B-lead >wire from the battery. It's interesting to read about this >over-current scenario that could end up blowing the ANL-40 in a >"normal" situation, i.e. something designed to protect has introduced >a new failure mode. > >However, I read on the B&C Specialty web site that the ANL-40 can >handle 80% more current than its rated capacity on a continuous basis. > It sounds as though this is going to stand anything extra the >alternator can put out. Is this assertion correct? Correct. One COULD use a fuse or breaker in the b-lead. They just need to be sized such that the alternator would NEVER open the breaker even when temporarily "overloaded". ANL limiters use the same schematic symbol as a fuse because they ARE a very robust, one-time, melting element protector, i.e. "fuse". But the differences in response time for the ANL limiter and the ATC fuse are huge. Circuit breakers fall in between. A fundamental of power distribution system architecture is to install over-current protection devices (1) to prevent a wire from becoming overheated to the point of becoming hazardous and (2) isolate the faulted branch of the system without propagating the failure to other branches. This means that as you move from the load to the source of power, the circuit protective devices must become increasingly robust as you move toward the source. This idea is common to all reliable, failure tolerant power distribution systems. For example: A fuse inside a toaster is much less robust (faster acting) than the breaker in a home's power distribution box. The breaker in the box is much less robust than the protection for a transformer on the pole which powers multiple houses. As one moves upstream toward the power source, the relative robustness of each protective device must be sized to allow operation of any single protective device in the system without tripping any protection upstream. This prevents a short in a toaster from turning out lights in the whole neighborhood. A design goal for the crowbar ov protection system is to place the responding circuit breaker in reach of the pilot. IF your airplane is fitted with legacy panel mounted bus-bars and acres-of-breakers, then integration of the crowbar-ov protection system is no big deal. If you're using remotely mounted fuse blocks, then there's got to be a piece of wire that runs from the bus (fuse block feed terminal) to the circuit breaker on the panel. Legacy design practice and common sense tells us to protect that wire with some device that is more robust than the breaker, hence the fusible link . . . which is a little brother to an ANL limiter. Compare the operating characteristics of the ATC plastic fuse with ANL limiters . . . http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ATC_Specs.pdf http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf and a typical miniature aircraft circuit breaker. http://aeroelectric.com/Mfgr_Data/Breakers/Eaton/Eaton_4200.pdf Under mild overload (2x rating) a fuse will be expected to operate in about 50-100 mS, the breaker in 1-2 seconds and an ANL never. These differences in robustness suggest their proper position in a power distribution system where they might be in series with each other. Getting them out of order can produce some unhappy results in a system that is not failure tolerant. Bob . . .


    Message 4


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    Time: 06:54:51 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Fusible links vs fuses
    At 07:31 AM 4/4/2010, you wrote: > >Thanks for that rck. > >So the fusible link is just intended to be a worst-case-scenario, >probably-won't-ever-blow fuse. Correct. > Makes sense as it reduces joints. That was the goal. Automobiles have See: http://www.aeroelectric.com/articles/fuselink/fuselink.html There's a lot of discussion on the whys and wherefors for fusible links in the FAQ http://www.aeroelectric.com/FAQ/AeroElectric-List/AeroElectric-List_FAQ.pdf Do a search on "fusible" to get a good review of their development, application and incorporation into AEC Z-figures. Bob . . .


    Message 5


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    Time: 07:01:37 AM PST US
    Subject: ANL-40 mounting
    From: James Kilford <james@etravel.org>
    Gents, I forgot to ask when on the subject of ANL-40s, if there is a slightly less "industrial" way of mounting an ANL-40. The holder I have for it looks as though it's from an electricl sub-station, and weighs about 50lbs (a slight exaggeration perhaps). Is it poor practice to mount the ANL-40 in some other way, perhaps in-line to the B-lead close to the starter contactor? Thanks in anticipation, James


    Message 6


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    Time: 07:27:42 AM PST US
    Subject: Re: Fusible links vs fuses
    From: "rckol" <rckol@kaehlers.com>
    Bob, Am I correct in thinking that in the rare "shorted alternator diode" scenario, the alternator is providing a low resistance path to ground and the power source that the big breaker or fuse is interrupting is in fact the battery? -------- rck Read this topic online here: http://forums.matronics.com/viewtopic.php?p=292940#292940


    Message 7


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    Time: 07:34:25 AM PST US
    Subject: Re: Fusible links vs fuses
    From: James Kilford <james@etravel.org>
    Bob, The FAQ is an awesome body of knowledge! I started reading it from top to bottom... about 20 pages in I noticed it's 310 pages! After that, Control-F became my friend! I can't remember how I stumbled across your Aeroelectric Connection book, and this list, but I'm extremely glad I did. It's funny how we spend all this time and money building our planes, knowing every part and rationalising every decision... until we get to the electrics... then we just do exactly what Cessna and Piper have done forever, because "it must be fine". It's great to have done an electrical system the AC way: to plan properly, to question it all in the same way, and learn about why something is or isn't appropriate. It's also good to be able to answer people's questions ("why don't you have breakers?" or "why can't you change your fuses in flight?", etc) from a position of knowing that, even if something turns out not to be perfect, at least it was thought about in the first place. James On Sun, Apr 4, 2010 at 2:54 PM, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com> wrote: > <nuckolls.bob@aeroelectric.com> > > At 07:31 AM 4/4/2010, you wrote: >> >> >> Thanks for that rck. >> >> So the fusible link is just intended to be a worst-case-scenario, >> probably-won't-ever-blow fuse. > > Correct. > >> Makes sense as it reduces joints. > > That was the goal. Automobiles have > > See: > > http://www.aeroelectric.com/articles/fuselink/fuselink.html > > There's a lot of discussion on the whys and wherefors > for fusible links in the FAQ > > http://www.aeroelectric.com/FAQ/AeroElectric-List/AeroElectric-List_FAQ.pdf > > Do a search on "fusible" to get a good review > of their development, application and incorporation > into AEC Z-figures. > > Bob . . . > >


    Message 8


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    Time: 09:24:33 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Fusible links vs fuses
    >Am I correct in thinking that in the rare "shorted alternator diode" >scenario, the alternator is providing a low resistance path to >ground and the power source that the big breaker or fuse is >interrupting is in fact the battery? Absolutely. Compared to the alternator, the battery is the single most "dangerous" in terms of energy dumped during a fault . . . a new 35 a.h. RG battery can source over 2000 amps when presented with a short. So yes, the b-lead protection is not going to be tripped by the alternator but the battery when some (very rare) failure in the alternator presents the short. I've seen alternator stator leads burn before the ANL in the b-lead burned. So it may be that most alternators are pretty well "self limiting" in terms of effects on the rest of the system during and right after a fault. But without extensive testing/analysis, I wouldn't want to bet on it. I forgot to ask when on the subject of ANL-40s, if there is a slightly less "industrial" way of mounting an ANL-40. The holder I have for it looks as though it's from an electricl sub-station, and weighs about 50lbs (a slight exaggeration perhaps). They are pretty beastly . . . consider the miniature automotive equivalents to the ANL. Or, if you're doing b-lead protection on a 40A alternator, how about a 60A maxi-fuse. The ANL is not the be-all-end-all solution to the design goal. You can build your own holder for a mini-anl out of phenolic, delrin or other robust insulator material. This was discussed a few days ago here on the List. Is it poor practice to mount the ANL-40 in some other way, perhaps in-line to the B-lead close to the starter contactor? The goal is to place circuit protection as close as possible to the SOURCE of the energy likely to open the fuse. Note in all the Z-figures (at least I think I got it done on all of them) the wire on the battery side of the b-lead protection is marked with a (*). That symbol on the drawing suggests "make this wire as short as practical". Bob . . .


    Message 9


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    Time: 12:17:45 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Fusible links vs fuses
    At 09:33 AM 4/4/2010, you wrote: > >Bob, > >The FAQ is an awesome body of knowledge! I started reading it from >top to bottom... about 20 pages in I noticed it's 310 pages! After >that, Control-F became my friend! Yeah, a reader on the List compiled that document some years ago . . . it needs updating and editing. But as you've discovered, the "find function" is very useful for sifting all the sand. >I can't remember how I stumbled across your Aeroelectric Connection >book, and this list, but I'm extremely glad I did. It's funny how we >spend all this time and money building our planes, knowing every part >and rationalising every decision... until we get to the electrics... >then we just do exactly what Cessna and Piper have done forever, >because "it must be fine". And that's not wrong . . . but it does carve your airplane's electrical system into "legacy stone". Probably 90% of all OBAM aircraft are wired like Uncle's Walter, Duane, and Bill have been doing it for 60+ years and it works as advertised. >It's great to have done an electrical system the AC way: to plan >properly, to question it all in the same way, and learn about why >something is or isn't appropriate. It's also good to be able to >answer people's questions ("why don't you have breakers?" or "why >can't you change your fuses in flight?", etc) from a position of >knowing that, even if something turns out not to be perfect, at least >it was thought about in the first place. Exactly! It would not yank my chain in the least if EVERYBODY wired their airplanes like a C-150 if I thought they understood how all the parts worked and made their decision from informed choice based not upon tradition or authoritative suggestion but from understanding. Thank you for the kind words. I'm pleased that you find the work informative and useful. Bob . . .


    Message 10


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    Time: 02:41:29 PM PST US
    From: Jae Chang <jc-matronics_aeroelectric@jline.com>
    Subject: Re: Radio mounting
    http://lh4.ggpht.com/_E3nI7J8M6Iw/S51_ptBMY7I/AAAAAAAAAsI/GKgzSIQV4jk/s800/IMG_0180.JPG I discovered this very same thing between an GTX-327, SL-30, and GMA-240. I was surprised when the Al strips I was using to mock things up bent wide. It turns out the transponder and audio panel are about the same width. The SL-30 was narrower. Go figure. I ended up adding some thin washers (AN960-6L, i think) washers as shims for the SL-30. http://lh5.ggpht.com/_E3nI7J8M6Iw/S7FQD00QWnI/AAAAAAAAA00/5M3r8fpRx3E/s800/IMG_0195.JPG http://lh3.ggpht.com/_E3nI7J8M6Iw/S6uYQIP_1LI/AAAAAAAAAzM/4wXobq_U904/s800/IMG_0192.JPG The above are some pictures of how I mounted my 3 items. All this is completely new to me, so I have no idea if this is right or wrong. Also, in my setup, to get the flush fit I wanted, the racks extend into my panel cutout a bit. The install manuals have plenty of warnings about making sure the connectors get seated properly. Jae RV-10 Bill Schlatterer wrote: > Pix worth a thousand :-) This is a 430W tray and a SL40 Tray from Garmin. > Definitely not the same size but I think I remember the SL40 is slightly > smaller than the 430 as I had to add shims and the 430w tray was 6.25. 6.38 > would have been a little better as mine is snub. Note that Garmin didn't > design the SL40 and SL30, those came with the Apollo acquisition as I > remember which probably accounts for the difference in tray sizes. > > Bill S > 7a just weeks away :-) > > > >




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