AeroElectric-List Digest Archive

Mon 08/13/18


Total Messages Posted: 2



Today's Message Index:
----------------------
 
     1. 08:35 AM - Re: Y connections (FLYaDIVE)
     2. 09:28 AM - Nanosecond fast circuit protection - for what risk? (Robert L. Nuckolls, III)
 
 
 


Message 1


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    Time: 08:35:25 AM PST US
    From: FLYaDIVE <flyadive@gmail.com>
    Subject: Re: Y connections
    Huh! I don=99t know what point you are trying to make??? I see you like Mil Specs when you can warp them. Wasn=99t it you that proselytizes with dogma that fuses and CB =99s do not protect the avionics, they protect the wires? So, what is wrong about hoping that someone - hopefully not bogged down with Mil-Specs developed a faster acting CB? I just don't get the point you are trying to make? I really try not to hypothesize, if you do too much of that one can convince the Millennium Generation that black is white. Actually, that is not too hard to do! Barry On Friday, August 10, 2018, Robert L. Nuckolls, III < nuckolls.bob@aeroelectric.com> wrote: > The old thought process is the fuse/CB only protects the wires. That may > be so for things like the avionics - the thought process on that is the > protection device is not fast enough reacting to save the avionics. > > But from what risk? Can you hypothesize an avionics > failure that would benefit from fault protection > OUTSIDE the device? > > BUT! That is now. What about in the future? What if a product comes ou t > that will > not only protect the wire but the avionics? Wouldn't it be nice to alread y > have your > system wired and ready to accept the change? > > But who might design a 'new' device that is not already > independently immunized from known and quantified > external effects? DO-160, Mil-Std-704 and countless > commercial/industrial design guides strive for minimizing > the effects of external risks to system components and > appliances. > > Sticking with what already exists, wouldn't you want to protect the switc h > as well? > What would happen if a short would happen BEHIND the circuit protection? > Everything behind the protection would turn to smoke! > > Keep in mind that for over a century, airplanes (indeed > most vehicles) have been hauling around thousands of TONS > of circuit protection never called upon to do > its job: prevent a hard fault from (1) creating > an untenable risk and (2) preventing the effects of > a fault from propagating across multiple systems. > > In nearly 60 years of driving and 50 years of working > on airplanes and flying them, I can count fuse blowing > events on the order of ten or less. Countless > fuses and breakers have gone to the scrap yard > never having been called upon to do its job. > > While interesting to hypothesize about 'new' or > 'future' challenges to low risk design, let us > not ignore the foundations on which the science > of our craft is based. The well of knowledge and > lessons-learned is rich and deep. I wouldn't > discourage anyone for searching a root cause > and preventing re-occurrence. But let's be > cautious about conjuring up prophylactics against > heretofore unknown demons. > > > Bob . . . >


    Message 2


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    Time: 09:28:43 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Nanosecond fast circuit protection - for what risk?
    At 10:34 AM 8/13/2018, you wrote: >Huh!=C2 I don=99t know what point you are trying to make??? > >I see you like Mil Specs when you can warp them. > >Wasn=99t it you that proselytizes with dogma >that fuses and CB=99s do not protect the avionics, they protect the wires? > >So, what is wrong about hoping that someone - >hopefully not bogged=C2 down with Mil-Specs developed=C2 a faster acting CB?=C2 =C2 For protection against what risk? Those 'warped' design guides are an encyclopedia of known, quantified, qualified and ultimately managed risks. "Proselytize"? Those guides have stood the test of time . . . designing and testing to those documents has helped produce a constellation of robust systems and appliances for hundreds of millions of vehicles. >I just don't get the point you are trying to make? Okay, you want a nanosecond fast breaker? I can design you one. But it would cost a lot and nobody would want it. Go study the I(squared)t characteristics of the popular breakers . . . they are anything BUT nanosecond fast . . . not even millisecond fast . . . for good and well understood reasons. Magnetic breakers are millisecond fast but I've never seen one employed in a GA aircraft. There is nothing inherently 'wrong' about hoping for the next generation of circuit protection to offer further reductions in risk. But first one must have a qualified and quantified risk to mitigate. 'Bogged down' in mil-specs? I cannot know your experience working with those documents . . . I spent a goodly proportion of my career studying and exploiting the value of those publications. I'd like to believe that products I designed nearly 40 years ago, still in service, benefited from that tribal knowledge. Knowledge offered at virtually no expense to me but undoubtedly very expensive to those who had to tackle those risks for the first time. So the point is: what risk? Bob . . .




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