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Shorts & Blown Fuse

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Voyager

Joined: 30 Jun 2020
Posts: 77

Posted: Fri Jan 26, 2024 2:11 pm Post subject: Shorts & Blown Fuse

Fuses failing from old age is a thing of the past, unless you uses fuses from the past. Modern auto blade fuses will likely outlast your airplane if uses within their specifications.  https://www.eaton.com/us/en-us/support/eaton-answers/what-is-fuse-fatigue.html



Matt

Sent from my iPad



 	  Quote: 	
		  On Jan 26, 2024, at 4:29â€¯PM, user9253 <fransew(at)gmail.com> wrote:



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



This is the link that I use for the AeroElectric List:

http://forums.matronics.com/viewforum.php?f=3

-

Fuses can blow from old age or vibration, excessive ambient temperature, 

excessive current, or a loose fuse holder which makes heat.  Glass fuses such

as AGC are prone to fail due to the long element and due to poor fuse holder 

spring tension.  Make sure that fuses are held firmly with lots of spring tension.

-

A short circuit is an unintended current path which is usually shorter than the

intended current path.  A wire that vibrates against a sharp metal can result 

in a short circuit when the insulation is worn away and the copper wire 

contacts the aluminum airframe.

-

It is not clear from Patrick's description where the problem fuse is located. 

Is the fuse part of the aircraft electrical system or is the fuse located within 

the navigation power supply?  If the blown fuse is contained within avionics, 

there is not much that the average person can do except replace it, making 

sure it is held in place with lots of spring tension.  A fuse holder with weak 

springs will result in a poor electrical connection that has resistance.  Current 

flowing through resistance makes heat which can cause the fuse to blow.  A 

poor electrical connection can also cause intermittent failures.



--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=513147#513147

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jan 28, 2024 11:54 am Post subject: Shorts & Blown Fuse

At 04:10 PM 1/26/2024, you wrote:

  	  Quote: 	
		  Fuses failing from old age is a thing of the past, unless you uses fuses from

 the past. Modern auto blade fuses will likely outlast your airplane

 if uses within their specifications.  https://www.eaton.com/us/en-us/support/eaton-answers/what-is-fuse-fatigue.html 	


    The key phrase here is "within their specifications".



    The document cited doesn't describe 'fuses' but 'current

    limiters'  These are exceedingly robust devices like

    the ANL/ANN/MIDI series devices along with fusible

    links. They are intended for protection within a

    distribution system . . . often upstream of multiple

    feeders unique to individual systems or appliances.



    There is no mention of the low level, fast operating

    devices like the ATC fuses and their cousins.



    True, fuses operated within their specifications

    can be expected to go to the scrap yard with

    the rest of your airplane, hopefully decades

    hence. The same is true of circuit breakers.



    This fact underscores what I would describe as

    poor return on investment for the $, time and

    panel space to fit your airplane with 'acres

    of breakers'. We've long suggested that your

    time, talent and resources would be better

    spent.



       An anecdotal aside on this topic: Missed

       my one and only chance to participate

       in the development of Jim Bede's BD-10J

       way back when. Had a phone call from his

       project manager asking if I had any

       recommendations for hardware and

       architecture. After a month of conversations

       and exchange of data, I submitted a 'z-figure'

       starting point for future discussions.



       The next call informed me that "Jim wanted

       breaker panels" . . . seems he want his

       future customers to feel like they were

       flying some form of military hardware.



       For the sake of simplified installation

       and lower weight, I had a number of fuse

       blocks located remotely from the cockpit.



       Hmmm . . . thought about it for awhile

       then emailed them to respectfully bow

       out of the program. Included an invoice

       for time-to-date . . . never heard back!



    That specifications thingy represents the

    greatest risk to the application of fuses

    in our projects. The fusible element is a

    thermally responsive device that can be

    'hammered' . . . a phenomenon that happens

    only with the modern plastic fuses and their

    legacy counterparts - glass cartridge fuses.



    A fuse should not be continuously loaded

    to more than 75-80 percent of rating with

    careful attention to knowing if it's subject

    to short duration excursions to 'peanut-butter-

    metal' territory.



    Recall the discussions about characteristics

    of solder . . . review those pages in the

    'Connection if you don't remember the details.



    As you depart either side of the eutectic melting

    point for the alloy, the melding temperature

    goes up and the 'plastic' range gets wider.

    The operating element in a fuse does exactly

    the same thing . . . for some range of heating

    due to flow of current, the element will become

    soft and may well change shape while not

    actually opening up. However, these events

    will reduce the element's cross section/

    density and cause its operating current

    to GO DOWN.  Repeated events will eventually

    cause the fuse to fail.



    This is what happened in the crash of

    N811HB in California in 2008. Readers new

    to the List are invited to review details

    of this even at:



  https://tinyurl.com/2j7yytto 



    So yeah, fuses in our airplanes are as

    likely to go to the scrap yard as fuses

    in our cars. Treat 'em nice and they'll

    treat you nice too.



 



 



 

   Bob . . .



                    //// 

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    on physics and good practice.

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