Today's Message Index:
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1. 11:54 AM - Re: Re: Shorts & Blown Fuse (Robert L. Nuckolls, III)
2. 09:43 PM - Re: Z-12N based architecture review request (esco)
Message 1
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| Subject: | Re: Shorts & Blown Fuse |
At 04:10 PM 1/26/2024, you wrote:
>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>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 . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Message 2
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| Subject: | Re: Z-12N based architecture review request |
Overview architecture updated to include MonkWorkz-specified installation.
Engine bus (approved by SDS) also attached.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=513156#513156
Attachments:
http://forums.matronics.com//files/20230118_eng_bus_schematic_v11__165.pdf
http://forums.matronics.com//files/20240128_z12_140455_v2_196.pdf
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