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chenoweth(at)peak.org
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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 Posted: Mon Jan 30, 2023 11:34 am Post subject: fusible link construction |
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On Mon, Jan 30, 2023 at 1:26 PM William Chenoweth <chenoweth(at)peak.org (chenoweth(at)peak.org)> wrote:
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I’ve been reading the daily digests of the posts for a whole lot of years but this is my first post.
I’ve used fusible links following Bob’s instructions thru three airplanes. It has occurred to me that using DB9 pins secured with heat shrink instead of butt splices makes them more easily replaced. Do any of you have reason(s) to suggest this is a bad idea?
Bill
Kitfox 4 flying since 2001, RV9 project, and Kitfox 7 nearing completion.
[url=#m_-3662357522631235072_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2][/url]
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I can understand the motivation, but my attitude is that as reliable as subD pins are, it does add more joints to the path. And links are typically used where there's virtually zero risk of them blowing, unless there's some sort of catastrophic failure, so the risk of issues from the extra joints may well be higher than the odds of needing to replace the link.
Just my opinion, though.
Charlie
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rnjcurtis(at)charter.net
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| Posted: Mon Jan 30, 2023 11:47 am Post subject: fusible link construction |
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Bill,
Lines with fusible links are usually relatively high current. You need to be sure that the wires going into the pins and the pins themselves can handle the current. Otherwise the pin connection might become the fusible link
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Jan 30, 2023 12:13 pm Post subject: Re: fusible link construction |
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Agree with Charlie. How often do you replace fusible links in your car?
Simpler is better.
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Mon Jan 30, 2023 1:31 pm Post subject: fusible link construction |
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There are a few places where relatively low current links are used; the alternator field circuit comes to mind. You certainly wouldn't want to try the little pins for really high current.
Charlie
On 1/30/2023 1:47 PM, Roger & Jean wrote:
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Bill,
Lines with fusible links are usually relatively high current. You need to be sure that the wires going into the pins and the pins themselves can handle the current. Otherwise the pin connection might become the fusible link.
Roger
From: William Chenoweth (chenoweth(at)peak.org)
Sent: Monday, January 30, 2023 2:24 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: fusible link construction
I’ve been reading the daily digests of the posts for a whole lot of years but this is my first post.
I’ve used fusible links following Bob’s instructions thru three airplanes. It has occurred to me that using DB9 pins secured with heat shrink instead of butt splices makes them more easily replaced. Do any of you have reason(s) to suggest this is a bad idea?
Bill
Kitfox 4 flying since 2001, RV9 project, and Kitfox 7 nearing completion.
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nuckolls.bob(at)aeroelect
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| Posted: Tue Jan 31, 2023 6:53 pm Post subject: fusible link construction |
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At 03:33 PM 1/30/2023, you wrote:
| Quote: | There are a few places where relatively low current links are used; the alternator field circuit comes to mind. You certainly wouldn't want to try the little pins for really high current.
Charlie |
COTS (commercial off the shelf) fusible link wire
is generally not offered in smaller than 20AWG.
https://tinyurl.com/282kj2w3
This means the SMALLEST wire protected by
COTS FLW would be a 16AWG (4 steps larger
that 20AWG). This condition alone suggests
that fusible links are suggested for relatively
fat wires carrying 15A or more.
Fusible links are the same class of circuit
protection as the ANL/ANN style CURRENT LIMITERS.
While they function like a FUSE (melt to clear
a faulted feeder) they are intended for
protection of DISTRIBUTION feeders, not
specific APPLIANCE feeders.
Note the ratings differences between the
plastic ATO fuse and the MIDI current
limiter.
https://tinyurl.com/2dfpw7qw
A 3A fuse loaded to 4A is
on the feather edge of melting. It might
open in as little as 1 second. A 30A
limiter loaded to 40A may never blow;
and it takes about 100A to open in
in 1 second. They don't mix-n-match.
Fusible links are on the same order of
fusing performance as current limiters.
Probability of opening is probable two
orders of magnitude smaller than probability
of a fuse having to do its job . . . and
how often do you ever need to replace a
fuse in your car? I can recall perhaps
a half dozen instances in 60+ years
of driving.
A further point to consider is that
a d-sub pin is maxed out with 20AWG
wire and 7A . . . use of 'barefoot'
d-sub pins on individual wires should
be limited to low current situations
were space is tight . . . like connecting
a MAC trim servo to the ships trim
system wiring.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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