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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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 Posted: Fri Jan 26, 2024 6:35 am Post subject: Shorts & Blown Fuse |
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Hello Joe, hello Bob.
Apologies for e-mailing you both off forum but I have difficulties when trying to post to the AeroElectric forum.
I'd like to ask a couple of questions and if it is possible, could I ask you to also post this request to the forum please.
General question; what are the events that will actually cause a fuse to blow?
Also, the word "short" is mentioned together with blown fuses, but what exactly is meant by a short in our amateur-built aircraft?
I have yet to find a really good source for advice on fault-finding. If you know of one, I'd appreciate hearing of it please.
Specifically I have a nav/com unit that has blown the fuse of its nav board.
The unit has separate power supplies for nav and com and also for light dimming capability.
This nav/com is connected to a cdi that has its own separate power supply and again a supply for light dimming.
In the past the cdi vertical needle fluctuated, after having been steady, and if I remember
correctly shortly afterwards the nav/com display showed nav receiver and gs receiver failure.
It was on checking that I found the nav board power supply 5amp fuse had blown.
I have replaced it and the fault messages have disappeared and the cdi needle is currently steady.
But I am concerned that the fuse may blow again.
If it doesn't, the issue that caused it to blow in the first place may
damage the nav side of the unit with ensuing expensive repair charges!
So you can see that I am trying to fault-find and hence my initial general questions.
Any direction/guidance/information you and the forum can provide will be extremely helpful, thanking you both in advance.
With kind regards
Patrick Elliott, Surrey, England
Long-EZ, G-LGEZ
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Joe Gores |
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Fri Jan 26, 2024 1:27 pm Post subject: Re: Shorts & Blown Fuse |
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This is the link that I use for the AeroElectric List:
http://forums.matronics.com/viewforum.php?f=3
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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.
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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.
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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.
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Joe Gores |
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