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Author Topic: fuses that insulate them self  (Read 1595 times)

johno 52-11

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fuses that insulate them self
« on: June 21, 2010, 09:59:46 PM »

Don't know if anyone can explain a little problem I had with fuses yesterday.

I had last week done a bit of work on my Atlantic 21 after the mayhem weekend. Check it all out last weekend all working fine. Put the boat back on the shelf out the way. I got it out on Saturday and charged it up to go to the National Model Lifeboat Rally Yesterday. Time came for me to put the Atlantic on the water, switched it on and NOTHING not a twitch of the servo no sing of life. So toolbox out check the battery that' s fine pulled the connection from the speed controller with BEC hecked that no power going to the receiver. Moved the receiver out the way to get to the fuses, pulled both the fuses they looked fine but the legs looked a different colour set the multimeter to test resistance put it cross the fuse and it showed an open circuit scratched the surface with the probe and got a closed circuit.

It seems that the fuses had developed an insulation coating while the boat had been standing. Just wondered if anyone else has ever come across this or could explain it.

Put new fuses in and all work fine for the rest of the day.

Here is a picture of the fuse (blue) next to a new one (brown)





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knoby

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Re: fuses that insulate them self
« Reply #1 on: June 21, 2010, 10:12:05 PM »

Hi johno, my first thought was if you had left the battery connected there may have been some form of electrolysis taking place. It look far to uniform a coating to be just corrosion. I have never seen this on a model boat , but have had similar problems on full size boats. leaving the battery disconnected reduced the problems on the full size boat considerably.


Cheers Glenn.

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malcolmfrary

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Re: fuses that insulate them self
« Reply #2 on: June 21, 2010, 10:32:12 PM »

It could be a similar phenomenon to what was known as "silver migration" where a standing voltage could cause a thin spread of conducting metal to travel across the surface of an allegedly insulating material, or through a porous one, especially in a damp atmosphere. 
It could be that that particular fuse and its holder had the right sort of different alloy to allow a coating to form.  Having said that, I would expect enough grip from the leaves in the holder to scrape any layer of during insertion and/or removal, and for the pressure at the contact points to exclude air well enough to prevent a layer forming just there.
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hazmat

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Re: fuses that insulate them self
« Reply #3 on: June 21, 2010, 11:02:28 PM »

We got the same effect with automotive fuses in our fishing boats.
Whilst large current is flowing, no problem, leave the engines off for a week or so and the only circuits that never failed were the automatic bilge pump and anchor light.
We tried to cure it by spraying the fuse box with canned 3 in 1 once in a while but even then lesser used circuits continue to fail.
The fix was to move to circuit breakers (push in not household mcbs) and soldered in auto reset fuses.
i.e Bussman ATC Type 2 Modified Reset Circuit Breaker.

Electrolysis was the reason we were given for this effect.

Paul
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FullLeatherJacket

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Re: fuses that insulate them self
« Reply #4 on: June 21, 2010, 11:14:37 PM »

We bought some very cheap fuses and found that they had a coat of lacquer on the blades and were making very little contact with the fuse-holders. Several users of P92 reported that the fuseholders were melting. Changed the supplier and solved the problem.
FLJ
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malcolmfrary

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Re: fuses that insulate them self
« Reply #5 on: June 22, 2010, 02:12:25 PM »

A few drinkies and more thinking back 20 years reminds me of a problem with base metal to base metal contact joins - being dry connections, i.e. unsoldered, with access to air and not enough pressure, if there was ANY moisture, with a standing voltage, they would go high resistance unless there was a small current constantly flowing, typically more than 1mA being the magic figure.  A sudden burst of high (more than 60) volts would cause the unwanted insulation to break down and the circuit would then work until the next time.  In a model, of course, there is no source of this higher voltage, so once the problem is there, it will stay there.
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johno 52-11

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Re: fuses that insulate them self
« Reply #6 on: June 22, 2010, 07:51:00 PM »

Thanks for your thoughts and comments

As to there being power there is a switch between the battery and the fuses and that was off, so there was now power going through them.

One thing reading Malcolmfary's first comment I did when I put the new fuses in have to crimp the holders up as the new fuses where a little loose in the holders so that could explain why they are covered.

I guess its one of those things I am going to have to live with. The Atlantic is quite a wet boat when its on the water and we know water and electrics don't mix to well still knowing what the cause is when you switch it on and nothing happens will be a lot quicker to fix in the future. Just need to keep a few spare fuses in the tool box.

Reading malcolm's last comment I had a friend who used to run the lighting on his yacht on 24 volts to stop a smiler problem with the bulbs.

John
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