An Inexplicable Phenomenon

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John Vardanian
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Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

An Inexplicable Phenomenon

Post by John Vardanian » Sat May 14, 2005 2:47 am

I had a slow electrical leak that drove me crazy for a long while.

About a year ago I found this little insulator bushing under the horn button to be badly deteriorated. This bushing looked to be nothing more than a holow rubber cylinder, so I cut a short piece of ordinary heater hose to substitute. Sure enough the heater hose proved to be just the right ID and OD for the job. I put things back together and all was well.

Fast forwarding to last week, I isolated the mystery electricl leak to the piece of wire that runs from the horn button to the horn relay. After poking around for a couple of hours I found the problem. The problem was that little piece of heater hose. It was actually acting as a semiconductor.

I went to the shelf and got the section of heater hose that I had cut that little piece from and did a continuity test with an ohmmeter... sure enough it conducted, albeit at about 2k ohms, but it conducted.

Got another section of hose and did the continuity test... no conducting at all. So I used as setion of that hose for the job. Needless to say no more leaks.

john
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Ruedi
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Post by Ruedi » Sat May 14, 2005 4:41 am

I vaguely recall that one of the reasons why some rubbers (such as tires) are black is that carbon or graphite is being added to keep them flexible and reduce wear. Obviously, carbon and graphite are conductors.

The reason why you encountered some sections of rubber to act as insulators, semiconductors or conductors may be the result of random clustering of carbon molecules during the manufacturing process. And that would be ignoring other factors such as the composition and texture of reinforcing materials (which could also be carbon based).

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John Vardanian
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Joined: Wed Sep 04, 2002 12:13 am
Location: San Francisco Area

Post by John Vardanian » Sat May 14, 2005 9:32 pm

Ruedi,

Bingo! I think you solved our mystery.

john
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