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#201979 - 07/07/11 03:27 AM bulb element lost its resistance?
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1308
Loc: Alaska
Hello fellow sparktarians. I had what I feel was a bit of an odd ball situation today. It was a my g-friends truck but it could happen on any electrical circuit.

Lost a light circuit and determine that there was a short by how the fuse blew plus I ohm'ed out the circuit. I traced it to a bulb that the element had no resistance across the leads and until recently it worked. I have heard of conductive material becoming more resistive over time but not less. Has anyone come across this before? Thoughts?
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#201981 - 07/07/11 05:34 AM Re: bulb element lost its resistance? [Re: sparkyinak]
Alan Belson Offline
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Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Unlikely, it probably shorted out between the support wires or to the cap. Occasionaly, a part of a filament can reconnect to a support wire as it disintegrates. This can produce a brief period of lower resistance, but the filament is much hotter and usually blows again quite fast. Fuses are even more vital in cars than dwellings BTW. A mate once replaced his with solid wire in an old banger as they kept blowing. His 'prize' was a lapfull of molten copper drops raining from under the dash - and a morning in casualty having them dug out of his legs!
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#201982 - 07/07/11 11:11 AM Re: bulb element lost its resistance? [Re: sparkyinak]
gfretwell Online   content


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Registered: 07/20/04
Posts: 9059
Loc: Estero,Fl,usa
Compare it to a new bulb. I bet you will be surprised how low the resistance of a cold bulb is. The resistance rises as the temperature of the filament rises.
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#201984 - 07/07/11 11:51 AM Re: bulb element lost its resistance? [Re: Alan Belson]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1308
Loc: Alaska
I'm going to look into the bulb more but the elements are intact and there's no conductive base on the bulb. One element ohms out at 0.00 ohms the other was low like 1.4. It does not appear that anything on the bulb fooling my meter. Replaced the bulb, ohmed the circuit, fused it and it works fine
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