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Topic Title: LED Lamps
Topic Summary: Blown one at last - but oh dear !
Created On: 19 June 2012 07:20 PM
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 19 June 2012 07:20 PM
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ady1

Posts: 766
Joined: 19 April 2005

So finally, after about a year - one has blown.
Unfortunately it has blown leaving a full short ....
Surely that's going to be a problem.... i'm thinking of all them jobs with the wrong fusewire in their 3036's

Your thoughts pls

Ady

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Resistance is futile.
 19 June 2012 07:33 PM
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OMS

Posts: 19471
Joined: 23 March 2004

Well, even if they have got 30A wire in the carrier, an impedance of 2.64 Ohms will get disconnection in 5 seconds.

There won't be that many domestic lighting circuits that exhibit that impedance. Even if Ze is approaching the 0.8 ohm value that would still allow about 40m of cabling to be in circuit before disconnection time started to rise. Much more if Ze was lower

Ideally you would want disconnection in less than 3 seconds to ensure a 1.0mm was still in good nick at the end

Regards

OMS

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Failure is always an option
 19 June 2012 07:46 PM
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ady1

Posts: 766
Joined: 19 April 2005

Interesting - probably not that dangerous then.
But - nuisance value ?? Lights off till removed. Customer will call us out. We will have to remove each one till we find it (when multiple downlights for example)
Putting me right off them ...

Ady

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 19 June 2012 07:48 PM
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OMS

Posts: 19471
Joined: 23 March 2004

For sure ady - although I guess we should ask is the failure mode always to short circuit - or do you have a "rare" one

Regards

OMS

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Failure is always an option
 19 June 2012 07:52 PM
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keylevel

Posts: 456
Joined: 31 October 2003

Hmm. It'll depend on what's failed of course, but a lot is semi-conductors do fail short-circuit. When I worked on large motor controllers we had special circuitry to detect when this happened so we could stop them running off at full power. Some then go on to produce some rather colourful flames shortly afterwards, but I would hope LED lamps would be better behaved ;-)
 19 June 2012 08:34 PM
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davidwalker2

Posts: 189
Joined: 29 April 2009

The one I had just stopped working, the led's showing a dull flicker. My experience is that many halogens fail short circuit.
 20 June 2012 12:23 PM
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AJJewsbury

Posts: 11297
Joined: 13 August 2003

i'm thinking of all them jobs with the wrong fusewire in their 3036's

Many older GLS lamps used to (temporarily) short as they blew (I suppose technically arc rather than short, but the effect was the same) - I've lost count of the number of pieces of 5A fusewire I've had to replace over the years.
- Andy.
 20 June 2012 05:58 PM
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alancapon

Posts: 5746
Joined: 27 December 2005

Originally posted by: AJJewsbury
Many older GLS lamps used to (temporarily) short as they blew (I suppose technically arc rather than short, but the effect was the same) - I've lost count of the number of pieces of 5A fusewire I've had to replace over the years.

When they fail, a ball of glowing plasma is produced inside the glass that shorts the filament connections briefly. The better quality lamps include fused inserts in the connecting wire and these operate, a lot of the cheaper lamps do not, and present a short to the supply until the fuse / mcb operates.

Regards,

Alan.
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