Low voltage spotlight not working...

18 Feb 2012
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United Kingdom
I'm new to posting on the forum, although I have used it for reference for several previous DIY projects. It the moment I have an electrical problem that is puzzling me.

Our first floor landing has 2 low voltage halogen spotlights. Although both have worked in the past, one of them has not worked for some time. I've checked the bulb- that is not the problem.

Today I bought a new transformer (12v, max 50W) and fitted it, reusing the old bulb holder as none was supplied with the new transformer. With it fitted, the fuse constantly tripped. I refitted the old transformer and the bulb did not work but the fuse did not trip.

I assume that if the fuse tripped there is no problem with the power to the main lighting ring (and because the other light works). Do you have any suggestions or tests that I could do to get to the bottom of the problem? Could it be the bulb-holder? If so, why does one transformer trip and the other not?

I'd welcome any advice. I'm hoping it's something straightforward that I've overlooked!
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Odds on it`ll be the Lampholder , you can buy them seperately at any good WHOLESALER

Did you fit the transformer the right way?
If not it may be fried.
Is it one transforer per light?
If the circuit tripped as riveralt has suggested you may have installed the trany in reverse. This will cause the circuit to trip and the trany will now be ready for the bin!
If the other light is working, try connecting the non working lamp holder across it, this can rule out or confirm if the lamp holder is failing.
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Well I've dug out my multimeter and tried to go about things in a more ordered fashion:

Old transformer in:
240v ac at input from lighting circuit.
No output (dc) at transformer output
Other light still works without tripping fuse
- so I concluded the transformer has failed.

New transformer
Trips fuse immediately when light turned on (without any lamp holder attached)
On checking continuity with my multimeter and the live/neutral inputs on the new transformer it appears there is a short.

So in conclusion, I guess the transformer has been faulty all along, as it has tripped the fuse every time. I'd guess even an incorrectly fitted and therefore cooked transformer would just not work like the old one rather than develop a short circuit.

If this is the case it's a shame B and Q's quality control isn't better- would have saved me an hour!
what brand of trany did you buy? It wasn't B&Q's own brand was it? I don't know what peoples preference of trany is.

I don't remember which brand I've used, but I know of locations they've been installed in for around 3 /4 years, running 24/7 the majority of the time and out of the 80 or so trany's, only 3 or 4 have failed.

the Philips ones are very nice, but also, very pricey

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