12 Volt domestic lighting transformer - excess heat

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Welly
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12 Volt domestic lighting transformer - excess heat

Post by Welly » Mon Nov 25, 2019 3:13 pm

Picture the scene:

I have a 240 > 12v transformer up in the loft (rated to suit 5No. 20 watt GU5.3 lamps). The 5 x lamps are wired in parallel.

The problem: The lamps are slower than before in lighting up, just a short delay, the last one on the line is dimmer than the first (progressively worse along the line) and the transformer is hot. Not only that but the first meter of 12v wiring to the first lamp is worryingly warm :shock:

What could be going on? too much current draw? transformer failing? why the hot cable?

On the strength of what I found I'm ripping them out at the weekend and converting to 240v LED but just want to better understand what's going on.
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Re: 12 Volt domestic lighting transformer - excess heat

Post by steve_earwig » Mon Nov 25, 2019 3:41 pm

Wiring not up to the job, poor connections, psu dying. Mind you, if the lights are getting dimmer the further away that says the wiring has too much resistance, maybe the connections if they're done one to the other. But that wuldn't explain the PSU getting hot. Nah, it's cattled.
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Re: 12 Volt domestic lighting transformer - excess heat

Post by Doggy » Mon Nov 25, 2019 11:08 pm

Probably a partial short circuit in the transformer, may well have increased the secondary voltage and hence current. The first bit of wiring carries the current for all the lamps so will be hottest, last lamp suffers most volt drop so will be dimmest. I would stop using it.

Time to update 'em. I recently fitted some very nice GU10 warm white LED downlights under my stairs, fed from little power supplies the same shape & size as those 12V transformers, (all from that there Screwficks - other suppliers are available).
One word of caution - if you go this route make sure the powers supply(s) have are least 30-40% over rated to avoid flashing light syndrome.
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Welly
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Re: 12 Volt domestic lighting transformer - excess heat

Post by Welly » Tue Nov 26, 2019 10:54 am

Had another proper look last night, about 5 years ago I altered the upstairs landing layout which moved the 5 x downlighters around a bit.....the last one needing a 'temporary' extension of wire (of the correct gauge) to complete* the job....I'd completely forgotten about it :shock: I guess I'd introduced too much cabling for the poor transformer :oops:

Lesson learnt sharpish!

I've pulled three of the lamps temporary and full brightness is restored, then convert to LED this weekend.

Doggy - good shout on the Warm White colour, I've tried Cool White and Daylight and they're horrid.
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