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Fredxx Fredxx is offline
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Default Using a dimmer with 12V halogen lamps


"ppmoore" wrote in message
...
I installed have two halogen light circuits, each consisting of three
12V 35W halogen bulbs. Each circuit is fed by its own 150W 230/12V
transformer. Both circxuits are connected in parallel to a 500W
dimmer.

I put in the lights about five years ago, and all was fine until about
two weeks ago, when both transformers failed about the same time. The
transformers gave off an overheated smell, and a cable that must have
been in contact with one of the units was badly charred.

Strange coincidence, I thought as I replaced the transformers two days
ago. Even weirder, I thought as the lights worked fine for about one
day and again stopped working, with the same symptom: overheating of
the transformers and even melting of one of the transformer plastic
casings. I checked the bulbs and are all rated 35W, so the 105W load
per circuit is confortably within the rating of the transformer.

So my attention turned to the dimmer. Can this be causing the problem?
Do dimmers fail with symptoms like this?


If an old fashioned TRIAC dimmer, I would guess that at part load there's a
significant DC content, which lead directly to heat in your transformers. A
TRIAC triggering is inherently asymmetrical, and I'm guessing this has
deteriorated over time.