In article 6cada57a-ef1e-42a1-bedf-
, says...
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?


Two problems here.

Firstly, transformers do not regulate their output voltage accurately.
Their specified voltage is usally at their rated power - so you only get
12V at 150W in your case - running at lower load may well cause the
output voltage to rise - overdriving your lamps somewhat.

Secondly, unless you've the right sort of dimmer, then you're asking for
trouble dimming an indcutive load. Dimmers work by only turning on the
device for part of the AC waveform. Doing that cheaply involves a very
sharp rise-time in the voltage - something which inductive (and
capacitative) loads won't be happy with. The result is a sort of
electical "BOINGGGG" 100 times a second, with voltage spikes rather
higher than the equipment may have been designed for.


Of course, if you're using a dimmer/transformer combination which are
designed to cope with this, then you can ignore all that!

--
Skipweasel - never knowingly understood.