dimmable extra low voltage bathroom lighting

[mutter]

I am fitting extra low voltage lighting (three 20W lights) and an extractor fan in my bathroom, but would like advice about where to locate the transformers for these...

1. For a dimmable transformer for the lighting, i gather i should use a dimmable transformer, (100W rating) and that it should ideally have ?3 outlets for each bulb, with an output to the dimmer switch (100W) outside the bathroom...
Because of the relatively high current carried in low voltage circuits, the transformer should be close to the lights, but my bathroom is in the roof space, with little access above, so i was thinking of having the transformers in the hall, high up on the wall, with a run of about 2m for each light, using 1.5mm2 cable.
Does this sound practical, and feasable?

2. What ELV lighting can you use with a dimmer? I have read that Halogens don't like dimmers, but a google search comes up with lots of alternatives. Does it shorten their life, What is the best alternative?

thanks for any reply

rem

 

[mapj1]

Hmm.
OK, either a tranformer with three independant outputs, one per bulb or a transformer with 1output split between 3 bulbs, either is actually fine. (an output is a pair of terminals of course.)
The transformer should be able to cool itself, and dry, so not in the steam of the shower, nor wrapped in loft insulaton. In the hall would be fine, if you can stand the aesthetics, but if the cable run is long you may wish to use a larger size cable. 1.5mmsq will do, but 2.5mm isn't much dearer. Where it enters the fittings, it may need heat sleeving or a join and a short length of hi temp cable - depending on the thermal design of the fittings.
Q-H can be dimmed, but the natural filament repair mechanism only works at full power,and they tend to fog up and fail early if under run without a 'clean-up' burn from time to time.
Resist the temptation to by the smallest cheapest transformer, - these run hot and live very near the edge of early death at full load, particularly the 'electronic' types, which are really a high frequecy ferrite transformer core and a transistor chopping circuit that slices the mains into thin pulses.

The extra cost of a 25 to 50-% little 'safety margin' will pay for itself very soon.
Not all transformers can be dimmed, and not all dimmers like transformers being designed to see a resitive lamp filament - please realise most dimmers work by slicing the waveform too, but on a cycle by cycle basis - the effect of two lots of electronics fighting it out can be wierd stroboscopic effects, or just instant failure of dimmer or lamps.
Talk to your supplier, and accept nothing that is not guaranteed to work together.

 

[mutter]

Hi Mike,

thanks for the advice, i'll definitely use 2.5mmsq cable, and look for a matched dimmer/transformer combination...

thanks

rem