Low voltage lighting and extractor fan off dimmer switch?

[orbis]

I'd like to fit some low-voltage halogen spotlights in our bathroom, and change the current light switch to a dimmer.

After reading many threads on this, I'm fairly happy with what's involved, but what I can't quite get my head around is how the bathroom extractor fan fits in with this setup. It's the timed sort - comes on automatically when the light is switched on and switches itself off a few minutes after the light goes off.

Am I safe to use a low-voltage-compatible dimmer switch in this situation? The ones I've seen state that they can't be used with inductive loads, motors, etc. But is the dimmer switch circuit not effectively just connected to two transformers - one for the LV lights and one for the extractor fan - and therefore ok?

A-level physics badly letting me down here, I think....!

Thanks for any advice.

[Sparks]

You *may* be looking at dimmers suitable for use on the low voltage side?

I have one of these in my bathroom, and it works a treat!

long as you have at least 50w and no more than 250w, then this will do the job fine.

The way it works with an extractor is, it always turns the lights on full brightness to start with, to make sure the extractor is activated. Normal dimmers (mounted in a switch plate) don't usually do this.

Sparks...

[Owain]

The (mains) extractor fan won't be using a transformer - it will use a mains motor. However the trigger wire from the switch won't be connected to the fan motor, but to the timer electronics, which I would expect to be just a voltage sensor.

Dimpull says it is suitable for use with bathroom fans.

[John Rumm]

Fairy snuff... just make sure you get a dimmable transformer and suitable dimmer. The range done by TLC seems OK.

One thing I did notice however is that if you buy a biggish transformer (say one that can do 50 to 250W) and use it with a dimmer, then it won't behave correctly unless you have at least 100W of load on it.

There will be two live feeds to the fan, a permanent one and a switched one. If you use a dimmer then the switched live will also be "dimmed". Given that the dimming is achieved by pulse width modulation rather than varying the actual voltage, the fan should still be triggered by the dimmed signal. It *ought* to draw its power from the permanent live only and not the switched one. However you will only find out one way for sure!

The lighting "transformer" will probably not look that inductive since most electronic transformers are in fact small switched mode power supplies and not your old style wound transformers. What the switched live input circuit of the fan looks like is anybodies guess, but I doubt it is directly connected to the motor, and hence may not be that inductive either.

[orbis]

Sparks - John - Owain - many thanks for the advice. I feel a bit happier to experiment with a dimmer in this setup now.

The TLC pull-cord dimmer was exactly the *kind* of thing I've been searching for - with info specifically saying it should be ok to use with the fan... except I was after a 'standard' light switch - anyone know of such a thing?

I'm guessing that those switches that are electronically controlled are also going to switch on initially at full power. Suck it and see then I guess...

Cheers, Dave