How to use an extractor fan with a dimmer switch?

[HappyHippyDad]

Evening all....

My son is 14, he seems to be taking ultra long baths and showers and the bath/shower room is drenched afterwards.

I have just bought a pretty good inline fan and was planning on fitting it on its own switch as the existing lights are on a dimmer. I would love the fan to come on with the lights so that it is guaranteed it comes on when he is bathing.

Is there any way of doing this on a dimmer? The dimmer will be staying as it's too bright at night when on full.

I thought I could install a standard plate switch which switches power to both the fan and the dimmer switch. in other words the dimmer switch doesn't get power unless the fan is on. However, this is too cumbersome. Is there any way the fan can work with a dimmer switch?

A few more questions..

What actually happens to a fan if you install it on a dimmer switch? I'm guessing it would work fine if the dimmer is on full, but problems occur if the dimmer is lowered? Would this be dangerous or would the fan just cease to work as it doesn't have the required voltage?

 

[Flanders]

Evening all....

My son is 14, he seems to be taking ultra long baths and showers and the bath/shower room is drenched afterwards.

I have just bought a pretty good inline fan and was planning on fitting it on its own switch as the existing lights are on a dimmer. I would love the fan to come on with the lights so that it is guaranteed it comes on when he is bathing.

Is there any way of doing this on a dimmer? The dimmer will be staying as it's too bright at night when on full.

I thought I could install a standard plate switch which switches power to both the fan and the dimmer switch. in other words the dimmer switch doesn't get power unless the fan is on. However, this is too cumbersome. Is there any way the fan can work with a dimmer switch?

A few more questions..

What actually happens to a fan if you install it on a dimmer switch? I'm guessing it would work fine if the dimmer is on full, but problems occur if the dimmer is lowered? Would this be dangerous or would the fan just cease to work as it doesn't have the required voltage?

Could you put a motion sensor in . Then it would work any time you enter the bathroom

 

[Avo Mk8]

I thought I could install a standard plate switch which switches power to both the fan and the dimmer switch. in other words the dimmer switch doesn't get power unless the fan is on. However, this is too cumbersome.

You can obtain single plate switches with a rotary dimmer and a rocker switch side by side, with independent connections, so that is a viable method - is it cumbersome because of having two 'knobs'? Or is it because of having to add/re-route cables?

Is there any way the fan can work with a dimmer switch?
What actually happens to a fan if you install it on a dimmer switch? I'm guessing it would work fine if the dimmer is on full, but problems occur if the dimmer is lowered? Would this be dangerous or would the fan just cease to work as it doesn't have the required voltage?

Edit - assuming it's a timed overrun fan, the dimmed connection will act as the trigger for the fan to come on, but surely the motor will be powered from permanent live, so will either work properly, or not come on at all? I suspect the dimmed feed to the fan might trigger it more or less at any setting?

 

[Pretty Mouth]

Yes, it can be done, but the dimmer module will need modification.

I initially tried to do this using the dimmed switch live from the dimmer to the SL of the fan. It sort of worked, but the fan took ages to be triggered, about a minute or more IIRC. Back to the drawing board.

The modification to the was easy enough to do, and worked perfectly. John Ward has a video on how to do it on old leading edge module, but the way I did it on a V-pro module was less faff. I'll PM you details.

 

[brianmoooore]

There were dimmer switches, such as the old MK one's I recently sent to Lucien, which had a switched live terminal and a dimmer output terminal. The first would control the fan, and the second, the light.
Don't know if there any modern dimmers available with this feature.

 

[Spoon]

Could you not use a current detector switch on the light, that switches the fan, through a timer relay?
Sounds expensive though..

 

[brianmoooore]

Haven't fitted a dimmer switch since the rise of cfls and now LEDs, so a bit out of touch with what's on the market, but if your dimmer has a physical mechanical on/off switch incorporated into it's design, and is dismantlable, you should be able to solder a fly lead onto the switch output, before it feeds the dimmer.
Wouldn't be acceptable for a customer, but if it's for your own house...

 

[Dustydazzler]

Motion detector fan , problem solved

 

[nicebutdim]

Humidistat fan. If your son spends that long in the bath, timers won't be much use in clearing the aftermath.

 

[HappyHippyDad]

Really appreciate all the answers, thanks all.

Umming and arghing between PM's idea of playing with the V-Pro or just putting in a sensor.