Dimmer switch prevents extractor fan timer from working?

fandangobelch · 29 Jun 2006

Hi, I've installed a pull cord dimmer in the bathroom which controls the 3 looped low voltage light transformers. The problem is that although the extractor fan comes on when the lights are on, the timer fails to turn the fan off when the lights are off. The only way to stop the fan is to interrupt the permanent live going to it. The switched live is coming from the dimmer pull and being a dimmer still leaks current to the extractor even when the lights are off. I don't want to replace the dimmer with a standard pull switch. Is there anything out there that I can install between the dimmer and the switched live of the extractor that will prevent any input to the extractor if the output from the dimmer falls below a certain threshold? ie: Undervoltage Lockout or similar?

This is now starting to really peck my head!! Any advice would be greatly appreciated.

Thanks

johnb80 · 29 Jun 2006

You could add a relay with a 240v coil. Connect the coil to the lights, connect the contact from a live source to feed the fan and that should work. If you can, get a relay with a large voltage range to take into account when the load i.e. the lights are dimmed.

Regards - JB

ban-all-sheds · 29 Jun 2006

Rumour has it you can buy dimmer switches with an undimmed output for fan use...

RF Lighting · 29 Jun 2006

ban-all-sheds said:
Rumour has it you can buy dimmer switches with an undimmed output for fan use...

...From Here

ban-all-sheds · 29 Jun 2006

Yes - I know the website says "The product is also suitable for use where Bathroom fans are installed.", but neither the wiring instructions there, nor the manufacturers website, gives any hint that this might be true...

RF Lighting · 29 Jun 2006

Sorry you are right. I seem to remember having being told that the switch had an extra undimmed terminal for the fan, but this is not mentioned anywhere in the tech spec.

securespark · 29 Jun 2006

I have e-mailed them to get clarification.

sweavo · 11 Aug 2010

I know this is an old thread but it keeps cropping up on searches for dimmers with undimmed outputs.

If that's you, try searching for "switched live" instead of "undimmed". I found some useful pages that way.

sweavo · 26 Apr 2011

This is the only one I've managed to find for my setup, and I'm getting it.

http://cgi.ebay.co.uk/DIMMER-MK-GRI...515510381&po=&ps=63&clkid=8735897541455843002

(if that doesn't work, search ebay for DIMMER - MK GRID - 400W WITH SECONDARY SWITCHED LIVE )

securespark · 26 Apr 2011

It might have taken five years, but the company who makes the pullcord dimmer tells me it cannot be used with fans or for dimming wirewound trannys.

If you are going to use the MK dimmer, then this is a standard wall-mounted module that needs to be installed outside the zones (and preferably outside the bathroom). And remember it is not suitable for use with GU10's.

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Dimmer switch prevents extractor fan timer from working?

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