Adding a run on timer to an existing fan

[Taylortwocities]

OK...
You must have a permanent live at the switch.
Just connect a piece of twin&earth from the switch. You'll need perm live and earth.
Poke it to the fan inlet hole. Then grab your existing fan cable. You then have all that you need for the over-run add-on unit. You'll have to decide where (accessible) that you can locate this.

That should sort the over-run issue. The you have the issue of the fan extract pipe, oh yes and what you do when the fan dies.

 

[littlespark]

Update on this.

Added in a FCU before the bathroom switch, back up the wall and mounted a manrose timer unit, 3 core and earth from switch, and t&e from unit to fan.
Lights are on a different t&e from switch.

Works fine, or so I thought. Lights and fan come on with switch, lights go off with switch, fan runs on for set time....

Except. The inlet grill of the fan has a 12v led lamp built into the centre of it. Wired correctly on the lighting side. With the lights on, it works ok. With the switch off, and whether the fan is running or not, this lamp flashes once about every 5 seconds.

Reason? I think it’s getting a back feed from the timer unit back down the switch wire which is making the light flash.
It may be that the transformer for the12v isn’t right. Meaning it’s designed for a halogen lamp rather than LED.
I’ll change that first to a LED driver.
If that doesn’t work, double pole switch in place of light switch. Using the second pole to isolate the timer sw from the lights.


Not asking a question. Just thinking out loud.

 

[Taylortwocities]

It may be that the transformer for the12v isn’t right. Meaning it’s designed for a halogen lamp rather than LED.

That will be the reason. Most of the halogen "transformers" don't work unless they have around 20VA on the output, and your LED will be way less than that.

May just be easier to pop a holgen lamp back in there.

 

[littlespark]

It's been working with an LED in it up til now. Its just adding the timer that has caused a problem.
I'm not actually sure the transformer that's there is original.

Tomorrows job is to wire the kitchen best way I can with limited wall space and more appliances than kitchen units

 

[Toneyz]

Yes. I’ve only got a sw and n. What I need is the fan to be powered from a timer unit which is triggered by a light switch, not from the light switch itself.
I realise I need a 3 core to operate the timer... but that is straightforward from the switch as there’s a live, sw an neutral there.

Swapping out the fan for a timer version or 12v is impossible without taking down the ceiling.

It may be I could use a humidistat?

or a PIR unit.

 

[Taylortwocities]

or a PIR unit.

A bit late with that bit of advice, Tone

In any case, Murdoch suggested it about two weeks ago!