12v circuit switch for 240v fan

[laferret]

Hi,
Electronics novice but I have managed to wire in a 12v vanity LED light circuit in my bathroom. It is from a 12v 15W (Max) driver which is housed inside a boxed in cabinet space. The light circuit uses a standard wall switch.
I've just had to replace a humidity activated extractor fan which was mounted on the same cabinet with one that is switch controlled with a timer function. The new fan is 240v 14W and has its own isolator switch (again, inside the cabinet) and supply.

Q: Can I use the 12v switch to activate the fan? It is very conveniently placed and i'd rather avoid more switch installations if possible.

 

[endecotp]

Is what you're calling the "12v switch" actually switching 12 volts, or is it switching the 240v supply to the 12v LED driver?

 

[ericmark]

Optical isolators and relays can work wonders so can it be done yes, but can you do it is another question.

 

[laferret]

The 12v switch is after the driver

240v > LED Driver > 12v switch ------ 2x LED 5w bulbs

I wanted the switch to be 12v for safety reasons

The fan will have its own 240v supply I just wondered if the fan will switch on safely using the same circuit. Probably no harm in trying!?

 

[RF Lighting]

So the driver is powered all the time? Not the best idea, and connecting the 12V output to a 230V fan is going to result in one big bang

Probably best is you leave mains wiring to someone who's actually got a clue to what they're doing.

 

[endecotp]

Probably no harm in trying!?

Stop immediately, and get someone competent to do it.

 

[Astra99]

So the driver is powered all the time? Not the best idea, and connecting the 12V output to a 230V fan is going to result in one big bang

I think you may have omitted an adjective (for emphasis) before "big bang" which takes the format of a gerund!

 

[JohnW2]

... connecting the 12V output to a 230V fan is going to result in one big bang

I think you may have omitted an adjective (for emphasis) before "big bang" which takes the format of a gerund!

If I understand (guess) correctly what the OP was proposing, although it's a crazy idea (indicating, as has been said, that the OP should not even be thinking of attempting this work) and certainly wouldn't work, I don't think there would be any bangs.

I think he was probably suggesting that the 12V supply could somehow be used for the 'trigger' input to the fan (whose perm L and N came from the 230V supply). Even if he connected the switched 12V supply to the N and trigger inputs (the latter usually being connected to the 230V S/L) of the fan (creating an undesirable connection between LV and ELV circuits), it wouldn't work - but nor would it go bang ... unless I'm missing something.

Kind Regards, John

 

[laferret]

thanks to everyone for your prompt replies. John has it nailed in what I appear to have been unable to articulate. I just needed the switch to act as a trigger.
Even in my ignorance I was sure no bangs would ensue. I thought it wise to seek advice before bothering a sparky and shall refrain from my original course.
Thanks again

 

[JohnW2]

thanks to everyone for your prompt replies. John has it nailed in what I appear to have been unable to articulate. I just needed the switch to act as a trigger. Even in my ignorance I was sure no bangs would ensue. I thought it wise to seek advice before bothering a sparky and shall refrain from my original course.

Indeed. The 'trigger input' (usually called 'switched live') of a timer fan requires a substantial voltage to be applied to it to result in triggering - so, even if there were no bangs (and forgetting various other issues which your approach would have raised), 12V would just not do the job. You could theoretically use a 12V relay to switch 230V to the trigger input of the fan, but that's really getting a bit complicated!

Kind Regards, John

 

[Dazz0i]

Using a 12v dc conractor. Would do what you require.

Switched 12v and neutral across the coil.

A 240v ac to a normally open contact with the 240v returning to the fan.

Just seems a lot of effort though if you've already got a 240v supply to the fan.

 

[JohnW2]

Using a 12v dc conractor. Would do what you require. Switched 12v and neutral across the coil. A 240v ac to a normally open contact with the 240v returning to the fan. Just seems a lot of effort though if you've already got a 240v supply to the fan.

That's what I said - a '12V relay' (or contactor) - but, as both you and I have said, that's all a bit OTT for this particular purpose!

Kind Regards, John

 

[Dazz0i]

Indeed john, I hadn't read all the responses to OP before posting.

 

[ban-all-sheds]

Switched 12v and neutral across the coil

No no no no no.

That would be at best incredibly inconvenient as it instantly tripped the RCD, or at worst highly dangerous.

[EDIT]On second thoughts, the best outcome would be that it just doesn't work.[/EDIT]

 

[JohnW2]

Switched 12v and neutral across the coil

No no no no no. ... That would be at best incredibly inconvenient as it instantly tripped the RCD, or at worst highly dangerous.

I suspect (and assumed when I read it) that when Dazz0i wrote 'neutral', he was actually referring to the other (unswitched) side of the 12V supply (rather than the LV neutral).

Kind Regards, John