Running a Bathroom Fan without the lighting being on.

[daver]

Finished a bathroom several weeks ago which included 4 downlights, mirror light, timed fan, Fan iso above door, occupancy sensor and a switch outside to override the occupancy. All was good or so I thought, till the snag list came to the builder.
It read, I wanted blue LED GU10 over the shower, A red one over the bath and I want the fan to come on without the lights.

I can see her point, but with only 20W of LED Lighting it certainly is not going to break the bank.

My thoughts are to run a piece of 1.5 to the switch, change the 1 gang to 2 gang (1 for fan), and switch between the perm live and the sw live to the fan, but knowing this would just turn the lights on. I remember years ago, I used diodes to stop current flow when fitting car alarms and wondered whether the same principle would apply with AC circuits.

If so, what would I use??? Any help or alternative method would be appreciated.

Regards


Dave

 

[trev]

Why not just fit a fan with a humidistat?

 

[daver]

Long Day, Brain Tired and thinking to hard. Thanks

 

[davesparks]

How have you ended up installing something which is not what the client wants?

To make a timer fan work as a standard fan link it's permanent and switched live connections and connect to a switch.

 

[tazz]

Diodes only block current flow on dc, so using on ac will chop the wave and alter the frequency.

 

[davesparks]

Alter the frequency?

 

[tazz]

Alter the frequency?

Yes, used 4 diodes as in rectifier circuit, then the input is ac 50hz and after rectification, it will be 100 hz

 

[davesparks]

Right, I was trying to work out how 1 diode was going to alter frequency! I didn't think my memory of A level electronics was that bad.

 

[tazz]

Think how a diode works on ac...depending on it polarity in the circuit, it either chops the positive cycle or the negative cycle (top or bottom cycle)
Hopefully this will help, out of interest.
Full Wave Rectifier and Bridge Rectifier Theory

 

[daver]

How have you ended up installing something which is not what the client wants?

To make a timer fan work as a standard fan link it's permanent and switched live connections and connect to a switch.

Lol. And why is the customer always right.

Without pulling up Part F, I think the rule is a new bathroom should have a fan which extracts at a rate of at least 15 litres per minute and continues to run for 15 minutes after the light has been switched off.

She wants it running, when the lights are out. But who says she will turn it on anyway and what stops her turning the isolator off.

Humidistat it is.

Thanks to everyone and especially the lesson on diodes. It has been a long time.

Dave

 

[Octopus]

Lol. And why is the customer always right.

Without pulling up Part F, I think the rule is a new bathroom should have a fan which extracts at a rate of at least 15 litres per minute and continues to run for 15 minutes after the light has been switched off.

She wants it running, when the lights are out. But who says she will turn it on anyway and what stops her turning the isolator off.

Humidistat it is.

Thanks to everyone and especially the lesson on diodes. It has been a long time.

Dave

Applicable to new builds yes, bathroom updates - NIMHO

 

[Geordie Spark]

Applicable to new builds yes, bathroom updates - NIMHO

Stop trying to confuse the poor lad.

Wor Trev's just managed to persuade him to fit a Humidistat Fan.