Extractor fan timer and energy saver bulbs

charlieconnelly · 26 Oct 2009

Hi,

I've just changed my bathroom light to an energy saver and found that my fan doesn't go off. With the old filament bulb it usually stayed on for about 5 mins before clicking off.

I'm guessing that this is to do with the the fact that filament bulbs allow current to pass through them when they are switched off, but energy savers don't. I thought a solution could be a resistor in parallel with the light so the switched live still has some current passing through it. Will this work? I'm not sure how the timer in the bathroom fan is set up. If it will work should the parallel resistor be roughly equal to the resistance of a filament bulb, or should it be high resistance so I don't mess up the voltage to the energy saver bulb?

Thanks a lot!

RF Lighting · 26 Oct 2009

Did you just replace a standard filament lamp with a compact fluorescent lamp, or did you actually replace a fitting for a low energy type?

charlieconnelly · 26 Oct 2009

nope, just took the filament bulb out and put the low energy bulb in. I actually didn't know you could get different fittings...

RF Lighting · 26 Oct 2009

Does the fan return to normal operation if you take the CFL out?

charlieconnelly · 26 Oct 2009

Yes, I've put the old bulb back in now and it's back to turning off after around 5 minutes. There are two bathrooms in the house that both had the same problem, so I'm pretty sure it's not the fans themselves going wrong.

RF Lighting · 26 Oct 2009

Well I think you've beaten me

Maybe someone else will have an idea as to what might be happening?

I can't think of how putting in a CFL would stop your fan functioning properly.

charlieconnelly · 26 Oct 2009

Thanks anyway, if all else fails I'll just have to rely on black market sources of filament bulbs!

ricicle · 26 Oct 2009

I can only think of the control gear in that particular brand of CFL 'spiking' the fan timer into staying on.

flameport · 26 Oct 2009

Presumably this is a result of the resistance of the lamp filament:

with an incandescent lamp, this has a very low resistance so the switched live is the same potential as the neutral with the switch off.
with a CFL, which has a high impedance due to electronic gubbins inside, the switched live is not at neutral, but some other voltage due to capacitance in the (long?) wires from the switch.

If you switch on, switch off and then remove the lamp (leaving the socket empty), does the fan stay on?

charlieconnelly · 26 Oct 2009

I'll try experimenting with a few other brands at some point then, unfortunately all I have in the house are identical as they're selling them for 10p each in Homebase at the moment!

tim west · 26 Oct 2009

probably not enough holding current through the triac when using the CFL?

TicklyT · 27 Oct 2009

How does the fan behave without a lamp in the fitting?

bernardgreen · 27 Oct 2009

When the lamp is switched off without the resistive path through a filament to neutral the switched live conductor will be able to drift and capacitively induced voltages on it ( that would have leaked to neutral via the filament ) appear to the timer in the fan as being Live hence the fan keeps running.

Fitting a capacitor and resistor in series across the lamp MAY leak enough of the capacitively coupled voltage away such that the fan timer does not see the switched live as being "ON".

A more reliable method if an energy saving lamp must be used is a relay adjacent to the fan. The relay coil supplied by the switched Live from the lamp and neutral, The relay contact connecting Permanent Live to the switched live input into the fan.

charlieconnelly · 27 Oct 2009

Thanks for all your comments. The fan behaves the same way if I set the fan going then remove the energy saver and have no bulb as it did with it in, so I guess the high impedence of the energy saver is the issue.

Bernard: I'll give your suggestion of inserting a relay a go when I get a chance, sounds like a better plan than my idea of putting in a resistor and capacitor in parallel with the lamp fitting.

Cheers all!

flameport · 27 Oct 2009

The relay idea will probably work even if the relay contacts are not connected to the fan. Just having the coil connected will provide the path between switched live and neutral.

Before buying anything, check that the earth wire in the switch cable (and others) is connected properly.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Extractor fan timer and energy saver bulbs

Similar threads