Extractor fan (timed) and energy saving bulb!

[smu]

I have a timed extractor fan in a toilet. I am replacing all my bulbs with low energy equivalents. However when I fitted an 11W low energy bulb the fan comes on with the lamp but never times out! I have changed the bulbs back to be sure it is the low energy lamp which is causing the issue.
Anybody seen this one?

 

[breezer]

no.

but its backefeeding through the lamp

 

[bernardgreen]

There is capacitive coupling between the live wire and the switched live wire in the cable to the fan. With an ordinary lamp bulb the energy in the switched live from the capacitive coupling is able to go through the filament to neutral and no voltage (other than a few millivolts) is generated on the switched live. With an energy saving bulb without a filament the coiupled energy is able to create a voltage on the switched live that is high enough to retrigger the timer in the fan.

Solution is a resistor between neutral and switched live to remove the capacitively couple energy before it can create a voltage high enough to trigger the timer.

A 270Kohm 0.5 watt resistor should be OK for the task. So err on the side of caution and use a 270Kohm 1 watt resistor.

 

[smu]

Thanks for the quick reply. I'll fit a resistor as soon as I can get to Maplin!

 

[Adam_151]

The next guy to IR it will be cursing you...

 

[bernardgreen]

I should have said provided the wiring is correct the most likely cause and solution is ............

There is no quarantee the resistor will solve the problem. But worth a try.

Ensure it is fitted where the 1/4 watt of heat produced while the light is on can be dissapated without damaging anything.

 

[JohnD]

or maybe fit a small filament light bulb and pretend it's an indicator lamp.

Would a neon do?

 

[bernardgreen]

or maybe fit a small filament light bulb and pretend it's an indicator lamp.

Would a neon do?

Small 230 volt filament would be ideal. Also would give immediate illumination while the energy saver powers up to full brighntess.

A neon probably wouldn't prevent the timer being triggered as the neon is open circuit until the voltage across it reaches about 90 volts and it strikes. That 90 volts may be enough to re-trigger the timer.