Flicker bulb and continuous on exhaust fan in bathroom

[Msiddiqui135]

Hi, I just moved to a new house and the bathroom has a CFL bulb and a exhaust fan. the problem is that it switches on well but when you switch it off the bulb flickers and the exhaust fan is on continuously. I have a two way hanging switch in the bathroom. can anyone help me with this problem. There are two wires which connect to the switch one is green and another black. Any help would be appreciated

 

[JohnD]

sounds like it is incorrectly wired.

Who fitted it?

post some pics of the wires and connections please.

 

[Msiddiqui135]

It was somewhat working when i moved in...although there were some problems with the 2 way switch and the bulb....but the exhaust fan was working fine and my guess is that it has a timer..since yesterday night the exhaust fan has not gone off even when you switch it off.......

 

[DetlefSchmitz]

As an experiment try swapping the lamp for an 'ordinary' incandescent one. I'm guessing that would fix it. If so then you could try a different brand of lamp, or someone on the forum who has done it before can tell you a suitable component to add to the lamp circuit.

 

[Msiddiqui135]

Ok...Lemme try changing the bulbs and see if it works....but the question is what the bulb has to do with the exhaust fan working normally???

 

[DetlefSchmitz]

The fan has a circuit which uses the lamp to determine if the lamp is on. This works well with a filament lamp, but may with a CLF it is possible that it thinks the lamp is still on.

It may not be the problem, but it's quick to try...

 

[Msiddiqui135]

Ahh well ...it did work....Seriously i never thought it would be so simple. The fan did go off once the replaced the bulb.

Although the fan did stop....but it takes very long time for the fan to go off even after switching the bulb off....can I reduce the time for the fan to go off after i switch the bulb off.......although i can live with it.

THANK YOU VERY MUCH FOR YOUR HELP

 

[DetlefSchmitz]

There's often an adjustment somewhere on the fan. Might be a small hole for a screwdriver. The fan stays on for a reason though; it may be annoying but it helps stop mold growing in your grout.

 

[ban-all-sheds]

The fan has a circuit which uses the lamp to determine if the lamp is on.

No it doesn't.

If it did that would make it impossible to have the fan in a situation where there was no light, which is not the case.

The fan has switched live, permanent live and neutral, none of which are anything to do with the type, or presence, of a light.

It's wired incorrectly.

 

[DetlefSchmitz]

I'm sure you can work out that the lamp is effectively part of the circuit in the case where the timer circuit input has a high impedance, and the switched live has a lot of capacitive coupling to the live.

 

[ban-all-sheds]

I see what you mean - I got a tad diverted by "The fan has a circuit which uses the lamp to determine if the lamp is on".

But a fan whose SL detection cannot reject capacitive coupling could not be used with a dedicated switch. Do they make them like that?

 

[DetlefSchmitz]

All I can say is that it seems to be a common problem.

 

[bernardgreen]

But a fan whose SL detection cannot reject capacitive coupling could not be used with a dedicated switch. Do they make them like that?

Yes they do. The circuit that senses the voltage on switched live is high impedance and like a digital voltmeter is easily fooled by stray capactive coupling.

One reason it is high impedance is to prevent a damaged timer from putting live onto switched live when the switch is OFF and thus creating a safety hazard.

Hazard as in switch OFF the lamp to change the bulb but there is still live coming back on the switched live from the timer. The high resistance limits the current to a level that is not harmfull.

 

[ban-all-sheds]

So what do you do if you want the fan on its own switch, not a light switch?

 

[bernardgreen]

If there is no requirement for the fan to run on timer after the switch is turned off there is no problem as the "permanent" live to the fan goes through the switch.

If the fan is required to run on timer after switched live is removed then fit a snubber between switched live and neutral such as

Capacitor 0.047uF micro Farads 250 volts AC in series with a resistor 100 ohms

Which come pre-packaged as a contact suppressor from RS Components

RS Stock No. 206-7847
Manufacturer Evox-Rifa
Manufacturers Part No. PMR209MB5470M100

There are other sources of the contact suppressors