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Interaction between Ventilation fan and LED light

Tim Truscott

I was asked to investigate an issue, an extractor fan had been installed in the loft above a bathroom, connected to an LED light fitting in the bathroom. When the light is turned on the fan runs, when the light is turned off the fan ‘pulses’ and the light ‘strobes’. ie both are on for ~1 sec then off for several seconds repeatedly. There are two bathrooms (family and en-suite) with identical fans but different LED light fittings. Both fans work correctly with the en-suite light, both fans exhibit the same problem with the main bathroom light. I believe that my tests have also excluded any local wiring faults 

I have raised the issue with the fan manufacturers and they say they have only seen this once before and was cured by fitting a ballast resistor (presumably in the light). I don't really want to do this as it negates the energy saving of the LED (and will generate unwanted heat). I suspect some strange interaction between the LED driver circuit and the fan timer circuit, either due to power factor or resonance (the light flash is similar to a faulty fluorescent light), in which case a coil or capacitor might be more appropriate.

Has any one else seen this? If so what did you do to solve it?

 

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    well the fan trigger line (switch live) is in parallel with the existing switch and my increase the coupling. 3 and earth cable has one core near earth and the outerjacket, and one core near another live core. You may win a little by using the core that only has earth as the neighbour as the trigger (switched live) but I'd be very wary of saying that will be enough.

    I will note that my toolbox has a few CR  units both for ghost voltages and for ‘declicking’ switches with those funniness where the security lights come on when the motor starts that sort of thing, a few surgegards for limiting inrush and some clip on ferrite rings to go RFI hunting as things I can go to and try in a few mins, and rather like the ferrule crimpers, its not often needed, but when it is,  just the ticket. It depends rather what sort of thing you do for a living though.

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  • 0

    well the fan trigger line (switch live) is in parallel with the existing switch and my increase the coupling. 3 and earth cable has one core near earth and the outerjacket, and one core near another live core. You may win a little by using the core that only has earth as the neighbour as the trigger (switched live) but I'd be very wary of saying that will be enough.

    I will note that my toolbox has a few CR  units both for ghost voltages and for ‘declicking’ switches with those funniness where the security lights come on when the motor starts that sort of thing, a few surgegards for limiting inrush and some clip on ferrite rings to go RFI hunting as things I can go to and try in a few mins, and rather like the ferrule crimpers, its not often needed, but when it is,  just the ticket. It depends rather what sort of thing you do for a living though.

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