LED bulb blinks with switch off, only when smoke alarm installed

[diywedders]

Hi all,

I know this is a commonish problem but Googling gives me lots of different advice - I tried the thing I saw most often and it didn't work, so I'm asking.

This is a two-way switched light on the stairs.

Long story short I swapped every bulb for LEDs when I moved in but this one flashed/blinked when off, so I left the filament until it burnt out.

I then discovered that if I removed the smoke alarm - which is a few feet across the cieling and presumably spurred off this light - it stopped flashing.

On Googled advice I got a potted suppressor module with a 0.1uf cap and 120ohm resistor and put it across the lamp in the cieling rose, but that made zero difference.

I've just metered the connections in the cieling rose with the switches off (in both off positions) and am seeing 240v at all times.

Also - if it helps at all - with both up- and downstairs lighting circuits off at the fuse box I still read ~2.6v across this fixture, unplugging the smoke alarm drops that to ~2v.

Any thoughts? Or am I going to have to rewire the smoke alarm to come off a different circuit?

 

[FrodoOne]

This is a two-way switched light on the stairs.

Long story short I swapped every bulb for LEDs when I moved in but this one flashed/blinked when off, so I left the filament until it burnt out.

I then discovered that if I removed the smoke alarm - which is a few feet across the cieling and presumably spurred off this light - it stopped flashing.

The smoke alarm should not be "spurred off" any "light"
It may be connected to the Line and Neutral at/near the light fitting.

A mis-connection of the wiring to the smoke alarm may be suspected.

I've just metered the connections in the cieling rose with the switches off (in both off positions) and am seeing 240v at all times.

Who knows where you are measuring?
It seems that you are measuring between the supply Line and the Neutral (or Earth.) - if the Light is not on.

Also - if it helps at all - with both up- and downstairs lighting circuits off at the fuse box I still read ~2.6v across this fixture, unplugging the smoke alarm drops that to ~2v.

You are using a High-Impedance (digital) Voltmeter and "seeing" a "phantom" voltage.

Also, why do you state "~2.6v" etc.?
(This indicates that you are attempting to measure DC on an AC circuit.)

 

[ericmark]

AC can have capacitive and inductive linking, and the longer the switch wires, the more of a link we have, so two way systems are more prone to the problem.

So the voltage slowly builds up in the lamps smoothing capacitor, until high enough to light the LED's when it discharges through the LED's as a flash or keeps the LED's on dim.

I cured by changing bulbs, the smoothing capacitor in the large bulb was nearly as big as the whole of the small bulb, and it was a higher wattage to start with, so swapping to the larger bulb stopped both staying on dim and the flicker when on.

The load capacitor should stop the flashing or staying dim when off, don't really know why it did not work for you. But I found it hard to fit in the limited space inside the lamp fitting.

Using a relay so the wiring to the two way switches is extra low voltage DC is another method, also allows switching with phone and voice control.

The other problem with landing lights, is often we have a borrowed neutral, actually it is a borrowed line, where only two wires are run between the two way switches, and the line is taken from an adjacent switch, this was OK when same circuit used for upper and lower floors, but not once the circuits are split. The way around this problem is often to use wireless linked switches, like the kinetic switch where the moving of the switch generates enough power to send a radio signal to master unit.

If you have split supplies upper and lower floor, I would test first, switch off first one, then after test the other breaker and try the switches in all of the four options, if one breaker off stops the lights working and the other breaker they work in two for the four options, then all is good. However if the light works in one options of the four with either breaker then you have a borrowed neutral, which will need correcting, likely with kinetic switches.