Flashing LED lamps

[Tipper]

We have a pair of lights in our hall controlled by 3-way switching. Last week I replaced the existing CFL bulbs with LED versions to get more and instantaneous light when switched on. The house was fully re-wired in 2013 and certificated as OK by the installing electrician.

Last night I was woken by the two LED bulbs flashing like strobe lights. I thought at first the smoke detectors were flashing but no. The wall lights themselves were flashing about once per second. No other lights were affected. I loosened the bulbs to stop them flashing and all appeared OK. Today I switched off that lighting circuit for safety as we are away overnight.

What's causing this? Is it likely to be a fault on the 3-way switching? If so, what do I check/do? All ideas would be appreciated.

Thanks.

 

[Iggifer]

It's not a fault per se, it's called capacitve coupling. Have a read here, and get one of these

 

[ericmark]

I just fitted a bigger bulb and it all stopped. As said nothing wrong it's caused by the way we wire switches. It would need the neutral and line to run together to switch and we only run the line. So the circuit is not balanced. As to if the inductive or capacitive link causes the problem I am unsure. But I am told a power tool suppressor stops it happening. Some lamps come on dim and some flash and some clearly have some network to stop it as they work A1.

Using two way lights makes it worse simply as there is more cable going to the switch. Any load will likely stop it. But to me it goes against the grain to fit a load as when you swap the bulb it may not be required it would just waste power even if very small amount.

 

[bernardgreen]

These also work to suppress the flashing of LED lights. http://www.maplin.co.uk/p/rc-contact-suppressor-rg22y but wired across the lamp and not across the switch contacts.

As to if the inductive or capacitive link causes the problem I am unsure

As there is no significant current flowing ( switch is OFF ) there can be no significant electromagnetic field so induction plays no significant part.

 

[Tipper]

Thanks guys, that explain it well.

Presumably the cheaper the LEDs the more likely it will happen as the suppressor won't be built in.

I will get hold of the suppressor/capacitor thingy and fit it to stop the flashing.
Thanks.

 

[ericmark]

These also work to suppress the flashing of LED lights. http://www.maplin.co.uk/p/rc-contact-suppressor-rg22y but wired across the lamp and not across the switch contacts.

As to if the inductive or capacitive link causes the problem I am unsure

As there is no significant current flowing ( switch is OFF ) there can be no significant electromagnetic field so induction plays no significant part.

So if a capacitive unbalance then cure should be inductive so why try to cure with a capacitor?

 

[bernardgreen]

It is not un-balance but a bypass of the switch

The stray capacitor between Live and Switched Live allows a small amount of current to flow to the lamp. Hence the lamp has some power when teh switch is OFF

Adding the dump capacitor across the lamp creates a voltage divider with the stray capacitor. With C dump much larger than C stray the divided voltage across the lamp is reduced to near zero.

 

[Tipper]

Thanks guys, that explain it well.

Presumably the cheaper the LEDs the more likely it will happen as the suppressor won't be built in.

I will get hold of the suppressor/capacitor thingy and fit it to stop the flashing.
Thanks.

Just to close this out I fitted the Maplin sourced suppressor across one of the lamps and that cured it.

Thanks