Flickering LED and electronic switches why and how to stop?

[ericmark]

The question is if switch, or lamp or interaction between the two, and how to stop it? I see many reports of flickering with dimmer switches, but in my case the electronic switches are on/off with no neutral and recommended wattage over 5 watts. They are Energenie MiHome switches but it is unclear if it is switch or bulb.

I have 5 smart switches with no neutral, you can hear them click so assume must have a relay inside them, and with a single 10 watt BA22d bulb they work A1, also with 8 and 5 E14 (SES) bulbs not dimmable also work fine, the instructions say to use dimmable bulbs, I would assume this is so some current can flow through switch when off to work electronics, removing a bulb and replacing, or any other interruption of supply turns the switches off.

The three GU10 bulbs in my bedroom flickered, so swapped bulbs with those from kitchen, and in the main it has stopped the flicker, but every so often it can be noticed.

Wife's bedroom has been a real problem, 5 G9 2.4W bulbs in a chandelier, on fitting the smart switch they would not turn off, but would flash, bulbs all say dimmable, so load capacitor fitted, this allowed lights to turn off, however still a flicker, not all the time, it seemed what ever is done stops it, then it returns, then one bulb failed, since in lock down, a quartz tungsten bulb taken from another room, and fitted in the chandelier, all flicker stopped, and you can't tell which bulb is the odd one out.

So if it is load, then why no flicker with single 10W BA22d bulb? If switch then why do all bulbs stop flicker with extra load? It does seem to be connected to bulb size, the 5 watt E14 bulbs have no problem but there are 5 in smallest chandelier, with 3 x GU10 I would guess also 5 watt on the odd time there is a problem, but very rare, and with the 2.4 watt x 5 G9 bulbs there was a problem until one bulb changed for halogen, so some things point to switch and some things point to bulbs so seems likely an interaction between bulbs and switch, and neither is faulty as such.

But is there a cure? What I hope is people will add to this with their experience, and maybe we can actually work out why LED bulbs some times flicker with electronic switches?

 

[bernardgreen]

The flicker is almost always due to the driver in the LED lamp becoming unstable and thus unable to correctly control the current through the LED element(s).

Transient pulses on the supply to the driver can trigger this instability in the driver.

electronic switches are on/off with no neutral and recommended wattage over 5 watts.

With no Neutral the switch has to obtain power from some where. There is a pseudo Neutral via the lamp on the Switched Live when the switch is OFF, When the lamp is lit and the switch is closed then the Switched Live is Live and hence the pseudo Neutral is not available.

But there has to be some power to the switch's electronics to enable the switch to function when it is commanded to turn the lamp OFF

The switch may not be a zero Ohm contact but instead have a resistance across which the lamp's current through the contacts can create a small voltage to provide power to the switch's electronics.

A variation in the current through the lamp would vary the voltage supplying the electronics in the switch. This could then cause a variation in the supply to the driver in the lamp and vicious circle is created

you can hear them click so assume must have a relay inside them,

This might be a bi-stable relay that is mechanically latched ON by a pulse to the coil and un-latched by a pulse of opposite polarity to the coil. A switch using these would be able to hold enough charge in a capacitor or small battery to provide the un-latch pulse and would not need a pseudo Neutral while the lamp was lit. ( though there may be a time limit that the lamp is lit before the capacitor is depleted and thus unable to power the un-latch pulse to the relay ).

 

[ericmark]

I would say with 0.6 volt across a diode then easy enough to get multiples of 0.6 volt to drive the electronics, I would assume bulbs and switches work in a similar way to 5 to 20 mA sensors in that all dimmable bulbs must let enough power through the bulb without lighting it to drive the electronics of the switch. Clearly this was not the case with the G9 bulbs, hence needing the 100 μf capacitor.

In the days of the old tungsten bulb they were that cheap no one worried about the price of a bulb, but 5 x G9 LED bulbs looking at around £3.50 each, so you don't want to buy one just to try, the MiniSun 3W and the one odd Prolite 2.4W should last around 20,000 hours so even at 8 hours a day over 6 years, so really don't want spares in the house, when one blows then you get a replacement not some thing one needs to hold in stock. I should with only 6 G9 bulbs in whole house need around one per year. OK with GU10, E14 and BA22d I have a lot more, so may be one or two in stock, but not G9.

I did try swapping the switch and with BA22d bulb no problem, only G9 is really a problem, did get some flicker with some GU10 but not anywhere near as bad as with G9 bulbs, one would expect 5 bulbs would not flicker in unison, so would be really not problem, however it seems they do flicker in union. Had not swapping switches left the problem still with G9 bulbs I would have said faulty switch, but since only seems to happen with G9 bulbs it seems to point to the bulb. As long as G9 tungsten are available not a problem, but if they stop making them, then there is a problem again.

 

[bernardgreen]

I agree that tungsten are the easiest to control in a reliable way,

For dimming LED elements there is a lot to be said for using a variable and smoothed DC voltage with a series resistor as current control

 

[ericmark]

Point is I am not trying the dim the lights. Only switch on/off. But as said as long as I can run with 4 LED plus 1 tungsten then great, but if you can't get tungsten then it means need to re-wire and use two way switching. So much easier to use a remote control.

 

[flameport]

I have 5 smart switches with no neutral,

That is the problem.
Devices like that will never work properly.

 

[DetlefSchmitz]

Devices like that will never work properly.

I think they could, but only if:
a) both supply and lamps designed by the same company
b) the assumptions (e.g. how many lamps, what rating) are also followed by the user

In practice the parts usually come from different companies and are fitted in random quantities, so there will continue to be problems. There is no point in expecting otherwise.