Buzzing LED dimmable bulbs

[Edward]

Forgive me but I am a complete layman when it comes to electricity. We have in our kitchen a pendant with 8 bulbs installed, specifically these in various shapes.

 

https://www.thelightbulb.co.uk/4watt-pear-led-es-e27-screw-cap-very-warm-white-gold-finish-equivalent-to-30watt-dimmable/

 

The wiring, switch, the circuit into the distribution box including the box itself is all new.

 

We replaced the current bulbs because they buzz, however these bulbs are worse. What’s the solution? Is it likely to be a new switch? Are the bulbs not suitable? 
 

id be grateful for some insight and some product recommendations to help stop the buzz!

[MJNewton]

At the risk of not being any use whatsoever it's usually down to the bulbs, the dimmer, or both... ?

 

Joking aside (although that wasn't actually a joke!) if you like the bulbs then I'd look more into what dimmer you've got. Varilight V-Pro are often recommended as being compatible with a wide variety of bulbs, have a couple of different operating modes and are easy to get hold of. (Make sure you get a V-Pro - they have other, sometimes cheaper, models that aren't necessarily as good)

Edited March 17, 2021 by MJNewton

[BobAJob]

Are you sure it's the bulbs that buzz?

 

I've had dimmers buzz. I replaced it with a standard switch, so no more buzzing. 

[Radian]

That kind of 'fliament' LED bulb is often a bit crude in terms of the driver electronics inside the screw cap (note there's not much room down there). Despite being claimed to be dimmable I wouldn't put it on a dimmer. If it isn't on a dimmer then it's even cruder than the usual Chinesium offering.

[SteamyTea]

Try without a dimmer and see if it is still noisy.

I think there are two basic types of dimmer, leading and trailing edge.

No idea which is best.

 

I get my LEDs from Poundland. They work a treat.

[Temp]

I tried numerous LEDs over the years. Had great success with cheap non-dimmable bulbs but getting anything dimmable to work has been a struggle. I tried several makes of filament type bulbs on a variety of dimmers and always had horrible flickering.  This was only/most apparent when several bulbs were used in one room/fitting. 

 

Then last year I tried some Osram candle style dimmable bulbs and they are working well on a Varilight dimmer.

 

This year I tried some Osram GU10 downright bulbs and they worked very well on a dimmer until I blew them up. Think a spike on the mains from a fluorescent light on same circuit took them out. Have replaced with same and seem OK so far.

 

So in short I would ditch the filament style and go for a well known brand.

 

Trailing edge dimmers are best for LEDs.

 

[Temp]

The Candle bulbs I'm using are..

 

Osram Parathom Dimmable 6.5W LED E14 SES Candle Very Warm White - 287907-438835

 

I'm sure they make as E27 similar.

Edited May 2, 2022 by Temp

[Radian]

5 hours ago, SteamyTea said:

I get my LEDs from Poundland. They work a treat.

 

I always enjoy watching Big Clive's teardowns. For your delight, here's a complete investigation of a Poundland LED:

 

 

If you watch the video you'll see it uses the cheapest kind of 'driver' - not really a driver at all. Just a reactive capacitive voltage dropper (hence the PF of 0.5). This is most likely the sort found in the base of the filiament style LED's where space is at a premium. The problem with these is that the expected reactance of the capacitor Xc)  only applies when fed with a full sine wave:

 

Xc = 1/(2 π f C)  which, In the case of the 6W poundland LED above, C=1.1uF so Xc= 1/(2 π 50 1.1e-6)=2894 Ohms

This limits the current in the ~180V LED string to something like (240-180)/2894 = 20mA

 

A conventional leading edge dimmer switches in the AC supply voltage by a variable time delay each cycle so rather than a smooth sine wave the capacitor sees part of a sine wave introduced with sudden sharp edges 100 times a second. The harmonics of this go way up so the f term in the reactance formula becomes much more complicated but essentially higher - hence the reactance decreases and the current increases. It's all very messy because at the same time the delayed peak voltage is reduced. The manufacturer simply slaps a non-dimmable label on the box so the problem goes away. Except when it doesn't.

 

The other kind of "trailing edge" dimmer doesn't hit the capacitor with a sharp edge 100 times a second, but whips the voltage away at some point before each half cycle ends. This is less stressful on the circuit but still has harmonics that alter the reactance.

 

One other relevant point is that capacitors can make audible noises as the charge flows in and out due to piezoelectric forces. The higher harmonics introduced by phase angle dimmers make this noise more apparent.