Flickering and Buzzing LED on dimmer switch


Postby iamstimpy » Sat Sep 17, 2016 8:48 am

Hi

I have a set of 8 spot lights on a dimmer switch in a play room that used to have Halogen bulbs in.
I swapped 7 of them for LED's as I could not get the 8th out and all worked fine. However I have now managed to get the final Halogen removed and changed it to an LED however this last bulb now has a slight flicker and a very quiet but very annoying buzzing.
I have swapped the LED's around with new ones as well as swapping the locations of each bulb but this does not change anything, its always the same spot that flickers and buzzes.
The spot lights have transformers and the flickering never occurred when I had all Halogens. The dimmer was replaced to cater for lower energy bulbs.
Help, its driving my wife mad - which basically means I am getting it in the ear, badly!!
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Postby kbrownie » Thu Sep 22, 2016 6:34 pm

Firstly can you confirm, the you have changed all the Halogen for dimmable LED lamps/bulbs. Also have you replaced the transformers for dimmable drivers?
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Postby ericmark » Fri Sep 23, 2016 5:36 am

I can only guess. My guess is as you dim the lights the minimum output of the power supply has not been reached.

Most GU5.3, 12 volt spot lamps are powered using what are called "Electronic Transformers" these units unlike normal transformers regulate the voltage which was an improvement for the quartz lamps.

However I have never really worked out why dimmable units were ever made, as the whole idea with quartz lamps is to keep that quartz at exactly the right temperature, too high and the lamps burn out, too low and the lamps blacken and fail, so it seemed daft to dim any quartz lamp.

The LED replacement lamps often state 50 Hz, this is in the main because they need to old type transformer without any voltage regulations, the new "Electronic Transformer" has an output well over 50 Hz, however some lamps do come with instructions showing how to ensure the "Electronic Transformer" is loaded high enough to work. So for example 8 x 7W = 56W so if the "Electronic Transformer" says 60 ~ 300 VA then they are 4W short, it may work 4W short but when you dim then it is even more watts short of the load required.

What is often the case is the original set up will have 2 or 3 "Electronic Transformers" but the new set up will use just one "Electronic Transformer".

However there is another problem, most the "Electronic Transformers" due to the high frequency have a limit of 3 foot extra low voltage connection lead, extending to over this length can cause interference and you may not be aware what it is doing, broad band running slow for example.

One way to stop the interference is to go to DC, however the lamps are designed for AC that is what 50 Hz tells us. So what ever you do it still may cause problems unless you fit wire wound transformers which in the main will not work with dimming switches.

There are now some "Electronic Transformers" rated 0 ~ 60 VA but again not a 50 Hz output.

Likely it will work with high frequency, but that is not what it says on the packet.

So unless fitted in a bathroom where you NEED extra low voltage then best option is to move to low voltage (230 vac) and replace with GU10 fittings with no transformer.

I will admit I would have told people a few weeks ago to buy "Drivers" you don't really want a true driver as a true driver controls current not volts, but manufacturers have started to call anything which powers an LED lamp a driver so google "driver" and you will find DC power supplies with a fixed voltage of 12 volt.

But last week I bought some LED GU5.3 lamps from Lidi and noted it stated 50 Hz, also noted the LAP GU5.3 lamps in Screwfix also state 50 Hz so at least 2 manufacturers are clearly making the lamps for an AC supply.

In the bathroom using LED lamps can be a problem, with quartz lamps the glass was hermetically sealed so no splash could get into the lamp, however that is not the case with LED, you need to select a lamp designed for the bathroom, the lamps I bought did not have any IP rating marked on the lamp, although the fitting may have an IP rating it expects you to use a lamps which has a glass front 16/8" (2") across with a multifaceted reflector that is what MR16 means, so a LED lamp with cooling fins will allow splashes and moisture to the back of the fitting. Also unless you put frosted glass in front of the lamp, instead of 2" often you only have 1" of light which often fails to distribute the light around the room.

In bathrooms normally one replaces the whole lamp for a flush fitting LED, even in rooms where there is no IP rating restriction the physical size being reduced to 1" instead of 2" can mean although you get the lumen, that lumen is adsorbed into the floor rather than lighting the room.

Having a light fitting where the bulbs face up and reflect off a white ceiling works well, giving a shadowless general light, OK the fluorescent tube is likely better but who wants fluorescent tubes in their living room. But without some form of defuser the spot lamp can be rather poor.

With LED lamps they do not produce the heat like the older lights, so they can be flush mounted unlike the older lamps. So fitting flush lamps over the holes where the old spots were is likely the best option, but swapping to GU10 is likely the easy option.

Although you can swap the power supply, it is a suck it and see job. I now have 4 Lidi 3W LED spots in my bathroom, the previous 4 LED's all failed, and this was with a wire wound transformer so in theory they should have worked OK. But they did last 6 months, so by time they failed did not have a receipt. No 230 volt LED lamp in the house has failed, only the 12 volt ones have given any problems, so if you can get rid of 12 volt.

Sorry for delayed response, the forum would not let me log in.
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