12V halogen bulbs buzz and flicker with dimmer

[zzz]

Hello,

I just had a dimmer switch installed, replacing a simple on/off switch. The bedroom light fitting has 5 x 20W 12V G4 dimmable halogen bulbs (supplied originally with the light), so total load 100W. The dimmer is from Screwfix (LAP brand), it's a leading edge type, and is rated 35-350W for low voltage halogens. The light fitting itself was bought as dimmable - I specifically checked with the online retailer. As far as I recall there was a white rectangular block inside it - which I assume was the transformer!

Perfect fit of components, I would have thought... But no - the lights buzz when on, the higher the brightness the higher the pitch. And when left on, after 5 seconds or so they start flashing on and off fairly quickly.

I'm just so puzzled why these ordinary 12V halogens are misbehaving with the dimmer. The load is neither too low or too high!

The dimmer instructions mention not to use it with trailing edge, lagging edge and phase lagging transformers - but I've no way of checking if my light fitting has such a transformer.

The electrician was saying something about getting a trailing edge dimmer but why should this help? To be honest I became dubious about his expertise because he was also suggesting getting LED bulbs for our installed leading edge dimmer, which isn't the best combo!

Thanks for any suggestions...

 

[PrenticeBoyofDerry]

Are the transformers dimmer compatible?

 

[zzz]

Do you mean the transformer inside the light fitting? Well - I'd have thought so because on the website where I bought the light (and on others) it says "dimmable - yes". And I rang them to check. I'll be calling again tomorrow, but for now I assume it is capable of being dimmed per se. There's also a review online where they say they are using it with a dimmer. But nowhere says what kind of dimmer is required!

 

[ericmark]

1) Quartz should be kept white hot to stop the tungsten from being deposited on the quartz, so although they are often dimmed they should not be dimmed.
2) The whole idea of the switch mode power supply used to supply a quartz lamp is to ensure what ever the mains voltage does the electronic transformer output is steady, rather defeats the object fitting a dimmer.
3) Since the bulb has a coil of wire as a filament some times with a switch mode power supply that can react with the frequency of the output, dimming may upset the power supply so combined with the coil formed by the bulbs filament it can become unstable.

What we hope happens is the electronic transformer (switch mode power supply) detects the wave form chopping and reads it as a command to reduce output, to do this the dimmer and electronic transformer must be reading the same hymn sheet, i.e. leading or lagging, although today manufacturers must declare if the item is not dimmable that was not always the case, and nothing says they have to state how to dim them. So bulb, transformer, and dimmer should all be same make.

 

[PrenticeBoyofDerry]

Do you mean the transformer inside the light fitting? Well - I'd have thought so because on the website where I bought the light (and on others) it says "dimmable - yes". And I rang them to check. I'll be calling again tomorrow, but for now I assume it is capable of being dimmed per se. There's also a review online where they say they are using it with a dimmer. But nowhere says what kind of dimmer is required!

Link to the product may help

 

[zzz]

Link to the product may help

Of course, I wasn't sure if links to products were allowed.

The light: https://www.illumination.co.uk/brilliant-maira-pendant-light-g14773-15.html

The dimmer: http://www.screwfix.com/p/lap-1-gang-2-way-push-dimmer-switch-400w-400va-polished-chrome/77563

 

[StephenOak]

Sorry if this is dragging the thread off topic. If necessary I'll start a new one.

1) Quartz should be kept white hot to stop the tungsten from being deposited on the quartz, so although they are often dimmed they should not be dimmed.

I have heard that and I understand the reasoning (at least in principle even if not mathematically), however I do wonder how much impact it really has.

We have a mother & daughter lamp, 300W & 50W, where the controls are a pair of dimmer switches. We brought that with us from our previous house so it must be over 10 years old. It is in the living room and gets used a lot and virtually always not at full power.

I would have said that I am pretty sure I have not replaced either bulb in that time, but I just checked the power rating and in doing so I saw that they are not G9 bulbs but GY6.35 (50W) and RS7 (300W) and so now I am certain that I have never bought either of those types.

So whilst dimming a bulb like this may cause it to work less than optimally and thus impact its lifetime, my experience says that the impact will not be that significant.

 

[zzz]

Sorry if this is dragging the thread off topic. If necessary I'll start a new one.

I'm just looking for a practical tip about what's going on in my particular case and how to fix it. I've contacted the manufacturer and they are puzzled - they say I have the correct dimmer and it should be working.

 

[SFK]

ZZZ,
I have not had experience in dimming 12V Halogen bulbs powered by a 240V-12V convertor, only on dimming LEDs.
But I am wondering if it is your leading edge dimmer that is not compatible with the 240V-12V convertor that is in your light fitting (lamp). In other words is your dimmer chopping the 240V 50Hz sine wave in a manner that is not being understood (or liked) by the 240V-12V convertor as a request to dim.

As a possible solution, you could try a "Varilight V-Pro dimmer" like this (note that although this is my second recommendation for this in two days I am not affiliated at all with them):
http://www.screwfix.com/p/varilight-trailing-edge-push-dimmer-1g-1-2w-400w-va/94816
This is a Trailing Edge Dimmer and does say that it is suitable for "Good quality dimmable electronic low voltage transformers (including those requiring trailing-edge control)"
and can also be programmed to be a "alternative trailing-edge dimmer" and a "leading edge dimmer" so you can try three different dimming methods with your lamp.
The manual is here:
https://www.varilight.co.uk/leaflets/VARILIGHT V-Pro Dimmer Instructions JP003.pdf

ps, I noticed you wanted polished chrome finish so there are more styles of Varilight V-Pro dimmers here (just make sure it is V-Pro):
https://www.tlc-direct.co.uk/tcl/search?query=varilight+v-pro&Submit=Search
or just the module to go inside the LAP chrome fitting:
https://www.tlc-direct.co.uk/Products/VLMJP300.html


Hope this might work and you find a solution,
sfk

 

[securespark]

You say the dimmer is rated 35-350 but I can't see that. All I can see is 60-400.

And the light fitting voltage is 230, not 12.

 

[flameport]

If you buy the white Varilight one, you can just swap the module onto the chrome plate of the existing dimmer.

 

[ericmark]

Reading the adverts dimmer switch minimum power 60W and lamps rated 20W so you would need 4 lamps connected to that dimmer so when dimmed still over 60W.

Since bulb is 12 volt and lamp is 240 volt there has to be a voltage dropper of some type inside the lamp, it does not state if the unit is dimmable. It gives LED bulbs as an option, however it also lists bulbs of 20W which would if all 5 used be 5 times the rated wattage. So in a nut shell can't trust supplier and the unit to drop the voltage could be unsuitable for both dimming and LED bulbs.

You say you have 5 x 20W which is 5 times rating of the lamp, you also said 35 to 350 watt for the dimmer but linked to a 60 to 400 watt device. Again clearly some errors, and it is hard when remote to work out who made the errors and what is the correct information. I will guess what is written on the devices is not what is shown in the advert? I have seen this a lot, it does not help when people selling the items make errors on the advert. The built in voltage dropper could well be rated 105 VA (VA nearly same as watts) but without looking you don't know.

The bulb could be dimmable they have to write on the packaging if it's not, but that does not mean the voltage dropper is dimmable. I call it a voltage dropper as there are a few methods of dropping the voltage, a transformer would be rather chunky at 100 watt and heavy so unlikely it uses one of them, more likely a switch mode power supply often labelled electronic transformer. In theory the electronic transformer is better as it can regulate the output and has a smaller in rush on switching on, but to dim it needs to read the signal from the dimmer switch as a command to dim, unless it can do that, it will try to compensate for what the dimmer is doing.

I would say step one is remove lamp and read details on the device which drops the voltage, don't trust what the advert says, if the advert is correct as to bulbs which can be used it should be able to supply 6 - 100 VA likely it would say 0 - 105 VA however that may not be the case, it should also state dimmable if not likely it is not.

 

[zzz]

Hope this might work and you find a solution,
sfk

Thanks SFK! Very helpful and practical. And thanks for the links. I think I will get an electrician to try the dimmer switch / module you recommend, which can be changed to different modes.

I was in touch with the manufacturer and they were puzzled. The light is capable of dimming, and they thought the dimmer I got shouldn't cause any issues. But clearly there is some mismatch and it seems worth experimenting with a different dimmer. It won't blow anything up, right?!

 

[zzz]

You say you have 5 x 20W which is 5 times rating of the lamp, you also said 35 to 350 watt for the dimmer but linked to a 60 to 400 watt device.

Hi ericmark, the instructions leaflet for the dimmer has a table which gives min and max loads for different types of bulbs. They are all slightly different but around the same ballpark. There's no mistake. For low voltage halogens it says 35-350W. As I have 5x20W low voltage (12V) G4 halogens, the way I see it is that the total load is 100W. Which is comfortably within the 35-350W range of the dimmer and shouldn't cause an issue.

The manufacturer said the light is capable of being dimmed. The supplied bulbs also have the "dimmable" logo on them.

I think I will do as SFK suggested and get a dimmer which you can toggle between leading and trailing edge modes, and when the electrician comes also get him to check the transformer inside the light fitting...

Thanks

 

[SFK]

ZZZ,
Famous last words, but no using a trailing edge dimmer instead of a leading edge dimmer on a dimmable appliance will not blow anything up.
Presuming you fitted the LAP dimmer yourself, if I was you I would get the Varilight from screwfix and being careful to keep the packaging try it out and see if it works in place of the LAP to drive/control the 240V to 12V converter inside the appliance.
Please tell us how it goes, as will be interested to see if it works.
SFK