12V halogen bulbs buzz and flicker with dimmer
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No, it was an electrician. But he was puzzled as to why the dimmer was buzzing and the lights flashing. As I mentioned, he suggested trying LED bulbs first - but with the existing leading edge dimmer, and if that didn't work to try a trailing edge one. But I was dubious because I thought LEDs required a trailing edge dimmer! He also didn't go back into the light fitting to check the transformer. Kinda lost confidence in him to be honest...
ZZZ,
Changing a dimmer yourself is a relatively simple job - but please please do not do it if you do not feel up to it.
Regarding the electrician - I can sympathise with him - I would say that complex driving methods behind these dimmers and then matching them to other probably not-labeled white boxes that (in the case of variable supplies) or bulbs (in the case of LEDs/luminescent) is a bit of a minefield of knowledge, experience and luck. I feel it can be seen with those Varilight instructions - they are 2 pages of small writing only for a simple dimmer and 4 pages of evening reading showing how dimmers work.http://www.ilight.co.uk/downloads/iLIGHT Binder-HowDimmers.pdf
It makes nice reading for DIYers like me, but horrible for someone who is on a clock and not wanting to overcharge you.
:>
SFK
Changing a dimmer yourself is a relatively simple job - but please please do not do it if you do not feel up to it.
Regarding the electrician - I can sympathise with him - I would say that complex driving methods behind these dimmers and then matching them to other probably not-labeled white boxes that (in the case of variable supplies) or bulbs (in the case of LEDs/luminescent) is a bit of a minefield of knowledge, experience and luck. I feel it can be seen with those Varilight instructions - they are 2 pages of small writing only for a simple dimmer and 4 pages of evening reading showing how dimmers work.http://www.ilight.co.uk/downloads/iLIGHT Binder-HowDimmers.pdf
It makes nice reading for DIYers like me, but horrible for someone who is on a clock and not wanting to overcharge you.
:>
SFK
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I would also be interested to know how the dimmer works, we know it chops a wave form at the switch, but this in its self would not cause the light to dim and the switch mode power supply turns that chopped wave form into DC charges a capacitor with it to smooth it and then turns it back into Mhz AC and transforms it down, then samples the output and adjusts the mark/space ratio to keep the RMS voltage to 12 volt. With a standard switch mode power supply this would mean any dimming done by chopping wave forms would be removed by the switch mode power supply. So some thing in the switch mode power supply has to read the chopped wave form as an instruction to reduce the output voltage, how it does this I don't know, but it does.
This is why the dimmer and the electronic transformer must match each other.
Even without a dimmer some times the coils of wire inside the bulb are a critical inductance and can cause the electronic transformer to hunt, add a dimmer and it is more surprising that they ever work, it must have been a nightmare to have designed a switch mode power supply that could work in this way, hardly surprising some don't.
So in real terms you buy the dimmer, the electronic transformer, and bulb all from the same manufacturer. Or at least from a list published by the manufacturer of known units from other manufacturers that match.
As I said we are trying to do something which the bulb and power supply were not designed to do, the whole idea of using extra low voltage was that the voltage was precisely regulated and the thickness of the filament was thicker to try to extend bulb life. Then we try and dim it after going to all that work to ensure it did not dim.
Dimming a 230 volt bulb is reasonable as there was nothing to try and maintain the voltage, I say was, as with LED bulbs and tubes you can get switch mode drivers in the bulb to try and smooth out any voltage fluctuations, I have a R7s tube in an outside light rated 85 ~ 250 volt it would be very hard to dim that tube. LED's formed into a bulb shape do tend to be designed to dim, using a very basic current control often a capacitor, this is OK with 230 volt lamps as we can be reasonable sure it is a 50 Hz supply, however with extra low voltage it may have a Mhz supply which would preclude the use of a capacitor to control current. Many MR16 compatible LED bulbs are marked 50 Hz, and can't be used with a switch mode power supply.
In some cases they have given up with AC and use DC for extra low voltage, I would simply not try to dim extra low voltage, if I want to dim then I stick to low voltage, however I know the problems, I can understand why people try dimming extra low voltage as they simply don't realise how hard it is. It of course can be done, go into any cinema and they even dim fluorescent lamps. But there is a health and safety issue plunging people into darkness, far better to slowly dim lights.
I am sure you can find a dimmer and an electronic transformer to match, but even then, swap the bulbs as they fail and it can all start again, is it really worth the hassle fitting a dimmer? When on holiday in Turkey I found they split their lighting into two sections with a 1/3 and 2/3 split so with just two simple switches they have three levels of lighting. Unfortunately it needs to be wired that way to start with.
This is why the dimmer and the electronic transformer must match each other.
Even without a dimmer some times the coils of wire inside the bulb are a critical inductance and can cause the electronic transformer to hunt, add a dimmer and it is more surprising that they ever work, it must have been a nightmare to have designed a switch mode power supply that could work in this way, hardly surprising some don't.
So in real terms you buy the dimmer, the electronic transformer, and bulb all from the same manufacturer. Or at least from a list published by the manufacturer of known units from other manufacturers that match.
As I said we are trying to do something which the bulb and power supply were not designed to do, the whole idea of using extra low voltage was that the voltage was precisely regulated and the thickness of the filament was thicker to try to extend bulb life. Then we try and dim it after going to all that work to ensure it did not dim.
Dimming a 230 volt bulb is reasonable as there was nothing to try and maintain the voltage, I say was, as with LED bulbs and tubes you can get switch mode drivers in the bulb to try and smooth out any voltage fluctuations, I have a R7s tube in an outside light rated 85 ~ 250 volt it would be very hard to dim that tube. LED's formed into a bulb shape do tend to be designed to dim, using a very basic current control often a capacitor, this is OK with 230 volt lamps as we can be reasonable sure it is a 50 Hz supply, however with extra low voltage it may have a Mhz supply which would preclude the use of a capacitor to control current. Many MR16 compatible LED bulbs are marked 50 Hz, and can't be used with a switch mode power supply.
In some cases they have given up with AC and use DC for extra low voltage, I would simply not try to dim extra low voltage, if I want to dim then I stick to low voltage, however I know the problems, I can understand why people try dimming extra low voltage as they simply don't realise how hard it is. It of course can be done, go into any cinema and they even dim fluorescent lamps. But there is a health and safety issue plunging people into darkness, far better to slowly dim lights.
I am sure you can find a dimmer and an electronic transformer to match, but even then, swap the bulbs as they fail and it can all start again, is it really worth the hassle fitting a dimmer? When on holiday in Turkey I found they split their lighting into two sections with a 1/3 and 2/3 split so with just two simple switches they have three levels of lighting. Unfortunately it needs to be wired that way to start with.
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Eric,
Your comment "something in the switch mode power supply has to read the input chopped wave form as an instruction to reduce the output voltage" is discussed in detail here:
http://www.powerelectronics.com/lighting-systems/dimming-techniques-led-drivers
The basic paragraph that I have taken from this is that to address the Capactive smoothing issue that you highlighted:
A triac-dimmable LED driver activates the LED output drive with a PWM signal only during the time that the triac in the dimmer is switched on. The LED driver contains a dc bus storage capacitor, so it is able to continue running on stored energy for much of the period when the triac is switched off. This stored energy is then replenished during the “on” periods.
But this has issues of increasing off periods as the dimmer is turned down, so the improved circuit:
The triac firing angle information is converted to a dc level that varies as the dimmer is adjusted up and down. This dc lvel is then compared with a dimming ramp waveform at a high frequency to eliminate flicker and shaped to provide the best possible linearity and range of dimming. The resulting comparison between these signals produces a PWM signal, which is used to pulse the LED driver output on and off and provide smooth dimming over a wide range.
This is for LED's, and so I am interested a regulated 12V PWM signal (if this is what is inside the lamp of ZZZ) will effect the lifetime of the bulbs used in ZZZ's lamp.
And of course, after all this we might find that ZZZ's lamp does not contain a 240V-12V dimmable-power-supply, only a 240V-12V power-supply, and all this discussion and my suggestion of a Varilight dimmer is mute. :<
sfk
Your comment "something in the switch mode power supply has to read the input chopped wave form as an instruction to reduce the output voltage" is discussed in detail here:
http://www.powerelectronics.com/lighting-systems/dimming-techniques-led-drivers
The basic paragraph that I have taken from this is that to address the Capactive smoothing issue that you highlighted:
A triac-dimmable LED driver activates the LED output drive with a PWM signal only during the time that the triac in the dimmer is switched on. The LED driver contains a dc bus storage capacitor, so it is able to continue running on stored energy for much of the period when the triac is switched off. This stored energy is then replenished during the “on” periods.
But this has issues of increasing off periods as the dimmer is turned down, so the improved circuit:
The triac firing angle information is converted to a dc level that varies as the dimmer is adjusted up and down. This dc lvel is then compared with a dimming ramp waveform at a high frequency to eliminate flicker and shaped to provide the best possible linearity and range of dimming. The resulting comparison between these signals produces a PWM signal, which is used to pulse the LED driver output on and off and provide smooth dimming over a wide range.
This is for LED's, and so I am interested a regulated 12V PWM signal (if this is what is inside the lamp of ZZZ) will effect the lifetime of the bulbs used in ZZZ's lamp.
And of course, after all this we might find that ZZZ's lamp does not contain a 240V-12V dimmable-power-supply, only a 240V-12V power-supply, and all this discussion and my suggestion of a Varilight dimmer is mute. :<
sfk
ZZZ,
don't worry I too am very hopeful that it will work. Although I have just thought there is even the chance that the 240V-12V power supply has failed and only working in a on/off mode.
So I am very conscious that the wonders of internet forums means that I can give the impression of 'positive, defining and accurate advice' about a little white box that I cannot see, to you who I do not want to upset if I am wrong. So crossed fingers and hope it works, which I think it will with the Varilight dimmer.
sfk
don't worry I too am very hopeful that it will work. Although I have just thought there is even the chance that the 240V-12V power supply has failed and only working in a on/off mode.
So I am very conscious that the wonders of internet forums means that I can give the impression of 'positive, defining and accurate advice' about a little white box that I cannot see, to you who I do not want to upset if I am wrong. So crossed fingers and hope it works, which I think it will with the Varilight dimmer.
sfk
Please show a credible mechanism whereby zzz getting his terms incorrect could lead to someone getting killed.
Well - If some one has 240V thinking it 12V then, presumably, it is possible.
I take it you think it is alright to use this error one way round but not the other.
I take it you think it is alright to use this error one way round but not the other.
The dimmer manual referred to "low voltage halogen bulbs". As the ones supplied are labelled as 12V bulbs I just assumed this referred to them, i.e. they required a drop in voltage from 240 to 12. I'm not an electrician obviously, not even a DIY one - but I don't think there's any danger of me or anyone else killing themselves... I wouldn't treat any part of mains circuitry lightly!
Yes, I appreciate that but the manufacturer is wrong.
All people are doing is pointing out this error in order that we know accurately what is meant.
The terms Extra Low Voltage, Low Voltage and High Voltage with Medium Voltage sometimes are Bands.
None of them accurately describes what anyone has and so the actual Voltage should be stated, as you did in the heading.
Like describing someone - a crime suspect, for example - as Human. True, but not a lot of help.
All people are doing is pointing out this error in order that we know accurately what is meant.
The terms Extra Low Voltage, Low Voltage and High Voltage with Medium Voltage sometimes are Bands.
None of them accurately describes what anyone has and so the actual Voltage should be stated, as you did in the heading.
Like describing someone - a crime suspect, for example - as Human. True, but not a lot of help.
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The result is we will always get grey imports which use the American definition, and likely internet search will from time to time show the American rather than British.Wikipedia said:
It is NOT the manufacturers who are wrong, they don't have control of how their products will cross boarders. Some times things like white and black wires rather than blue and brown or the spelling of colour will alert us. If it gives color temperature the it is American and if it has Colour temperature it's British.
That may or may not be so. I have never bought anything in the UK with black and white wires.
But that does not excuse UK distributors such as Screwfix, Tool Station, and many others from printing wrong information in their UK catalogues.
Are you suggesting that it is only grey - unofficial - imports causing this confusion?
Of course they do. The EU is very strict on such matters.
Would you be happy if your local filling station started selling fuel (litres apart) in US gallons and charging you as Imperial gallons?
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