Author Topic: EEVblog #533 - LED Fluoro Tube Teardown  (Read 16592 times)

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Offline NiHaoMike

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #25 on: October 18, 2013, 02:16:41 am »
Fluorescent lamps are infamous for EMI issues since they deal with high voltages at high frequencies. LEDs are DC so the EMI they produce is comparable to that of a common switching power supply. In applications where the EMI must be kept as low as possible, LEDs can be driven with a linear power supply and still get very good efficiency.
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Offline peteroakes

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #26 on: October 20, 2013, 11:20:35 pm »
With all the chatter over the quality Dave, now that these have been up for  few weeks, are you still getting the same light output from them, From experience with some 12V strings from china  :-[ I placed under the counters in the kitchen, I am noticing a distinct reduction in brightness after a month or two, the voltage supplied is stable and the same as day one, but it defiantly seems dimmer. I do not have a meter to test the output but based on the fact that when they went in, we did not have to use the older tube lights or the central incandescent at all and now am finding it is almost every time I'm in the kitchen to do anything... there going down fast.

If yours are truly top notch German engineering rather than the cheaper china made brand, the proof would be in the longer term light output stability ?

Up for a re-measure Dave, and quieting down the crowds, although every couple of months a re-test would be nice also, maybe just posted in this thread ?
 

Offline classical

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #27 on: August 24, 2014, 03:55:57 am »
Thanks for this fine teardown. I run the lights for a year both in continuous operation and intermittent operation. They work well and I like the neutral and flicker-free light.
So I like to see what is in.
as a hobbyist : can't do that.. put resistors.
In my opinion you can omit the series resistors in the 4 LED strings for statistical reasons.
In each string we have 24 LEDs in series. So the statistic helps to reduce or the tolerances of the stings. This follows the "Central Limit Theorem".
The more components are connected in series in a string, the lower the deviation in the total resistance. So, the single strings gets more equal to each other by increasing the number of components in a string.
To see this, you can play with the following Java-Applet:
http://www.chem.uoa.gr/applets/appletcentrallimit/appl_centrallimit2.html
Probably you have to add the url into the sitelist of the JAVA control center first.
Select a distribution using the radio buttons, e.g. normal distribution or Gaussian and increase the sample size up to 24. So you can see how the relative tolerance decreases.
It is interesting to see that this works not only for Gaussian distribution but also with "odd" distributions.
 

Offline mikerj

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #28 on: August 24, 2014, 08:52:55 pm »
I wonder if they will be/are marketed with the same name in the UK.  The Müller dairy have been selling Müller Light yoghurt here for many years.
 

Offline HackedFridgeMagnet

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #29 on: August 25, 2014, 12:34:34 am »
Quote
In my opinion you can omit the series resistors in the 4 LED strings for statistical reasons.
In each string we have 24 LEDs in series. So the statistic helps to reduce or the tolerances of the stings. This follows the "Central Limit Theorem".
The more components are connected in series in a string, the lower the deviation in the total resistance. So, the single strings gets more equal to each other by increasing the number of components in a string.
To see this, you can play with the following Java-Applet:
http://www.chem.uoa.gr/applets/appletcentrallimit/appl_centrallimit2.html
Probably you have to add the url into the sitelist of the JAVA control center first.
Select a distribution using the radio buttons, e.g. normal distribution or Gaussian and increase the sample size up to 24. So you can see how the relative tolerance decreases.
It is interesting to see that this works not only for Gaussian distribution but also with "odd" distributions.

Sorry but this is a newbie mistake.
You can't assume a gaussian distribution because chances are the LEDs resistors or whatever are from the same batch, or come from the same manufacturer, made with the same machines etc.
This much I know but I am sure that someone else who knows more about this can explain more fully.
 

Offline FrankBuss

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #30 on: August 25, 2014, 09:46:22 am »
Sorry but this is a newbie mistake.
You can't assume a gaussian distribution because chances are the LEDs resistors or whatever are from the same batch, or come from the same manufacturer, made with the same machines etc.
This much I know but I am sure that someone else who knows more about this can explain more fully.
Looks like the gaussian distribution describes resistor variations very accurately, even from the same machine and the same batch:
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Offline HackedFridgeMagnet

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #31 on: August 25, 2014, 02:49:25 pm »
 

Offline classical

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #32 on: August 31, 2014, 12:48:27 pm »
Sorry but this is a newbie mistake.
Really is it? May be yes. The question is by whose side? ;-)

You can't assume a gaussian distribution
I totally agree. But this is not necessary. The Central Limit Theorem does not need a Gaussian distribution as an input. You can take nearly every distribution as an input, the Gaussian distribution will be the OUPUT. Please take a few minutes playing withe the applet in http://www.chem.uoa.gr/applets/appletcentrallimit/appl_centrallimit2.html . It ist amazing to see that almost "all gets Gaussian" if the number of members in the chain is high enough. And 24 seems to be high enough. The convergence is faster if you have already Gaussian input data but it also works with oher input distribution.
 

Offline HackedFridgeMagnet

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #33 on: August 31, 2014, 10:56:29 pm »
Quote
But this is not necessary. The Central Limit Theorem does not need a Gaussian distribution as an input.
Ok I'll concede this, It seems I didn't read your earlier post properly.
You are only looking for similarity between the strings, you are not looking to reduce the overall tolerance.
I was using discussion in this thread as a basis for my statement.
https://www.eevblog.com/forum/projects/tolerance-of-resistors-in-series-and-parallel/

but I will admit that statistics is not my strong point.
At uni I remember sitting in stats and thinking fondly about jumping out of the window. Whereas I enjoyed almost all the other subjects.

As far as the LED flouro design goes, it does seem to pose a number of risks. Especially in the grouping of the strings that will mean they have slightly different thermal operating points. Also I doubt a pick and place machine is a truly random selector.
But on the other hand, the tubes seem to work, they are probably running comfortably within spec.  So they are moot points.
Any knowledge of a failure rate?

« Last Edit: September 01, 2014, 12:37:18 am by HackedFridgeMagnet »
 

Offline lowimpedance

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #34 on: September 01, 2014, 12:31:36 am »
 I currently have a number of the 2 ft tubes operating for short periods a day for the last 6 or so months and have not noticed any light output reduction, perceptible at least!, or outright failures. So will just keep going until there is a failure, either light output or completely dead, and report such here.
 Other than personal experience I suspect it will be unlikely any one will get hold of any statistical info relating to these 'cheapo' lights!.
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Offline capslock

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #35 on: December 01, 2014, 09:53:04 am »
Bought four of these last autumn but only installed one at the time. That was a single fixture with a conventional ballast. There was a slight hum which I suspected came from said inductor/ballast, but it was quite ok.

Now I installed two in a fixture that had a dual electronic ballast. I rewired the fixture so both LED tubes are fed directly from mains. All four produced very audible hum, but in some it was more of the 100 Hz type, in others, it was higher order harmonics. Interestingly, the one that was quietest in the conventional setup was loudest when connected directly to mains.

Looking at the video, it seems the 1 mH inductor from the data sheet is there (actually, I can see two black inductors) but the 10 R inrush limiter has gone missing. I suppose they omitted it because your average conventional ballast will have at least that resistance. So I wonder if putting that resistor back in will get rid of the noise.

If all currents were sinosoidal, at 18 W, the lamp would be drawing 78 mA, hence the resistor would dissipate 780 mW or 4.3% of rated power. It is probably even worse because the capacitor gets charged only at peak voltage, so this could easily be 1 to 1.5 W.
 

Offline classical

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Re: EEVblog #533 - LED Fluoro Tube Teardown
« Reply #36 on: December 02, 2014, 04:03:00 am »
So I wonder if putting that resistor back in will get rid of the noise.
It is an easy try, so it is worth while to check this.
But I do not expect too much. Noise is created in some cases by capacitors but mostly by inductors.
I assume that the LED driver has some kind of closed loop. So introducing an additional resistor you will decrease input voltage and the controller will increase input current. 
 


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