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Discussion board help and admin topics => Skeptical views and scam alerts => Topic started by: mondrasek on November 16, 2013, 11:18:28 PM
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Sorry for this NON OU question.
I purchased (6) Cree 60W (equivalent lumen output) light bulbs less than 8 months ago. They are advertised as lasting up to 25 time as long as a conventional incandescent bulbs. But one of the six failed last night. So (guess what) I took it apart to try to learn what went wrong with it. I had assumed that something in the built in Cree electronics between my (in the US) 120V 60hz mains and the LEDs had failed (similar to CFL bulb failures), but now I'm not sure.
After disassembly I plugged in the base of the Cree bulb that contains the electronics and it provided a steady 288V DC output. That output would have gone directly to the LED module that appears to only have (20) surface mounted LEDs.
So my question is: What in this Cree bulb stopped working properly? The electronics (ie. does the 288V DC output mean there is a problem with the circuitry?), the LEDs, or possibly the connections in between?
Thanks for your consideration, and sorry again for being off topic for this forum. It is just that I know there are many electronic experts that participate here.
M.
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It's probably the number 7 Fetzer valve....
http://www.youtube.com/watch?v=Hjsfs49SRbc&t=1m41s (http://www.youtube.com/watch?v=Hjsfs49SRbc&t=1m41s)
I kid....
Seriously though, these guys eat LEDs for breakfast:
http://www.ledforums.net/ (http://www.ledforums.net/)
http://www.candlepowerforums.com/vb/forumdisplay.php?91-LED (http://www.candlepowerforums.com/vb/forumdisplay.php?91-LED)
I'd bet you'd find the answer pretty quick at either forum.
TS
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Hmmm... if the 20 LED chips are in series, the voltage you are measuring might be appropriate to drive them, and the failure of a single LED chip, or a bad connection to the LEDs, would kill the whole light output.
Can you test the LEDs individually by applying power from a regulated DC supply to each chip in turn?
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Thanks TS. Interesting forums, but I didn't find anything quickly while searching on "Cree." The majority of posts I saw appeared to be more about the "use" of LEDs rather than the inner workings of a bulb assy.
@TK, the LED assy is what they call the "Cree LED Filament Tower" in the video here: http://www.youtube.com/watch?v=jnVw0doTbJ4 It appears to be made from some sort of flexible pcd type film that is laminated to an aluminum substrate which is bent into the decagonal "sleeve" that slides onto the main heat sink mast. It is really a very nicely designed package, quality control issues aside. No contacts are visible for any of the individual LEDs. Only the entire assy's + and - poles that slide into clips going to the AC/DC convertor circuit are accessible as far as I can see.
If 288V DC is about right then I will assume the circuitry is sound and that a connection problem or LED defect caused an LED to blow? At least I then can feel confident about the product's design and that my failure was a fluke. But does that make sense after the bulb has been in daily use (several cycles per day) for over 8 months?
Now that I know how to disassemble the unit I can do less damage to the next victim if another expires. If they do continue to fail I may end up with enough pieces to test by swapping components. Until then, I have a neat little AC/DC converter from 120V AC to 288V DC if anyone wants one.
Is there any chance that a component failure on the converter could jack up the DC output to a stable value that blew an LED while not popping the cap? I doubt that, but until I have another to compare the 288V with it is something I am curious about.
M.
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No, 288 volts would be way too high for 20 LED's in series. BTW I was an active member of one of the forums mentioned above for many years. Unless that 288 volts drops a lot under load it's way too high. LED's like these on average need around 4 volts. So about 80 volts if in series. Cree makes the LED's but most likely the electronics were done in China and may not be the best quality. Did you see a bright flash before this went out - most likely with a bluish tint? You can test the LED's with a meter or put around 4 volts across one but most likely they are toast along with the electronics.
Just guessing here but after looking at the picture I think this may have been setup as 5 groups of 4 LED's in series so it's more likely to have been fed by around 16 volts when it was working correctly. The idea of putting all 20 led's in series would not be a very smart design since if one went out the whole light goes out whereas if one goes out with 5 groups of 4 then you only lose 20% brightness.
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The answer to this mystery is probably quite trivial. One of the LEDs or the interconnect went open-circuit and the bulb failed. The power supply in an LED light bulb converts mains power into a current source output. Look up LED power supplies online and you will see that the vast majority of them are rated in current output and not in voltage output.
When you open-circuit a current output style of power supply the output voltage goes as high as possible.
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Yes current regulation is very important for LED's but they also need voltage limited. I can't imagine why there would be a step up to almost 300 volts in a setup like this. I've never seen an single LED that could tolerate 14.4 volts. Arrays of LED's often run at higher voltages but they are made up of individual chips that all run around 4 volts more or less. The highest voltage LED I know of off hand was the old Luxeon V that ran from close to 8 volts. That's about 10 year old tech and definitely not being used in LED light bulbs as they were very low efficiency compared to today's Cree LED's. However not knowing the designs they use in all these bulbs I suppose some might have had a circuit that could go that high when open circuited but it seems like a poor design IMO.
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@e2matrix, I was not there when the bulb failed. My wife may have noticed it. It is in the area where we do laundry and she said she was folding clothes when she "thinks" she saw the lights flicker. Afterwards she thought the light was a bit dimmer in that area. The fixture in that area holds two bulbs and only one failed, so that would make sense. But it is all subjective evidence. She also has a cold at the moment and may not be a reliable witness.
@MH, that is very interesting info. So, is there a way to test the converter further? The bulb assy is rated at 9.5W, so I assume that the converter would regulate down to it's design voltage if given the appropriate load?
I seem to remember having the heating elements from a toaster around somewhere...
And yeah, all this is trivial. But still something to do on a cold, rainy day.
Thanks,
M.
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Sorry, there are many high-power LED chips that use 10-12 volts supply. Yes, it's stupid to put 20 LEDs in series, but we've all seen stupider things from Chinese designers.
http://www.youtube.com/watch?v=BkUGNtYKasU
please read the description on the YT page
http://www.youtube.com/watch?v=j2DFJo90JUA
gahh... where do these people get these musics....
It would be extremely unlikely to have a power supply fault that caused it to produce much higher voltage than normal, rather than simply stopping working at all. I'm not saying it's impossible....
(later)
I found this article which you may find interesting.
http://ledsmagazine.com/features/10/4/1
Turns out the Cree bulb uses a 10series2parallel arrangement, so a single LED failure would knock out half the bulb.
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Mondrasek:
It will regulate down to it's design _current_. If you assume that it's a current source output you could short the outputs and then nothing should happen. Assuming that's true, then you could then connect an ammeter across the outputs and chances are it will read close to 350 mA or 700 mA, which are the standard currents for driving LEDs.
However, I don't recommend that you do this test, it's not worth the fuss and you can't forget that you are very close to mains power and therefore it's dangerous and potentially lethal.
Instead, read up on current sources and LED lights and how they are rated in by current draw and not by voltage.
Cheap and dirty direct from China:
http://www.meanwell.com/product/led/LED.html
MileHigh
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Sorry, there are many high-power LED chips that use 10-12 volts supply. Yes, it's stupid to put 20 LEDs in series, but we've all seen stupider things from Chinese designers.
http://www.youtube.com/watch?v=BkUGNtYKasU (http://www.youtube.com/watch?v=BkUGNtYKasU)
please read the description on the YT page
http://www.youtube.com/watch?v=j2DFJo90JUA (http://www.youtube.com/watch?v=j2DFJo90JUA)
gahh... where do these people get these musics....
It would be extremely unlikely to have a power supply fault that caused it to produce much higher voltage than normal, rather than simply stopping working at all. I'm not saying it's impossible....
(later)
I found this article which you may find interesting.
http://ledsmagazine.com/features/10/4/1 (http://ledsmagazine.com/features/10/4/1)
Turns out the Cree bulb uses a 10series2parallel arrangement, so a single LED failure would knock out half the bulb.
They may use 10-12 volts as a supply but the individual LED's will be a quick blue flash bulb if you put that much across them with any current at all behind it. Check the spec's on the Cree web site for an individual LED. Unless it has it's own regulator in front of the LED or is an array of LED's they do not run on 10 or 12 volts. You will find some that are on a single board under one dome in an array but if they use more than about 4 volts they are individual led's wired in series and you can usually see the separate diodes under the dome. Most less expensive LED 'bulbs' made for 120 VAC use individual little LED's like mondrasek showed and those are generally less than 4 volts each. Newer high power LED's putting out the equivalent of a 60 watt bulb or more are often higher voltage only because they are an array on one chip. So not to confuse or refute anything here I'm just saying a single individual Light Emitting Diode is almost always limited to around 3 to 4 volts or so.
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I run all of my Cree 60 watt equiv. LED bulbs on 350-400 volts (each) with no problems at all. I have many of them and all are still working just fine. The best LED bulb out there I have ever used. I am using a JT circuit and the bulbs are gutted. (Driver board removed) I have many Youtube videos of this.
Bill
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They may use 10-12 volts as a supply but the individual LED's will be a quick blue flash bulb if you put that much across them with any current at all behind it. Check the spec's on the Cree web site for an individual LED. Unless it has it's own regulator in front of the LED or is an array of LED's they do not run on 10 or 12 volts. You will find some that are on a single board under one dome in an array but if they use more than about 4 volts they are individual led's wired in series and you can usually see the separate diodes under the dome. Most less expensive LED 'bulbs' made for 120 VAC use individual little LED's like mondrasek showed and those are generally less than 4 volts each. Newer high power LED's putting out the equivalent of a 60 watt bulb or more are often higher voltage only because they are an array on one chip. So not to confuse or refute anything here I'm just saying a single individual Light Emitting Diode is almost always limited to around 3 to 4 volts or so.
But we aren't talking about "individual LEDs" are we? We (most of us except you) were talking about the LED chips that are in the Cree light bulb. Try to access one of the individual LEDs in such a chip. You cannot... they are all made on a single substrate and the CHIP itself needs 10-12 volts! So to have a power supply that puts out 288 volts _unloaded_ might be perfectly reasonable to power a 10-series 2-parallel array of such CHIPS as appear in the Cree bulb.
http://lighthouseleds.com/downloads/dl/file/id/145/10w_led_cool_white_datasheet.pdf
Note the forward voltage (typical) is given as 10.5 volts @900 mA. You cannot get to the individual LEDs inside that chip!
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Yep and I was talking about individual LED's because that is what was common in many LED bulbs in the past and it is what appeared to be in the pictures in the OP. However they could very well be LED array chips and without knowing the model # or having a much closer look it is all speculation.
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Houston (or Austin), we have a problem.
A second Cree LED bulb has blown in the same fixture as before. The fixture holds two bulbs. The bulb that blew today has been installed in that fixture since the first incident of failure when I started this thread.
When the first LED failed I replaced it with an incandescent. That bulb is still fine.
New info: The fixture is in my "mud room" that incudes the clothes washer and dryer. So there is a 240V outlet in use near by. The new failure also occurred while I was using the 240V dryer unit. BUT, the LED bulb went dark for a short time earlier when I stopped the dryer to check on the clothes inside. It came back on a few seconds later once I restarted the dryer.
When the most recent failure occured I turned off the light fixture with the LED bulb after it did not re-ignite when power was cycled to the dryer (and the fixture) and let it sit idle for about 10 min. After that it still did not ignite, so it was replaced by another incandescent.
The failed LED's glass dome has obvious residue on the inside now! Definitely on one side, so I assume one of the multiple LEDs actually exploded.
So I am looking for advise (again). Is there anything to be learned by dissecting the latest burnt out bulb? What is the likely root cause of the LED bulb failures? (I am thinking the fixture is probably on one leg of the 240V circuit in that area and inrush currents are f-ing up the silicon based elements in the LED's circuitry?)
Let me know what you guys think. Especially if there is anyway to test besides "borrowing" a Power Analyzer from work.
I'd like to know that I don't have a potential fire hazard in the construction of this home's wiring.
M.
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Houston (or Austin), we have a problem.
A second Cree LED bulb has blown in the same fixture as before. The fixture holds two bulbs. The bulb that blew today has been installed in that fixture since the first incident of failure when I started this thread.
When the first LED failed I replaced it with an incandescent. That bulb is still fine.
New info: The fixture is in my "mud room" that incudes the clothes washer and dryer. So there is a 240V outlet in use near by. The new failure also occurred while I was using the 240V dryer unit. BUT, the LED bulb went dark for a short time earlier when I stopped the dryer to check on the clothes inside. It came back on a few seconds later once I restarted the dryer.
When the most recent failure occured I turned off the light fixture with the LED bulb after it did not re-ignite when power was cycled to the dryer (and the fixture) and let it sit idle for about 10 min. After that it still did not ignite, so it was replaced by another incandescent.
The failed LED's glass dome has obvious residue on the inside now! Definitely on one side, so I assume one of the multiple LEDs actually exploded.
So I am looking for advise (again). Is there anything to be learned by dissecting the latest burnt out bulb? What is the likely root cause of the LED bulb failures? (I am thinking the fixture is probably on one leg of the 240V circuit in that area and inrush currents are f-ing up the silicon based elements in the LED's circuitry?)
Let me know what you guys think. Especially if there is anyway to test besides "borrowing" a Power Analyzer from work.
I'd like to know that I don't have a potential fire hazard in the construction of this home's wiring.
M.
If you take the bulb apart, you will probably find that an electrolytic capacitor failed. The problems with LED bulbs fall into: Electronics vulnerability, and combined LED and electronics temperature limitations. Whose bulbs are you using? I would go with bulbs that have good heat sinks.
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MarkE,
The bulbs are manufactured by Cree. TK provided some great links to a tear down that showed the "innards" earlier in this thread.
I initially bought a "six pack" of these bulbs and, so far, none, have failed except for the two that were installed in the fixture described before.
Here is another piece of info I just thought of that might me relevant: When I am in the area that is illuminated by the fixture that has the LED bulbs that I am inquiring about, I believe I have seen flickering of the light level. The flickering always makes me look at the fixture, but the flickering does not repeat (immediately). So I have dismissed that flickering thus far. Hell, I have written it off (as it were) to my aging eyesight.
Thanks for giving this some thought.
M.
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OH! After walking around (blood flow) and thinking, I believe you might be on to something...
The fixture where the two LED bulbs have failed is a ceiling mounted unit that is completely surrounded by a glass dome "lens." So it does not have good heat transfer capabilities by design AKAICT.
The other places that I have installed those similar LED bulbs are open air and therefore have convective cooling in their favor. So the whole "heat" conjecture is a good possibility that I had not considered previously. So thank you.
I am still concerned about the residue on the inside of the glass bulb however. As far as I recall, the electronic circuit for these particular bulbs is isolated in the base of the unit and should not be able to reach the glass bulb. So I can't see how a popped cap in that circuit could have created the debris on the inside of the bulb. But it is something cool to check out on a tear down I think.
Let me know if you (or anyone else) has other ideas!
Thanks,
M.
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OH! After walking around (blood flow) and thinking, I believe you might be on to something...
The fixture where the two LED bulbs have failed is a ceiling mounted unit that is completely surrounded by a glass dome "lens." So it does not have good heat transfer capabilities by design AKAICT.
The other places that I have installed those similar LED bulbs are open air and therefore have convective cooling in their favor. So the whole "heat" conjecture is a good possibility that I had not considered previously. So thank you.
I am still concerned about the residue on the inside of the glass bulb however. As far as I recall, the electronic circuit for these particular bulbs is isolated in the base of the unit and should not be able to reach the glass bulb. So I can't see how a popped cap in that circuit could have created the debris on the inside of the bulb. But it is something cool to check out on a tear down I think.
Let me know if you (or anyone else) has other ideas!
Thanks,
M.
Once the electrolytic capacitor fails the circuit cannot regulate. Thre's lots of energy available to cook the LED.
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Since heat is the enemy to all high powered leds, I add a heat sink as seen in this photo. It is made from an adult beverage can and works really well. I have never experienced a failure of any of my Cree LED bulbs. (Almost a year and counting) Some of them, as you may know, I have gutted the driver board and use a high voltage JT circuit to drive them, and none of these have failed to date.
Now, if you want to talk cfls, I have had so many failures with them that I will never buy another. 3 of them actually caught fire while I was home...I mean...burst into flames and if I were not here, it could have been terrible. I had to unscrew them while they were burning and toss them into the sink. The ones that did not fail this way only lasted maybe 2-4 months. The longest I have ever had a cfl last was possibly 8 months.
So, as you may be able to tell, I am a big fan of these Cree LED bulbs, both modified, and unmodified. I am sorry you are having this problem with them and I suggest contacting Cree, and even offering to send them some of your failed bulbs for analysis. I am sure that they really care about their products and, if this is some kind of design error, they must have had other complaints as well. Have you checked your home wiring for spikes? If you live near any large manufacturing companies, when they start up their equipment, there could be over voltages on your end or other damaging spikes possibly.
If your dryer is leaking moisture into the room, that could be a factor as well. All of my cfl's that caught fire were in my bathroom, where there is high humidity after a shower.
Again, contact Cree and let us know their response. This might help them improve their product so we can all get rid of those stupid cfl's!
Bill
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No, 288 volts would be way too high for 20 LED's in series. BTW I was an active member of one of the forums mentioned above for many years. Unless that 288 volts drops a lot under load it's way too high. LED's like these on average need around 4 volts. So about 80 volts if in series. Cree makes the LED's but most likely the electronics were done in China and may not be the best quality. Did you see a bright flash before this went out - most likely with a bluish tint? You can test the LED's with a meter or put around 4 volts across one but most likely they are toast along with the electronics.
Just guessing here but after looking at the picture I think this may have been setup as 5 groups of 4 LED's in series so it's more likely to have been fed by around 16 volts when it was working correctly. The idea of putting all 20 led's in series would not be a very smart design since if one went out the whole light goes out whereas if one goes out with 5 groups of 4 then you only lose 20% brightness.
Series requires only one current limiting component, parallel requires lots.
More volts at lower current (series) is easier than lower voltage at higher current (parallel).
The last decent Philips LED I used had a Vf of 68V. What looks like a single led can typically have multiple die bonded to each other and a metal substrate to get rid of the heat more effectively (when bonded to a larger sink!).
I agree, parallel would eliminate a total failure to product light if a led failed but there are more things to consider ie cost. Design choices always have cost in mind....it's why your TV doesn't cost £50k - it could, but it was designed to a price point.
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Again, contact Cree and let us know their response.
I used the Cree website contact form to explain about the two bulb failures and offer to provide one for them to analyze should they want to do so. One week later and absolutely no response.
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I used the Cree website contact form to explain about the two bulb failures and offer to provide one for them to analyze should they want to do so. One week later and absolutely no response.
The failure rate, of that product over its sales, is probably within acceptable limits and they wouldn't learn anything new. Nothing will last forever, failures are always expected and numbers calculated.
An email from them would at least be nice though :-)
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An email from them would at least be nice though :-)
Especially since they advertise these bulbs with a 10 year warranty! But then again I have received many replacement parts and items from other manufacturers after sending in an Internet claim without ever receiving even an auto-reply. So I still wait patiently...
But I see no reason why even an auto-reply, as cold as they are, is not considered the minimum responce for such an organization.
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Especially since they advertise these bulbs with a 10 year warranty! But then again I have received many replacement parts and items from other manufacturers after sending in an Internet claim without ever receiving even an auto-reply. So I still wait patiently...
But I see no reason why even an auto-reply, as cold as they are, is not considered the minimum responce for such an organization.
If it's under warranty then a replacement, in theory, should come...although they may question its failure mode if you've already dismantled it :D
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If it's under warranty then a replacement, in theory, should come...although they may question its failure mode if you've already dismantled it :D
I only dismantled the first failure that occurred last year. I did not expect that to be covered under warranty. I did not dismantle this second failure.
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I received an e-mail from Cree today stating they would ship two warranty replacement bulbs on 10/13. That was all. I am satisfied with that response at least.
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That is as it should be and it is good to hear. It would have been much better if they wanted to dissect the failed bulbs to find the problem but...I guess we can't have everything. Thanks for keeping us up to date.
Bill
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Two replacement bulbs arrived yesterday. I have no idea why they sent me an e-mail saying they would ship them out on 10/13!
The new bulbs have a slightly different cooling fin design. The fins are a bit longer and extend down over the electronics holder in the base a few millimeter where they round (taper) inwards to a point in an aesthetically pleasing way. This would provide more surface area for improved convective cooling. And since modifying the dies for this change and possibly use of more cast material are both cost increases, I have to believe it was done to improve these bulb's tolerance to a heat issue (at least in some applications).
I'm still not putting them back into the same fully enclosed ceiling fixture that has no openings for air exchange with the rest of the room.
M.
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Good news. I will have to look for some here with the new fin design, then I can stop making my own additional heat sinks for them. So far, however, I have not lost any of them after about 6 months or so. I am running them in open fixtures like table lamps though.
Bill