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Author Topic: Dissecting a Cree LED Incandecent Bulb Replacement  (Read 20756 times)

Offline MarkE

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #15 on: September 07, 2014, 08:55:08 PM »
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.

Free Energy | searching for free energy and discussing free energy


Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #16 on: September 07, 2014, 09:30:08 PM »
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.




Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #17 on: September 07, 2014, 09:46:19 PM »
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.

Free Energy | searching for free energy and discussing free energy

Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #17 on: September 07, 2014, 09:46:19 PM »
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Offline MarkE

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #18 on: September 07, 2014, 10:01:20 PM »
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.

Offline Pirate88179

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #19 on: September 07, 2014, 10:56:29 PM »
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

Free Energy | searching for free energy and discussing free energy

Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #19 on: September 07, 2014, 10:56:29 PM »
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Offline Madebymonkeys

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #20 on: September 08, 2014, 11:54:09 PM »
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.



Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #21 on: September 15, 2014, 03:12:02 PM »
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.

Free Energy | searching for free energy and discussing free energy

Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #21 on: September 15, 2014, 03:12:02 PM »
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Offline Madebymonkeys

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #22 on: September 15, 2014, 11:13:55 PM »
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 :-)

Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #23 on: September 16, 2014, 12:20:57 AM »
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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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #23 on: September 16, 2014, 12:20:57 AM »
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Offline Madebymonkeys

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #24 on: September 16, 2014, 12:47:31 AM »
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

Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #25 on: September 16, 2014, 03:04:44 PM »
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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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #25 on: September 16, 2014, 03:04:44 PM »
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Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #26 on: September 18, 2014, 04:56:41 PM »
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.

Offline Pirate88179

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #27 on: September 19, 2014, 03:10:13 AM »
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

Offline mondrasek

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #28 on: September 26, 2014, 02:36:16 PM »
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.

Offline Pirate88179

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Re: Dissecting a Cree LED Incandecent Bulb Replacement
« Reply #29 on: September 27, 2014, 02:42:35 AM »
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

 

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