What killed this LED?

[paulr]

I gave my buddy a white Countycomm keychain light that worked fine for a while (I saw him using it several times). One day I borrowed it from him and it didn't work. I asked what happened and he said he thought he'd sat on it or something. I knew he'd slept with his clothes on the previous night and I figured his weight had just kept it lit all night til the battery was dead. I gave him another light and later snarfed back the dead one, figuring I'd use its LED in some project.

I just got around to trying the LED in something but to my surprise, the batteries from that light are fine and it's the LED that's dead. What could have killed it? At least by eyeball inspection, it looks fine. I don't have instruments to measure whether any battery current goes into it, but it makes no light when I apply voltage. The Countycomms are tough little lights and should withstand being sat on just fine.

Do 5mm LED's simply crap out once in a while? The two 2016's do presumably overdrive it somewhat, but there are zillions of these things out there and I don't remember hearing of one popping before.

Thanks for any thoughts.

 

[shiftd]

my first bet is it being overdriven. Yea, there are a zillion out there and never heard thing like this happened before. But what other probable cause? I cannot think of anything else. Maybe the lead cropped out? rust? /ubbthreads/images/graemlins/icon3.gif

 

[BLU3_SHOCK]

this is very very weird can i ask you a question what color was the led it is most likly over driven because 5 mm leds norm life time is 11 years unless if it is over driven or moistre got to it which is pretty weird because one that i have fell in a empty sink and was in there for 10 seconds and it still worked beats me. oh and paul r since i am in with you in that group buy if you dont want those batteries and that led or that full setup i will take it off your hands for free of charge or .25 cent just my 2 cents.

 

[paulr]

This was a white LED as mentioned in the original post. I put the batteries into another light. They are not dead but I think they're a little weak. You don't want them.

 

[James S]

It's almost certainly the LED's forward voltage was too low. In my very first batch of lights from CC (2 years ago now, the squeeze model) there were 4 that gave out the angry blue/green overdriven HELP sign /ubbthreads/images/graemlins/smile.gif I pulled those aside for testing. I think it's just natural variance in the LED's once in a while you get one that lets too much power through.

The most recent batch I have from them, the switched ones has not so far yielded a single one that is so obviously overdriven. So I think the quality control of the LED's is getting better. I don't think the batteries are changing at all, they are a pretty stable product by now.

 

[paulr]

Interesting. I didn't think any LED's were intended to run at 6 volts, but rather, current was limited by the batteries' internal resistance.

Apparently the original Photon lights all used a single CR2025 or 2032 cell, which made the white ones pretty dim. The trick of using two 2016's for more brightness and less runtime was discovered by users on the photonlight.com discussion forum and then adopted by Photon itself and I guess copied by other coin light manufacturers. So I guess if I find I get any more overdriven ones, I'll set them up with single 2032's. They're bright enough that way.

This particular dead led had been in use for a while, enough that the 2016's running it were somewhat weak and it had gotten dimmer, so it's a bit surprising that it burned out all of a sudden. But I guess it's possible.

Thanks.

 

[Willmore]

I would guess static, myself. LEDs are static sensitive if you hit them backwards--their reverse characteristics are very weak.

 

[PhotonWrangler]

I'm guessing that it was overdriven and due to manufacturing flaws or poor q/c, it couldn't tolerate that.

I would think that a static charge would have been dissipated evenly across the entire lamp. In order to zap it with static, you'd have to be able to deliver the static charge to one of the leads to produce a damaging voltage differential across the LED.

On the other hand, my opinion is worth every penny you're paying for it!
/ubbthreads/images/graemlins/tongue.gif

 

[gadget_lover]

Static discharge is one possibility. Never under estimate the ability of 50,000 volts to penetrate seemingly solid objects. /ubbthreads/images/graemlins/smile.gif

Another (very likely) possibility is that he laid on it so it stayed on for X hours with no air circulating around it. These LEDs are not built to dissipate much heat. The semiconductor junction may have failed.

Lastly, many pocket LED lights have the LED mounted by the leads. Is that the case here? Any shock against the LED will be transmitted through the plastic to the leads, which are are actually used to create the semiconductor junction. This can ruin the semiconductor.

OK, I have'nt seen the light and haven't finished my first cup of coffee, so take with grain of salt.

Daniel

 

[INRETECH]

I bought my son one of those cheap White LED keychains, and a few days later he noticed that it would BLINK

I suspect that the LED is being overdriven so much that the bond wire is heating up and being detached from the die; and then when it cools down - reconnects like a automobile blinker with the small heater inside

The cycle time is very reliable at approx 2hz

 

[The_LED_Museum]

I've seen both white LEDs and yellow-green (not InGaN) LEDs blink as Mike described above. But when LEDs go out permanently, there's usually smoke and a bad odour. Not always, but usually.

My guess here is that one of the bond wires came off the LED die, and did so in such a manner that it cannot reconnect.
The LEDs in all two-cell coin cell lights are significantly overdriven, so I'm guessing this LED was easier to kill than most others.

If you want to send the LED to me for analysis, I have a variable voltage current-clamping PSU and a meter; and could tell you for certain if it's bad or not, and maybe even what killed it if it really is bad.

 

[paulr]

The led is definitely dead. It's from one of the CC squeeze lights, meaning the led isn't really "mounted", it just has a pair of coin cells between the leads and you squeeze one lead down to make a connection. Visual inspection doesn't show any mechanical damage to the leads or lead frame inside the package.

Craig, sure, PM me your address and I'll send the led.

 

[The_LED_Museum]

PM on the way...

(Edit, a few moments later)
PM sent...thank you! /ubbthreads/images/graemlins/smile.gif
Like I said in there, I'll try to figure out what killed the LED, but no guarantees. I will try though.

 

[PhotonWrangler]

/ubbthreads/images/graemlins/popcorn.gif

 

[drs2000]

I've got a Photon knock-off that also blinks. Anywhere from 5Hz to .5Hz. Very short burst, slows down and more off time over 10 sec or so. Thermal bond wire like Mike's, I guess.
Could send it to you if you want, Craig..

Keep up the good work!

Have you played with those RGBs I sent ya?\

drs

 

[The_LED_Museum]

Hi drs,

If you want to send me the faulty LED for analysis, please, be my guest. Send to the same address you sent the other goodies to last month. /ubbthreads/images/graemlins/smile.gif
The address is:

Craig Johnson
The LED Museum
1531 1st Ave #305
Seattle WA. 98101-1557

in case you lost or forgot it. (This is common knowledge, and I don't mind displaying it on a public BBS)

As for the RGB LEDs, I have the "RGB Pixel" LEDs you sent me right here if you're interested.
First entry on the page, so they shouldn't be hard to find. /ubbthreads/images/graemlins/grin.gif

 

[Marked]

God needed more light in heaven and called it home. May the light rest in peace.

 

[MrAl]

Hello there,

Another idea is that possibly the batteries were inserted
in backwards by accident. If the voltage is over 5v there
is a possibility the LED would blow out. When the
batteries were put back in correctly, the LED wont light up.

Take care,
Al

 

[paulr]

I think there's no chance the batteries were inserted backwards. The batteries are installed at the factory and the light worked fine. I don't think anyone removed them and put them back in. That would involved taking the light apart, which is a pain in the neck.