*Update*Back from the dead!

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jdriller

Flashlight Enthusiast
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Feb 9, 2003
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OK LED gurus, please tell me what happened in this scenario:

I put 3, hot off the charger, c batteries in my FTC. Lit it up, and saw one angry blue 3 watter /ubbthreads/images/graemlins/icon8.gif. I turned it on and off a few times, just because I like to see the little guys get pi$$ed /ubbthreads/images/graemlins/nana.gif. Then it started to get dim. Just to torture it /ubbthreads/images/graemlins/evilgrin07.gif a little more, I took out the old DMM to check the voltage across the led. Ooops! /ubbthreads/images/graemlins/ohgeez.gif I guest you're not supposed to short the led with the test leads. Ut-oh, no more light /ubbthreads/images/graemlins/frown.gif, must be dead. I let it rest for a day, and before doing a little surgery, I said, "Let's throw some very old c batteries in that thing and see what happens. /ubbthreads/images/graemlins/eek.gif Oh my! It was alive!! Back from the dead. Very dim, but alive! It has been running, at about .060 A for two days now.

Please O' LED masters, tell me how this abused, beat, and once dead 3 watter has come back to life. /ubbthreads/images/graemlins/icon3.gif
 
Re: Back from the dead!

How would checking the voltage across the LED 'short the LED'? I doubt you ruined the LED by using the DMM. If you had the DMM set to measure current, you could have shorted the flashlight by bypassing the LED. The electricity would have then taken the path of least resistance (the DMM), and the LED would not have lit. Try those original rechargeables again.
 
Re: Back from the dead!

Tried the rechargeables again, only the same dim output.
 
Re: Back from the dead!

Measuring voltage would not have shorted your light. Measuring current in the ten amp range could have heated a resistor, but only after a prolonged test. Something else is going on. Keep us posted.
 
Re: Back from the dead!

Nasty little problems are best solved by isolating one item at a time. Kinda like children.
Look for the more obvious things first, of course.
Good advice to check the health of the rechargeables.

-(a different) Craig
 
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Re: Back from the dead!

Hi,
Bad heat transfer (ie. led not properly connected to heatsink) will cause the led to light up bright blue for a while and then the led will be dead /ubbthreads/images/graemlins/frown.gif. I don't know if partially "dead" leds would let out a dim light though.
Maybe you could test the leds by connecting 3V directly across the leds, but make sure to get the anode and cathode correct.
 
Re: Back from the dead!

sounds like the led just gave up from all the abuse right at the time you got your test probes close to it. So you missed out on measuring right before it died.
 
Re: Back from the dead!

Since you need 3 batteries, I think it's a resistored DD type of light. Then you can fry the resistor if you had used the 10A current mode when testing the "voltage".
 
Re: Back from the dead!

I've killed a few LED's....just to watch them die. Don't really know what happened but I do recognize the result. Yeah, it will give you a glow of light at normal voltages (current) but that's about it. You have to almost double the input to get the light going again but then almost as soon as you do you start to smell that smell that makes you a little sick to your stomach and see that little wisp (sometimes alot!! ='<) of smoke curl up and away rather peacefully from the blackening heart of your poor dear now departed LED...
 
Re: Back from the dead!

Thanks for all of the replys /ubbthreads/images/graemlins/buttrock.gif Here is some new information:
I hooked up a 123 directly to the emitter. No good, same dim beam.

I looked carefully at the emitter, and it looks like one of the grills is out. There is a dim line in the pattern.
One final observation. I pressed on the dome, and then on the positive lead and it brightened up, but only for a few seconds.
Any ideas with this new information? /ubbthreads/images/graemlins/icon3.gif
 
Re: Back from the dead!

Hi,
I think you should send it back to get it fixed.
Measuring voltage across the led should not damage the led, and I don't think it is your fault.
Anyway, I still think that bad heatsinking was the cause of the damage.
Best luck
 
Re: Back from the dead!

I had the same thing happen b4.. the cause was bad heat sinking and the result was a luxIII that no longer lit up the way it should... under close examination only half of the emitter lit up and very dimly at that.
 
Re: Back from the dead!

Thanks for all the help /ubbthreads/images/graemlins/bowdown.gif
I'm sure that the bond between the emitter and heat sink was poor, at best. Only part of the emitter has burned out, but it still puts out a small amount of light. I will try to put it into some type of light, for fun. /ubbthreads/images/graemlins/grinser2.gif
 
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