"Breaking in" cheap CoB LED, internal configuration?

lf-mark

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Jul 14, 2016
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I'm making a quartet of lights for our folding camper (halfway between a trailer tent and a caravan: rigid base, canvas top held up with poles).

I'm using some cheapo Chinese CoB LEDs: the D0389-0422-20010, 200×10mm, for economy and compatibility with a bunch of drivers I already own and the size I want. These are billed as 14W, 1300lm units at 1000mA, 11–14V. I am running them at a constant 500mA for longevity and cooling, which seems to require about 11.4V.

They are physically arranged as an array of 42×2 chips (the 0422 in the name), and from the Vf, I'd imagine they're wired as 28p3s.

Three of the units worked perfectly on initial connection. The photos here are severely underexposed: these were too bright to look at comfortably and are photographed on a pale work surface lit by a fluorescent tube in the ceiling. You can click for larger versions:



The fourth seemed to have a section that had failed: one die appeared to be completely out of action, and ten surrounding ones were dim:



I left it running for a couple of hours as I had with the others, to check it wasn't going to fail or get too hot (mounted in an aluminium channel). When I went back to check, to my surprise, it was working fine — it is the right-hand unit in the photo below. The previously faulty die (17th down on its left-hand column) is still slightly dimmer in the photo, but its neighbours are all at full chat.



So:


  1. What is the internal "wiring" of these things, that would cause the temporary failure I saw where a section of eleven dies were not working properly due to the apparent failure of one of them?
  2. Any thoughts as to what could have happened to cause the "self-healing"?
 
Last edited:

FRITZHID

Flashlight Enthusiast
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Jun 20, 2011
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Icelandic wastelands of Monico, WI
sounds like a bad bond wire to me, after the whole strip warmed up it could easily have reconnected itself but this may only be a temporary situation. this happens alot in the cheap high power led flat packs arrays. tons of youtube vids on them.
 
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