1 watt, 10mm ebay leds - Page 1
Forum section: electronics / projects

author: gobo
author_rank: Newbie
timestamp: October 26, 2014, 07:36:42 pm
content: been working on an outdoor landscape lighting project. trying to use1W 10mm white leds from ebay (china). most likely these leds arerejects or seconds of some sort. they work fine for a few weeks thenbegin to turn blue, get dimmer and then die.they are driven with a pwm current limited supply, I=0.21A, or about0.6 watts. on the bench, the leds run about 88 degrees F (31C).i took one of these leds and fried it just to see what would happen.my bench supply is limited to 2A, so i couldn't hit it harder than that.while cranking it up one of the bonding wires went poop. that wasanticlimactic. tried again not going so fast. it went from warm whiteto blue, then the chip turned black and it went out. oops. but ididn't think to measure the temperature while i did this.in the ones brought in from the yard, most look ok. well... those thati could scrape the silicon goo off of. the ones in 3m 5200 had to betossed. one had a thin black line at the bottom of the chip. (bondingproblem? don't have a microscope.) one did have the yellow die turnedblack.so what's the deal with these things? are they just that crappy?

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 08:09:03 pm
content: Probably they were regular 20mA 10mm LED units that were mislabelled and sold as 1W units. 10mm led packages are not capable of any thing like 1W of power handling, seeing as the only heat path out is via the leads, and a 20mA die is thermally limited to this same path and will have the same limit of around 100mW. They are just being grossly overdriven. Basically fakes.That they go blue before failure and have a black burnt inner layer is an indication of very high temperature internally first breaking down the colour changing phosphor overcoat and then the black is decomposition of the binders in the layer and the clear casting resin around the die.

author: george graves
author_rank: Super Contributor
timestamp: October 26, 2014, 08:19:52 pm
content: There is a forum calledhttp://www.candlepowerforums.com- it's basically all about LED's. They even got some decent testing going on there.In this threadhttp://www.candlepowerforums.com/vb/showthread.php?89607-White-LED-lumen-testingsearch for "Jeled" and 10mm. There is an ebay seller (named Jeled) selling a 10mm LED with 5 chips in it. I'm not sure how they deal with heat - perhaps the 10mm plastic is helping some what with that(?) - and they didn't do any long term testing.Note the extended part of the leads. Must be to help carry the heat away.If you fond some very bright 10mm LEDs - please let me know - I'm looking for something like that as well.Quote

author: gobo
author_rank: Newbie
timestamp: October 26, 2014, 08:38:35 pm
content: fakes, yeah probably. their construction is drastically different from some old AND 20ma 10mm parts i have. these may not be 1W devices, but they are not 20ma devices.i knew there would be a heat problem, so they are mounted to not quite a square inch of copper pcb. soldered as close to the component body as i could get. it's not much of a heat sink, and i've not calculated it. it was just what i could make fit.Quote from: SeanB on October 26, 2014, 08:09:03 pm

author: gobo
author_rank: Newbie
timestamp: October 26, 2014, 08:48:04 pm
content: i stumbled onto that forum searching for chinese led failure modes. they claim the 1W devices are not. but i kind of thought that would be the case. with some of my own testing, i found that dissipating 1W and 0.5W did not appreciably change the light output. so i grabbed the closest resistor and ended up 0.602W.these are single chip. but they have the larger leads and bonding as can be seen in that photo. i've not seen any 5-chip in a 10mm package.Quote from: george graves on October 26, 2014, 08:19:52 pm

author: george graves
author_rank: Super Contributor
timestamp: October 26, 2014, 09:10:39 pm
content: Quote from: gobo on October 26, 2014, 08:48:04 pmhttp://www.ebay.com/itm/290559381321?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIThttp://www.ebay.com/itm/250856878048?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

author: gobo
author_rank: Newbie
timestamp: October 26, 2014, 09:55:19 pm
content: have you purchased any?Quote from: george graves on October 26, 2014, 09:10:39 pmhttp://www.ebay.com/itm/290559381321?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIThttp://www.ebay.com/itm/250856878048?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

author: george graves
author_rank: Super Contributor
timestamp: October 26, 2014, 09:56:47 pm
content: Most likely will this week, unless I can find something better to test out.