Very quick question - Page 1
Forum section: electronics / beginners

author: LinkZ
author_rank: Contributor
timestamp: August 11, 2015, 08:44:07 pm
content: Hi, I bought lots of those leds:http://www.aliexpress.com/item/10-pcs-white-3W-High-Power-Chip-light-bead-emitter-LED-Bulb-Diodes-Lamp-Beads-with/2040746197.html.My question is: do those leds require an heatsink, or the one integrated is enough?

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2015, 08:51:14 pm
content: The page linked doesn't appear to exist.... Allexpress 404 error.Please change the thread title to something meaningful. "Very quick question" doesn't convey any useful meaning.

author: grumpydoc
author_rank: Super Contributor
timestamp: August 11, 2015, 08:57:33 pm
content: Quote from: Gyro on August 11, 2015, 08:51:14 pmThere's an extra "." at the end which needs to be removed. The page ishereQuote+1I can't see a datasheet but a couple of square cm of ali is going to be in the region of 25-30oC/W (Edit: on reflection probably abithigher) so if you like your LEDs 90oC or so above ambient it will be fine, otherwise I'd bolt them to something.

author: Augustus
author_rank: Regular Contributor
timestamp: August 11, 2015, 09:06:54 pm
content: They definitely need additional heatsinking if you want to drive them at full power...

author: Gyro
author_rank: Super Contributor
timestamp: August 11, 2015, 09:07:16 pm
content: QuoteDarn, should have spotted thatAt 3W I'd agree that it's much more of a heatsink coupler than any sort of heatsink.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 12, 2015, 06:49:57 am
content: No heatsink is needed under most circumstances. For example if you are just soldering them up to 1mm square cable that you salvaged and they are suspended in air, never need any heatsink. If they are in metal fitting never need a heatsink. Think of each one as a most pitiful 3w soldering iron, you can sit there with it on the cable all say long and that cable ain't going to get any hotter because it is dissipating the 3w as fast as it can get in there. at 10w you would want a heatsink more. Cable is a heatsink, and if it was flat on a metal fitting, then it won't do much heating at all. So no heatsink for this one. You could tell for sure by posting pics of how you fit it to something, or testing it and seeing if it gets hot beyond maybe 70 or 80 degrees. At the price you can really afford to test them to destruction.

author: codeboy2k
author_rank: Super Contributor
timestamp: August 12, 2015, 07:12:09 am
content: It's times like this when I wish I had an IR camera; I have some of those 3W leds, and I've driven them in still-air at 1W without any heatsink or star carrier as in the picture. I had them running like that for about an hour. They were much too hot to touch but I have no idea of their actual temperature.There was no brightness change, and no "hot smell of silicon", so I think they were OK, and they still work now, but I admit I was running them blind. But at just 33 cents each, I didn't care at the time.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 12, 2015, 07:20:19 am
content: You can improve the effectiveness of wire to be a heatsink. Look at thishttps://wannatinker.wordpress.com/2012/05/26/wire-heat-sink-for-to39-transistors/One image is included here as 'fair use' commentary on the page which belongs to, as does the image, to 73, Dick, W6BKY "wannatinker"

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2015, 05:37:36 pm
content: That brings a whole new dimension to the Luxon StarThe only concern is the amount of heat you end up pumping in whilst soldering it together.

author: Chris C
author_rank: Frequent Contributor
timestamp: August 12, 2015, 05:59:59 pm
content: Quote from: codeboy2k on August 12, 2015, 07:12:09 amLOL. Yup, you can get away with a lot for tests. A few times when I didn't want to bother with a heatsink, I've run LEDs and other components in a cup of water!But just to be clear, if too hot to touch, LED lifetime does drop. Expect a few months at best. White LEDs in particular like to be kept cooler still, as the phosphors that convert the blue LED light to white degrade at a lower temperature than the silicon.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 12, 2015, 06:04:12 pm
content: Quote from: Gyro on August 12, 2015, 05:37:36 pmglad you like it. Yes, a temperature controlled soldering station is your friend there.

author: ez24
author_rank: Super Contributor
timestamp: August 12, 2015, 06:12:58 pm
content: QuoteHow about using a cheap IR meter, likehttp://www.amazon.com/Etekcity-Lasergrip-Non-contact-Thermometer-Temperature/dp/B00837ZGRY/ref=sr_1_1?ie=UTF8&qid=1439403094&sr=8-1&keywords=ir+thermometercould this be a poor man's FLIR ?

author: Chris C
author_rank: Frequent Contributor
timestamp: August 12, 2015, 06:19:45 pm
content: Quote from: ez24 on August 12, 2015, 06:12:58 pmThey work OK. Just remember that you'll want to use them close up, so that the hot component fills the entire sensor field-of-view. And that at that distance, the laser pointer that these usually include doesn't indicate the field of view, so don't use it as a guide. Just move the meter until you get the max reading.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2015, 06:27:05 pm
content: Although you do need to worry about emissivity a bit - especially if you're spending most of your time measuring uncoated aluminium (not sure about PCB material). You might be as well off with a cheap thermocouple one and a reel of kapton tape.

author: codeboy2k
author_rank: Super Contributor
timestamp: August 13, 2015, 03:19:07 am
content: Quote from: Chris C on August 12, 2015, 05:59:59 pmGood to know. These days I have some Kapton tape handy, so the next time I get a chance to run them up like that I'll do what @Gyro suggested and tape a thermocouple to the bottom of one of them (on the exposed metal there) and get a better reading.Then assuming a worst case 1 degC/W thermal resistance from junction to case, I can estimate the die temperature at about 1 degree higher than the measured temperature (at 1W power)

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 13, 2015, 03:41:52 am
content: Sharp spec sheet says 85C max. Alibaba spec sheet mentions 50000 hours life. So you can afford to lose life (though most of those life specs assume 30% loss of brightness at EOL) if you are out of your teens or you don't need your grandkids to use this light. Life will go down rapidly as you go above 85C so it would be good to verify that a simple heat sink is enough. Particularly if you live in a hot climate where you start at 40-50 C.More concern than life is all of the warnings on time out of package and RH when soldering. These repackaged parts probably aren't so carefully environment controlled, so time in a dry box or other means will probably be needed to avoid "popcorn" failures.