Powering cheap 10w LED from eBay - Page 1
Forum section: electronics / beginners

author: skillz21
author_rank: Frequent Contributor
timestamp: August 06, 2019, 11:22:41 am
content: I bought some 10w LEDs off eBay for dirt cheap: I got 10 for just over $3, so I had my expectations set very, very low. I did initially test how well balanced they were, and, to my surprise, only two had dead chips, the rest were, as far as I could tell, perfectly balanced. I used one of these balanced ones for the testing that follows.The seller lists them as 10-12v, but does not list Amps. I tested them today. I set my power supply to 12v, but I was really confused when they only drew just over 200mA. I then tried increasing the voltage until they reached 10w. But, after about the 14v mark, they actually began to dim, and the colour temperature changed. After realising I was going way past the recommended spec of the LED, I dropped back down. After some experimentation, I found that the peak brightness was at around 13.5v, drawing 380ma. I was getting just over 5w, literally half of what it should be.I guess I got what I paid for. For future reference, can anyone give me some more info about these LEDs, and why they are not actually 10w?

author: amyk
author_rank: Super Contributor
timestamp: August 06, 2019, 11:34:41 am
content: Quote from: skillz21 on August 06, 2019, 11:22:41 amBecause the seller lied? Also, in case you didn't know, LEDs of such wattage need a good heatsink to run at their rated power --- if you run them without a heatsink, they will overheat very quickly.

author: skillz21
author_rank: Frequent Contributor
timestamp: August 06, 2019, 11:36:45 am
content: Yes, I have a heatsink connected.So, the seller just lied then. Thanks for clearing that up, I thought that they were such low-quality chips that they wouldn't do 10w.

author: tszaboo
author_rank: Super Contributor
timestamp: August 06, 2019, 11:56:27 am
content: You should know, that Chinese watts are less than it is defined in SI. Also hours are shorter there, thats why you can buy 10000 mAh batteries.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 06, 2019, 12:07:33 pm
content: just as 2.2lb = 1kg, 10Wch = 4.54545454545454Wsi... the thing is, you get what you pay for... a picture might help, maybe i can get some

author: ledtester
author_rank: Super Contributor
timestamp: August 06, 2019, 12:35:52 pm
content: Quote from: skillz21 on August 06, 2019, 11:22:41 amBut you got 10 of them, so your actually got 50w!

author: skillz21
author_rank: Frequent Contributor
timestamp: August 06, 2019, 01:05:01 pm
content: I was completely unaware that they had different units in china, can some give me a link/search term so I could learn a bit more about this?

author: tszaboo
author_rank: Super Contributor
timestamp: August 06, 2019, 01:32:09 pm
content: Quote from: skillz21 on August 06, 2019, 01:05:01 pmSure, here is a link about it:https://en.wikipedia.org/wiki/Joke

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 06, 2019, 02:04:07 pm
content: and this...https://dictionary.cambridge.org/dictionary/english/experiencein all seriousness... they can claim whatever they want to increase sale. half the price, double the watt... there is no standard whatsoever, only money.

author: ledtester
author_rank: Super Contributor
timestamp: August 06, 2019, 02:04:47 pm
content: It also could be they are "10W equivalent" bulbs...https://www.thelightbulb.co.uk/resources/lumens_watts/

author: amyk
author_rank: Super Contributor
timestamp: August 07, 2019, 12:04:48 am
content: Quote from: ledtester on August 06, 2019, 02:04:47 pmAccording to that chart a 5W LED would be around 30W incandescent equivalent...

author: sleemanj
author_rank: Super Contributor
timestamp: August 07, 2019, 12:56:21 am
content: Ok there is either,a> something wrong with your measurement/supply; orb> these are not bare ledspost a photo of the led, or a link to the listing.You drive bare LEDs with a constant current (or at least with a suitable resistor to limit the current), typical 3x3 die arrangement 10W leds should be run at about 900mA, and the much less typical single series arrangement of die should be run at about 300mA.

author: John B
author_rank: Frequent Contributor
timestamp: August 07, 2019, 03:09:50 am
content: If it is one of those 3x3 die 10W chips on ebay or ali express, as you've discovered they are generally rubbish.However if you find them cheap enough, they can have their purposes. I've made a few light bars with 20 or more of these chips in parallel, with each chip running under 100mA and no heatsink. Generally this is frowned upon due to the uneven current distribution from manufacturing variation, but I haven't found an issue when all the chips are running just on the start of the conduction curve. They're in use all day.

author: Brumby
author_rank: Unknown
timestamp: August 07, 2019, 04:06:46 am
content: Quote from: skillz21 on August 06, 2019, 11:22:41 amThat's a sound philosophy you need to keep in mind at all times.When you see "cheap" there will be a reason. Maybe it's an oversupply someone wants to clear out - or maybe they're substandard in some way.When you see "cheap" from China there will be a reason - and the clearance of an oversupply is NOT likely to be one of them. (It's not impossible - but it's not the value bet.)

author: sleemanj
author_rank: Super Contributor
timestamp: August 07, 2019, 04:51:34 am
content: Quote from: John B on August 07, 2019, 03:09:50 amIf die matching is anything to go by, and opinions differ, but there is very high variability in "quality", I test and "grade" my batches of 10W leds, one batch I can get they will all match perfectly at 10 or less microamps, other batches a few hundred microamps, and other batches you have to push 10s or even more milliamps to get all the die lit.Even in good batches I get I find one or two bad ones.Just the usual Chinese "QC".

author: skillz21
author_rank: Frequent Contributor
timestamp: August 08, 2019, 09:21:09 am
content: Quote from: sleemanj on August 07, 2019, 12:56:21 amHere's the link:https://ebay.us/zCxCaz. I bought the cool white.

author: sleemanj
author_rank: Super Contributor
timestamp: August 08, 2019, 10:16:40 pm
content: Listing doesn't say but I'd wager they are 3x3, and there is something wrong with your measurement setup or supply. You should have no trouble, with a current limited supply which is capable of providing 10W at 10-12v, of pushing 900mA through these.At it's most basic, get a 12v 1A+ supply, and a 2.7 Ohm 5 Watt Resistor will be in the ball park. Remember you can measure voltage drop across the resistor and calculate current rather than adding multimeter current shunt into the mix.

author: skillz21
author_rank: Frequent Contributor
timestamp: August 09, 2019, 12:58:45 am
content: Quote from: sleemanj on August 08, 2019, 10:16:40 pmI have a buck converter that is capable of supplying up to 3A (I tested by setting a current limt and shorting the output), If this is the case, I also tested with a much beefier power supply, still the same result. What's the difference between using a resistor and the built in current shunt of my multimeter??

author: sleemanj
author_rank: Super Contributor
timestamp: August 09, 2019, 06:41:19 am
content: Once again, LEDs are current controlled.Your current shunt in your multimeter is like 100mR maybe.The forward voltage of a white led is around 3-3.3v, your LED will have a 3x3 arrangement giving a forward voltage of 9-10v.You supply 12v, through a 100mR resistor (shunt) to your 9-10v LED, how much current are you pushing (or attempting to make the power supply push), use Ohm's law.

author: skillz21
author_rank: Frequent Contributor
timestamp: August 09, 2019, 01:09:00 pm
content: Quote from: sleemanj on August 09, 2019, 06:41:19 amI feel like I'm missing something here, so please correct me if I'm wrong. The listing said 9-12v, so I'm guessing that it's fine to drive them at a bit higher than their forward voltage... right? As for the current, going off their maximum recommended voltage of 12v, I should be trying to push about 830mA to achieve the advertised 10w... right?

author: Audioguru again
author_rank: Regular Contributor
timestamp: August 09, 2019, 02:21:12 pm
content: Quote from: skillz21 on August 09, 2019, 01:09:00 pmWhy do you think the ad for the extremely cheap LEDs is truthful? Maybe the LEDs are defective and will never draw as much current as you calculated without burning out.

author: soldar
author_rank: Super Contributor
timestamp: August 09, 2019, 03:12:51 pm
content: A lot of these people selling on eBay from China have no idea about what they are selling. To them 500,000 mAh and 100 W are just labels they stick on products. I hope no one thinks Chinese engineers are selling stuff on eBay.Whenever I have bought stuff like that, that did not measure up to the specs published in the listing, I have messaged the seller with a detailed explanation, photos of the testing setup and of the readings, and they have always, invariably reimbursed my payment. If it is worth your time you can do it.As I say, most of the time the sellers have no idea what they are selling and I have ended teaching them some electronics. Some sellers just copy the text of a similar listing and you end up with an AC item when it was listed as DC, or a battery with tabs when it was listed as no tabs, etc.

author: sleemanj
author_rank: Super Contributor
timestamp: August 09, 2019, 09:50:14 pm
content: It is not a magic led, it has no active current control, no built in resistance, it is just 9 led die arranged in a 3 parallel strings of 3 in series, you need to drive it properly like any other led, you hang it on an unrestricted power supply above the fwd voltage (~10v) then it will not survive long and will fail in some way, yours appears to be failing to a high resistance state.Get a fresh one you have not abused, dial your current limit to 900mA or use a 2.7R-ish 5W resistor, and try again.

author: skillz21
author_rank: Frequent Contributor
timestamp: August 10, 2019, 12:25:47 am
content: Quote from: Audioguru again on August 09, 2019, 02:21:12 pmI don't think that it's truthful. @sleemanj is telling me that the listing was correct and that I'm not powering it correctly.