10 watt LED and power supply - Page 1
Forum section: electronics / general

author: slburris
author_rank: Frequent Contributor
timestamp: September 17, 2010, 09:21:41 pm
content: More neat stuff I picked up from Sure electronics. A 10watt LED on a heatsinkplus a 1.5amp constant current supply:http://www.sureelectronics.net/goods.php?id=340http://www.sureelectronics.net/goods.php?id=1125The LED I received looks essentially like it does on their website. No markingson it that I could see. I removed the screws and there was heat sink compoundbetween it and the heat sink. No idea who actually makes this LED, could it befrom Seoul Semiconductor? Looks like there 4 dice inside.The power supply is actually two converter boards. They are paralleledon a carrier board to provide the 1.5amp constant current. The carrierboard places them a little too close together. The converters don't bothfit well, so either these boards need to be trimmed more, or the carrier boardisn't laid out correctly. Still it's possible to smash them together as shown.I've tested the LED with an external supply -- it is very bright. I accidentallylooked at the LED while it was on, and I was seeing afterimages for about 10minutes. The heat sink didn't seem to get very warm, so that's encouraging.Next up, I need to test the converters. My plan is to build this into a floodlightfor some nice LED lanscape lighting. I'll use this as a wall washer type light.Two LEDs should be about 900 lumens -- I think that's sufficient for what I havein mind.Scott

author: slburris
author_rank: Frequent Contributor
timestamp: September 18, 2010, 10:52:09 pm
content: Time for some testing!I soldered the boards into their carrier, wired up a power supply and connected theoutput to the 10w LED on a sink.In the first picture, you can see that the supply is providing 1.238amp to the LED,measured with my UniTrend UT70D meter. I put a large washer with a hole overthe LED, otherwise it hurts my eyes to be this close.Next, you can see the power supply which is feeding this. 11.98v at 0.956amp.Things are heating up, so let's pull out the IR thermometer.Continued in next post.....Scott

author: slburris
author_rank: Frequent Contributor
timestamp: September 18, 2010, 11:11:29 pm
content: In the first photo, we're measuring the temperature of the heatsink, 89F.The second and third photos are the temperature at the middle of eachof the two buck converter boards. They seem to be be pretty evenly matched.The last photo is the setup with the washer removed. Although the LED looksbright, the iPhone camera doesn't have the dynamic range to fully capture howbright this is compared to its surroundings.All in all, I'm pretty happy with both the LED and the power supply. Next I'llbe integrating it into a floodlight case and see how it looks as a landscape light.Scott

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2010, 08:32:49 am
content: Quote from: shafri on September 19, 2010, 04:17:02 amBecause it requires a constant current source and a battery gives constant voltage. You can use a power resistor but the efficiency will be poor and the LED will dim as the battery voltage drops. A SMPs such as the once shown above wastes little power and the LED stays the same brightness until the battery voltage drops too low for it to work properly.

author: slburris
author_rank: Frequent Contributor
timestamp: September 19, 2010, 02:42:05 pm
content: Quote from: shafri on September 19, 2010, 04:13:49 amNote that LED sees about 8 volts at 1.2amps, which is close to 10 watts.The forward voltage of the LED is 8 volts (I think because there are 4 LEDswired in series). The switcher has a constant current output, instead of theusual constant voltage output, which is what you want for driving LEDs.Scott

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2010, 05:47:05 pm
content: Quote from: shafri on September 19, 2010, 03:37:49 pmWell the minimum current is specified at 1.3A and he measured 1.238A which is still a little low so perhaps his meter isn't very good? Either way, it doesn't surprise me it doesn't match up to the specification, being cheap and Chinese.

author: slburris
author_rank: Frequent Contributor
timestamp: September 19, 2010, 06:44:14 pm
content: Quote from: Hero999 on September 19, 2010, 05:47:05 pmNo, the problem is that at 12 volts input with an 8 volt LED the constant current supply doesn'thave enough headroom to supply the specified current. If I increase the voltage toaround 15 voilts or higher, I get 1.5 amps.I haven't studied the design well enough to figure out why this is, but for my landscaping application,1.2amps is fine.Scott

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 19, 2010, 07:22:59 pm
content: Quote from: slburris on September 19, 2010, 06:44:14 pmThat's logical and it happens all the time ,because we always forget to calculate the energy losses in the equitation.I bet that even the carrier board gets hot too !!

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2010, 07:39:54 pm
content: That makes sense.To be honest, I thought it could've been that but I thought a drop out voltage of over 4V was too poor.I can't think why, the data sheet for the MBI6651 implies it uses a low side driver, had it been an N-MOSFET switching the high side it would've made sense. It's probably something obvious I've missed.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 19, 2010, 07:40:48 pm
content: Quote from: Kiriakos-GR on September 19, 2010, 07:22:59 pmyes the energy loses, but..... when it says 1.5A out, then it should be 1.5A out, i dont care, they should already calculated it for us. but the cheapo unbranded reason is acceptable.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 19, 2010, 07:44:20 pm
content: Quote from: shafri on September 19, 2010, 07:40:48 pmBlame the white papers , and the reference boards ....

author: slburris
author_rank: Frequent Contributor
timestamp: September 19, 2010, 07:49:11 pm
content: Sure Electronics has this little graph on their website:Which seems to match my experience pretty closely.Scott

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 19, 2010, 07:55:23 pm
content: Wait a minute Scott , just noticed that you are using testing cables with crocks !!Well that's an mistake, causing extra losses ... Use proper cable at list 0.75mm diameter ..

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2010, 07:56:37 pm
content: Quote from: slburris on September 19, 2010, 07:49:11 pmYou say little graph, I can hardly read that.Apart from being too small it's saved in low quality JPG format which is fuzzy, especially when zoomed in, which might be deliberate.

author: Simon
author_rank: Unknown
timestamp: September 19, 2010, 09:22:22 pm
content: 66% efficiency does not sound very good, considering the controllers are targeted at a specific current they will always operate at they should have nailed it at 80-90% for the target output

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 19, 2010, 09:51:13 pm
content: With out the use of proper wires - cables .. what ever , any measurements are inaccurate .For 1.5 A constant juice , 1mm or 1,5mm car cables are the minimum diameter , that will keep them cold enough, so to not have an high resistance or thermal losses ..

author: slburris
author_rank: Frequent Contributor
timestamp: September 19, 2010, 10:26:55 pm
content: Quote from: Simon on September 19, 2010, 09:22:22 pmI'm not sure I follow your calculations.The input is 11.98v @ 0.956a, which is 11.54 wattsOutput is 8v (if the datasheet on Vf for the LED is right) @ 1.238a, which is 9.90 wattsDividing 9.90 by 11.54, we get 0.857 or 85.7%With alligator clips and less than ideal wire sizes, this is a lower bound onefficiency. Wired into the landscape system, which is 16gauge wire --1 mm for the metric world (everyone but the US it seems),I don't expect any issues.Scott

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 20, 2010, 12:37:29 am
content: Quote from: slburris on September 19, 2010, 10:26:55 pmI do not see why, just the words are stopping you from testing it , with better cables.

author: Simon
author_rank: Unknown
timestamp: September 20, 2010, 06:32:43 am
content: Quote from: slburris on September 19, 2010, 10:26:55 pmyes sorry your right I forgot to consider the lower current in, another silly late night post

author: Zero999
author_rank: Super Contributor
timestamp: September 20, 2010, 06:56:49 am
content: Quote from: Kiriakos-GR on September 19, 2010, 09:51:13 pmIt depends on the length of the cables.Have you actually done any calculations or are you just guessing?0.5mm2should be more than enough to satisfy the thermal requirements and shouldn't effect measurements too much for short runs (under a meter).The resistance of a two core 0.5mm2piece of cable is 93m? per meter, if the current is 1.5A the loss will be 209mW, if the power dissipated by the LED is 10W the inaccuracy due to the cable is just under 2.1%.Even better, measure the voltages directly at the board (which is what he's doing according to the photograph), that way the cables will be taken out of the equation.