Mounting 10w LEDs  to aluminum flat bars - Page 1
Forum section: electronics / beginners

author: ez24
author_rank: Super Contributor
timestamp: November 01, 2015, 02:28:33 am
content: HiI have some 12v power supplies and need more light. I would like to get some of thesehttp://www.ebay.com/itm/10pcs-10W-LED-pure-White-High-Power-Bright-900LM-LED-Lamp-SMD-Bulb-Chip-9-12V-DC-/231052870552?hash=item35cbd30398:g:77EAAOxyxnJR6Qjzand mount them to aluminum angle bars that I have. I do not want to get into drilling and screwing. I would like just to glue these to the aluminum.Are there any glues that would work? I also have some small heat sinks that have self stick on them so if I can glue these LEDs I could stick some heat sinks on the other side to help.thanks

author: deadlylover
author_rank: Frequent Contributor
timestamp: November 01, 2015, 02:50:32 am
content: Look for some thermal adhesive.You should be able to find some Arctic Silver Thermal Adhesive pretty cheap at any decent computer shop. Keep an eye on temperatures though, thermal adhesives aren't the best performers.

author: fivefish
author_rank: Frequent Contributor
timestamp: November 01, 2015, 02:57:16 am
content: I did the same thing, mounted these LEDs on an aluminum panel.https://www.eevblog.com/forum/beginners/cost-effective-magnification-solutions/msg789758/#msg789758I would discourage you from gluing them.... not unless it's not permanent glue and you can easily remove the glue and replace the LED units.Each unit have several LEDs embedded in it. But on some of the units I got, there may only be (2) good tiny LEDs working. As time goes on, more tiny LEDs stop working, or start to consume more and more current. You definitely want to be able to replace the bad LED units down the road with good ones.

author: nowlan
author_rank: Frequent Contributor
timestamp: November 01, 2015, 03:01:42 am
content: SEKISUI #5760 thermal tape

author: ez24
author_rank: Super Contributor
timestamp: November 01, 2015, 03:09:58 am
content: Quote from: fivefish on November 01, 2015, 02:57:16 amThis is where I got the idea - thanksLooks like tape for me

author: Marco
author_rank: Super Contributor
timestamp: November 01, 2015, 03:12:38 am
content: There are thermally conductive epoxies (or you could make your own) butthisshould be strong enough and is probably easier to remove.

author: SeanB
author_rank: Super Contributor
timestamp: November 01, 2015, 07:23:59 am
content: I use Pratley quickset steel, but pretty much any 2 pack epoxy will work for this, preferably a quick setting one. Clean the aluminium bar with soap and water first, then at the places the LED units will mount use some 200grit wet and dry paper with soapy water to clean the surface, or do the whole one side for a consistent look, then wash again with water and dry with a clean paper towel. then place a drop of the epoxy in each spot and place the LED, complete with leads soldered to them ( going to be hard to solder on afterwards if the thermal resistance to the bar is low) and press down firmly, so you see a little come out on all sides, then hold down with some painters tape till the epoxy has cured.

author: Zero999
author_rank: Super Contributor
timestamp: November 01, 2015, 10:46:10 am
content: Quote from: ez24 on November 01, 2015, 02:28:33 amI hope you're aware that these LEDs require a constant current source and are not designed for direct connection to 12VDC. If you connect them directly to a 12VDC power supply there's a good chance they will draw more than 1A, overheat and fail.I would advise using a current regulator and running them at less than 1A. I'd recommend 0.7A as it will maximise their efficiency, life and reliability and won't reduce the brightness by much.

author: fivefish
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:55:45 am
content: I have (3) of them connected in series and just connected directly to my PSU. I have my PSU adjusted to about 27Volts.At about 27Volts supply (roughly 9V per LED), it's already pretty bright (hard to look at them directly). Current is 0.47Amp for the whole string.No problems.

author: Zero999
author_rank: Super Contributor
timestamp: November 01, 2015, 11:01:48 am
content: Quote from: fivefish on November 01, 2015, 10:55:45 amYes it can be done, as long as you assume the minimum specified VFper LED and accept the current will be under half the rated value. I've done it myself before.However it is not recommended and in this case using a DC power supply equal to the maximum specified VFis going to cause problems.

author: ez24
author_rank: Super Contributor
timestamp: November 01, 2015, 05:06:02 pm
content: Quote from: Hero999 on November 01, 2015, 10:46:10 amI have something like thishttp://www.ebay.com/itm/AC-100V-265V-To-DC-12V-10A-120W-Power-Supply-for-3528-5050-LED-light-strip-/261556717484?hash=item3ce5fec7ac:m:mF8e6Pqj8e0kl827hmLIR8Aand I see there is no current limitation. Would I set up individual current limiters (.75a) to each LED or set up say 7.5a limit from the PS (for 10 leds in parallel)Then (sorry for this) how would I do this ? I am not worried about efficiency because I would use this light for short periods of time. Using power resistors may be too inefficient but I do have a bunch of 300w variable 2 ohm resistors and winter is coming. I also have a bunch of 317sEdit: Or should I just toss the PS and get the right kind?thanks

author: Zero999
author_rank: Super Contributor
timestamp: November 01, 2015, 07:27:25 pm
content: Quote from: ez24 on November 01, 2015, 05:06:02 pmThat power supply is designed for LED strip which already has resistors built-in and can run directly off 12V DC.The simplest way to do this is to add a resistor in series with each LED. It's not easy to predict the current accurately since the forward voltage can vary both with the current and temperature and there's hardly any headroom. Start with a 3.3Ohm resistor rated to 5W or more.Another option is to build a constant current sink using a couple of transistors.RG= 10kRS= 1R

author: fivefish
author_rank: Frequent Contributor
timestamp: November 01, 2015, 08:58:46 pm
content: One thing I've learned is having only all cool white LED colors is un-natural looking. And I think a mix of both cool and warm LED lights is the way to go... (the ratio of cool/warm units I don't know yet). I'll buy some warm white LEDs to play with it.On my bench, having the fluorescent lights ON, in combination with the cool white LEDs give a nice color render and lots of available light.But using just the LED lighting alone, I didn't like it.

author: onlooker
author_rank: Frequent Contributor
timestamp: November 01, 2015, 10:15:09 pm
content: I just modified my son's 35W halogen goose neck table lamp to use such 10W LED ($0.75 each).I decided to use one of the many 12V/18W SMPS I have as the 1st stage (CV) supply. The CC driver is from Ebay which cost $1.13 each. This CC driver is speced for 0.9A (the IC PT4115 can supply 1.2A) and has a diode bridge to take AC input.For my use, I removed the diode bridge and changed the current sensing resistor to supply 0.7A. The CC driver, now, consumes about 0.5W, instead of, about 1.5W for if using a resistor (my 12V supply is unregulated and actually supply 13V+).The temperature of the CC driver is stabilized at about 50C. But, at 0.7A and without using thermal paste, the LED base reaches about 80C+. I am not sure if my heat-sink is adequate or if I can get by without using thermal paste.BTW, does anyone have the explanation as to why the 3 leds in series have very different brightness at 20mA, but about the same brightness at 200mA? I just feel that bad Ebay/Chinese quality that some youtube attributed this to can't really explain it. Eye-light sensitivity is not the correct reason either since I looked into the LED with a dark-welder glass.

author: ConKbot
author_rank: Super Contributor
timestamp: November 02, 2015, 04:36:02 am
content: Quote from: onlooker on November 01, 2015, 10:15:09 pmSome led dies have a minimum threshold to turn on, the luminus devices "big chip" leds (at least the cst 60 and 90 of a few years ago ) for example have a minimum specified current of 1A. Under 1A it might dim fine, only partially illuminate the die, or just not light at all.On a array led like that with multiple series strings in parallel, the Vf of each string will vary, so current will vary. Some strings may not have enough current to light up, some may get less and be dimmer, etc. Good array leds will be matched so that the vf of the strings works out to close to the same value, and so that the color temperature of the final array is within a certain value. I'd imagine a cheap array manufacturer gets the array or tray of dies, slaps them down, wire bonds them, encapsulates it and calls it done.As for attaching them, ones with a metal base plate like that aren't a particularly high density heat source (the wattage is spread over a big area) so if you can't screw it down and use thermal paste, and don't want to shell out for thermally conductive adhesive like arctic alumina thermal adhesive, feel free to use normal epoxy if you can compress it hard enough while curing to get a super thin bond line. I've used jb weld to attach LEDs before and if you're not running everything on the hairy edge, it's fine.

author: Nerull
author_rank: Frequent Contributor
timestamp: November 02, 2015, 05:15:44 am
content: Quote from: SeanB on November 01, 2015, 07:23:59 amMost two part epoxies are going to have awful thermal conductivity so there had better not be any between the LED and the heatsink. They also get soft when heated, so watch for that.

author: ConKbot
author_rank: Super Contributor
timestamp: November 02, 2015, 12:34:36 pm
content: Quote from: Nerull on November 02, 2015, 05:15:44 am0.218 W/m·K for MG chemcials 832HT epoxy encapsulant (most epoxies dont have thermal conductivity listed, so lets call an epoxy potting compound close enough)Ive seen 7.5 W/m·K thrown around for arctic alumina thermal adhesive.Expand that back out (W*T)/(L*W*K). T, L, and W being thickness, length and width in meters. Eyeball that LED to be ~12mm square (144*10^-6 m^2 for L*W), and a 5 mil (0.127mm) bondline, and 10w of heat dissipated by the 10W ledPlug the numbers in, get K^-1, inverse it to get K.The relatively shitty non-thermal epoxy potting gets ~0.5K across the bondline. The relatively good thermal epoxy gets 0.015K across the bondline. Is the thermal adhesive better? Yes, obviously. Is it needed not unless 0.485 degrees hotter is gonna break the thermal budget thoughIf you can get the compression to keep the bondline thin, for a heat source like a LED (large area per watt) if you're not running it to the extreme and want the led performing at its absolute max it really doesnt matter

author: wraper
author_rank: Unknown
timestamp: November 02, 2015, 12:39:29 pm
content: Quote from: nowlan on November 01, 2015, 03:01:42 amThis tape is good adhesive but it's not thermal. At least manufacturer itself don't know about this. For some reason all Chinese sellers advertise it as the thermal adhesive.