Author Topic: LEDs overheating  (Read 5185 times)

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FoggyNotion

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LEDs overheating
« on: March 21, 2016, 03:44:32 PM »
Hey gang, I hope you can help me.
I purchased some 12 volt LEDS for my camper interior, and I began to notice a smell like burning plastic, it even made me ill.  I discovered it was coming from the light fixture and I removed the LED only to find it very hot.
These probably came from China, but I assume by now the know how to make things correctly.  It was always my understanding that LEDS don't get hot.  I also assumed I need only replace the bulbs, and no rewiring involved.  Any comments?  Thanks.
« Last Edit: March 22, 2016, 01:30:57 AM by DamonHD »

Mary B

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Re: LEDs overheating
« Reply #1 on: March 21, 2016, 04:47:45 PM »
LED's do generate heat, they are far more efficient than an incandescent or CFL but some heat is still there. You may need to modify the fixture to allow some air flow for cooling.

"The energy consumed by a 100-watt GLS incandescent bulb produces around 12% heat, 83% IR and only 5% visible light. In contrast, a typical LED might produce15% visible light and 85% heat.

Especially with high-power LEDs, it is essential to remove this heat through efficient thermal management. Without good heat sinking, the internal (junction) temperature of the LED rises, and this causes the LED characteristics to change. "

http://www.ledsmagazine.com/articles/2005/05/fact-or-fiction-leds-don-t-produce-heat.html

Pair of 7 watt LED's mounted on an old CPU heatsink. I had to fan cool it or it over heated!







I use one of these as a front door light and it lights up a good part of the yard. Also use one over my desk as a light running off my solar battery bank. Building single ones for room lighting all over the house.
« Last Edit: March 22, 2016, 01:31:19 AM by DamonHD »

Bruce S

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Re: LEDs overheating
« Reply #2 on: March 22, 2016, 07:00:28 AM »
Mary B
Is correct! I'm not using anything as high-powered as hers, but even down in the 1 watt area cooling is necessary.
Using lesson from GHURD, Commanda & Rich Hagen, I've been toying with lowering the current. Since there is a point where the light amount is just noticeable I have lowered the current  to 75% of max . Cooling is still necessary but not as much. 66% seems to my eyes the lowest before I really notice.

Mary B? is that standard chip paste your using? OF did you go with the newer high-temp stuff?

Cheers
Bruce S
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richhagen

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Re: LEDs overheating
« Reply #3 on: March 22, 2016, 08:10:36 AM »
I have been building LED lights for a number of years.  An early example here:
http://www.fieldlines.com/index.php?topic=131303.0
a couple of those were installed in Fiji and were still working to the best of my knowledge up until cyclone Winston took the ceilings they were attached to away this year.  An extra one I built still lights my basement kitchen tied directly to a solar panel to this day. 

They are driven by a circuit I learned from one of my favorite people, Commanda, which was part of the Master Class Faq posted in the LED lighting section here. 
http://www.fieldlines.com/index.php/topic,131217.0.html
In this way the current can be limited even with significant changes to supply voltage.  A buck converter could be used to feed it if optimum efficiency is a concern. 

I tend to drive LED's on lights I have at half of their rated current or less.  Heat degrades the phosphor's used in white LED's and changes the color output overtime.  Heat is the enemy of longevity in LED's.  So if I build something to last I want it to run cool.  The case on these is a giant passive heat sink as well so there is nothing to break and no power requirement. 

Here is a current smaller iteration from a batch I finished a couple days ago intended as part of a batch I tend to send out as relief supplies. 

9614-0



















It uses Cree LED's mounted on what have become standard 20mm Star aluminum bases and is driven at approximately 400mA.  At 9-12V supply voltage it runs cool, with current increasing to full at around 12V where it consumes about 4.8W.  The light becomes warm to the touch after running for extended time at higher supply voltages.  It is intended to be run from a 12V battery, however, it can be connected directly to 12V panels, running at up to 20V, it just will run a bit warmer as the driver will essentially be wasting 3.2W to heat which is dissipated by the case.  These are not built to optimize efficiency at higher voltages, but to survive. 

9615-1



















Heat is the enemy of longevity in these.  Rich
A Joule saved is a Joule made!

Bruce S

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Re: LEDs overheating
« Reply #4 on: March 22, 2016, 01:51:11 PM »
Rich;
Thanks for posting those! Still a very nice build.
I wonder how the unit in the Philippines are doing.

Cheers
Bruce S
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Mary B

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Re: LEDs overheating
« Reply #5 on: March 22, 2016, 02:30:44 PM »
Thermal adhesive pads. Otherwise I would have needed to tape micro holes in copper... and I hate tapping copper.

Mary B
Is correct! I'm not using anything as high-powered as hers, but even down in the 1 watt area cooling is necessary.
Using lesson from GHURD, Commanda & Rich Hagen, I've been toying with lowering the current. Since there is a point where the light amount is just noticeable I have lowered the current  to 75% of max . Cooling is still necessary but not as much. 66% seems to my eyes the lowest before I really notice.

Mary B? is that standard chip paste your using? OF did you go with the newer high-temp stuff?

Cheers
Bruce S

Mary B

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Re: LEDs overheating
« Reply #6 on: March 22, 2016, 02:42:59 PM »
I also back down the current until the light just dims, typically about 75% of rated on these big modules. The difference in light output is slight and they run a lot cooler. But with 14 watts of LED on one heatsink I have to use a fan to keep things cooler.

phil b

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Re: LEDs overheating
« Reply #7 on: April 05, 2016, 06:06:59 PM »
I'm getting 'file not found on this server' on Commanda's LED installments here;
Part 1
http://fieldlines.com/index.php/topic,131213.0.html
Part 2
http://www.fieldlines.com/index.php/topic,131214.html
Part 3
http://www.fieldlines.com/index.php/topic,131215.html
Part 4
http://fieldlines.com/index.php/topic,131296.0.html

For convenience sake, I merely modified your links.
They all work now :)
« Last Edit: April 06, 2016, 07:24:40 AM by Bruce S »
Phil

Simen

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Re: LEDs overheating
« Reply #8 on: April 05, 2016, 10:35:48 PM »
Didn't someone say 'Remove the "board" word' in the address, and it works?

I tried it for the first one, and it did. :)
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

Mary B

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Re: LEDs overheating
« Reply #9 on: April 06, 2016, 04:17:26 PM »
with the price of a constant current LED supply down under $10 in a lot of cases building a circuit doesn't make economic sense unless you already have the parts in your junk box. http://www.ledsupply.com/dc-input-constant-current-led-drivers