Remote Living > Lighting
LEDs overheating
FoggyNotion:
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.
Mary B:
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.
Bruce S:
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
richhagen:
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.
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.
Heat is the enemy of longevity in these. Rich
Bruce S:
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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