Thermal management - The Planted Tank Forum
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post #1 of 4 (permalink) Old 11-14-2016, 05:05 AM Thread Starter
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Question Thermal management

I am running a led fixture made out of a fluorescent fixture and a MC PCB: 8 1W are soldered to a MCPPCB which is glued to the aluminium shade by means of a glue and thermal paste. See photo for your reference.
The 8 leds are mounted into 2 series of 4 leds.

When leds are supplied with a 175mA current, the temp on the aluminum shade (right at the back of the PCB) is about 35C while the ambiant temp is about 30C. But when supplied with 350mA, the nominal current, the temperature would raise up to roughly 60C.

In my opinion, the heat is partly because those led are cheap and ineffcient. My question is if i swapped them agaisnt better chip leds with proven efficiency of about say 130lm/W, Would i still need to add up radiators to my homemade fixture ?
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Last edited by Tran; 11-14-2016 at 05:07 AM. Reason: add photos
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post #2 of 4 (permalink) Old 11-15-2016, 02:29 PM
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Complicated question really..
Much depends on the thermal characteristics of the LED..
Some would care less about 60C (140F) though at the diode itself temp is higher..

To get the same photon output w/ more efficient diodes you run them at lower currents..

Next cheap diodes can be damaged even at lower temps as well..

If you make your own boards then it is relatively easy to find more efficient/higher tolerance diodes..
These are
very unassuming numbers because, as many designers will explain, heat dissipation is a
priority. The junction temperature of a standard LED should not exceed 85-100C,
depending upon the design’s construction. Incorporating these standard LEDs into a
design is relatively simple because the small size and low power consumption generates
little heat. Therefore one needs only to design around the environment, not the specific
The challenge that has arisen stems from the new, high-power LEDs that have emerged
into the marketplace. A high-power LED can draw 1 watt of power or greater and output
more than 80 lumens. That’s a 90% increase in power consumption (98% for a 5-watt
LED). Therefore the amount of heat generated becomes significant. A typical 1-watt
LED will have a maximum junction temperature (a point of failure or reduced life) of
125C. However, left to its own devices a 1-watt LED can increase the temperature in its
immediate environment by 55C or more. Heat management is now a critical
consideration to the overall product functionality, performance and, possibly, safety.
40-50C is a fairly safe target for the "heatsink" temp.
more efficient and lower current diodes will make this easier to achieve w/out more parts..

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post #3 of 4 (permalink) Old 11-15-2016, 02:37 PM
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That's how the physics of it works. The more current you supply, the hotter it gets. You can always attach a heat sink and fan to the metal attachment. You might have to take that back cover off.

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post #4 of 4 (permalink) Old 11-25-2016, 05:10 AM
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what about attaching a fan to the outside surface? it might help cool down the LEDs

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