How big of a heat sink do I need for these LEDs?

Thread Starter

-live wire-

Joined Dec 22, 2017
901
I got some 4W RGBW leds to RGB everything! I am not sure what heatsinks to get for them. So to keep them within a reasonable temperature to get a long life span, under 60⁰C, how big of a heatsink do I need? And are there any options for active cooling where it's just a few 100 milliwatts for the fan and it allows a much smaller heatsink? I don't want to spend more than $10-15. These are the LEDs:
https://www.amazon.com/300mA-350mA-Multicolor-Intensity-Components-Lighting/dp/B01DBZIXJ0/ref=sr_1_1?keywords=chanzon+rgbw+led&qid=1560980489&s=electronics&sr=1-1-catcorr
 

danadak

Joined Mar 10, 2018
3,785
I do not see any thermal specs for the part, eg. thermal resistance J-C so you
will have to measure that using a T sensor gun and a known Pdiss. Or do it
empirically in lab. You are basically trying to measure die temp and case temp
for a known Pdiss that you force LED to dissipate.

You might tery to find this package at another mainstrewam vendor and look at
their data sheet for the thermal R J-C (junction to case).

Then you can proceed with tools to find heat sink options.


https://www.analog.com/media/en/training-seminars/tutorials/MT-093.pdf


Here are some heatsink tools - https://www.smps.us/thermal.html


Regards, Dana.
 
I have had good luck using surplus computer fan/sink combinations, often available for less than $10 to cook 10 watt leds. The area is probably only enough for one led. How are you driving the leds? There may or may not be an available power source for the fan,which I run in series with a large enough resistor to slow (and quiet) the fan.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
901
I will probably use constant current, not a resistor. But since the end goal is RGB for more stuff and an RGBW flashlight, the fan shouldn't be too big or consume more than .5 watts.
 

danadak

Joined Mar 10, 2018
3,785
Is there a good way to estimate the required heatsink size?
What I posted was the methodology on how to get to a heat sink size.

It depends on a number of variables, air flow, thermal mass, heat flux
that has to be removed.......

Its like getting open heart surgery, not done winging it if you want reliable
solid design results.

Youtube and some of the heatsink vendors have training videos, that may
lend a guiding hand to your effort.


Regards, Dana.
 

oz93666

Joined Sep 7, 2010
724
This doesn't seem a very convenient way to do what you want .... this is the way a manufacturer buys them , then put them on a spreader , or in completed products ... you are going to find soldering very fiddly , and applying thermal compound messy on that small area....

You need to consider the end product , are these going to be all in one tight location ?? tricky for dissipating the heat .... you cannot allow the eye to see directly the light source , this will leave after image effects in the eye and is very unsatisfactory ... the light must bounce off a wall or ceiling first ....

Much better put those leds away in a cupboard and buy some like this ....

Self adhesive RGB strips , each chip is around 20 to 100mW so no head build up or heat-sink. but with many per meter you get plenty of light output .... many different types , very cheap , some with remote , see eBay ... some consume 30W/meter , some , like the strip pictured alternate RGB with white

Even these low power leds are not comfortable to look at directly ... this arrangement is best ...



The spreader mvas linked to is what you need for the leds you have ... then some thermal compound ... THEN you need a heat sink of some type ...at the end you will spend a fortune , and the result will look a mess .... Don't go down this route !!!
 
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Thread Starter

-live wire-

Joined Dec 22, 2017
901
I am thinking of using them in a flashlight or in a PC, not for lighting a room. So is there any good rule of thumb or way to estimate a good heatsink size for the LEDs I have? Maybe that will involve getting a slightly larger heatsink to be safe? There isn't any datasheet containing details on the exact thermal properties.
 

BobTPH

Joined Jun 5, 2013
2,198
If you can buy the same already soldered to the stars it would be a good start. And again, those are not the heat sink, they are the interface to the heat sink.

That said, if you run them at about 1/4 power (1W total max) the star itself might be enough heat sinking. I have used them this way without problems.

For a little more heat sinking, the star can be fastened to the computer case.

Bob
 
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