Heat issues

A project log for MoRaLiS: Modular Rail Lighting System

A very affordable lighting system that can be used as efficient grow lights for indoor plants and customizable ambient lighting.

Prof. FartsparkleProf. Fartsparkle 04/01/2017 at 23:073 Comments

Previously I ran the 3W LED Quartets at about half the maximum current, heat dissipation worked fine with some big exposed pads on the PCB. With the new modules I wanted to run them at their full specified current of 700mA but that turned out to be a thermal nightmare. I would have to add a huge heatsink to the LEDs in order to keep them at around 50°c.
So I have two options, stick with 3W LEDs and limit the current to 400-500mA or go with 1W LED chips.
Considering a low price point while still being a very usable thing is my main selling point for this project I will probably switch my design to 1W LEDs and do some testing if I can get a way with exposed pads on the back side of the PCB. If not I'm thinking about attaching some thin copper shims to the back, you can get them for around 17 cents for a 20x20x1mm one (at qty 50, see the link below).


Yann Guidon / YGDES wrote 04/01/2017 at 23:12 point

Personally I would stick to the 3W LED because the larger die makes them more efficient, more photons per unit of current. The price difference might not be large but you decide :-)

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Prof. Fartsparkle wrote 04/01/2017 at 23:23 point

The price difference is about 0.40€ in total. I was thinking that as
well that the 3W version might be more efficient, I will do some testing
and get a lux meter to compare the two. I guess in the end the user can
decide what to use. I will try my best to make the design modular
enough so you can attach more or less heatsinks to the back depending on
your needs. If you want to use 1W, limited 3W or full 3W LEDs is then
just a matter of choosing the correct current sense resistor and
slapping a big enough heatsink on.

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Yann Guidon / YGDES wrote 04/01/2017 at 23:35 point

Exactly : in case of doubt, measure ;-)

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