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Miniaturization of the LED modules

A project log for MoAgriS: Modular Agriculture System

Growing food crops and other plants in small indoor spaces using established containers like regular plant pots and very little money.

timonskutimonsku 03/22/2018 at 23:170 Comments

I wanted to get the system down to a 12v power supply instead of the current 24v that #MoRaLiS: Modular Rail Lighting System used. Technically you only need 14.4V as the LEDs usually have a Vf of 3.2-3.6V.

24V is just a more convenient voltage standard so I designed everything around at least supporting 24v.

Which makes components also slightly more expensive and now that I want to incorporate an MCU on each board its getting hard to find a affordable and small LDO that can take 24v.

So I had two choices either have a 2 Series LEDs in Parallel which would be not so optimal as you can't mix LEDs with different forward voltages anymore and even within the same batch you would get variances of 0.1-0.3v. So I instead went with having only 2 LEDs and heavily reduced the size of the boards.

I always wanted smaller boards anyways, the biggest show stopper so far was thermal concern, with the current design and size 4 LEDs had just enough dissipation through the copper of the board to operate below their max. temperature.

I now plan on trying out 2 oz. copper boards instead and maybe add a little cut out on the back to drop in a tiny heatsink on the thermal pads of the LEDs if necessary but I have hope that 2 oz. copper will be enough.

This has another benefit, you can stack much more LEDs in a row and also distribute lighting much more evenly which has been a problem in some situations before.

Here a first prototype. I also went for some smaller inductor and capacitor. The inductor has always been over specd, lets see how one operates that just meets the specs.
Technically a 100uF capacitor is nicer but I think with so many devices on the rail with their own cap, 47uF might suffice. Though now that I only need a 12v supply, finding smaller 100uF caps that don't cost a fortune becomes easier.

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