It is all about aluminium, metal PCBs and old beer cans.

A project log for Brightenmacher

A biodegradable flashlight, build with recycled laptop batteries that you can repair yourself.

Peter FröhlichPeter Fröhlich 04/25/2017 at 19:500 Comments

I have build my fair share of regular FR4 PCBs but the metal core PCB for the LED was a bit different.

There was a lot of reading and asking around on what to keep in mind when designing one, there have been four iterations and i finally got it somewhat right with this board.

The thermal pads are not like the manufacturer recommends, it seems when reflow soldering these they are usually modified for the home marked with small areas were excess solder can escape to.

The NTC should hopefully be sufficiently coupled to the board, the intention is not to keep precise measurements but to just roughly guesstimate that the LED might be starting to melt the 3D printed enclosure and dial back the power.

The silkscreen it a bit more creative on this board.

The schematic is right on the board, as you can see there are three LEDs on this.

The outer two wired in series and the middle one in parallel, this gives the option to populate it either with a single or two LEDs to increase efficiency.

Since the LEDs only cost 70 Cents, this is a pretty good deal for a efficiency increase of 30 Lumen/Watt with less thermal problems.

In theory the driver should be able to provide more current to two series LEDs to increase the light output as well, but this will have to be tested in the real world and not on paper.

At the moment the output is 1.65W and the theoretical output of the LED driver should be 3W, at 70% electrical efficiency that the LEDs could be driven at a bit over 2W.

But 70% is the absolute worst case for the driver, with the new improved layout it should get to around 85% efficiency.

But again, this will have to be tested with the new boards.

Soldering this will be a bit of a challenge, i only got a little bit practical experience with this, the colossal thermal capacity of this board will be a challenge.

Connecting the wires to the board as well, since i do not want to use a connector.

I got a PID controlled hot plate and a hot air station, the rough idea is to pre-heat the board on the plate and then re-flowing it with the hot air.

As for the wires, my idea is to use either silicone or PTFE wire to keep the insulation from melting and to solder the wires while reflowing the LEDs.

Apply solder paste, tack wires onto board with kapton tape, apply extra solder paste to the wire and pads, place the LEDs, pre-heat the board, reflow it with hot air.

And while we are on the subject of LEDs and aluminium, at this point i am dead set on building my own reflectors out of old beer cans.

The idea is to design a few drawing die and press them out of shin aluminum stock, to keep up with the slight recycling theme i decided to use old beer cans.

There are pre-made reflectors out there, but were is the fun in that?

The possibility to waste huge amounts of time and effort into a senseless endeavor were i can learn a bunch of new skills far outweighs the simple process of buying something pre-made.

If i would want that, i could have bought a simple Nitecore TIP keychain flashlight for 35 bucks that would be smaller, brighter and delivered by the mailman in 24h.

There were concerns about the efficiency of home made aluminium reflectors and while they are completely reasonable after a few test the performance was significantly increased by home made aluminium tape reflectors when compared to the lens i am using at the moment.

So, while in theory a home made reflector will not perform very well, real world tests have already shown that it will out-perform the pre-made lenses i have been using.