Many of us store a flashlight around the house for use in emergency situations. Usually, regular alkaline batteries are fine for this task, as they’ll last a good few years, and you remember to swap them out from time to time. Alternatively, you can make one that lasts virtually indefinitely in storage, and uses some simple chemistry, as [JGJMatt] demonstrates.

The flashlight uses 3D printing to create a custom battery using magnesium and copper as the anode and cathode respectively. Copper tape is wound around a rectangular part to create several cathode plates, while magnesium ribbon is affixed to create the anodes. Cotton wool is then stuffed into the 3D-printed battery housing to serve as a storage medium for the electrolyte—in this case, plain tap water.

The custom battery is paired with a simple LED flashlight circuit in its own 3D-printed housing. The idea is that when a blackout strikes, you can assemble the LED flashlight with your custom battery, and then soak it in water. This will activate the battery, producing around 4.5 V and 20 mA to light the LED.

It’s by no means going to be a bright flashlight, and realistically, it’s probably less reliable than just keeping a a regular battery-powered example around. Particularly given the possibility of your homebrew battery corroding over the years unless it’s kept meticulously dry. But that’s not to say that water-activated batteries don’t have their applications, and anyway it’s a fun project that shows how simple batteries really are at their basic level. Consider it as a useful teaching project if you have children interested in science and electricity!

The host of problems to deal with when you’re feeling the need for FDM speed are many and varied, but high on the list is figuring out how to melt filament fast enough to accommodate high flow rates. Plus, the filament must be melted completely; a melty outside and a crunchy inside might be good for snacks, but not for 3D printing. Luckily, budget-minded hobbyists can build a drop-in booster to increase volumetric flow using only basic tools and materials.

[aamott]’s booster, which started life as a copper screw, is designed to replace the standard spacer in an extruder, with a bore that narrows as the filament gets closer to the nozzle to ensure that the core of the filament melts completely. Rather than a lathe, [aamott]’s main tool is a drill press, which he used to drill a 0.7 mm bore through the screw using a PCB drill bit. The hole was reamed out with a 10° CNC engraving bit, generating the required taper. After cutting off the head of the screw and cleaning up the faces, he cut radial slots into the body of the booster by threading the blade of a jeweler’s saw into the bore. The result was a bore wide enough to accept the filament on one end, narrowing to a (roughly) cross-shaped profile at the other.

Stacked up with a couple of knock-off Bondtech CHT nozzles, the effect of the booster was impressive — a 50% increase in flow rate. It’s not bad for a prototype made with simple tools, and it looks a little easier to build than [Stefan]’s take on the same idea.