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!
Yes! I remember as a kid doing projects in school where we ran a clock on a lemon, a LED on a bunch of apples in series, and with one potato we ran a whole ass GLaDOS!
Same technology/chemistry as used in the older Vaisala Radiosonde batteries?
This reminds me of torpedos. (Those big things in submarines). It is (or was) common for these to have dry batteries with a long shelf life and after firing the sea water acts as an electrolyte that activates the battery. For an “emergency battery” (light, homing beacon, whatever electrical gadget) something with a bag or bottle of salty water could be made.
Many household items can be used to make rudimentary batteries, even potatoes which can even be recycled (baked with some sour cream). Or you can use sea water in coconut shells to recharge your radio (that strangely never runs out of power) that you took on your 3 hour tour…a 3 hour tour….
Mmm, the extra heavy metal ions cuisine.
Damn. You mentioned sea water in coconut shells and that scene immediately came to mind. Showing my age and ADHD, I suppose.
I wonder if that works. I wonder if that’s ever been tested?
I believe emergency lights (and radio locators?) on lifejackets work the same way. Not sure how common it is, but definitely read somewhere once.
Lifejacket lights – at least the USCG approved ones for maritime vessels – use a ‘normal’ battery and a water-activated switch.
Some do. You can tell because they have a pull handle to remove a set of plugs from the flood holes in the sides of the battery before they’ll work. They aren’t the “automatic activation” kind. Used to be a routine job for me to check ours were in-date and plugs were in place. No idea what the chemistry was, but the light was anemic.
I was expecting the magnesium to generate light more directly…
If you get the right oxidizer to go with it…
Don’t want to produce that light tooo fast, nor too slow.
I’m a bit confused. In the instructions for building this battery I miss the CuCl2. But the cotton ball is blue, it seems that it is impregnated with CuCl2.
Interesting project but what an odd premise. I get the common household items but than you go on to need a 3D printer.
How about an emergency light that you make out of a broken piece of phosphor coated neon tubing from an old sign and fill it up with tritium gas? The sign parts should be pretty easy to source, aliexpress for the rest…
We had a project to make a galvanic cell in a beaker in school, and I used the same pair of ions. But my experience was that with about 15 square inches of electrode area, even a fairly concentrated solution of what was probably the sulfate salts of both ions didn’t allow an incredibly powerful result. And even though I sanded off the magnesium oxide from the magnesium rod before starting (Which forms even when it’s inside a typical zip-lock bag), it also quickly formed magnesium hydroxide when immersed in the solution, which kept the cell from powering much of anything for long. To fix that, I dumped in a bunch of concentrated sulfuric acid, which brought my open circuit voltage up to 2.1. That’s not bad; you could light a red LED with that, or use two of them for any other leds. Water is already decomposing at that voltage which is somewhat like an internal short dragging the voltage down – you use non-aqueous solutions in practice. More importantly to me at the time, my measurable short circuit current went up to about 140 milliamps. Of course, the magnesium electrode was visibly bubbling because in addition to dissolving the hydroxide off, it easily dissolved the bare metal too. An option more suited to this project may be citric acid powder or something else readily available and safe. I don’t know, but it may be able to get the hydroxide off without bothering the metal as much. I was going for maximum output at the time, and didn’t care if it didn’t last very long.
You’ve invented the potato in a world where you have enough electricity to run a 3D printer but no light. Where you goin’ with this?
Yeah, 3D printing is a bit overkill. It should be made with whatever plastic container one can find in their trashcan (or on the way towards it).
Also, I’m not great at chemistry, but I suppose this could also run on urine? (Considering the situations you’ll be solely relying on this thing). Would be a bummer if it doesn’t.
just use disposable lithium cells for your emergency flashlight.