Magnesium & Copper Water Activated Emergency Flashlight!

Hello fellow makers,

A few years back I made an Instructable showing the process to make a emergency galvanic AA cell, expanding on that project I will be making an emergency flashlight with hot swappable magnesium and copper water activated cells that can be easily recharge with a new cathode and anode once depleted.

Emergency Mg/Cu Galvanic AA Battery

The inspiration for this project is to be able to make an emergency light source at home that is cheap, does not require any dangerous or exotic materials and can be stored indefinitely so that you don't get surprised with expired batteries in your time of need.

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To build your own you will need the following:

For the galvanic cell:

• Access to a 3D printer Amazon - Creality Resin 3D Printer Halot-Mage 8K
• 4mm Magnesium ribbon Amazon - Magnesium Ribbon High Purity
• 6mm Copper self adhesive tape Amazon - Copper Foil Tape with Double-Sided Conductive
• Cotton balls Amazon - Amazon Basics Cotton Balls
• 1mm EVA foam Amazon - Black Eva Foam

For a completely DIY light source:

• 1206 White LED Amazon - 1206 White SMD LED Diode Lights Chips
• Pogo pins Amazon - Golden Plating Copper Spring Pogo Pins Probes 2mm Dia 6mm Height
• Single sided blank PCB Amazon - FR-4 Copper Clad PCB Laminate Circuit Board, Single Side
• Hydrogen peroxide Amazon - Amazon Basics Hydrogen Peroxide
• Hydrochloric acid Amazon - Hydrochloric Acid 10%
• Photosensitive resist film Amazon - Photosensitive Dry Film for Circuit Photoresist

*As an Amazon Associate I receive a small percentage from sales made through provided links at no cost to you, this helps fund future projects.

A galvanic cell (or voltaic cell) is an electrochemical cell that derives electrical energy from spontaneous redox (reduction-oxidation) reactions taking place within the cell. It typically consists of two different metals connected by a salt bridge, or two half-cells each containing an electrolyte and a metal electrode.

The main components of a galvanic cell is:

• Anode - The electrode where oxidation (loss of electrons) occurs. It is the negative electrode in a galvanic cell.
• Cathode - The electrode where reduction (gain of electrons) occurs. It is the positive electrode in a galvanic cell.
• Electrolyte - An ionic substance that allows ions to move between the electrodes, maintaining electrical neutrality.
• Salt Bridge - A pathway that permits the transfer of ions between the two half-cells to maintain electrical neutrality, preventing the solutions from becoming electrically charged.
• Connection between cells - A wire that connects the anode and cathode, allowing the flow of electrons from the anode to the cathode.

In operation, the chemical reaction at the anode releases electrons, which travel through the external circuit to the cathode, where they are consumed in a reduction reaction. This flow of electrons constitutes an electric current, which can be harnessed to perform work.

Anode and cathode metals in a galvanic cell

The best metals to use in a galvanic cell are typically those that have a significant difference in their standard electrode potentials (also known as reduction potentials). This difference creates a higher voltage and more efficient energy conversion.

Commonly used metals include:

• Zinc (Zn): Often used as the anode because it has a relatively low reduction potential.
• Copper (Cu): Frequently used as the cathode due to its higher reduction potential compared to zinc.
• Magnesium (Mg): Another good option for the anode, especially in cells requiring a higher voltage, because it has an even lower reduction potential than zinc.
• Silver (Ag): Used as the cathode in some high-efficiency cells due to its high reduction potential.
• Iron (Fe): Occasionally used as an anode, although it is less common due to its tendency to rust.
• Lead (Pb): Sometimes used in specific types of galvanic cells, like lead-acid batteries.

A common example is the zinc-copper galvanic cell:

Anode: Zinc (Zn) undergoes oxidation: Zn → Zn²⁺ + 2e⁻

Cathode: Copper (Cu) undergoes reduction: Cu²⁺ + 2e⁻ → Cu

The choice of metals depends on the desired voltage and the specific application of the galvanic cell.

The reusable battery cases and clip on flashlight module will be 3D printed so I started by designing both of these using Fusion 360.

As my FDM printer is set up to print large objects with composite filament and a 0.8mm nozzle it cannot handle small prints like these so I went with my Halot One resin printer but the files should work perfectly well on a 0.4mm nozzle FDM printer.

You will only need one of each of the "Water Lamp Top.stl" and "Water Lamp Battery.stl" to build the flashlight but I recommend printing a few of the batteries to have extras ready to go in an emergency.

The "PCB Mask.stl" is only needed if you want to etch your own PCB that will be explained further in Step-4.

This is completely optional of course but after curing the print I used a permanent marker to fill the embossing for some extra style points! 🤣

With the battery case printed we can start assembling the batteries.

I start with the cathode that will be made from self adhering 6mm copper (Cu) tape. Without removing the paper backing from the copper tape I press the tape through the 6mm slit on the top of the battery and push it through the bottom opening, I then remove a piece of the paper backing from the end of the tape that is just slightly longer battery case, I can now pull the tape back through the top and stick the tape with the exposed adhesive on the inside of the battery case.

On the top of the battery case we leave a little tab of the tape to make a connection to the neighbouring cells and light contacts.

Now we move onto the anode that will be made from 4mm magnesium (Mg) ribbon.

As with aluminium, magnesium oxidizes rapidly when exposed to moisture and when you receive your roll on magnesium ribbon you will most likely notice that unlike the advertisement your magnesium will be a dark dull grey instead of bright silver. Don't worry though as this is completely normal but we will need to clean it up to get maximum efficiency of our voltaic pile, I simply use some fine steel wool to rub away the oxidation until I'm left with a bright shiny strip.

TIP: To minimize the oxidation in the future I recommend storing your roll of magnesium in a zip-lock bag with some desiccant pouches.

For each battery module I cut three pieces of the magnesium ribbon just slightly longer than the battery length, then using flat nose pliers I bend a 90 degree tab on the one end of each of the strips this will act as our connection points.

Now press each of the strips through the 4mm slit on the top of the battery so that the bent tabs sit on top of the copper tabs and cut off any excess ribbon from the bottom with some flush cutters.

To finish the battery modules we will need to create a "salt bridge".

In this build it will simply be some cotton wool packed in between the anode and cathode that will hold onto the electrolyte.

Using a wooden toothpick I used one cotton ball per battery module divided into three pieces and then stuffed into each cavity in the battery.

You want to make sure that your hands and cotton balls are completely dry before doing this as moisture will slowly degrade your anode and cathode.

In this step I will show you how to make a PCB from scratch for the light but as this is such a simple circuit you can completely omit the PCB and pogo pins and go for a simple 5mm LED with its legs bent into pins to contact the battery module pads.

First we need an etch mask for the PCB, this is simply a barrier that prevents the copper layer from being eaten away by the etchant to make the traces for our circuit.

There are a few different methods that can be used to make the mask.

One I use often is a photoresist, this is a light sensitive film that gets adhered or sprayed onto the PCB and is then exposed to UV light to develop a negative mask on the PCB. All the areas exposed to the UV will not get etched.

An easy way to create a photoresist is to simply use the screen of a resin 3D printer, as the process of resin printing is exactly the same as creating a photoresist.

Another method is to simply draw your PCB traces with a permanent marker or paint marker.

But as I was already printing the two components for the flashlight on the printer I decided to just print a thin template of the circuit that I can then just use my airbrush to spray onto the PCB.

With the etch mask made you now need to etch the PCB.

- WEAR ALL NECESSARY SAFETY EQUIPMENT! -

In a well ventilated room or outside mix two parts hydrogen peroxide and one part of hydrochloric acid together in a separate container. Ferric Chloride can also be used instead of this solution if you have some available. (this is your etching solution so handle with care)

Tip: The hydrogen peroxide + hydrochloric acid is a safer alternative to Ferric Chloride and is great to use when making your own PCB's

Carefully submerge the PCB into the etching solution, the copper that needs to be etched has to be completely submerged and facing upwards.

Agitate the mixture regularly.

Leave it in the solution until it has dissolved all of the exposed copper leaving behind only the copper under the resist.

When done rinse thoroughly in clean water.

You can now simply cut out and shape the boards then drill the holes needed for the pogo pins.

With the PCB now made we can assemble the flashlight module next.

With the PCB made we need to solder on the three components, I start by soldering on the 1206 white LED. On the LED you will notice there is a green line on the one side, this is the negative (anode) of the diode and will go the the magnesium side of the battery module.

Next you need to solder in the two pogo pins into place so that they face to the back of the board.

In any circuit involving an LED you will always find a current limiting component in line with the diode but for the size of this cell the measured current output was between 15 and 20ma, this is perfect to ensure maximum brightness for this light and will not cause any damage.

To ensure that the PCB is waterproof I smeared some UV resin into the cavity of the PCB before pressing it into place and curing it from behind with a UV flashlight.

I used the same resin from my printer used for the parts to fill the cavity of the light in order to create a protective waterproof lens for the LED. You can also use UV curable craft resin if you FDM printed the flashlight or don't have transparent 3D resin.

With the LED section finished I cut out a piece of 1mm EVA craft foam to fit into the back of the module between the two pogo pins, this will help press the connection between the three galvanic cells together when the flashlight is clipped onto it.

Your flashlight module is now ready for use.

• Testing of the cell with plain tap water gives a voltage of 4.5V volts and a short circuit current of around 20ma.

• For long term storage I recommend getting some heat shrink PVC packing tubes and then to seal each battery module along with a small desiccant pack, this should give you an indefinite storage life until activating.

• If you want to scale up this project you will need to add a current limiting resistor in line with your LED as the battery will produce more current and damage the diode.

The time has come to test out your flashlight, to activate it simply submerge the battery module in plain water for a few seconds so that the cotton is saturated, shake off any excess water and clip on the flashlight module.

I hope you guys find this Instructable useful and if you have any questions please feel free to leave me a message or comment bellow.

Thank you for taking the time to read through my project and as always..

Happy making!