Emergency Mg/Cu Galvanic AA Battery With Tinkercad Tutorial

Hello everyone,

In this Instructable I'd like to show you how I made these emergency AA batteries.

They are Magnesium and Copper galvanic cells and are only activated once you add an electrolyte so technically you can store them indefinitely in a sealed bag with some desiccant.

I store them with some home made joule thief lights but they easily power led and low amperage devices when connected in series.

Join me if you want to make some for yourself...

To replicate this Instructable you will need the following:

- Access to a 3D printer

- About 3 meters of filament

eSun PLA+ (what I used)

- 6mm Copper tape

6mm Copper Tape

- 4mm Magnesium ribbon

Magnesium Ribbon

- Thin absorbent material (I used 20mm cotton wick)

Cotton Wick

I have included Amazon links as a reference to what I have used in this build.

Please make sure of sizes/length etc. before purchasing.

Working of Galvanic Cell

-In a galvanic cell, when an electrode is exposed to the electrolyte at the electrode-electrolyte interface, the atoms of the metal electrode have a tendency to generate ions in the electrolyte solution leaving behind the electrons at the electrode. Thus, making the metal electrode negatively charged.

-While at the same time metal ions in the electrolyte solution too, have a tendency to deposit on a metal electrode. Thus, making the electrode positively charged.

-Under equilibrium condition, charge separation is observed and depending on the tendencies of two opposing reactions, the electrode can be positively or negatively charged. Hence, a potential difference is developed between the electrode and electrolyte.

-This potential difference is known as electrode potential.

-Out of two electrodes, the electrode at which oxidation takes place is called anode while the electrode at which reduction takes place is called cathode.

-The anode has a negative potential with respect to the solution while the cathode has a positive potential with respect to the solution.

-Thus, a potential difference develops between two electrodes of the galvanic cell. This potential difference is known as cell potential.

-When no current is drawn from the galvanic cell, cell potential is known as the electromotive force of the galvanic cell.

-When the switch is set on, due to the potential difference, electrons flow from the negative electrode to the positive electrode.

This is a really simple beginners projects to learn the basics of Tinkercad and get a really useful item in the end.

Start with a cylinder the size of the battery you want, for this tutorial I made a D-cell that is 33mmx61.5mm. So my cylinder is 33mm in diameter and 60mm high leaving 1.5mm for the "button" on top.

Make a duplicate ( select object -> ctrl+D ) of the cylinder and set aside.

Now for the centre slit and the triangle at the bottom to allow the battery to fold open.

The triangle is 4mm wide 35mm long and 4mm high, for ease of printing keep the angle 45 degrees or more.

The slit is a cube that is 35mm long, 1.2mm wide and 55mm high ( height of cylinder - 4mm of the triangle - 1mm gap between triangle and slit )

Select the slit and triangle and make them a "Hole"

Now select the cylinder, triangle and slit.

Press "L" on your keyboard and center everything by pressing center dot on the X and Y axis.

Select the cylinder and slit, Press "L" then click on the cylinder and select the top dot. This will move the slit to the top of the cylinder. Group the 3 items.

Now place a new cube that's 6mmx6mmx1.5mm and make a duplicate of it and turn the duplicate into a "hole".

Resize the duplicate to 6mmx4.1mmx0.4mm so that when grouped the it creates a 2 layer gap on the bottom like pictured.

Centre the "button" on your main cylinder and move it up 60mm.

Group.

For the bottom slits where the magnesium strip will go into we take two cubes 1mmx5mmx5mm and 1mmx5mmx8mm. The 8mm high one gets angled at 22.5 degrees and moved 6mm away. Select both cubes, make them a "hole" and center them on the main cylinder as pictured.

Group.

Now for the closing ring you take the main cylinder that you duplicated in the beginning and reduce its height to 10mm. Duplicate it, reduce its size to 30mm and make it a "hole".

Centre the two cylinders and group.

Duplicate the ring and make one a "hole".

Now take the "hole" ring and centre it on the main battery cylinder and move it up 50mm.

Select main battery and "hole" ring and group.

And that's it!

Now export as .STL and get printing.

The body of the battery was designed in TINKERCAD and is printed in one piece with just the closing ring printed separately.

Initially I wanted the whole body to be printed in a single piece but I couldn't find a way to make the closing mechanism work consistently on this scale, so I decided to just go with a simple closing ring that slips over the top when you're done and is held in place by the layer lines.

I'm happy with how this design turned out but if anyone wants to improve on it feel free to post your updated design.

Print settings:

Nozzle: 0.4mm
Material: I used eSun PLA+
Temp: 220 deg C
Speed: 30mm/s
No support needed

This is a quick print with no waste and I suggest printing a few models at once.

Depending on your printer you might need to use a hobby knife to cut free the positive button (the side opposite the slot as pictured), it is designed with a single layer gap but sometimes the layers still fuse.

Our cathode is made using self adhesive 6mm copper tape, this will be your battery positive terminal.

In a galvanic cell your cathode is positive and your anode is negative whereas in a electrolytic cell the cathode is negative and the anode is positive.

Initially I started by sticking the tape on the top "button" of the battery then feeding it through the slot down into the body of the battery, after feeding it through the slot you have to twist the tape 180 degrees so that your adhesive is facing right way again.

This is a bit more difficult but it ensured the best electrical connection as it wouldn't rub against the body.

My next one I decided to not feed the copper tape through the slot but to tape it over the opposite side of the slot (as pictured).
This made the assembly much quicker and it's holding up well after testing.

I have kept the design as is with the slot so you can decide which way you want to assemble yours.

The anode of this cell will be made using 4mm magnesium ribbon. This will be your negative terminal.

First you'll want to take some steel wool and clean off any oxidation that has formed on the magnesium, this will ensure optimum performance of your cell.

Now take about 60mm of ribbon and heat it with a lighter, if you don't anneal it first you'll find it difficult to work with as it is very brittle. Just be careful to not hold your flame on one spot for too long, you do not want to light magnesium on fire!

Now bend a "hook" on the one end of your ribbon the size of the two slots on the bottom of the battery body. (As pictured)

Then feed the other end through the slot completely until "hook" pushes into place.

Now trim any excess from the top so that it is about 8mm shorter than the battery body.

Now you can take your absorbent material and place it in-between the magnesium and copper making sure the magnesium and copper do not make contact with each other anywhere.

With my 20mm wick I was able to wrap it around the magnesium strip without having to trim any excess.

Now push the two halves of the battery body together and slip over the ring, the pressure from the wick should hold it together quite well.

And that's it your battery is assembled.

When dry your cell shouldn't give any voltage readings and that's good as there is no moisture to degrade your cell.

When an electrolyte is added (in testing I used plain tap water) I got a good 1.488 volts, perfect for a AA battery.

I also got a steady 60ma which is perfect for my application.

Note that adding salt to your electrolyte will boost the performance considerably at the cost of greater cell degradation.

-

To increase the output power slightly you can take some thin copper wires like ones from a stripped cable and criss-cross them over the copper strip to get more surface area.

In addition to the copper wire you can also add some of the off-cut pieces of magnesium ribbon across the original magnesium ribbon as well.

Just double check that the copper and magnesium does not make direct contact anywhere as this will short the connection and you will not get any power output at your terminals.

And that's it, now you have a stash of long lasting emergency AA batteries.

Remember to store your dry cells with some desiccant in an airtight container/bag and it's also a good idea to keep some additional strips of cut to size magnesium and copper to rebuild used batteries.

Hope you guys find this Instructable useful.

....Happy making!