STEM Science Fair 2026

A Battery That Makes Cents

Recreate Alessandro Volta's original voltaic pile using euro coins — and discover how stacking more coin pairs generates more voltage.

Explore the Project ↓
20 cent
— paper —
5 cent
20 cent
5 cent
20 cent
foil base
↑ more pairs = more voltage ↑

How a Coin Battery Works

You're recreating Alessandro Volta's voltaic pile from 1800 — the world's first true battery. Volta discovered that stacking two different metals separated by a moist conductor could produce a continuous flow of electrons.

The vinegar-salt solution acts as an electrolyte. Charged particles in it react with the two metals, triggering an electrochemical reaction that releases electrons. When those electrons flow in one direction, it creates electric current.

Each coin pair acts as one "cell." Just like AA batteries in series, stacking more cells adds their voltages together — giving you more total power.

"Does the number of coin pairs in a stack affect the voltage produced?"

📐
Independent Variable
Number of coin pairs in the stack
Dependent Variable
Voltage measured (Volts, DC)
🔒
Controlled Variables
Same coin types, same electrolyte mix, same paper thickness
💡
Hypothesis
More coin pairs = higher voltage — each pair adds ~0.5V

Materials

Everything is easy to find. The multimeter is the most important item — borrow one if you can.

🪙
Coins
8–10 × 5 cent (copper)
8–10 × 20 cent (gold)
Keep separate!
🧪
Electrolyte
¼ cup white vinegar
1 tablespoon table salt
Small bowl to mix
📄
Separator
Paper towels
Cut to coin-sized circles
Soak before use
🔌
Base Contact
Aluminium foil strip
~2 cm × 8 cm
Fold lengthwise 3×
📏
Multimeter
Digital multimeter
Set to DC Voltage (V—)
Most important tool!
🧹
Prep Supplies
Dish soap (clean coins)
Ceramic or plastic plate
Lab notebook + pen

Euro Coin Substitutes

The original project uses US pennies and nickels. Here's exactly what to use with euro coins.

US Coin Metal Euro Equivalent Role in Battery
Penny Copper-plated zinc 1, 2, or 5 cent Use 5¢ Gives off electrons
Nickel Cupro-nickel alloy 10, 20, or 50 cent Use 20¢ Receives electrons
Best combination: 5 cent vs 20 cent. These two have the largest metal composition difference, which produces the strongest electrochemical reaction and the most measurable voltage. Clean both sides with dish soap before the experiment — oxidation on old coins weakens the reaction.

How to Build It

Follow these six steps in order. Each step matters — don't skip the cleaning!

1
Mix the electrolyte. Combine ¼ cup of white vinegar with 1 tablespoon of salt in a small bowl. Stir until the salt dissolves.
2
Clean your coins. Wash all coins with dish soap, rinse thoroughly, and dry completely. Oxidation reduces the reaction.
3
Prepare separators. Cut paper towel into roughly coin-sized circles. Soak them in the vinegar-salt solution and let them sit.
4
Build the stack. On your plate: 5 cent → wet paper → 20 cent → 5 cent → wet paper → 20 cent… repeat for the desired number of pairs.
5
Add the foil base. Place your folded aluminium strip at the bottom of the pile for a solid, clean electrical contact point.
6
Measure. Set multimeter to DC Voltage. Touch red probe to top coin, black probe to foil base. Read and record the voltage.
Stack Order
20 cent
— wet paper —
5 cent
— wet paper —
20 cent
— wet paper —
5 cent
— wet paper —
20 cent
foil base
↑ repeat to add voltage ↑

Recording Your Results

Run 3 trials per stack size. Average your results — it makes your data much more convincing to judges.

Coin Pairs Trial 1 (V) Trial 2 (V) Trial 3 (V) Average
2 pairs
4 pairs
6 pairs
8 pairs
💡
Re-wet the paper towel circles if the stack dries out mid-experiment — moisture drives the reaction.
📊
Plot a bar graph: X-axis = coin pairs, Y-axis = average voltage. You should see a clear upward trend.
🔄
If your multimeter shows a negative value, just swap the probes — you had them reversed.
📸
Take a photo of the multimeter reading for each trial — great evidence for your display board.

Display Board Layout

Science fair boards follow a standard 3-panel structure. Here's what goes where.

Left Panel
❓ Research Question
🔮 Hypothesis
📚 Background Research
Centre Panel
🏷️ Project Title (large)
🧰 Materials List
📋 Step-by-Step Procedure
Right Panel
📊 Data Table + Bar Graph
✅ Results & Analysis
🎓 Conclusion

Quick-Start Checklist

Click each item as you complete it. Good luck!

Gather 5 cent & 20 cent euro coins (10+ of each)
Buy white vinegar, table salt, paper towels, aluminium foil
Borrow or buy a digital multimeter
Set up lab notebook with the data table above
Do a test run with 4 coin pairs to check your setup
Run full experiment: 2, 4, 6, and 8 pairs × 3 trials each
Calculate averages and draw a bar graph of results
Write your conclusion: did more pairs = more voltage?
Assemble display board: Question → Hypothesis → Materials → Procedure → Results → Conclusion
Take photos at every stage for your board