Measuring the Power of a Fuel Cell

Introduction

The fuel cell is an ideal source of electrical power for experiments on power measurement. Unlike other electrical power sources it can be run at full power indefinitely, without causing any damage. No fuses will blow, no overheating, and no expensive dry cells will be consumed. Furthermore its power is very stable at all electrical loads.

The idea of this experiment is to put a variable resistance load on the cell, and measure the voltage and current. The resistance can be varied from infinity to short circuit, and a very good power/voltage curve obtained.

This experiment cannot be done at reasonable cost with any other equipment commonly available in schools. It is an experiment that gives a very good balance between equipment handling, observation and processing of results.

Each group of students will require:-

Ammeter (0 - 1A)

Voltmeter (0 - 1V)

Variable resistor (0 - 25 ohms)

Connecting wires

Air cathode

Fuel cell anode

KOH solution and methanol OR NaCl solution

Instructions

1) Set up the fuel cell in the normal way.

2) Connect the voltmeter to cell, and measure the no load voltage.

3) Connect the ammeter, resistor and voltmeter as in the circuit diagram. Use the variable resistor to adjust the voltage to be 0.55 volts. Measure the current.

4) Repeat step 3 at voltages of 0.50, 0.45, 0.40, 0.35,....etc. Keep going to as low a voltage as possible. The value of the lowest voltage will depend upon the resistance of the ammeter.

5) Calculate the power from voltage x current. Plot a graph of power against voltage.

Likely Results

Using the fuel cell, and methanol fuel, the power will be a maximum at between 0.2 and 0.3 volts. The maximum power will depend strongly on the temperature of the cell and the concentration of the KOH solution, but should be between 50 and 100 mW.