Science Buddies: "Ask an Expert"

Hi,

My son did the Fueling the Future, fuel cell project last year in 5th Grade. It was hard for him, but he loved it! I purchased the wrong fuel cell, a less powerful one, but it ending up working okay. Now my son is in 6th Grade and will be starting his science fair in a week or two. He would like to do another fuel cell project. Does anyone have any ideas?

Last year in his conclusion he had put that if he did this project over he "would change the load or motor to see if it would change the results." He likes his ideas of changing the load, but would like other ideas as the project would be more or less running the same test with a different load and comparing the results from those of last years.

On another note, the fuel cell he has is only a single cell and not that powerful. He really wants me to purchase a larger fuel cell, but I am trying to be cost effective. The results he got last year were a little less effiency (44% instead of 50-70%) and the judge at the science fair for Regionals did say that the kind of fuel cell he has is a little touchy. Meaning that it doesn't always give the most accurate results. My question to you is should I purchase another fuel cell or do you think it would be fine to just keep the one he has for his 6th grade science fair? He won 1st place in Regionals and really wants to make it to State this year. Not being a science person, I would really like your opinion.

Thanks,
Shannon

ShannonE13 - The optimum transfer of power from the fuel cell to the load will occur when the impedences of the source and load are the same. If the specifications of the output impedence of the fuel cell can be determined from spec sheets, just use that value as your load. If it is not available you can determine the output impedence by conducting load line experiments using several values of resistance and measuring voltage and current. Do a search on 'load-line' to help your experimentation. Good luck.

Rick Marz

Note: The output impedance of a fuel cell may not be constant so be sure to use multiple load points to characterize its impedance at multiple load factors.

Thanks for the reply. I must admit that as the parent I am completely lost, but will have my son view your post. It is hard, because he is so good in science and I am not. He wants to become a Nuclear Physicists.

So is it okay to keep the same fuel cell? And his idea about changing the load would be a good science project?

Shannon - You centainly you can use the exiting fuel cell for an experiment. As Craig pointed out the impedence of the load cell is not necessarily a fixed value. My suggestion to calculate the load line of the fuel cell using a number of resistive load values will help characterize the device. The load line would consist of a graphic plot of the voltage and current using different load values. From the curve of these plotted values, the impedence can be estimated and further refined. A graph of power equations with different loads could be calculated and demonstrated. This could become the thesis of his experiment. How fuel cells work and how to optimize power transfer from the fuel cell by matching it to the load impedence. He can probably find many suitable references on the web.

Rick Marz

Thanks Rick!

I will have Craig read your post.

Shannon