Hi. I'm Gary Raposa with Agilent Technologies and today I'd like to talk to you about testing
a fuel cell using an Agilent electronic load. So first just a little brief information about
fuel cells. This is actually a 20-cell stack. It's a stack of 20 individual cells. An individual
cell would look something like this. And it's made up of several graphite plates like this.
There's 20 of them in this stack. And these graphite plates are stacked together with
membranes in between. And the purpose of the membrane is to allow a fuel like hydrogen,
and we have a tank of hydrogen back here, to flow. And the membrane and also oxygen
flows on the other side. And the membrane acts to separate the hydrogen and oxygen into
electricity, which is what comes out of the fuel cell, which we can test with the load.
And the only by-product is water – H20. So it's a very clean source of energy using
pure hydrogen as a source of fuel. All right. So I've actually hooked up this fuel cell
stack to our source of hydrogen and I've actually purged any of the air that was in here out.
And I've got a fan on top of the stack, also. It's forcing the oxygen, just in the regular
ambient air here, down through these graphite plates that can go down this side. The hydrogen
is trapped in this cutout on each of these plates and it runs through holes in the plates
as well but the oxygen is free to flow from the air. So I've got a fan hooked up to another
DC power supply here just forcing oxygen down. Hydrogen is coming from the tank through a regulator.
And I've got the plus and minus of the fuel cell stack running to my electronic load,
which is down below here. So we can see actually right now I've got about 14.5, about 14.6
volts coming out of the fuel cell stack and I've got the load set to roughly 0.2 amps.
So we've got 0.2 times 14 - 2.8 watts. Let's see. We can look at the power on here.
So,yeah. We've got about 2.8, 2.9 watts of power coming out of there. So I can increase the
current. The current, let's say even a half an amp, and now a half an amp at about – the
voltage dropped a little bit to 11.6 volts so that's about five watts of power, almost
six watts. And I could increase the current further, probably get several amps out of
here but not too much. The voltage will begin to drop. It can get probably about maybe between
10 and 20 watts total out of this particular stack. And I might have to adjust the flow
of both the hydrogen and the oxygen a little bit in order to maintain that, but this is
just a good starting point just to get you to see that the load is able to draw DC power
from the fuel cell stack. The other really interesting thing that we can do with this
electronic load is I can use a function generator, which I have set on top here. And the output
of the function generator is actually run around to the back of the load. And I've got
this set for a sign wave and I can make small perturbations on the DC current that's flowing
by programming an external current on the back of the electronic load. And so riding
on top of this DC is a small AC current. Now this load is also capable of digitizing its
own output voltage and its own output current. And I have a program that can read those digitized
values back and it can actually calculate the impedance of the fuel cell based upon
those sine waves. Even a complex impedance, with a real value and an imaginary value.
So, if you do that over a spectrum of frequencies, you get what’s called an electro-chemical
impedance spectroscopy measurement. And actually, I have a product note here which you can download
from Agilent’s website and we also have some software that is also free to be used, which
controls one of these function generators and this electronic load. You can set a start
frequency, a stop frequency, it will run through various frequencies in between those ranges,
calculate the impedance, and plot that out on a graph in an Excel spreadsheet so you
can see what that impedance of the fuel cell looks like over a frequency range. Once again,
that software is free and can be downloaded from our webpages. So just to summarize, the
Agilent N3300 DC Electronic Loads have some very unique properties that are quite useful for testing
fuel cells, for pulling DC power from them, but also for superimposing that AC waveform on top of the
DC in order to make impedance measurements.