# Efficiency of a hydrogen fuel cell

1. Nov 4, 2007

### redsox5

I'm trying to calulate the efficency of a small hydrogen fuell cell that I built. I have all of the measurements, but I'm not coming up with a resonable effiency.

The power to electrolyze the water is the P IN.
3.25 W =2.5 V x 1.3Amps (.21 mA)

We measured the electrical power out finding the voltage and amperage.
P OUT = V x I
2.01 x 10^-4 W=.96 V x .00021 AMPS (.21 mA)

I caulcate the force to be 1.421 N

Then I take the electrical P Out and use it as the P IN for the car

the P IN for the car is the electrical P Out

and the P Out for the car is F x V

To find the % efficiency:

The avg velocity is .0198 m/s

For the car: (there is something wrong here since I'm getting more power out)

P in = 2.01 x 10^-4 W
P Out = F x V
2.81 x 10^-2 J = 1.421 N x .0198 m/s

I'm coming up with an unreasonable calculation

Isn't watts joules per second. Should I be including the time it took to electrolyze the water. I'm just using the formula i was given, but the units don't work out

Also I'm not sure if i'm calculating the force in th right way. We used a spring scale and my measurement was .160 kg. I'm I just supposed to multiply that by 9.8 m/s^2. I know that this way gives me Newtons, but the car isn't being affected by gravity anyways. If someone could look this over I'd appreciate it.