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Efficiency of a hydrogen fuel cell

  1. Nov 4, 2007 #1
    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.
  2. jcsd
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