[SteveJanesch]

Jose,

When you put two batteries with unequal voltages in parallel, the lower voltage battery acts as large load on the higher voltage battery. The stronger battery tries to recharge the weaker one in addition to drive whatever load is placed on them. The net output voltage is somewhere between the two voltages, depending on the relative strengths of the batteries.

When the fuel cell charges the capacitors, the caps' voltage will eventually equal the maximum voltage the fuel cell can produce. If you then stack the caps in series, that will nearly double their output voltage.

Question 1: What's the output voltage and current capability of your fuel cell?

Question 2: What happens when you put the stacked (double voltage) caps across the output of the fuel cell? I think that at best the output current of the fuel cell will drop to zero, since the higher voltage of the capacitor stack will dominate the cap/fuel cell combination. You'll be driving your motors off the capacitors only, which may be okay. Worse could be that the fuel cell draws current out of the caps, away from the motors, and you get no net benefit. Worse yet is that somehow the high voltage on the output prevents the fuel cell chemical reaction from happening, hydrogen gets vented from the fuel cell near something hot (from the overvoltage at the output), and manages to ignite outside the fuel cell. I'm dangerously ignorant about the fuel cell you're using, but I've seen a few things catch fire when too much voltage is applied.

I'd suggest you first check your data sheets for what happens when your fuel cell is subject to too high a voltage on the output. Next, if explosion is unlikely, you might try to mimic the situation you're proposing with a power supply or batteries. Good luck.

Steve