# Battery Charging Question: Is this Possible?

Discussion in 'The Projects Forum' started by PEM-Pal, Jun 13, 2007.

1. ### PEM-Pal Thread Starter New Member

Jun 13, 2007
2
0
Hi All,

I'm considering installing an electric bicycle kit that uses 3 12V batteries to power a 600W motor. At the same time, I'm designing a hydrogen fuel cell (Proton Exchange Membrane Fuel Cell) to add to the system. I can't afford to make a large enough fuel cell to power the bike alone (without batteries), so here are the questions I'm having trouble with:

If the small fuel cell is to act as a power supply to simply charge the batteries and extend the riding time, is it possible to charge and use the batteries simultaneously? Could I use something like an automotive voltage regulator?

If the 12v batteries are wired in series to provide 36v, should my "fuel cell charger" put out 12v or 36v?

Thanks in advance to all the senior and junior professors of the University of the Internet, "AAC" Campus!

Rich

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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For a charge in series, the fuel cell would have to provide enough voltage to overcome the total voltage. A lead-acid cell consists of 6 2.2 volt cells, so battery voltage at full charge is 13.2 volts. Your fuel cell would have to put out better than 39.6 volts.

It would also be the preferred current source, as it's voltage would be greatest. You will need to provide limiting resistors for the fuel cell to protect it, or usr a transfer relay to keep it out of circuit when the batteries are providing motor current.

3. ### cumesoftware Senior Member

Apr 27, 2007
1,330
11
Yes, if the current from the fuel cell is bigger than the one that is biasing the motor. If not, the battery would discharge.

4. ### PEM-Pal Thread Starter New Member

Jun 13, 2007
2
0
Great. So would it work if I use a 12v fuel cell with a step up DC/DC converter (12v in 42v out), and simply hook them up in parallel before the throttle switch? Could I then "trickle charge and ride" simultaneously (or in effect extend battery life)? Rich

5. ### cumesoftware Senior Member

Apr 27, 2007
1,330
11
To recharge the batteries, the voltage supplied by the cell has to be a little bigger than the voltage of the battery (or series of batteries). That is other condition you have to ensure.