circuit design

You could connect some of these MFCs together in a serial way to get the charge voltage for the battery you would like to charge. Then use a diode to allow the cell to charge the battery (and not pull the battery down when the cell isn't generating power). A series resistor might be needed to limit the current if the current output is greater than the battery can handle.

what is the current / power you are looking at?

Because the MFCs is in the lake, it could not connect together.

I do not understand what hesener means?

Hi, I was just asking how much power you would like to draw out of these cells - how many watts, and what would be the current level.

thanks

The cells only could supply about 0.5mW power and the current is about 1mA.

Thanks.

Hi, you will have to look at energy harvesting parts e.g. from Linear Technology

hope that helps!

Can you tell us more about the Microbial Fuel Cells? What do you use as fuel?

Cabe

Hi, first of all, its certainly cool working with MFC's

     now lets start with the design.

1. The necessary condition to recharge any kind of battery is that the charging voltage must be slightly greater than the voltage provided by the battery itself.
2. since the voltage provided by the mfc is arround 0.6v, a diode canot be used in between the battery and fuel cell as the knee voltage of a silicon diode is 0.7v and hence no conduction will occour. you may use a germanium diode but still a loss of .3v will occour.
3. in order to charge the battery, the voltage from fuel cell can be stepped up  by using a super capacitor. by charge slowly from the mfc source and discharge it in a very short period, the energy spread over a period of time is concenterated into a short burst of energy, there by increasing the voltage and current considerably. this technology is used in solar engines for BEAM Robotics.
4. the charging and discharging cycles of the super capacitor must be controlled such that the control circuity doesn't end up spending more energy than that created by the fuel cell itself. the 1381 based solar engine does the job pretty good!
5. thus the voltage from the solar engine would be arround 2.5 to 5v depending upon the design of solar engine and super cap used. this voltage can be used to charge a battery. here a diode can be connected in series to prevent the capacitor getting charged from the battery.
6. once the battery is sufficiently charged,it can be used to light up Leds(preferably).
7. for a 12v battery, the voltage from the solar engine can be stepped up to 12 v or more by using a pulse transformer but it will take longer to charge.

i belive it might be cool to connect the led directly to the solarengine. this way, the led flashes as the charging and discharging cycles takes place and the design remains simple and cheep. now imagine a pool full of such random flashing leds or patters forming in some synchronised manner!!

Hi all,

I would say that this diode businiess is not relevant as a MOSFET switch can be used instead with only millivolts of drop or instead, put several MFCs in series to make 5V, 10V, 12V or whatever and then a 0.3V Germanium or a 0.35V shottky diode won't be wasting much energy.To charge a 12V battery from the solar engine, no pulse transformer is needed, only an inductor, a switch (usually a MOSFET) and a diode to make a step-up or boost converter. Of course, it won't be isolated, but that doesn;t seem to be a requirement here.

Good luck.

Regards,

Kamran Kazem