Naked Science Forum
Non Life Sciences => Technology => Topic started by: YoungEngineer on 26/06/2012 18:58:27
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Hello all!
Currently I am doing a project on a chemical car and have some issues that I am not sure of how to tackle.
I am using a chemical reaction to produce both hydrogen and oxygen (not electrolysis) and passing it through a proton exchange membrane (PEM) to produce electricity to power a small engine (those tamiya engines).
The problem I am facing is that with only one PEM, it produces only 0.85 Volts and 350 mA where as the engine requires about 1.5 Volts and 660 mA. The question is, how do i step the volt and Amp up, and what parts do i need ? ..
p.s cant purchase another PEM as its the project constraint.
Warmest Regards and a thousand thanks !
Mod edit - formatted the subject as a question. Please do this to help keep the forum tidy and easy to navigate. Thanks.
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You can't, or at least you can't do it the way you want to.
The power is the product of the current and voltage.
What you have is 0.85*0.35 =0.2975 Watts
But what you want is 1.5*0.66 =0.99 Watts.
The only way to do it would be to find some batteries that you could charge from the PEM and then connect them in series to drive the motor. It would take roughly three times as long to charge the batteries as they would run the motor for.
But I don't think there are any rechargeable batteries rated for 0.85V
The other option would be to use a capacitor to store the energy.
And that gets even more complicated.
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If you could cut your membrane in half, you might be able to make two fuel cells out of one. Then, you should be able to wire the two haves in series to get about 1.6V (and 170 mA).
What happens if you increase the pressure slightly?
Are parts of either your chemical reaction or fuel cell exothermic?
What happens if you insulate the vessels for either the reaction or the fuel cell?
Many DC electric motors will run on slightly higher, or lower voltage than the rated voltage. And the rated amps may be primarily for starting the motor. And, thus, perhaps a capacitor in the circuit would get your motor turning, after which the power consumption might drop.
Will your motor run with the power supply you have, by manually starting it?
Here is a good description of why transformers don't like DC (http://wiki.answers.com/Q/Why_doesn%27t_a_transformer_work_on_a_DC_supply). So... what you would need is a very low power DC/DC converter. However, most of the ones I'm seeing seem to take about 3V input. I think this one (http://www.sii-ic.com/en/product1.jsp?subcatID=3&productID=1788) works on about the power range that you have. Obviously, if you double the volts, you halve the amps to preserve the same watts.
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May I draw your attention to these devices that will step up your low voltage source sufficiently to charge a battery or capacitor.
http://www.reuk.co.uk/DC-Voltage-Multiplier-Circuit-Plans.htm.