Science Buddies: "Ask an Expert"

I will be building an electrical generator as part of my project. It uses moving magnets to create a current of electricity in coils of wire. This generator is technically called an alternator because the electrons move back and forth in the wire, rather than flowing in just one direction as they do from a battery. A meter connected to the wire would show that the charge of the wire switches or alternates between positive and negative as the electrons change directions. Such an electrical current is called alternating current or AC.

My question is: How to make a portable CD players use a alternate current?

Science Mac,

Based on your project description, I assume your generator will be harnessing the energy of your wind turbine to produce the AC signal. Is this correct?

First--you've obviously done some research on AC and DC current--and it looks great! You have a good grasp of it.

The difficult part, as you've anticipated, is to provide a clean DC signal from the AC output of the generator. The first thing to do is characterize the output of your generator, and without an oscilloscope, that is difficult to do.

The real value of interest is power--how much power your generator is producing. If your generator were attached to some resistive load R, you could measure the power by finding the voltage drop across the load (using a voltmeter, measure the voltage over the load, which is Vrms; the power dissipated will be (Vrms^2)/R. If you compare this power with the power required to run a discman, you're probably going to see you don't have enough power.

Now, even if you DID have enough power, you'd have to build a rectifying and filtering circuit to turn the AC into DC; it would have to be custom made because the output of your generator is likely not 120 V at 60 Hz, which is what most proprietary AC/DC converters for consumer electronics are based on.

After this brief analysis--I'd urge you to think of other types of loads. Do you have an idea of the power output of your generator? A small incandescent bulb might be great, as it runs off an AC signal already. Or, you could consider running an LED (or two). Since LEDs require DC based devices, there are options to create a circuit in which each one turns on during each half of the AC cycle.

Be creative, have fun, and be sure to ask more questions if you have them.

Adam

You are correct! From what I have heard by blowing on it should be able to produce between 1 and two volts. But we should try a more consistent way to test the turbine by using a stream of air from an appliance such as a blow dryer or a vacuum cleaner with the hose plugged into the discharge end.

Hi Science Mac,

If I am not mistaken you can build a DC generator by not using the "alternator" portion in your generator.
Here is a link:
http://www.phys.unsw.edu.au/~jw/HSCmotors.html#mandg
All you need to do is average out the half sinusoidal waveform (which is already positive).

However based on that website above a DC generator is more inefficient due to mechanics of the brush and split rings which causes jumps and sparks.

Anyway read more about it in the website above.

Good luck

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This the example of the turbine. It consists of two simple scoops that catch the wind and cause the shaft to turn. The turbine relies solely on drag to produce the force that turns their shaft. One side of the turbine catches the moving air more than the other, causing the turbine to spin.