How do I convert a small AC current into DC current?

Thread Starter

b2386

Joined Feb 9, 2010
13
I'll make a longer reply/update post tomorrow, but I have a quick question. Let's say we use a rectifier/voltage doubler circuit on the generator output. What will this do to the coil (source) resistance as seen by my battery I am wanting to charge? Using 32 gauge wire, the total coil resistance is about 60 ohms.
 

wayneh

Joined Sep 9, 2010
17,496
I'll make a longer reply/update post tomorrow, but I have a quick question. Let's say we use a rectifier/voltage doubler circuit on the generator output. What will this do to the coil (source) resistance as seen by my battery I am wanting to charge? Using 32 gauge wire, the total coil resistance is about 60 ohms.
I can't think of how to do the math on that, but the guiding principle is that you can't get something for nothing. So I'd guess that doubling the voltage at least doubles the impedance and cuts the current in half that you can draw at peak power.
 
I can't think of how to do the math on that, but the guiding principle is that you can't get something for nothing. So I'd guess that doubling the voltage at least doubles the impedance and cuts the current in half that you can draw at peak power.
Add to that the conversion will also take some power.
 

Thread Starter

b2386

Joined Feb 9, 2010
13
Re: How do I convert a small AC current into DC current?
Question about the coil:

As you can see in the first attached picture of one of my previous posts, this coil is basically two smaller coils glued together with a plastic washer in between. During testing, all four leads (two per coil) are accessible. We have to connect a lead from each coil together such that the generated emf from each coil adds together. If we connect them together incorrectly, the emf's from each coil will subract and we will get a poor output. Correct?

This has been our thinking thus far. Well, today we made a coil about the same height as the one in the picture seen above, but it was made out of one continuous wire strand (basically one big coil). We did not get very good results with it. Here is my thinking:

Let's assume the magnet is in the middle of the coil and is moving upward. For the top half of the coil (where the magnet is moving towards it), the flux is increasing with time, and creating a positive voltage in the top half of the coil. At the same time, a similar thing is happening in the bottom half of the coil except, since the magnet is moving away, a negative voltage is created here. Since the top and bottom half of the coil have opposite voltages, the total emf(voltage) of the coil is very low.

Is this what is happening and does it make sense?
 

wayneh

Joined Sep 9, 2010
17,496
First, I'd check that the coil's resistance makes sense given the length of wire.

Is the magnet polarized along its axis? Assuming so, the field would be densest in the magnet itself and then would diminish rapidly as it spews out into the air and loops back around to the other pole. You might get a better result by providing a magnetic path for that, such as a U-shaped bracket around the coils two ends.

An emf is generated in the coil when it sees a CHANGING magnetic field. If your magnet was very long and uniformly magnetized, I think you'd see no emf at all as the coil moved along it, until you get to the end where the field changes. So your bigger coil adds more resistance but no more emf.
You may be right that part of the coil sees an increasing field as the magnet's leading edge goes by whereas another part of the coil sees a decreasing field as the trailing edge pulls away. Those ought to cancel.
 
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