Potential power output of Coil

[nattyb52]

Hi, I'm new here and I apologize up front if my terminology is incorrect. I've been a Civil Engineer for over 30 years, but am very far from an expert in electrical. Sorry if this is an elementary school level question for you guys!

I am hoping someone here can either give me a hand or point me in the right direction.

I have a proposed electric coil design and was wondering if I am doing my power potential calculations correctly.

My "coil" at this point will be wound on an 2.5" long by 1/2" wide by 2" high iron or ferromagnetic core or spindle. I am looking at about 70 meters of AWG#20 magnet wire for the windings.

If I pass a neodymium magnet, Grade 42, gauss 13,200, 3" long, 1/2" wide and 1/4" thick directly under it, at a velocity of 2 m/s and 90 degrees to the long side of the coil I would like to be able to verify what amount of voltage I can get out of it. And then, based on the proposed circuit resistance, what power and current I can expect.

I've found and used the following http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genwir3.html#c1" page to get an approximation. I will be supplying approximately 300 pounds of force to push the magnet past the coil.

My best guess, using the formulas from the above web page, is that I can get 730 Volts. And applying 200 ohms of resistance to the circuit will lower the push force required down to 300 lbs. This gives a current of 3.65 amps and a power output of 2674 watts.

I realize the calculations are only theoretical and there are probably many other variables that come into play, but if any of you could help me verify the numbers, or point me in the right direction, I would really appreciate it.

Thanks much in advance for any help you can offer.

 

[nattyb52]

I've attached a quick sketch of a yop view of the coil as a pdf for anyone who is interested.

Thanks

 

[nattyb52]

Never mind, so sorry if I bothered you all.

 

[vk6kro]

Welcome to Physics Forums.

Most replies take longer than 4 hours because potential answerers are spread around the world. People sleep and go to work or even answer other questions or prefer to leave such questions alone.

You seem to have done a reasonable job of answering it yourself. The problem then is that there are some approximations that are a bit hard to deal with. These are usually settled by setting up a test and measuring the results.

The opposite poles of the magnet will have opposite effects on the coil and the actual geometry of the layout has a big effect on the result.

Only part of the magnetic field will pass through the coil and this is hard to estimate because the magnetic field is not evenly distributed around the magnet.

You can just connect the coil across the input of an oscilloscope and move the magnet near it as you propose and see what voltage you get out of it without a load.
If the coil is open circuit, the force required will be very small and you can do it by holding the magnet in your hand.

I suspect that your estimate is very optimistic, though. That is quite a small coil and that seems like an unlikely amount of power.

 

[uart]

I suspect that your estimate is very optimistic, though. That is quite a small coil and that seems like an unlikely amount of power.

Very optimistic indeed. A "back of the envelope" calculation gives me an answer closer to about 20 to 30 volts.

Nattyb52, how much flux linkage are you counting on getting in your calculations?

 

[nattyb52]

Thank you both for you reply. I did make a mistake. the numbers I show were for 4 coils not just one, but even then it seems excessive.

 

[nattyb52]

Welcome to Physics Forums.

Most replies take longer than 4 hours because potential answerers are spread around the world. People sleep and go to work or even answer other questions or prefer to leave such questions alone.

You seem to have done a reasonable job of answering it yourself. The problem then is that there are some approximations that are a bit hard to deal with. These are usually settled by setting up a test and measuring the results.

The opposite poles of the magnet will have opposite effects on the coil and the actual geometry of the layout has a big effect on the result.

Only part of the magnetic field will pass through the coil and this is hard to estimate because the magnetic field is not evenly distributed around the magnet.

You can just connect the coil across the input of an oscilloscope and move the magnet near it as you propose and see what voltage you get out of it without a load.
If the coil is open circuit, the force required will be very small and you can do it by holding the magnet in your hand.

I suspect that your estimate is very optimistic, though. That is quite a small coil and that seems like an unlikely amount of power.

Thank you, I'm sorry to be so anxious. It's been a long week already. :-)