Generator coil output - Sorry if it's a stupid question 6

[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 HyperPhysics 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]

Waross, thank you for your input.

What you are describing sounds like a solenoid. Is that right?

I know a toroid is one of the most efficient shapes for controlling flux density, but I thought one of the important points for electricity generation was to have the magnet poles pass at 90 degrees to the coil windings. If the magnet were to be passed through the core/windings as you describe, how would you orient the magnet poles in relation to the wire? Maybe I'm not visualizing it correctly.

 

[electricpete]

I guess there are potential benefits and potential disadvantages of that construction. It definitely could work well depending on the geoemtry. If diameter of the cutout hole is same as width of the original ring, then the bypass path is narrow/limited and may even tend to saturate, which would help. And the benefit I'm sure Bill was envisioning is reduced airgap (the equivalent airgap when magnet aligned along the ring would be the width of the magnet)

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(2B)+(2B)' ?

 

[electricpete]

As clarification, my 10 May 11 11:21 post was followup to my 10 May 11 11:16 post, not to nattyb52's post.


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(2B)+(2B)' ?

 

[waross]

Hi guys. The purpose of my suggestion was to illustrate the relationship between MMF, total flux, flux density and the length of the magnetic path.
Pete, imagine the cutout circle to have a 1/4" slot cut midway across it and the magnet (i/4" thick) placed in this slot. No iron bridging across the ends of the magnet but of course some leakage flux.
We have a ring that is 1" across. Not the diameter but the external radius minus the internal radius. We have cut out of this ring a 1" circular piece and inserted the magnet into this piece. We have replaced this piece and are now rotating it. When the magnet is at right angles to the ring there will be maximum flux in the ring. 180 degrees later the flux will be maximum but in the opposite polarity. A wire coil wound around the ring (the wire passes through the hole in the center of the ring on each turn) will have a voltage induced in it by the varying magnetic flux in the ring. The ring may be replaced by a rectangular shaped core.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Thanks Bill. I agree, once it was clarified that the hole will be approximately the same width as the ring.

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(2B)+(2B)' ?

 

[nattyb52]

Pete and Waross, thank you for all your help. I really appreciate it.

I know that increasing the velocity will increase voltage, but is it proportional or exponential?

When you talk about cross sectional area, are we discussing only total winding cross section or is it core cross section, or both?

Thanks again

Jim

 

[waross]

Proportional.
Core area.

Bill
--------------------
"Why not the best?"
Jimmy Carter