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Calculating field density

  1. Jun 21, 2008 #1
    How do I calculate the field density, and mmf magneto motive force. I have the number of turns 750. The dia is 2.5 cm. The wire is #24 coated, copper magnet wire with a resistance of .025 ohms/cm/m. The voltage is 35,000v at 45 amps. the length of the solenoid is 10cm. the thickness is 50mm. the motive distance is 25mm to 9.5cm The duration of magnetic pulse is .10/sec. The core is iron 1018. how much mmf at the end of the rod and what is the field density at
    25mm and what is it at 9.5 cm? Im having trouble finding B. Im great with mechanics but formula's forget it. I tried plugging the numbers into the formulas I have, but It asks for B when Im trying to find B? Thought maybe you genius' could help. Thanks
     
  2. jcsd
  3. Jun 23, 2008 #2

    berkeman

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    What's the application?
     
  4. Jun 23, 2008 #3
    Ive designed an electromagnetic piston engine. I am affixing electromagnets concentrically to the cylinder bore of a 4 cylinder automobile engine. The pistons inside the cilynders are modified with a perminant magnetic N42 face. Polarity is +. The electromagnets are made of iron 1018 and act as the magnetic generator rod. The copper magnet wire is wound around the 25mm stem of the generator rod 750times.(starting point) I will excite the windings with 35,000 volts from an auto ingnition coil and generate a +polarity in the end of the rod which is closest to the piston face. I plan to follow the same timing sequence as the ECU of the automobile and intermittantly drive the N42 faced pistons away from the magnetic force down into the cylinder. I need to attain a piston speed of 16m/s. The piston weighs .76kg and requires a 6N force to move it. Basically the electromagnet is swapped in place of the spark plug. So the voltage and the duration are not changeable just the number of turns of wire.
     
  5. Jun 23, 2008 #4
    Well actually they are changeable but not as easily as adding or subtracting windings. The number of windings can go up quite a bit, theres plenty of room for it. The equation Im using asks for B over 2 to be multiplyed all the brackets off work done previously. Whats B ? Heres what ive got.
    B {_________( X+T)______ - ___________X________}
    2 [R*2+(X+T)*2]*1/2 [R*2 + X*2]*1/2
    The asterics show where the next number should be.
    Ie; R is squared. The lower case or divisor brackets are to the power of 1/2. One half. Ive never done it like that before. This is why im asking for help. Believe me Ive tried its just out of my depth. Im a mechanical designer.... But its not helping me much here. The formula gets squished in this little box The two sets of brackets go under the X+T and the X It begins with b over two. So if you dont know b how can you use it in the eqation? Any help would be greatly appreciated.
     
    Last edited: Jun 23, 2008
  6. Jun 23, 2008 #5

    NoTime

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    This will not work.
    What creates a magnetic field?
    What are the output characteristics of an auto ignition coil besides the peak voltage?

    Why would you want to try this?

    Normal electric motors are constructed the way they are for reasons.
    You need to understand the concept of magnetic circuit.
     
  7. Jun 23, 2008 #6
    The copper coil has 35,000v current running throught it. This current is distributed to each electromagnet intermittantly. It is wound around an iron core. The iron core becomes an electromagnet. A field of magnetic energy runs alog its axis out the ends creating a north and south pole. It returns through the air. This is my circuit. This energy can do work. Im asking for help calculating the field desnsity at one of the poles. The reason? To generate an electromotive force. Electric motors draw alot of current. Under load they draw alot more. A constant drain. This is not good for batteries. I have another electrical source besides batteries but the answers I need are based on battery capabilities. Can you help? Thanks
     
  8. Jun 24, 2008 #7

    berkeman

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    What does your 35kV waveform look like when driving just spark plugs? What does it look like when you try to drive a coil inductance with it?
     
  9. Jun 25, 2008 #8
    The primary wave has a spike @ 88*deg. starting at .009 and the secondary wave ending at .012 it peaks at 730 The electro magnet is a sine wave of unknow feq. Im not a pro at this. what numbers do you need to determine B?
     
  10. Jun 26, 2008 #9
    Any idea how much current is generated in your 35kV pulse?

    Magnetic field is related to current not voltage. <gentle hint...>
     
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