Ohms Law is E=IR
Volts equals Current times Resistance,
in Magnetics, Ohms Law goes like this:
Force = NI, where N is turns and I is current.
N can be thought of as a resistor in a circuit because the more turns you have, the more inductive reactance you will have due to the increased inductance,
and inductive reactance is the resistance to an AC voltage.
so F is E, N is R, and I is I , E=IR > F=NI
so if we increase current or turns, the force goes up,
there is another version of this formula that looks more like Ohms Law>
F = Φ R, where F is the MMF or Magneto-Motive Force, Φ is Flux and R is Reluctance.
Reluctance is the "resistance" of core to be magnetized,
The longer the magnetic path length, then the higher the reluctance,
adding an air gap does the same thing as increasing the magnetic path length,
if you hold Flux constant and raise the reluctance of the core by increasing the gap, then the force will go up.
but it will take more exciting current to keep the flux the same so you do not get anything for free by increasing the gap, you must make up for the loss of the increased gap,
increase the gap and increase the Flux by injecting more current, you will get a stronger magneto-motive force.
so you can think of F as the E in Ohms Law,
and Reluctance can be Resistance,
Flux can be thought of as current,
F = Φ R ,
F is "Magnetic Voltage", or "potential" , or "magnetic potential"
Φ is Current
R is Resistance (of the core)
see that raising the resistance of the core by adding a gap does Not "short out" the magnetic potential, but actually makes it increase, so yeah, the dude messed that up,
ok, this is a good summary>
Sequence of operation
In transformer design you would normally like to deal in terms of the voltages on the windings. However, the key to understanding what happens in a transformer (or other wound component) is to realise that what the transformer really cares about is the current in the windings; and that everything follows on from that.
The current in a winding produces magneto-motive force -
Fm = I × N ampere-turns
The magneto-motive force produces magnetic field -
H = Fm / le ampere-turns per metre
The field produces magnetic flux density -
B = μ × H tesla
Summed over the cross-sectional area of the core this equates to a total flux -
Φ = B × Ae webers
The flux produces induced voltage (EMF) -
e = N × dΦ/dt volts
If you can follow this five step sequence then building a mental image of a magnetic component becomes simpler. Remember, you put in a current and get back an induced voltage. In fact, if you can treat the permeability as being linear, then the constants N, le, μ and Ae can be lumped together into one constant for the winding which is called (surprise!) Inductance, L
L = μ × Ae × N2 / le henrys
Volts equals Current times Resistance,
in Magnetics, Ohms Law goes like this:
Force = NI, where N is turns and I is current.
N can be thought of as a resistor in a circuit because the more turns you have, the more inductive reactance you will have due to the increased inductance,
and inductive reactance is the resistance to an AC voltage.
so F is E, N is R, and I is I , E=IR > F=NI
so if we increase current or turns, the force goes up,
there is another version of this formula that looks more like Ohms Law>
F = Φ R, where F is the MMF or Magneto-Motive Force, Φ is Flux and R is Reluctance.
Reluctance is the "resistance" of core to be magnetized,
The longer the magnetic path length, then the higher the reluctance,
adding an air gap does the same thing as increasing the magnetic path length,
if you hold Flux constant and raise the reluctance of the core by increasing the gap, then the force will go up.
but it will take more exciting current to keep the flux the same so you do not get anything for free by increasing the gap, you must make up for the loss of the increased gap,
increase the gap and increase the Flux by injecting more current, you will get a stronger magneto-motive force.
so you can think of F as the E in Ohms Law,
and Reluctance can be Resistance,
Flux can be thought of as current,
F = Φ R ,
F is "Magnetic Voltage", or "potential" , or "magnetic potential"
Φ is Current
R is Resistance (of the core)
see that raising the resistance of the core by adding a gap does Not "short out" the magnetic potential, but actually makes it increase, so yeah, the dude messed that up,
ok, this is a good summary>
Sequence of operation
In transformer design you would normally like to deal in terms of the voltages on the windings. However, the key to understanding what happens in a transformer (or other wound component) is to realise that what the transformer really cares about is the current in the windings; and that everything follows on from that.
The current in a winding produces magneto-motive force -
Fm = I × N ampere-turns
The magneto-motive force produces magnetic field -
H = Fm / le ampere-turns per metre
The field produces magnetic flux density -
B = μ × H tesla
Summed over the cross-sectional area of the core this equates to a total flux -
Φ = B × Ae webers
The flux produces induced voltage (EMF) -
e = N × dΦ/dt volts
If you can follow this five step sequence then building a mental image of a magnetic component becomes simpler. Remember, you put in a current and get back an induced voltage. In fact, if you can treat the permeability as being linear, then the constants N, le, μ and Ae can be lumped together into one constant for the winding which is called (surprise!) Inductance, L
L = μ × Ae × N2 / le henrys
