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Comment 21 ... 30

date	article	author	comment
11 jul 2021 14:12:18	Magnetic circuits	Guy	Freddy, you wrote that the energy stored per volume in a magnetic field is calculated as: w = 0.5 * B^2 / μ. However, B conceals another μ, you could equally have written w = 0.5 * μ * H^2. And now the opposite is true, the higher the μ, the higher the stored energy. I need to refresh my physics studies but as far as I remember, H is invariant when crossing material boundaries while B by its definition is affected.
11 jul 2021 13:24:24	Magnetic circuits	TalkingElectronics	You wrote: "When the core is saturated, it will not "accept" or "deal with" further increases in current." When I connect an inductor to a DC power supply, the current will increase with a steady pace until the core approaches the saturation region. From here the current increasement wil accelerate to an much higher dI/dt as if there was no core present. There is no point where the current will reach a steady value. You have not understood what I am saying. When you apply current at a low value, it turns into magnetic flux and when the current is turned off the magnetic flux collapses and returns voltage and current into the winding. This process is effectively available up to the point before the magnetic circuit is saturated. If you apply current past the point of saturation, only the magnetic flux up to the point of saturation is returnable. The last section I can't follow. Magnetic flux is not lost unless you have an magnetic leak. Now every magnetic circuit has magnetic leaks, but this is not what you referring to. If air gaps wasted energy, then the air in the gaps would be quite hot. This is not the case. The whole idea of an air gap is to "use up" the magnetic flux that would be generated by the DC component of the waveform so that only the amplitude of the waveform above the DC component is delivered to the magnetic circuit.
11 jul 2021 13:15:52	Magnetic circuits	Freddy	The energy stored per volume in a magnetic field is calculated as: w = 0.5 * B^2 / μ How lower the permeability μ, how higher the stored energy per volume. This is also shown in the equations in this article by replacing H of equ. 13 with equ. 2. And it is also stated in the wiki article about magnetic energy. You wrote: "When the core is saturated, it will not "accept" or "deal with" further increases in current." When I connect an inductor to a DC power supply, the current will increase with a steady pace until the core approaches the saturation region. From here the current increasement wil accelerate to an much higher dI/dt as if there was no core present. There is no point where the current will reach a steady value. The last section I can't follow. Magnetic flux is not lost unless you have an magnetic leak. Now every magnetc circuit has magnetic leaks, but this is not what you refering to. If air gaps wasted energy, then the air in the gaps would be quite hot. This is not the case.
10 jul 2021 22:35:48	Magnetic circuits	TalkingElectronics	You have the wrong idea about an air gap. The magnetic core will store 1,000 times more energy than the air gap. When current flows through the turns of a coil it produces magnetic flux. Suppose the current flowing is 1 amp. If you have a magnetic circuit without an air gap, it maybe the case where it only takes 100mA to fully saturate the core. When the core is saturated, it will not "accept" or "deal with" further increases in current. So we introduce an air gap and 90% of the magnetic flux from the first 100mA is LOST in the air gap and the magnetic circuit only sees 10%. This allows the next 100mA to deliver some of the flux to the magnetic circuit and this concept will continue to 100%. An AIR GAP does not STORE - it WASTES
10 jul 2021 22:17:41	Magnetic circuits	TalkingElectronics	My discussion of a class-A amplifier is just an example of a DC component of current flowing all the time and the current reduces and increases slightly to create the AC component. This can occur in many situations including the old-style DC power supplies using a 3-terminal regulator.
10 jul 2021 20:52:55	Magnetic circuits	Freddy	Are you trying to tell me that class-A amplifiers with output transformers are the main usage for transformers and inductors? Are these devices not a little bit outdated or at least a rarity? I thought that Switch Mode Power Supplies the mayor usages where for core containing transformers and inductors. If an air gap can store more energy than the core is to be fair a tricky one. It really depends on de the reference parameters. Fact is that an inductor with the same core and inductance can handle much more current and store much more energy if it has an air gap. Be aware that the number of turns between an inductor with and without an air gap are not the same to obtain the same inductance value.
10 jul 2021 12:00:13	Magnetic circuits	TalkingElectronics	The main reason is that you can store more energy (per volume) in air than in ferrite or iron. This is untrue.\\ \\ Air gaps are usually applied in inductors. This is untrue. And inductor MAY have an air gap or it may not. \\ \\ Read my discussion above about the basic reason for an air gap. \\ Colin Mitchell\\ Talking Electronics.com \\ talking@tpg.com.au
10 jul 2021 11:48:35	Magnetic circuits	Freddy	Air gaps are usually applied in inductors. The main reason is that you can store more energy (per volume) in air than in ferriete or iron. But making a the entire core out of air is inpractical due to the low permeability of air. A low permeability requires more windings for the same induction value. This results in a bigger inductor bigger and the copper losses increases. So, the size of the air gap is a well calculated balance of the pros and cons.
10 jul 2021 11:06:44	Oscilloscope probes	Freddy	Maxwell says: don't look at me, look at Michael (Faraday). An object (core) that is magnetisize by an external magnetic field (a current through a wire) is called magnetic induction.
09 jul 2021 23:34:56	Magnetic circuits	Talking Electronics	AIR GAP IN A MAGNETIC CORE\\ There are a number of reasons why an air gap is NEEDED in a magnetic core. \\ Suppose we have an audio amplifier with a CLASS-A output stage. This is a stage where the output is biased so that 50% of the maximum current is flowing when the amplifier is at rest and the output device (such as a transistor) is turned on MORE during part of the cycle and turned on LESS for the other part of the cycle to produce a sinewave. \\ Because 50% current is flowing during QUIESCENT conditions, this current could quite easily be sufficient to fully saturate the magnetic core, so that when the transistor turns on MORE, the magnetic core cannot accept the increased magnetic flux. \\ The answer is to add an air gap by using sheets of paper between the stack of "E" pieces and "I" pieces where the end faces of the E laminations meet the I laminations. \\ What you do is simply add thin sheets of paper and deliver a sinewave to the transformer and use a CRO to detect the best output (without any clipping).\\ In other words, an air gap is used to eliminate the effects of DC SATURATION.

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