I was suggested to use an iron core for an inductor. I found that it has low permeabilty and good stability, but how does that make it a good material for the core. And is there a way to figure out the saturation condition for it?

The one i am using is: http://www.micrometals.com/pcparts/torcore5.html - T-130 - 52


Most applications of iron powder cores are substitutions of inductors made of ferrite cores. These applications include DC/DC converter output filter inductors and power factor correction inductors.

In these applications you need the energy storage capability (proportional to \$ B \times H \$; all quantities are magnitudes) of the inductor core. Ferrite cores have a high permeability so you need to introduce an air gap to reduce this permeability, thus increasing the magnetic field \$H\$ strength needed to magnetize the core to a flux density \$ B \$. This air gap has a severe disadvantage: within the air gap the relative permeability is reduced to unity and this causes the flux to exit the core and enter the winding, leading to eddy current losses in the winding. The power loss density is concentrated around the air gap, so there is the risk of a hot spot.

Iron powder cores do not need the additional air gap since it is integrated into the material and, in consequence, spread within the complete core volume. This reduces the eddy current losses in the winding and the remaining eddy current losses are distributed throughout the winding length.

Furthermore, energy storage is limited by the saturation flux density. In ferrite this saturation flux density is about 400 mT and decreases with temperature. In iron powder cores saturation flux densities of more than 1 T can be utilized, depending on the material.

As you mentioned Micrometals core: Micrometals, Inc. offers an Inductor Design Software that can be used to design basic inductors including power loss calculations.

  • \$\begingroup\$ Since B and H are linearly related (ignoring M - magnetization) could you explain why you wrote BXH ? \$\endgroup\$ – placeholder Sep 30 '13 at 16:29
  • \$\begingroup\$ For ferrite cores this linearity assumption is valid as almost all the energy is stored in the air gap. In powder cores the energy density is distributed in the core volume and because of this, besides other reasons, B and H are not linearly related. \$\endgroup\$ – realtime Sep 30 '13 at 17:02
  • \$\begingroup\$ More to the point, perhaps you can explain how the material generates a different vector direction that justifies the use of a cross product? \$\endgroup\$ – placeholder Sep 30 '13 at 17:11
  • \$\begingroup\$ It's not a cross product, B and H are scalars in this equation. If they were vectors (usually denoted by boldface) you would have to use the dot product to get the correct result. \$\endgroup\$ – realtime Sep 30 '13 at 17:15
  • \$\begingroup\$ Well that ONE convention, there are many. I suggest you edit the post to make that clear. \$\endgroup\$ – placeholder Sep 30 '13 at 17:18

If you know what flux density the material saturates at and you know what the BH curve for the mateial is you can calculate H: -

H = \$ \dfrac{ampere \times turns}{effective\space length\space of\space core}\$

The effective length of the core should be quoted in the product spec but for a toroid you can calculate it easily - take the mean radius (R) to the mid-point of the core and use \$2\pi R\$ as that length.

  • \$\begingroup\$ +1 I just want to add here, that if there is an air/plastic gap this doesn't apply anymore. Since most of the magnetic voltage will drop there. Hence H drops heavily inside the core. \$\endgroup\$ – Felix Crazzolara Feb 8 '17 at 16:40
  • \$\begingroup\$ I agree wholeheartedly. \$\endgroup\$ – Andy aka Feb 8 '17 at 17:37

protected by Community Feb 17 '17 at 11:24

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