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Summary of common problems with magnetic materials
Time:08/14/2020
1. Question: How to determine the AL value? Why was the determination made at 5 Gauss?
 
Inductance is measured using Bridges of different voltages and frequencies. The flux density should be less than 10
 
Guass (1 mt). Under the condition of magnetic is generally single-layer windings at a certain number of turns of tightly wrapped around the core surface. Under the condition of low Guass measurement is very important. Magnetic material properties at the time of high driving change is very big. Because a given by the application of the magnetic core is different, so for vendors, will be given a low state of nominal measurement characteristics under different requirements in order to ensure the use of. For details on this issue, please refer to Magnetics Brochure MMPA SFG
 
Magnetic material permanent magnet
 
2. Question: Why is the core different from the magnet?
 
Permanent magnet is hard magnetic material, which is its magnetic is almost constant, don't change with the external conditions (normal). The magnetic is delineated the. When I was by the manufacturers and the core is "soft Ci" material, its B - H curve. (B - H of hard magnetic material is a point). So, can be used for winding winding to make inductor or transformer, etc. (Magnetics (vendor) with permanent magnet products)
 
3. Question: What are the effective parameters of the magnetic core?
 
Magnetic core, ferrite materials, in particular, its various geometry size, etc. To meet the requirements of a variety of different design, the size of the magnetic core is to determine the optimal suitable for requirement and calculation. These existing core parameters, such as magnetic path, effective area, and physical parameters such as effective volume, etc. The specific content, please refer to the relevant manuals, such as the Magnetics MMPA SFG, etc.
 
4. Question: How does Magnetics measure insulation and how does it work?
 
Core to use two would be after making some pressure at both ends of the mesh line pad points way to measure its breakdown voltage value. Meanwhile, the applied pressure is 10 psi, simulation winding pressure. The experiment using the effective voltage value is 60 Hz. Query manual winding products catalogue in order to get the breakdown voltage of the magnetic core and their corresponding guarantee. Users should pays much attention to their actual use of winding number, especially when using large winding pressure, mechanical deformation may occur, so, it is possible to change the breakdown voltage of magnetic core values; Exceeding the pressure limit may damage the outer protection of the magnetic core, resulting in a decrease in its breakdown voltage.
 
5. Question: Why is the radius of the angular circle very important for winding?
 
The angular radius is important because if the core's edge is too sharp, it can break the insulation of the line during precise and tight winding.Magnetics takes great care to ensure that the core's edge is smooth. Ferrite
 
Core production mold. There is a standard roundness radius and the magnetic core is through polishing and deburring processing, in order to reduce its sharp edge. In addition, the most core after paint or covered with not only makes the Angle passivation, more make the wound surface smooth. Powder core has a radius is pressure, on the other side is a semicircle deburring processing. For ferrite materials, provide additional covered in a fringe.
 
6. Question: What kind of core is suitable for making transformers? What types of inductors are suitable for making?
 
Meet the need of transformer core should have on the one hand has the high magnetic induction intensity, on the other hand to keep the temperature within a certain limit. Strip (with) material should have high induction strength and is usually applied to 20 KHZ in the following situation. In the case of more than 20 KHZ, material can meet the requirements of the unity of, because of its high frequency of cases has lower core loss (low temperature) for inductance, magnetic core should have certain air gap to ensure its high dc or ac In the driving condition, there is a certain permeability level. Ferrite and band core can be treated with air gap. Powder core has its own air gap. The APB-2 and CG-02 manuals of Magnetics are available.
 
7. Question: Why is the AL value generally provided only in iron powder core and iron oxygen core, but not TapeCore core?
 
With wound core is generally applied to the transformer or square ring, so there is no point in AL. Its desired properties index is high magnetic flux density and low core loss and in some cases high B - H ring curve form of square. The square ring B - H curve of the materials used in belt around the magnetic core, its permeability changes when the ring was hengduan range is very wide; The inductance value can not be continuous and repetitive. Square ring materials usually used in applications of switch, etc. B - H in the ring ring curve of materials, such as ferrite powder core, and its permeability is relatively constant. AL as low drive case the measure values of permeability, when the ring material permeability is relatively stable.
 
8. Question: What kind of core is best?
 
It should be said that there is no answer to the problem. Because the choice of the magnetic core is determined on the basis of applications and application frequency, etc. Any material choice and market factors such as consideration. For instance, some material can ensure the temperature rise is small, but the price is expensive, so, when select material against high temperature, it is possible to choose a larger size but the material with a lower price to finish this work. Therefore, the choice of the best materials to application requirements for your first inductor or transformer. From this point, the operation frequency and cost is the important factor.
 
The optimal selection of different materials is based on switching frequency, temperature rise, magnetic flux density, etc.
 
9. Question: How to demagnetize the magnetic core?
 
The method is to apply a 60Hz alternating current to the core so that it starts with a drive current sufficient to saturate both the positive and negative ends, and then gradually lower the drive level several times until it drops to zero. This will restore it somewhat to its original state.
 
10. Q: What happens when the core temperature is higher than Curie point?
 
The Curie temperature is the temperature at which a material loses all of its magnetic properties. Above this temperature, the core will not be used. In fact, many cores have insulation, polishing, etc., which generally break down at temperatures well below Curie point. For these, consult the manual to determine the temperature limits of the insulation. The winding core has no insulation, so it can recover its magnetic properties even after reaching Curie temperature when the temperature drops. The ribbon around the core usually has a high Curie point (>450℃), which makes it possible for these materials to suffer oxidative damage before the Curie temperature is reached. Manganese-Zinc ferrite will have no effect unless there is an insulating dressing. This is because the Curie temperature of ferrite is relatively low, generally only 120OC -- 250OC. This temperature is not enough to change the structure of such ceramic materials. In general, the magnetic properties of the core can be restored after the temperature drops to the Curie point, as long as the material is not oxidized for a long time.
 
11. Q: What is the maximum frequency (switch) for the magnetic core you are using?
 
First, it depends on the material you choose. The tape - wound core usually has a lower operating frequency than ferrite. This is because of its low impedance, resulting in higher eddy currents and higher core losses. The thinner the band, the higher the frequency can be. On the other hand, the core loss depends on the designed operating flux density; Therefore, the working frequency can be increased by reducing the magnetic flux density. In general, for power cores, the saturation flux density of the material under certain driving constraints is not a limitation to the design frequency, and its maximum loss tolerance often determines the operating frequency.
 
See the Magnetics directory for frequency and flux density information related to core losses.
 
12. Question: Advantages of single layer winding?
 
Single-layer winding is easier. Moreover, the distributed capacitance is also the smallest. Can accommodate maximum frequency response. Copper loss temperature rise can also be minimized. For general purpose chokes, it is easier to maintain symmetry between the relative windings.
 
13. Question: What is a double wire winding?
 
Double wound wire, also known as stranded wire. Such a double winding is wound around the core or skeleton to produce two equal parallel windings instead of a larger single winding.
 
14. Q: What is the B-H (hysteresis) loop?
 
It is used to define the magnetic flux density, coercivity, drive values required for core saturation, and permeability of the magnetic material. The B-H ring varies with frequency and drive level. The frequency response and excitation level (current, voltage) of a material are important for its suitability for specific applications. Please refer to the relevant manuals and product catalogs for these.
 
15. Q: What is the effect of air gap setting?
 
After inserting an air gap into the core, the b-H ring can be modified or cut to make it suitable for higher H, so as to ensure that the core does not prematurely enter a saturated state. Because the permeability of a core decreases significantly when it becomes saturated, it is expected to slow down its saturation for a number of applications, such as inductance. The air gap has this control effect.
 
16. Question: What is magnetoelasticity (magnetostriction)?
 
After magnetization, there will be a small change in the geometry of the material. The size of the change should be a few parts per million, which is called magnetostriction. For some applications, such as ultrasonic generators, the advantage of this property is used to obtain mechanical deformation by magnetostrictive excitation. In other applications, a howling noise occurs when working in the audible range. Therefore, low magnetic shrinkage materials can be applied in this case.
 
17. Question: What is magnetic accommodation (disaccommodation)?
 
This phenomenon occurs in ferrite and is characterized by a decrease in permeability that occurs when the core is degaussed. This demagnetization can occur after the operating temperature is higher than the Curie point temperature, using alternating current or mechanical vibration with decreasing amplitude, etc. In this phenomenon, the magnetic conductance first increases to its original level and then rapidly decreases exponentially. If no special conditions are expected for the application, then the permeability change will be small, as many changes will occur in the months following manufacture. This reduction in permeability is accelerated by high temperatures. Magnetic dissonance will recur after each successful demagnetization, thus, unlike aging.
 
18. Question: Why does the inductance of ferrite windings decrease after winding and packaging?
 
Ferrite material is easy to be affected by mechanical pressure, which will be generated during winding process and packaging. The higher the permeability of the material, the greater the impact. The suggested methods are as follows: 1) After winding, roasting or high temperature treatment. 2) Some space should be left in the package or some filling such as sand or mica powder should be used. 3) Add some ribbon gaskets and 4) add some silicone ester software.
19. Question: Why is the actual value of core loss with air gap structure generally greater than the calculated value?
 
Because when we calculate the core loss, there is always an assumption that the core structure is uniform. In fact, when the two magnetic cores are half glued together, there is always more or less leakage inductance at the surface of their bonding. These leakage inductance and gap losses together constitute the total loss component. The air gap loss is determined by the magnetic flux density of the magnetic core and the eddy currents generated in the winding. When the magnetic core has an air gap, the air gap loss will increase exponentially. In addition, because the cross-section of many magnetic cores is not identical, in some part, the magnetic flux density is higher than that of other parts, so the loss of these parts is higher than the average value
 
20. Question: What is the difference between nickel-zinc and manganese-zinc ferrite?
 
The permeability of MnZn material is higher, while that of NiZn material is lower. Therefore, MnZn ferrite is generally used in applications below 5MHz, while NiZn can be used in applications above 2Mhz.
 
21. Question: How important is the permeability in power materials?
 
The permeability is the ratio of flux density B to drive level H (strength). Power materials are commonly used in high frequency transformers. Generally speaking, the important characteristic indexes are higher flux density and lower core loss. The permeability is correspondingly less important because it generally varies beyond the operating flux.
 
22. Q: Why is only the minimum value of AL given in the manual?
 
The permeability and AL vary with H. For power applications, there is no need to place a maximum limit on AL. And the minimum AL can represent the maximum excitation current.
 
23. Question: How do you know which ferrite (skeleton, etc.) hardware is right for your core?
 
The general core is a production standard, accepted by the industry as a whole. General selection can have a certain critical size tolerance. In general, hardware (skeleton, etc.) adaptation is not an issue. The safest thing, of course, is that you should buy both the hardware and the core from the same manufacturer if possible.
 
24. Question: Can ferrite be more closely matched?
 
During the core firing process, each part eventually shrinks to a certain size. Different materials and different firing methods make the shrinkage slightly different, generally about 10-20% difference (about 1-4% difference after final treatment). The geometry of some cores is not quite right at this point. And then you can go through the mechanical process, and then you should be able to do a good job.
 
25. Q: Can I customize the ferrite (core) size and materials to my specific needs?
 
It can be customized by users. Magnetics provides more than 500 to help machines with special handling. And more than 20,000 users can choose their own mold. The existing core height can be adjusted according to the user's needs to reduce the cost of machinery and tools.
 
26. Question: What is the appropriate clamping pressure for ferrite?
 
In general, the recommended core binding surface pressure is 700kg/m2(100PSI). For specific RM, PQ, EP and Pot cores, check out the Magnetics manual.
 
27. Question: Is there a "best" core shape?
 
You could say no. Because the shape of the core depends on application, shape constraints, temperature constraints, winding capacity, assembly, and a number of other factors; This means that "compromises" should be considered when choosing a magnetic core. Once you have an application, you can refer to several manufacturers' manuals to choose what is "best" for you.
 
28. Question: Why are ferrite cores worn flat?
 
Flattening the surface of the two halves of the core is due to the fact that the surface does not match properly after firing. This leveling process is very important to reduce the original air gap loss to obtain the optimized inductance.
 
29. Question: Why polish? What is surface polishing?
 
Polishing may be considered as a further step in the polishing process above. The aim is also to further reduce the possible air gap loss. The usual so-called "ground" finish is 25 micro-inchs, while the "polished" finish is up to 5 micro-inchs(.127 microns). There are no rules requiring surface finishes, such as polishing, but this is known by the determination of AL.