What is Eddy current: Definition and 83 Discussions

Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer, for example, or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material. When graphed, these circular currents within a piece of metal look vaguely like eddies or whirlpools in a liquid.
By Lenz's law, an eddy current creates a magnetic field that opposes the change in the magnetic field that created it, and thus eddy currents react back on the source of the magnetic field. For example, a nearby conductive surface will exert a drag force on a moving magnet that opposes its motion, due to eddy currents induced in the surface by the moving magnetic field. This effect is employed in eddy current brakes which are used to stop rotating power tools quickly when they are turned off. The current flowing through the resistance of the conductor also dissipates energy as heat in the material. Thus eddy currents are a cause of energy loss in alternating current (AC) inductors, transformers, electric motors and generators, and other AC machinery, requiring special construction such as laminated magnetic cores or ferrite cores to minimize them. Eddy currents are also used to heat objects in induction heating furnaces and equipment, and to detect cracks and flaws in metal parts using eddy-current testing instruments.

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  1. Z

    How does an eddy current brake work exactly?

    I read this explanation on the Wikipedia entry for "eddy current brake". Let me go through the reasoning there. We have the metal sheet ##C## moving to the right under the magnet. For the parts of the sheet moving toward the magnet, the magnetic flux from the magnet is increasing. From...
  2. Mr Nobody

    Magnets & Eddy Current Drag help please

    Hello everyone, I'm working on a home project to create AC current, using magnets (AC Generator). I understand the principles of how to generate AC current however, I lack the complex knowledge of the physics side. I have searched and watched various Youtube videos etc, but none of them answer...
  3. Narayanan KR

    A Question on Skin Effect and Eddy Currents

    When you try to create time varying magnetic fields in solid metals, there is severe heating due to eddy currents, when you increase the frequency, just like in NDT(non destructive testing) the magnetic field is pushed away from the core to the periphery due to eddy currents opposing the field...
  4. Rx7man

    Eddy current position sensor circuit

    I started a project, and where I thought I has a potentiometer position feedback, best I can tell I have an eddy current position sensor, which I'm absolutely not familiar with The application is a diesel engine injector pump (retrofitting to a different engine, it was from a Komatsu V12, no, I...
  5. B

    Torque Production in Eddy Current Motors

    Hi guys, The purpose of this post is to understand the actual phenomenon behind torque production in eddy current motors. This query is based on theoretical principles of torque production in AC motors. Consider a simple eddy current AC motor with a disc type or cylindrical rotor (Watthour...
  6. Gonzalo Lopez

    Motion Equation for a magnet on a spring

    Apart from the trivial elements of the motion equation (m z'' = -kz -mg), I am required to find the force produced by the Eddy currents induced by the moving magnet. To do so, I calculated the magnetic flux through the hole plate: For a magnet: Bz=μo m 4π. 2z^2−r^2/(z^2+r^2)^5/2 so Φ = a→ +∞...
  7. SwatiAnshu

    Calculation of Eddy Current Brake Force with a twist

    All the equations I have seen have a component that is unknown. Also, if possible do let me know if there is a software I can use to model or analyze data related to eddy currents
  8. K

    EMF shielding using a conductor

    So I've been trying to figure out how EMF shielding works. More specifically, I've seen videos where placing a metal conductor in front of a circular coil (with AC running through at radio frequencies) apparently shielded anything behind it. After searching online, I repeatedly saw Eddy...
  9. K

    Eddy currents in Faraday's Law Experiment

    My explanation: A circular coil is connected to an AC supply at a frequency of 30-50 kHz (radio frequency). Therefore, an alternate current will be running through this “primary” coil, producing an alternating magnetic field. This magnetic field periodically decreases in strength, alternating...
  10. Physics lover

    Eddy current Losses due to different materials

    I know only about Laminated,Iron and wooden coil.I don't know what is Air cored coil. So according to me,it should be Wooden cored coil because less current will flow through wooden cored coil.Ans it will be maximum in Iron cored coil. Please tell,am I correct or not?I don't know the answer.
  11. Yani Botsanovski

    Eddy current calculation question

    Hello there! I have seen some great eddy current brakes and wanted to learn more about it. The problem in the internet I can not the specific case I have in mind. I searched the internet and found a great deal of material about magnetic forces. I cannot, however, find the specific case I'm...
  12. I

    How to find the Braking Torque of an Eddy Current Braking Setup?

    Homework Statement: Finding the braking torque applied on a moving disk as a result of the Eddy Currents Homework Equations: $$F = \sigma v V B^2$$ So right, Basically my problem is how to find the torque exerted by an eddy current braking setup. My setup consists of a disk rotating on an...
  13. A

    Ansys Maxwell Simulation - Evaluation of Eddy currents in a Vessel

    Hi, guys, I am developing a simulation in Ansys Maxwell. I set up my simulation in the "transient mode", and I would like to evaluate the eddy currents that arise in a metal Vessel. The currents rise to a flat top in 20 ms and then after 20 ms in the flat top, it decreases to zero in 20 ms. I...
  14. P

    Silicon not heating with induction heater?

    I’m using an inductive heater to try to melt some 99.85% polycrystalline silicon, as would occur in the Czochralski process, but the silicon workpiece is not melting let alone even getting hot. The silicon workpiece is about the size of a playing dice. It becomes conductive at 200 F and becomes...
  15. fresh_42

    Eddy Current Brakes: where to with its current?

    I've seen a documentary about the Yukon Route Railroad. Some trains are run by old steam engines (with Diesel). They also equipped their engines with eddy current brakes and said, that the resulting current is conducted into resistors and via thermal energy removed into air. I assume that...
  16. P

    Are these instances of identical magnetic fields?

    Are both magnetic fields emanated from an electromagnet fed with a current spike from a charge capacitor and a rotating static magnetic field from permanent magnets instances of time varying fields? The permanent magnet would be attached to perhaps some rotating disc thus passing over a target...
  17. P

    Why won't my silicon melt with a zvs inductive heater?

    I’m using a zvs inductive heater to try to melt some 99.85% polycrystalline silicon, as would occur in the Czochralski process, but the silicon workpiece is not melting let alone even getting hot. The silicon workpiece is about the size of a playing dice, and becomes fully conductive after...
  18. P

    Medical Eddy Current Hazards: Magnetic Field & Human Body

    Suppose a 10k Gauss 3in diameter sharp magnetic field is made & collapses completely thru a standing human human body somewere made by an external electromagnet.. The electromagnet is held horizontally and not vertically against body. Is this hazardous? Can it become hazardous after some...
  19. T

    Eddy Current Speedometer Experiment

    Trying to create an experiment that utilizes a motor driven shaft to measure the angular velocity of another shaft via eddy currents. We made a mock experiment that uses 8mm shafts, pillow bearings, and ceramic magnets from home depot, but don't see a torque on a non-ferrous metal attached to a...
  20. Gyro de Pyro

    Magnetic plate eddy current braking effect on a copper disc

    Hi, I've seen many videos of neodymium magnets sliding slowly down an inclined copper plate, or slowly down a copper tube - due to eddy current braking,but never the other way around. My question is; will a copper disc sliding down an inclined magnetic plate, or down a magnetic tube act in the...
  21. Dustin

    B 4 Questions About Lenz's Law Experiment

    Hello, I have four questions. As it stands now, I don't have the necessary materials to test this myself, which is how I'd prefer to learn the answer. I still plan on doing this experiment for fun once I can acquire the necessary components. This deals with Lenz's Law. My goal is to maximize...
  22. Ron Burgundypants

    Altered inductance around a solenoid in a cryostat (from Eddy currents?)

    I'm trying to use a solenoid to measure the magnetocaloric effect of dysprosium. The effect is highest at the Neel temp which is down near 180K. I have a solenoid in a cryostat to get the correct temperature. The cryostat's heat exchanger is made of a thick copper cylinder and I think it is...
  23. I

    Mutual Inductance of Coaxial Tube and Coil

    In my lab we are working with a Coaxial coil and stainless steel tube, and are aiming to find the mutual Inductance. I've done some looking around and have easily found the Inductance of a Coaxial cable, and for that of Coaxial coils, but am having trouble with a combination of the two. The...
  24. Khang Vu

    Ansys Maxwell Magnetic Transient Help

    I am trying to simulate a linear eddy current brake. To do this, I am modeling my brake as a single magnet moving above an aluminum plate. I plan to measure the drag force on this magnet and calculate my braking force as a superposition of single magnets. Here's my current setup: Model: A...
  25. D

    BLDC motor as generator to power eddy current brakes

    Hi everyone - here's a concept that I'd like a few opinions on: As part of a project, I'm looking at using a brushless DC motor mounted on a high-speed vehicle as a generator. Once the vehicle hits its top speed, the batteries should disconnect from the motor and the vehicle's own velocity will...
  26. M

    Ansys Maxwell Contact Resistances

    Hello everyone, I am using Maxwell 16.2 with no chance to get an update. I want to do a 3D design Eddy Current Simulation to find out the Joule losses of my single phase GIS design. An important factor for the joule losses that I need to insert is the contact resistances of the several...
  27. G

    Eddy current losses in microelectric generators?

    For a microscale electric generator (where the driving force is a fraction of a Newton), can losses from eddy currents be significant enough to noticeably alter the rotational velocity of the rotor? Because my understanding is that the rotation is basically taken as a constant when examining the...
  28. J

    Eddy Current brakes operating at high speeds

    Hi all, I'm currently working on eddy current brakes designed to stop a vehicle from speeds around 135 m/s. While researching eddy current brakes, I found the equations used to find the force generated tend to break down at higher speeds. The design is linear, stopping on an aluminum rail...
  29. nothing909

    Types of eddy current couplings

    Homework Statement I have a really simple question, state two types of eddy current couplings and state a flexible coupling, but I've been googling it for the last half an hour and can't find an answer. The Attempt at a Solution Can anyone tell me two types of eddy current couplings? I know...
  30. Benoit

    Eddy current loss in solenoid half-filled with magnetic core

    Hey ! Let's say I have a solenoid that is only half-filled with a magnetic core. Now I want to know what is the loss due to Eddy currents. First, I want to find the magnetic field with Ampere's law. With this kind of geometry, I'm not even able to apply Ampere's Law ! have of picture here of the...
  31. G

    Textbook picture: Is direction of this eddy current wrong?

    Hi. This is from a high school textbook, in a chapter about eddy currents and Lenz's law. In a), a magnetic field is turned on, in b) it's turned off, which both induces a current in a suspended aluminium ring: I think the direction of the current is wrong in both pictures. Any opinions?
  32. mertcan

    Eddy Current Force: Equation & Derivation

    hi, I really wonder ıs there a equation related to force generated by eddy current? And ıs there a derivation of this equation? I am asking because the only thing I can find is the eddy current density equation, no force formula exist on internet.
  33. S

    Eddy Current Brake Behavior (Accelerating From Rest)

    Hey guys, So I'm interested in the application of an eddy current brake system as a high intensity shock absorber of some sort. The system would consist of permanent magnets concentrated on a stationary, non ferromagnetic metal. If a sudden, intense force were to act upon the non ferromagnetic...
  34. entity314

    Frequency appears to have to effect on hysteresis

    This question is primarily regarding transformers, particularly the impact frequency has on hysteresis loss. Given hysteresis loss = η×Bmax×f×V and Bmax = (V ×〖10〗^ 8)/(√2 π×f×N×A) This means that hysteresis loss = η (V ×〖10〗^8)/(√2 π×f×N×A) fV = (η ×〖10〗^8)/(√2 π×N×A) V^2 And as such...
  35. jeisson botache

    Seismic isolator based on magnetic forces

    Hi, i am an student of civil engineering and i am doing my graduate thesis. so sorry if i misspell, english is not my native languaje. so, here we go :D Homework Statement Before entering in details you (whoever you are) most know: The system is scaled for obvious reasons. The system consists...
  36. pompom15

    Make a Eddy Current to Hover - A DIY Project

    Homework Statement There is 4 neodynium magnets. It is 0.7 inch magnet. A 15,000 RPM motor. It does not hover. I am trying to make a eddy current to make it hover1. The attempt at a solution Getting a copper plate, having a better magnet.
  37. C

    Get core loss in Maxwell 3D eddy current solution type

    Hi. I use maxwell 3D eddy current solution type. i want to find out core loss. please help me.
  38. ZenSerpent

    Single Phase Transformer Losses -- Hysteresis, Eddy Current Constants

    Hi. My colleagues and I are doing a research on transformers (single-phase) and we stumbled across the following equations involving hysteresis and eddy current losses: Wh = ηBmaxxfV where Wh = hysteresis losses η = Steinmetz hysteresis constant Bmax = maximum flux density x = constant...
  39. A

    I need to build an electromagnet to provide 10mN eddy current brake

    Hi I am building a motor tester, for that I need to build a variable load. For which I was planning to use eddy current brake with electromagnet. Please help me to build a electro magnet which can provide more than 10mNm load to a DC motor with rotating disc of 75mm in a RPM of 6500. I tried...
  40. Kolton

    Solving Magnetic Field Problems w/ Ansoft Maxwell 14.0?

    So I'm trying to run some 3D transient simulations based on magnetic field focusing/shielding, but I'm not getting the expected results. Does anyone know if Ansoft Maxwell 14.0 will solve for the magnetic fields created due to the eddy currents? It doesn't appear to.
  41. kelvin490

    How to show laminations minimizes eddy current?

    In transformer, lamination is an effective method to minimize eddy current and thus energy loss. I just wonder how can we show that the energy loss due to eddy current in those laminates is added up to be less than that without lamination (suppose the total cross sectional areas are the same)?
  42. S

    Magnetic levitation using eddy current

    Hi, I am working on an experiment to investigate the effect of electrical conductivity of the metals on the levitating force produced. Basically the concept is this: when a metal plate is placed on top of a solenoid (but not touching), as the a.c. flows in the solenoid the change in magnetic...
  43. M

    Eddy currents and Torsion Pedulum

    I am having difficulties writing my damped oscillations lab report. We were asked to write a short essay on eddy currents (creation,direction advantage and disadvantage) and their relationship with torsion pendulums. Also,we have to explain if the copper wheel in the torsion pendulum could be...
  44. O

    Can Eddy Current Separators Revolutionize Recycling and Waste Management?

    Hello I am a graduate Mechanical Design Engineer who was recently offered a job (through a graduate scheme) at a company that develops Recycling and waste management systems. As part of this I have to design and develop an new eddy current separation system so that the company can build the...
  45. L

    Eddy Current Questions | Refresh Understanding

    Need to refresh my understanding on eddy current. Does every metal exhibit eddy current when it comes across a Mag field? If this is the case, then why do induction cook tops required ferrous utensils. A Metal detector also works on the principle of eddy current. correct?
  46. B

    How do I calculate eddy current losses in mains transformers?

    Hi all i hope some one can help but i have a feeling there will be no easy calculations for this one:confused: Im trying to calculate actual eddy current losses in 50hz mains transformers depending on lamination sizes and can't seem to find any info on the subject that's sub electrical degree...
  47. B

    Damping ratio from Eddy current breaking

    Hello All, I have been asked to design and build a rig that will introduce the concept of a mass spring damper system to mechanical engineers in their early years of university. To make it slightly more complex, the rig needs to be torsional rather than linear. My design so far is to use a...
  48. J

    Reducing Eddy Current Effects: How Laminated Cores and Reduced Area Help

    Dear All, How laminated core helps in reduction of the eddy current? How reduction of area is useful in reduction of eddy current? Thanks.
  49. C

    Eddy current damping - Analysis?

    I'm trying to damp an oscillating metal plate with a neodymium magnet. Things I know - Remanence of the magnet - The magnetic flux density at distance z (from the distributors site) - Dimensions of the magnet - Plate material (Aluminium) - Distance to the plate. What I'm trying to find out is...