What is Homopolar: Definition and 33 Discussions

A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder) with an electrical polarity that depends on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, or Faraday disc. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts, and some systems have multiple generators in series to produce an even larger voltage. They are unusual in that they can source tremendous electric current, some more than a million amperes, because the homopolar generator can be made to have very low internal resistance. Also, the homopolar generator is unique in that no other rotary electric machine can produce DC without using rectifiers or commutators.

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  1. S

    B Homopolar motor rotation in Vacuum

    Hi again, I've found interesting video. Roller homopolar motor : Roller Motor Do you think the motor from 1:08 min Will self rotate in Vacuum/Space (No other forces : Gravitational or Other type.) Thank you in advance.
  2. J

    I Homopolar generator question: Magnetic “wake”

    So faradays paradox is often depicted as a circular copper disk on a shaft with a donut or toroidal magnet on one or either side of the disk. Spin the disk and magnets together voltage is produced. Since the magnets are rotating along their poles the orientation of the magnetic field compared...
  3. J

    Homopolar Motor: Energy Input, Output, & Magnetic Field

    I was curious in regards to a homopolar motor where the energy imparted into the rotor comes from if the energy input is say 10v at 1000 amps and there is 10v 1000amps output. Aswell if the effect of the magnetic field produces a different power on the rim of the disk vs the input from the...
  4. jisbon

    Understanding a Homopolar Generator

    So I was searching up on the homopolar generator and found this explanation for the generator, as well as the proposed solution. However, I don't really understand what the solution is trying to do here. Ok, I understand to find the current, you will need the potential, which is the...
  5. S

    Homopolar, Brushless and Brushed DC Motors

    I've seen examples of each of these types of dc motors. What I haven't found is a dc motor that doesn't use pwm, commutators/brushes, or some sort of slip contact. Is there a such thing? If not, would there be a demand for such a motor?
  6. J

    Why do more magnets affect how long a homopolar motor spins?

    Hi All, My daughter did a science experiment on homopolar motors. The only variable was the number of magnets on each motor. We found out through the experiment that the more magnets we attached to the motor, the longer it spun before the battery died. I'm assuming it has to do with the...
  7. vanhees71

    The Homopolar Generator: An Analytical Example - Comments

    Greg Bernhardt submitted a new PF Insights post The Homopolar Generator: An Analytical Example Continue reading the Original PF Insights Post.
  8. Low-Q

    The problem explaining how homopolar motors work

    Since I discovered the homopolar motor, it has fascinated me a lot. Not because it has any practical use, but it works in spite of a non gradient magnetic field. Normally, an electric motor works because the rotor is allways "chasing" a sticky magnetic spot. The magnetic gradient between weak...
  9. G

    Homopolar generator: disk vs. helix

    Hi, I'd like to build a homopolar generator. Since generating magnetic fields of uniform density of any useful size is very tricky to do with off the shelf permanent magnets (I've tried!) I had the idea to use DC solenoids instead. But with a rotating helical plate in place of the cylindrical...
  10. ElPimiento

    Calculating a Homopolar Generator's EMF

    Homework Statement Homework Equations ##\omega = v/r## ##q\vec v \times \vec B\ =\ \vec F_B## ##|\vec F|d\ =\ |\vec E|## ##q \Delta V\ =\ E## The Attempt at a Solution (So, my answer is twice and large as the correct answer. This is the second time this has happened on a question like this ...
  11. B

    Exploring the Mechanics of Homopolar Motors: A Comprehensive Guide

    How these are working: Is current flowing? In the first case I don't think so. In the other... the wire is insulated like in a coil I think and then no current also. But why need the battery and why the battery is discharging? Can current flow through a magnet without demagnetize it? What...
  12. P

    I dont understand homopolar motors

    I understand the diagram above where the blue stuff might be mercury like in Faraday's mercury motor. I don't understand why the liquid moves but... it is a conductor so why doesn't the current (moving electrons) feel the force and leave the liquid stationary? Similarly in this motor its the...
  13. A

    Lorentz force in motor other than homopolar

    Hello, I am trying to build a motor. Just a prototype I guess and learning at the moment so just simple stuff but I can't make it work.. I have seen the examples of a homopolar motor and understand the direction of force due to Lorentz force. To be simple I don't want, and don't see the need...
  14. C

    Magnetic field rotation or not?

    Suppose for a moment you had a circular copper disc placed concentrically in the air gap between the poles of an upper and a lower circular magnet, the outer faces of the upper lower magnet being connected by a pole piece so as to complete the magnetic circuit. The edge of the copper disc is...
  15. S

    Homopolar generator / Faraday disc

    Hello everyone , as for starters I would like to ask two questions. As I've been reading about the homopolar generator I have the basic understanding of all the workings yet here are my questions. Since the rotatig disc produces a current within while rotating in an axial magnetic field...
  16. C

    Faraday's paradox: homopolar generator on a train

    There is a homopolar generator on a train moving at 215 km/h. The magnet of the generator is attached to the disk so they would rotate together, but they are stationary now, except that they are moving along with the train. Is there any current generated by the generator? I expect the answer...
  17. F

    How Long Does It Take for a Homopolar Generator Disc to Halve Its Speed?

    I have proven the induced emf between the centre and rim in a circular disc of radius a and angular velocity w, with a magnetic field B parallel to its axis is 0.5wa2B. I need to find the time taken for the disc to slow to half it's initial speed ignoring friction, given a resistance R is...
  18. M

    How does a homopolar generator produce current?

    Hi there , I would like to understand more about how exactly current is induced in a homopolar generator aka Faraday disc ? I have read some papers on this subject and so on and as far as I understand in a normal generator current is induced because magnetic field lines travel through a loop of...
  19. A

    Homopolar Generator Setup & Effect of Magnetized Conductivity

    The basic set up for a homopolar generator has a stationary magnet and a rotating conducting plate with contacts at the center and rim of the plate. I would think that even if magnet were spinning along the same axis, the magnetic field would not materially change and so the resulting current...
  20. E

    Homopolar Motor Limiting factor angular velocity

    I am doing an experiment involving determing the angular velocity of a homopolar motor (simple set up of the screw, battery, magnet and copper wire) and was wondering what the limiting factor on the speed would be. One website suggests that this might be back emf.
  21. K

    Homopolar Generator: 0.1V Output, No Current

    I've made a homopolar generator using Al disk, its giving me a output voltage of around 0.1V but shockingly der is no current ! a checked the resistance of the disk its very low as required, i checked for every other problem like : improper contact , smoothness of the disk , symmetry of the...
  22. Q

    Build a Homopolar Motor in 1 Week - Magnet & Screw Tips

    I have 1 week to build a motor. I'm looking at building a homopolar motor. I know I need a magnet. But does it have to be a neodymium one? And is Amazon a good place for such magnets? And does the screw have to be a ferromagnetic one? And if anyone has built such a motor, some hints and...
  23. D

    Building a Homopolar Generator: Step-by-Step Tutorial

    Let's begin. I have been assigned to build a homopolar generator, but I really don't know where to start. I searched the net for some info, but I couldn't find anything useful (for me). I tried to read and understand the wiki-page about this faraday disc, but it's kind of hard to understand...
  24. M

    Increase Speed of Homopolar Motor - Advice & Explanation Needed

    Hi Guys, I need some advice and hopefully an explanation. Does increasing the voltage on a simple homopolar motor increase its speed? and Why? If voltage doesn't increase the speed, how can we increase the speed? Thanks a lot, I've been searching for information but have not had a lot...
  25. M

    How Does a Rotating Disk Generate Voltage in a Magnetic Field?

    Homework Statement A little bit of background, my Phys 2 w/Calc class has only covered up to chapter 30(Inductance) in Fundamentals of Physics by Halliday/Resnick. I'm not even sure why this was my homework(turned it in partially completed with written physical reasoning, a picture, and a...
  26. L

    How does a homopolar motor work?

    How would you explain this homopolar motor seen on youtube? https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/3aPQqNt15-o&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess"...
  27. C

    Homopolar Induction: Where Can I Find Answers?

    Trying to talk about homopolar induction systems in the eng. forums got me locked cause the readers concluded for me that I was talking about overunity or perpetual motion. I have been conducting experiments on homopolar induction and there is little to no resourses out there concerning the...
  28. H

    Homopolar motor teaches about the Lorenz Force

    I have made a new version of Faraday's homopolar motor. This was the first device to demonstrate the connection between electricity, magnetism and motion. Faraday's motor included a beaker of mercury as the outer conductor. This has been demonstrated in classes. My motor comprises gold-plated...
  29. R

    How does the Homopolar Motor Work?

    how does this work? (i made one and it does work pretty well, mine was spinning for about 20 minutes) the wire has to be copper so it conducts the electricity, but is not directly magnetic until the applied current produces the magnetic field. Also the magnet has to be very strong, i used an...
  30. B

    The Homopolar Generator: Unanswered Questions

    I thought about the different configurations of the homopolar generator. Asking the right questions helps to lead me in a particular design direction. I will present the information I've found online, my questions, and my current (if partial) answers which may or may not be correct. I would...
  31. O

    Homopolar Generator: Experiences & Tips

    Does anyone out there have any experience with homopolar genterators?
  32. E

    Would Homopolar Generators Work with Magnet as Disc?

    Would Faraday's homopolar motor / generator work if it was rearranged to have the magnet as the disc and conductor / coils where the magnet used to be? A brushless version essentially. http://www.rose-hulman.edu/~moloney/AppComp/2001Entries/e11p/homopolar.htm Something tells me no, but...
  33. C

    Homopolar generator information

    Hello. I looked for information about how the homopolar generator works, because there are some claims (N-machine, Space Power Generator...) that say there is no backEMF or opposition to obtain the work. The homopolar generator is a disc magnet glued to a conductor disc. When you make it...