Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homopolar generator

  1. Sep 3, 2006 #1
    Does anyone out there have any experience with homopolar genterators?
  2. jcsd
  3. Sep 3, 2006 #2


    User Avatar
    Gold Member

    I've never heard of that term before. Can you elaborate upon the subject?
  4. Sep 4, 2006 #3
    Sure can hope this helps.

    A homopolar generator, also known as a unipolar generator, acyclic generator, or disk dynamo, is a DC electrical generator in which the magnetic field has the same polarity at every point, so that the armature passes through the magnetic field lines of force continually in the same direction.[1]. The device is electrically symmetrical[2], and generates continuous current. Some of these devices also have "homopolar magnets", which have pole pieces arranged around a common centre.
  5. Sep 4, 2006 #4


    User Avatar
    Science Advisor
    Homework Helper

    Ask a question.
    Generally they produce high current at low voltage.
  6. Sep 4, 2006 #5
    Um.... I thought I did....

    I am trying to see if anyone out there has any experience with these types of generators so that when I do put forward a more elaborate question concerning specific issues about them I can expect some kind of intelligent response to my question as apposed to a host of more questions in response to my questions.

    I suppose I was being a bit conservative. And didn’t want to post an extended exhortation on the subject I was looking to discuss here. But being encouraged as I am here I will elaborate.

    I am currently conducting preliminary experiments with the Homopolar design. The purpose is to try and establish the how and why it behaves the way it does. An example of a one of the main phenomena displayed by this method of producing electricity is the simple fact that it does so in a uniform magnetic field. Current induction laws as I understand them require a changing magnetic field to induce a current in any given conductor. Another interesting phenomena is the fact (and I have proven this with first hand experimenting) is that you can fix the magnet to the conductor and still produce a current in the conductor. Apparently the field is independent of the magnet as is theorized by some affluent physicists.

    I currently have measured results from a simple homopolar design I am using to experiment with. The results show consistent results. Some of the standard proof of principle results are as follows:

    1. symmetrical increase in voltage and amperage with an increase in armature RPMs
    2. reversing nodes reverses polarity
    3. reversing angular direction of the armature reverses polarity
    4. continuity between drive mechanism and experimental peace is zero
    5. providing a second induction magnet to the peace increases both voltage and amperage out put.
    Now all that being said (written). The particular peace I am experimenting with is producing almost twice the voltage as it does amperage. I understand that typical designs produce much more amperage than voltage so I have found myself a bit of an odd result in my experiments. I would like to discuss the exact nature of my experimental peace but truly if I have found something rare in this design I should try to protect it.

    So I put to you these two questions. What do you think would cause a high voltage low amperage result? And has anyone out there every experimented with this design?

    Thanks in advance for your response

    Attached Files:

    Last edited: Sep 4, 2006
  7. Sep 4, 2006 #6


    User Avatar

    Staff: Mentor

    I've had experience with the theory. I used an HPG concept in an electrical propulsion design. It is basically a moving 'conductor' in a static magnetic field (usually, although one can increase the magnetic field to increase the EMF and current). A moving conductor in a magnetic field experiences an EMF - Lorentz force effect.

    The homopolar generator allows for 'continual' movement of the conductor in one direction.

    Reversing the direction of the field reverse the EMF or polarity, although I am not sure why one would want to do this.

    The EMF is generated between the outer surface and inner axis. Using an HPG, one puts an electrical contact (pickup) on the circumference of the conducting disc (OD) and another on the conducting axis or as close to center of the disc. Then one can put a load between the contacts.

    What does one mean by high voltage? HPG's voltages are usually low, e.g. on the 100 V or so.

    Low current means high resistance/impedance load, or low HPG rotational speed, or low magnetic field.


    Here's a reasonable reference - http://en.wikipedia.org/wiki/Homopolar_generator

    Back in the mid 1980's, I visited Bill Weldon et al at UT's Center for Electromechanics to see what they were doing with HPG's.
    Last edited: Sep 4, 2006
  8. Sep 4, 2006 #7


    User Avatar
    Science Advisor
    Homework Helper

    Don't know anything about this configuration.
    It's one I havn't seen.

    Define high voltage.
    Low current = small load, disk very thin or bad contactor design.
  9. Sep 4, 2006 #8
    Looking at my last post there is an attachment that illustrates the general design layout. The arrangement I am referring to consists of physically fixing the conducting disk to the magnetic disk as they are illustrated in my attachment. By doing this both the conductor and inductor spin on the same axis at the same angular velocity creating a measurable current in the conductor. Literary grace is not one of my strong points so I hope you understand my explanation and I apologize if you don’t.

    My reference to high voltage is a relative reference. The measurements that I took on my test piece showed 1.5 times more voltage than amperage when measured at any particular RPM. I understood and this may be my misunderstanding, that I should produce a much lower voltage than amperage when producing a current using a HPG. This in the end is why I am here. If I am not taking or reading my measurements correctly then now is a good time to find out.

    Another good question to put forward is this. By fixing the inductor and conductor together what kind of resistance would one expect to impact the angular motion of the armature? As I see it only the physical friction in the system would impact the angular motion of the armature. If I am missing something please point it out.

    Again thanks for all your input
  10. Sep 5, 2006 #9


    User Avatar
    Science Advisor
    Homework Helper

    I understood you quite well.
    It's not a configuration I have seen.
    Frankly, I would have to see it replicated.

    The 1.5 times relationship is the load resistance.
    Change the resistance, change the current.
    E=IR and all of that.
    What is the voltage?

    Off the top, I would say any output current is getting generated in the frame of whatever it is you built.
    Try it using a plastic or wood frame.
  11. Sep 6, 2006 #10
    This is an exploded view of the piece I'm experimenting with. Current is measured from the conducting disk as described by Astronuc.

    I am not sure if I understand electrical generation as I should. I am taking measurements from this experimental peace and interpreting them the same way I would if I took the same measurements from a battery. If there are other considerations I should be taking into account I would be grateful for your (anyone’s) direction on that matter.

    Attached Files:

    Last edited: Sep 7, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Homopolar generator
  1. Homopolar generator (Replies: 107)

  2. Homopolar generator (Replies: 7)