Free 186 More Best Homemade Tools eBook:  
Get 2,000+ tool plans, full site access, and more.

User Tag List

Page 2 of 2 FirstFirst 1 2
Results 11 to 19 of 19

Thread: Dropping a magnet through a hollow copper bar - GIF

  1. #11
    Supporting Member Ralphxyz's Avatar
    Join Date
    Dec 2016
    Posts
    1,564
    Thanks
    2,378
    Thanked 279 Times in 228 Posts

    Ralphxyz's Tools
    There is something about that green film and the electric field that is generated that produce the moving image.
    I remember those ads.

    186 More Best Homemade Tools eBook

  2. #12
    Supporting Member DIYSwede's Avatar
    Join Date
    May 2019
    Location
    Stockholm, Sweden...
    Posts
    634
    Thanks
    415
    Thanked 799 Times in 319 Posts

    DIYSwede's Tools
    Quote Originally Posted by Ralphxyz View Post
    But why am I seeing the magnet? That's what I could not remember.
    Such as: https://www.amazon.com/Magnetic-View.../dp/B00129CCGS

    2000 Tool Plans

  3. #13
    Supporting Member Ralphxyz's Avatar
    Join Date
    Dec 2016
    Posts
    1,564
    Thanks
    2,378
    Thanked 279 Times in 228 Posts

    Ralphxyz's Tools
    Thanks DIYSwede, magnetic viewing screen, now if I could only think of something useful.

    Now this one claims "Test Cracks on Steel Surfaces" now what/how?
    That might be useful.

  4. #14
    Supporting Member Toolmaker51's Avatar
    Join Date
    Feb 2016
    Location
    Midwest USA
    Posts
    5,330
    Thanks
    7,041
    Thanked 2,977 Times in 1,892 Posts

    Toolmaker51's Tools
    Marv is correct. Copper tube being so easy to get is seen probably 99% of the time, and what we used demonstrating to STEM classes. Though bar would make the field appear broader, more visible.
    Glad I wasn't called to make it. I machine copper now and then, making spotweld electrodes and fixture plates. Politely, many grades are quite a bear to machine.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

  5. #15
    Supporting Member tonyfoale's Avatar
    Join Date
    Nov 2016
    Location
    Spain
    Posts
    1,549
    Thanks
    679
    Thanked 2,627 Times in 705 Posts

    tonyfoale's Tools
    Quote Originally Posted by Mikell17 View Post
    I wonder why they haven’t figured out or even tried to find a way to use these in at least trucks or airplanes. Maybe they have and they’re too abrupt or something.
    Eddy current brakes are common on trucks and buses, even large vans.

  6. #16
    Supporting Member mklotz's Avatar
    Join Date
    Aug 2015
    Location
    LA, CA, USA
    Posts
    3,433
    Thanks
    357
    Thanked 6,378 Times in 2,116 Posts

    mklotz's Tools
    Quote Originally Posted by tonyfoale View Post
    Eddy current brakes are common on trucks and buses, even large vans.
    I remember a sensitive analytic balance in college that had a tiny electrical eddy current brake that could be switched on to damp the oscillations prior to taking a reading.
    ---
    Regards, Marv

    Home Shop Freeware
    https://www.myvirtualnetwork.com/mklotz

  7. #17
    Supporting Member Ralphxyz's Avatar
    Join Date
    Dec 2016
    Posts
    1,564
    Thanks
    2,378
    Thanked 279 Times in 228 Posts

    Ralphxyz's Tools
    So are these eddy currents that are being viewed?

  8. #18
    Supporting Member hemmjo's Avatar
    Join Date
    Feb 2017
    Posts
    2,542
    Thanks
    224
    Thanked 1,446 Times in 820 Posts

    hemmjo's Tools
    I have a power scale that has a copper bar between too magnets to dampen the movement of the beam.

    Dropping a magnet through a hollow copper bar - GIF-magnetic-damper.png
    A web photo, of one like mine.

  9. #19
    Supporting Member tonyfoale's Avatar
    Join Date
    Nov 2016
    Location
    Spain
    Posts
    1,549
    Thanks
    679
    Thanked 2,627 Times in 705 Posts

    tonyfoale's Tools
    Eddy currents can be either beneficial or detrimental.

    All you need to generate eddy currents is a CHANGING magnetic field and a conductor in that field. You can get a changing field by relative movement between a magnet and a conductor, but also by passing an AC through through an inductor to create the field.

    On the detrimental side are the eddy currents generated in transformer cores and electric motors. The reduction of eddy currents is the reason that transformers and motors have laminated cores. Each lamination is covered with a insulating coating, this restricts the eddy currents to lots of small currents in each lamination rather than the large currents which you would get with solid steel cores. Without laminated cores transformers and motors etc. would be inefficient and the cores would heat up to excess. Ferrite material is often used in place of laminations because it is magnetic but non-conducting, so preventing eddy currents from circulating.

    On the beneficial side there are countless applications. One example is/was in electric utilities power meters which use an aluminium disc which rotates with a velocity proportional to the power being used. Voltage and current coils multiply to generate eddy currents in the disc proportional to the power being used and those currents create a magnetic field to oppose that from the coils and so the disc is pushed around. To prevent the disc spinning at at uncontrolled rate there is a magnet brake to apply a load torque. An eddy current motor in effect.

    Dropping a magnet through a hollow copper bar - GIF-watthour01.jpg Dropping a magnet through a hollow copper bar - GIF-watthour02.jpg Click for full size.

    As has been mentioned, some brakes and dampers can be made using eddy currents.

    Dropping a magnet through a hollow copper bar - GIF-eddybrake.jpg

    This shows a typical brake (often called a retarder) as used on trucks and other vehicles.

    Two ventilated cast iron discs and an axle close a magnetic circuit generated by coils (the white pieces) that are powered by a DC to produce a steady magnetic field of strength proportional to the current. As vehicle brakes they have the advantage of no wearing parts, but they are used in conjunction with friction brakes because the eddy current brakes produce no holding torque at rest. There are countless other applications for devices that use eddy currents. Brakes almost identical to these retarders are also used in dynamometers for measuring power, they have the advantage that they are so easy to control. The braking torque is controlled by changing the DC through the coils.



    186 More Best Homemade Tools eBook

  10. The Following User Says Thank You to tonyfoale For This Useful Post:

    hemmjo (Oct 11, 2023)

Thread Information

Users Browsing this Thread

There are currently 2 users browsing this thread. (0 members and 2 guests)

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •