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Dropping a magnet through a hollow copper bar.
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Previously:
https://www.homemadetools.net/forum/...197#post134712
https://www.homemadetools.net/forum/...4677#post80364
https://www.homemadetools.net/forum/...410#post122179
Damm trying to remember what/why is happening here, I have seen this on other post.
The moving magnet creates an electric current in the copper which in turn makes a magnetic field which slows down the fall of the magnet.Quote:
Originally Posted by Ralphxyz
If it wasn’t for this “technology” for lack of a better word, we wouldn’t have some of the great amusement rides we have, like the tower of terror and other rides that drop and also stop, like some roller coasters. It never breaks down and never wears out. 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.Quote:
Originally Posted by Ralphxyz
The magnet will, slowly, lose its flux, or magnetic power.Quote:
Originally Posted by Mikell17
In this maybe, but the rides use electricity, not just plain magnets. They will require replacement, but compared to brake shoes, it wouldn’t be anywhere near the same time. Besides, if they didn’t have this system there wouldn’t be a lot of the rides we have.Quote:
Originally Posted by Drew1966
It's my boy. Some know him as Eddy...Eddy Lenz Law.Quote:
Originally Posted by Ralphxyz
The copper bar is sort of overkill; you can get the same effect using ordinary copper plumbing pipe.
The magnet motion induced magnetic field must always be in such a direction as to oppose the motion of the magnet. Were it not it would be possible to build a perpetual motion machine and thermodynamics prohibits such.
But why am I seeing the magnet? That's what I could not remember.
You were probably wearing your X-ray vision specs that you bought off of the last page in your comic book.Quote:
Originally Posted by Ralphxyz
There is something about that green film and the electric field that is generated that produce the moving image.
I remember those ads.
Such as: https://www.amazon.com/Magnetic-View.../dp/B00129CCGSQuote:
Originally Posted by Ralphxyz
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.
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.
Eddy current brakes are common on trucks and buses, even large vans.Quote:
Originally Posted by Mikell17
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.Quote:
Originally Posted by tonyfoale
So are these eddy currents that are being viewed?
I have a power scale that has a copper bar between too magnets to dampen the movement of the beam.
Attachment 46324
A web photo, of one like mine.
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.
Attachment 46326 Attachment 46327 Click for full size.
As has been mentioned, some brakes and dampers can be made using eddy currents.
Attachment 46325
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.
