Eddy Current Braking

h1dd3n · 2005 January 4th, 08:32

I need a bit of help.

In eddy current braking; is regenerative braking the same as eddy current braking?

Sir_Zerp · 2005 January 4th, 10:44

Don\'t think so. Regenerative is using a motor like winding to generate current back to the system. If I remember right eddy is a form of loss do to a magnetic field.

Any load could be a loss, so eddy and regenerative might not be the same thing.

h1dd3n · 2005 January 4th, 12:32

is anyone able to define the difference between the two?

of what i know (if they are different)
regenerative braking is similar to rheostatic braking and the dynamo that it uses recovers the lost energy and turns it into a current, this is then fed to braking resistances and causes the slowing or stopping of a moving object.
eddy current braking however is a swirling current set up in a conductor in response to a changing magnetic field. the direction in which the swirls go (by lenz\'s law) gives the retarding effect on the disc or whatever ur slowing down.

nmondal · 2005 January 5th, 08:37

[What is regenerative breaking?]

Any motor, can be used as an generator in principle. Agreed?
So, if we disconnect the current source of the motor, and put the motor in Generator mode by putting it in a magnetic field, it will generate current , and that will be feed into the current source. See below:---
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One of the most unique elements of electric buses occurs during the braking process. As an electric vehicle slows down, the motor turns into a generator, adding electricity to the battery. Bringing an electric bus to a sudden stop reduces, or eliminates, energy generation. Slowing down gradually, and in many cases allowing the bus to come to a halt without actually breaking fully utilizes the system allowing the greatest amount of energy being produced that, in turn, increases the range of the electric bus. One of the ancillary benefits of regenerative braking is an increase in brake life.
---------------------Copied from : http://www.etvi.org/General/New_FAQ.html
__________________________________________________
Eddy Current Breaking:--
It is a lossy breaking technique, where we slow down the motor by putting it into a magnetic field and inducing eddy current loops, and thereby *loosing* energy, as the energy is lost by resistive heating.
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Used for breaking in some modern trains and
Wonderlands Space Probe. When the train comes to break electromagnets are
brought near the moving metal wheels eddy currents are induced in the opposite
direction to the wheel. The flow of eddy currents in the opposite direction to the
motion of the wheel take some kinetic energy which smoothly slow the train down.

:P

h1dd3n · 2005 January 5th, 14:08

thank you very much for your replies in this :)
I guess they are different then

Sir_Zerp · 2005 January 6th, 08:50

Not really.

You could argue that they are same with only different loads.

With regenerative you are generating power via EM and passing back to the control system of the car.

With eddy you are generating power via EM and directly shorting it to produce heat.

.1 ohms with 100 amps is still a load, which produces heat.

nmondal · 2005 January 6th, 11:47

See, Zerp,
It is Maxwell that is responsible for both.
It is the same law. But, the results are different, if you see.

Absolutely. How? When a generator rotates, there is an Eddy current loss. And also, note that, as the thing is rotating against the Magnetic field, the whole system tries to be stable. What that means? The generator is creating EMF, so that it can stop rotating! And exatly that is why we need external force to make it rotate. One of the reasons of \"breaking\" is Eddy one. :(
So there are always 2 reasons.
If we use the 1, to stop motor, we call it lossy because, it is not good use of power, [Eddy is lossy...] But if we use the generator mode, so that [Basically that\'s what u r saying...that is nothing but a different Load...] we can give back something to the power source...

So from a pure theorytical point of view, u r correct. But from a technical point of view : they are different.

:D

So, as physics oriented people we can see the seamless unified law, but from an engineering perspective there are plenty of things to be done!
:)

Jeff T · 2006 November 30th, 21:25

Anyone have expertise in the application of eddy current braking? I have an ABS 'control arm' that's 14" x 1.25" x .375". The arm is suspended to travel back and forth in its long axis. A 3 inch x .125" diameter drill rod sticks out the front. I want to pass that drill rod through a slot, or a donut, and pulse said slot or donut with current so as to create eddy current braking on the drill rod/arm.

Obviously this is not a locomotive, or a roller coaster. But, can't it please be done at this scale? Without risking the life of the user?

editor · 2006 December 1st, 15:20

You can do it with a mains voltage donut (coil) but the problem is you have to switch the coil off pretty quick or it slows and stops the rod, then shoots it out. maybe microswitches on the arm.