Why aluminum plate in eddy current device? 2

[ornerynorsk]

Could someone explain the purpose and function of the aluminum seperator plate within a magnetic resistance exercise device (eddy current)? We have just finished prototypes with and without said aluminum liner plate, and there seems to be no difference in resistance generated. Any help or insight would be greatly appreciated.

 

[hacksaw]

possibly heat removal

 

[durcan]

when aluminium is moved in a magnetic field it creats eddy current, the stronger the field the harder it is to move the aluminium, when the aluminium moves thru the magnetic field this will also create heat.

 

[hacksaw]

can you explain why the original question reports that there is no loss of mechanical resistance when it is removed?

 

[durcan]

the aluminium plate much be in a very low field or no field?
I would have to see the assembly set up

 

[howard1954]

Eddy current devices create drag (torque), whenever a conductive material is moved within a magnetic field. The more conductive the material, ie, Silver, Copper, Aluminum, the higher the induced eddy currents. The stronger the magnetic field, the higher the higher the induced eddy current. By varying the distance between the magnetic poles, you vary the resistance. Also, eddy currents are directly proportional to the square of the speed of movement of the conductive plate relative to the magnetic field,ie, doubling the speed will give four times the resistance.

For maximum torque, set the North and South poles directly opposite each other(maximum flux),bolted to the frame, with the conductive Aluminum plate connected to your moving part. Also, use steel/iron keeper plates behind the magnets preferrably connected together like a C-shaped magnet to concentrate the field.

 

[hacksaw]

A lot of excellent points.

Does anyone have an explanation as to why the originator reports that the alum. plate made no difference in the amount of mechanical resistence generated?

 

[ornerynorsk]

Thanks all! Howard1954, that's the answer I was looking for. In our original experiment, we were using extremely powerful rare earth magnets, and I believe now that the rpm was too low to discern a difference between "with plate" and "without plate". We are now modifying our experiment and gearing up the rpm.

 

[howard1954]

Actually, the effect can be seen at nearly any speed. With a 1/4" air gap, you can barely move a 1/8" thick aluminum plate thru the field by hand.