Electromagnet Question

[mondrasek]

Looking specifically at the example that Xaverius worked up, once the electromagnet field is established we will have 125 Newtons of repulsive force.  How high will the repelled perminant magnet go?  Pick whatever mass you want for the perminant magnet.  What matters is the potential energy of the perminant magnet at maximum height of the launch, so mass does not really matter.

We have the 125 Newtons pushing up (accelerating) but decreasing exponentially as the gap between the magnets increases.  Gravity pulling down (decelerating) at a constant (for these scales) rate.  This is relatively straight forward and I'd graph it in Excel if my home computer had that.  Anyone care to do it up real quick?

But what about the time lag for the repulsive force to reach 125 Newtons?  How long does the electromagnet need to be energized in order for the perminant magnet to reach it's maximum height?  How much lower than the theoretical maximum height would that be (due to the time lag)?   How much energy did the electromagnet require for this time period?  And how much energy can be reclaimed once the electromagnet is turned of by reclaiming the current generated as the magnetic field collapses again?

[Honk]

Make sure you use good core material or you will loose lot's
of power when you operate your electromagnet at 1ms pulsing.
I assume there will be more than just one pulse in your setup...
More like a 1ms pulse repeated at 50-200Hz or so.
Using pure iron is bad, it will run hot and consume lot's of power.

Core Loss:
---------------------------------------------------------------------
Core loss is extremely important in soft magnetics.
Core loss represents an inefficiency,
so it is highly disdained by the designer. In
many instances, core loss will render a particular
material unusable in an application. The most
glaring example would be the high-frequency
power-conversion transformer industry, which is
dominated by soft ferrites.

Powder cores are quite useful for high
frequency power conversion inductors.
The unit of core loss in both SI and CGS systems is
the Watt.
1 watt = 1 joule per second

Core loss is realized by two major components:
Hysteresis Loss and Eddy Current Loss.
Hysteresis loss results from the fact that not all
energy required to magnetize a material is
recoverable when it is demagnetized.
The wider and taller the hysteresis loop,
the more hysteresis loss a material has.
Eddy current loss is the result of small circulating
currents (eddy currents, not unlike eddy currents
produced in the wake of a boat) that are induced
when the flux density changes in the magnetic
material (see Figure 10). The amplitude of these
small currents is dependent on the Electrical
Resistivity of the material.
---------------------------------------------------------------------
Solid iron summarized:
It has very high eddy currents loss and pretty bad hysteresis.
You might end up getting a very hot electromagnet core.

[mondrasek]

I've set up and tested two electromagnets that I had available.  One was a potted solenoid coid from a pneumatic valve.  It draws about 310 mAmp at 24 Volts.  The second is a cylindrical cored industrial electromagnet that unfortunately has both poles on the same side, one in the center, and the other around the edge of the cylinder face.  It draws about 1 Amp at 24 Volts.

Both are capable of firing a sample neo permanet magnet over 12 inches vertical when energized momentarily by an industrial 24 volt supply.  I am able to place the neo inside the solenoid, a bit above center, for maximum acceleration.  The cored electromagnet needs to have a small gap pressent between it's core and the neo or the attractive force to the core will not be overcome.

My measurement equipment is anything but sensitive enough for looking for variations in Amps and Volts on samll enough time scales to convince me that I am not missing some variations.  I would expect to see more electrical power being consumed when the electromagnets are energized to launch the permanent magnet, vs. when they are energized without the permanent magnet present.  But I am not seeing anything like that.  Of further interest is when I force the permanent magnet back into the electromagnet field or move it around in it.  This also does not cause my Amps or Volts to noticably react in any way.  This makes sense to me since there is no additional power needed by a perminant magnet if it replaced the charged electromagnet in the same experiment.

So what is going on here?  Is my measurement abilities not able to show that the electromagnet requires additional energy in order to repel the permanent magnet?  Or is it the resultant Potential Energy of the raised permanent magnet not requiring an additional equal input of electrical energy to the electromagnet?

Thanks,

M.

[Honk]

I don't really get what you are looking for?
Is it simply repelling a neomagnet from 12 inches distance or what?

In this case I can tell you the field outside a solenoid is extremely weak due to the extremely large airgap between ends.
You cannot force the field outside simply because most flux takes the shortest return path, right through the solid core.
The only solenoid with a strong outside field (in the tesla range) is one that is supercooled into superconducting state.
This has to do with the molecular structure of materials when being superconducting.

Simply put.
A very strong solenoid has a weak outside field that diminishes very fast a couple of millimeters above surface.

[mondrasek]

@Honk,

If either electromagnet is energized momentarily it can fire a small permanent magnet from close proximity (zero inches away) to about 12 inches away vertically.  If the same electromagnet is energized for the same amount of time without the permanent magnet in place, does it consume the same electrical energy?  So far my gross test set up appears to show that the electromagnet consumes the same electrical energy in both cases.  Is my equipment not sensitive/sophisticated enough to measure the difference, or do both cases consume the same amount of electrical energy?

Thanks,

M.