Electromagnet Question

[gyulasun]

Hi Mondrasek,

Ok, no problem on misunderstanding.

In the meantime I learned about DC current probes as well but they use Hall effect device.  See this here:
http://www.testpath.com/Categories/Current-Probes-536114.htm   and their A622 would be good for you now  :
http://www.testpath.com/Items/ACDC-Clamp-on-Current-Probe-for-DMMs-and-Oscilloscopes-100kHz-100A-117-283.htm

It works from DC to 100kHz AC (has no toroidal core of course).  Other types with also both DC-AC ranges but with higher upper frequency coverage use both the Hall device and the toroidal core transformer.

I would suggest a very cheap but still correct solution both for DC and AC: use a 1 Ohm (or 5 or maybe 10 Ohm) value resistor and connect it in series with your electromagnet coil and measure the voltage drop across it by your oscilloscope.  Because your coil resistance is around 74 Ohm with this coil, the additional 1 Ohm (or say 5 or 10 Ohm if you wish to increase the current measurement sensitivity)  will not modify significantly the value of the original current (or if it does, you can correct it by some calculation).
And in the 50 or 100ms scope time range you surely will see the peak currents that are made by your moving the magnet in and out of the coil while your power supply or the 9V battery also feeds the coil . 
You can use several different value resistors to arrive at the final 1, 5 or 10 Ohm value, with the correct wattage, using the digital Ohm meter of the MM, no need for a high precision single resistor which tends to be expensive too.

rgds,  Gyula

[capthook]

If one is to energize any electromagnet (you pick the specs) for 1 msec, what is the power consumed by the electromagnet?
vs.
If one is to energize the same electomagnet for 1 msec, but this time, with a permanent magnet (you pick the specs) in close proximity such that the permanent magnet N pole is facing the electromagnet N pole so as to repel the permanent magnet, what is the power consumed by the electromagnet?

The power consumed is determined by Ohms Law.  See the attached pic I
find useful.
For this calculation:
P=U2/R
so if you apply 10 volts across a 5 ohm coil:
(10x10)/5 = 20 watts

Is this the thinking of your question? :
Will the electromagnet in proximity to a permanent magnet require additional energy because the field of the p.m. is 'sucking' up the field of the e.m. requiring additional input?

Has this been answered? What would be the answer?

At first blush I would have said no - but am now thinking - 'maybe'?
And why/why not?
And the variation due to induction of the moving p.m. near the e.m. windings would be negligable? (see following)

If the electromagnet is energized in proximity to a permanent magnet in repulsion the power consumption should be slightly more, maybe 21 of 22 watts.  When a magnetic force (the permanent magnet) is moved away from a coil of wire(in this case caused by repulsion) it generates electricity, so the power level rises, although only slightly.

So the power would rise because it's in repulsion resulting in an 'opposite flow' of charge due to induction of the p.m./windings to the e.m. requiring additional energy from the power supply?  And 1 or 2 watts?  Would that be a HUGE magnet?  Or would it be more like .1 or .2 watts (or less) for a small neo (.75x.5x.25)?  The p.m. is not moving ACROSS the windings but away, so even smaller?

Interesting thread - and I have alot of questions/thoughts to follow

tx

[capthook]

Here's my take/thoughts.  Hoping for further clarifications/corrections/thoughts

So, say one is to take a cylindrical electromagnet with opposite pole configuration.  Set it with the North pole facing up and uncharged.  Place a perminant magnet on top so that it's North pole is down and it is in contact with and in attraction to the ferous core of the electromagnet.  When you apply an electric source to the electromagnet it should repel the perminant magnet.

How much power is required to break the attraction of the perminant magnet to the electromagnet core?

That would depend on:
Magnet size/strength
Core surface area/composition/dimensions
Air gap

Testing would probably be easier than trying to plug numbers into formulas.
You might hang/place the p.m. BELOW the e.m. and put a potentiometer between the e.m. and power supply and adjust it until the p.m. drops.

If two perminant magnets are forced together in a vertical arrangment so as to repel, and then the top magnet is released, it will accelerate upwards to a height much greater than where it will eventually settle and hover over the bottom magnet. 
Can the electromagnet/perminant magnet arrangement be made to act the same?

Given enough power quickly enough - it could.

What is the relationship of the power consumed by the electromagnet to the strength/size of the perminant magnet to create this equal opposing force?

You would need to make your e.m. the same strength as your p.m.  This requires the appropriate AT (amp-turns).  This is achieved by combining the variables of:
wire size/length
# of turns
core size/permeability
coil resistance
voltage applied

This link is a java coil simulator.  It's for an aircore but is helpful for determing # turns, resistance, wire length etc.

http://www.coilgun.info/mark2/inductorsim.htm

Does the fact that we must first break the attraction require more power to the electromagnet than if there was not the attraction?

Yes 

Does the acceleration of the perminant magnet away require more power to the electromagnet due to the fact that the perminant magnet is moving through the electromagnet field?  Or will the electromagnet field generate outwords from the center of it's core and drive the perminant magnet away so that the two fields never overlap?

This goes to the question in your first post.  Not sure - hoping for further answers....

- - - -

Something similar I've been wondering:

The Adams motor design applies the principal that it uses less power to:
Have a p.m. attracted to the iron core of an e.m. and then pulsing the e.m. with just enough power to negate that attraction to the core allowing the p.m. to continue onwards. (kind of like turning the iron core into an air core).  Rather than using the pulsed e.m. as attraction or repulsion to the p.m.
Is this a valid principal?  Why/why not?  What might be a better principal?

tx

[mondrasek]

@capthook, thanks for all the thought and input.  I'm glad you are interested by these questions.  When I first asked them I thought I would receive a simple textbook answer or reference to experimental data that would make everything clear.  I didn't imagine this was going to be a testing/theory brain teaser.

@all

So after looking further into Bedini for a BEMF capture circuit I went ahead and made Imhotec's Bedini fan this morning.  Destroyed quite a few good fans trying to find one that had the correct coil wrap configuration as well as trying to understand the various instructions.  But it works and I'm trying it out now to recharge and old NiMH 9V that has been in a box for 6 or so years since I was last into micro electric RC planes.  That circuit is what I wanted to understand so I could apply my ideas *if* the permanent magnet does not consume an equal amount of power from the electromagnet when it is fired vertically.  I still look forward to trying everyone's ideas back at my deck at work with the test setup on Monday.

I've coorresponded with mscoffman a bit in the background as well.  He said he has some more info to forward once he has the time to collect it and pass it along.  I'm interested in his response to my questions about the Bedini SSG circuit as well.  I'm trying to understand it from a clasical EE point of view (ie without the "radiant energy" theories) for now.  I'd like to hear your opinions on that as well if you have any.

Thanks,

M.

[Honk]

A little tip on the way to perfection.

When you design the best electromagnet possible, used in pulsed mode you must avoid to deep winding layers.
In pulsed mode you have higher core loss than you have copper loss, due to the hysteresis of iron.
I calculated the surrounding flux of a current-carrying wire to how much it decreases by distance.
This affects the level flux that actually penetrates the core and gives you the magnetism you desire.
As you can see in the picture, you should aim for a maximum of 5mm deep winding and also try to keep it as
tight as possible to fit the most amount of copperwire. Using thicker wire gives you lesser turns at lesser
inductance and vice versa. It all depends on the speed you intend to pulse it. More turns = slower response.
The number of turn doensn't affect the flux output, lesser turn require more current and vice versa.
Most important for high flux efficiency is the winding depth. To deep winding gives a lot of copper loss at
small gain in flux output.

http://www.imstrading.com/cgi-bin/flux-graphs?page=fluxgraphs