Winding a strong electromagnet

[capthook]

Winding a strong electromagnet:

The strength of an electromagnet at its simplest boils down to amp-turns: N*I (# turns x amps).

Most discussion and information deals with a "traction" (attraction and in contact) style electromagnet. 
What about an electromagnet over an air-gap, and even more specifically, in repulsion against a permanent magnet? (polarised)
The information available on this type of electromagnet is severely lacking, and is of a primary interest of this post.

If attempting to obtain OU in a device using electromagnets - maximum effect for minimum input is a critical design goal.

Parameters:

1) CORE         
a) material                    
b) length            
c) width         
d) pole surface area   
e) permeability   

2) WINDINGS
a) length (depth)
b) width
c) wire size
d) wire length
e) resistance (OHMS)

3) power
a) amps
b) voltage
c) watts

So lets take a specific, practical example:

core: 1/2" x 3" hex bolt
windings: #26 AWG wound to 1.5" length x 1.5" width (1" windings + 1/2" core)
air-gap: 1/4"
Magnet being affected: 1.5"x.75"x.25" N42
power: 1 "D" battery

This is a relatively strong electromagnet- given the small size and power input - but what can/should be done to improve it?

Discussion:
what parameters will create the strongest repulsion electromagnet over an air-gap?
How might repulsion vs. attraction designs differ?

1) CORE
a) Material: a soft iron core, or electrical steel or laminated core are good options.
Is a hex bolt going to be acceptable - considering the permeability is sufficient given the small power?
It's easy and cheap to source.
Or - sparing no expense - would one of the other materials offer more strength as the domains will line up more readily?
And what would be THE BEST material of all?

b) Length: How long is too long?

c) Width: Will an over-all larger core mass create a stronger EM for the same power?

d) surface: in traction electromagents - surface area is of huge importance.  The more the better.  And round is better.
The same should apply for activation over an airgap.

2) WINDINGS
a) Length/depth: how long is too long? 
At what point does the length begin contributing just more resistance without additional  appreciable force as the windings are too far away?
What is the effect of unwound space at the end (for mounting etc)? So if windings are 1.5" deep - the core length should be as close to that as possible?

b) width: at some point - the windings are too far away from the core to be of significant value.
What would a rule of thumb be?  Some stated are:
   aa) no further than 1/2" from core
   bb) 1.5 times as wide as long  (so these two conflict)
   cc) twice the diameter of the item you are trying to affect?

c) wire size: the smaller the wire, the more turns, the stronger the EM. But the more resistance, requiring more voltage push the same amps through it.

Please post any comments, discussion, details, thoughts and links.

[capthook]

Something else you have to consider is the pulse rate of your electromagnet, the faster it is switched off and on the higher the Reactance which is a form of electrical resistance.  So the higher the Reactance then the more Voltage needed to produce the necessary Coil power.  One way around this is to wind multiple coils around the core and wire them in parallel.  For example if you are using 100 feet of wire for your coil, you can divide it up in to 10 foot lengths. Wind each ten foot section individually one on top of the other and attach the ends of the wires together at each end.  This will reduce the Reactance and keep the required voltage from rising.

Interesting idea... thoughts?

[capthook]

"there is known "trick"  or idea to defeat the attraction between the core and the permanent magnet so that you can even get a benefit of not using extra input power to defeat it.
About 2 years ago I mentioned this idea here, see:  http://www.overunity.com/index.php/topic,1621.msg16347.html#msg16347  and the link to that old patent is here, the old link mentioned there now needs log-in, this one is not: http://www.pat2pdf.org/patents/pat3670189.pdf
(explanation in Page 12, Column 2,  from line 31 and onwards)

With some tinkering of the size of the air gap between the bottom part of the electromagnet's core and a permanent magnet placed under the core and maybe using a slightly stronger permanent magnet there than the permanent magnet to be lifted above the electromagnet, you could reduce or totally eliminate the natural attraction between the core and the upper magnet and increase the 'tossing hight'  further upwards, with the same current into the coil.
The patent is rather long and needs patience to go through but may be worth studying from other aspests too, with respect to your gravity motor.

I agree, the energy in the flyback pulse (I prefer calling it flyback pulse instead of back emf) can also be regained when the electromagnet is switched off  (ala Bedini or by others) so this is another possibility to reduce input power.

rgds,  Gyula"

- -

Placing a small magnet at the far end of the electromagnet in repulsion to the armature magnet will negate the attraction of the armature to the core (providing a sufficient airgap) requiring less power to repulse.
Also, the electromagnet core now already has some of the domains aligned.  When the power is introduced, it provides a greater effect.
ie:
end magnet: 5,000 Gauss
power em: 5,000 Gauss
when used together: 20,000 Gauss - a doubling of the Gauss
(not exact figures - just presenting the idea)

[mondrasek]

capthook,

I hope you get good responses to those questions.  I am also very interested in them.  My own projects lead me to using air core EMs (solenoids) and I was lucky to already have the simulator here:  http://www.coilgun.info/mark2/inductorsim.htm  I would love to see something similar for cored EMs that allowed one to play with all the variables you have listed.  Unfortunately I have not found one on the web.  Maybe someone can point us to such a tool if one already exists.

M.

[Spider]

Google: Brooks Coil


Spider