Winding a strong electromagnet

[Xaverius]

Interesting idea... thoughts?

Actually if you use Ferrite or laminated electrical steel you will eliminate almost all of the Reactance but you still have DC resistance.  This can be reduced by using the parallel winding method.  Eighty feet of 27 guage wire has approximately 4 ohms of resistance.  If you used a bifilar winding, that is divide the 80 feet by 2 (40 feet) and wound each section in parallel the total resistance would drop to 1 ohm, meaning you could obtain 4 times the amount of amperage for the same amount of voltage.  Conversely, you can obviously increase the number of turns without increasing the resistance, by using this method.  Of course, if you increase the amperage or the number of turns or both you increase the magnetic field strength.  I'm presently pursuing an electromagnet using Ferrite, which has a permeabilty of around 2000.  I'm trying to optimize the design deciding how much wire to use, my voltage source is a bicycle generator, 8 watts @ 1amp, 8 volts.

[Xaverius]

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.

Please see replies 6319 and 6320 in the "Roll on the 20th" topic.

[capthook]

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.  M.

Hi mondrasek!  Yes - that online coil simulator is awesome.  I've used it often to determine wire length and resistance of coils of certain dimensions - works fine for cored-coils in that sence.
Have you done anything more on your gravity/latch wheel?

- - -
Spider - thanks for the suggestion - not too many hits.  Thoughts on a Brooks coil design in relation to an EM?  Would the recommended relative coil dimensions translate into a stronger/more effecient EM?

- - -

Actually if you use Ferrite or laminated electrical steel you will eliminate almost all of the Reactance but you still have DC resistance.  This can be reduced by using the parallel winding method.
...I'm presently pursuing an electromagnet using Ferrite, which has a permeabilty of around 2000. 

Thanks for the reply Xaverius!  I will wind my next EM using the multi-strand method (this weekend) and post results.  So if I'm winding 300' - break it out into 4 in-hand?

And on your ferrite rods - you have sourced 1"x7" size?  Any U.S. supplier links?
And is this just 'non-magnetized' ferrite/ceramic material, like is used to make ceramic magnets?
Results?  Remanence of the material?
And the math stuff is good - I have a minor grasp of it - but hands-on is really the only way I fully comprehend it!

"The permeabilty of ordinary iron/steel is ur=50"
See this link: http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/magprop.html#c2

Iron, 99.95% pure:
Initial Relative Permeability: 10,000
Maximum Relative Permeability: 200,000
Iron, 99.8% pure: 150 : 5,000
Steel, 0.9% C: 50 : 100
(amazing to see the huge disparity in the permability in relation to the purity of iron.  .15% equals a 40x increase!)

So a Grade 2 hex bolt is low carbon steel w/ perm. of 50-100.  So a pure iron core would boost the power of an EM by like 2,000 times?  Or would a small, low-power (1.5 watts) EM not see much difference?  Does the permeablility deal more with saturation point? Or does it also indicate "how easily the domains will align" thus offer a larger effect for the same power?


Any comments on core and winding dimensions?

2 interesting ideas you have presented - thanks!

Any progress on your pulse motor/generator?

[Xaverius]

Hi mondrasek!  Yes - that online coil simulator is awesome.  I've used it often to determine wire length and resistance of coils of certain dimensions - works fine for cored-coils in that sence.
Have you done anything more on your gravity/latch wheel?

- - -
Spider - thanks for the suggestion - not too many hits.  Thoughts on a Brooks coil design in relation to an EM?  Would the recommended relative coil dimensions translate into a stronger/more effecient EM?

- - -
Thanks for the reply Xaverius!  I will wind my next EM using the multi-strand method (this weekend) and post results.  So if I'm winding 300' - break it out into 4 in-hand?

And on your ferrite rods - you have sourced 1"x7" size?  Any U.S. supplier links?
And is this just 'non-magnetized' ferrite/ceramic material, like is used to make ceramic magnets?
Results?  Remanence of the material?
And the math stuff is good - I have a minor grasp of it - but hands-on is really the only way I fully comprehend it!

"The permeabilty of ordinary iron/steel is ur=50"
See this link: http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/magprop.html#c2

Iron, 99.95% pure:
Initial Relative Permeability: 10,000
Maximum Relative Permeability: 200,000
Iron, 99.8% pure: 150 : 5,000
Steel, 0.9% C: 50 : 100
(amazing to see the huge disparity in the permability in relation to the purity of iron.  .15% equals a 40x increase!)

So a Grade 2 hex bolt is low carbon steel w/ perm. of 50-100.  So a pure iron core would boost the power of an EM by like 2,000 times?  Or would a small, low-power (1.5 watts) EM not see much difference?  Does the permeablility deal more with saturation point? Or does it also indicate "how easily the domains will align" thus offer a larger effect for the same power?


Any comments on core and winding dimensions?

2 interesting ideas you have presented - thanks!

Any progress on your pulse motor/generator?

Hi Capthook, actually you can divide the 300 feet into as many smaller wires as you like. The more smaller wires the lower the resistance.  The formula is the number 1 divided by 1/r+1/r+1/r........r = resistance of each indivdual wire, ex: r=2 and you have 5 small wires, then total resistance is 1 divided by 1/2 + 1/2 +1/2 +1/2 +1/2 = .4 ohms.

Yes, the ferrite rod I have is 1" diameter and 6" long.  This is experimental, I don't know how effective it will work as an electromagnet although I've read the results of other experimenters has been favorable.  I'll post once it is wound and energized, a lot of work at the regular job, lately, LOL.  It is similar to ceramic magnetic material, specifically it is used in the Radio-Frequency field, usually for antennas, tuners, attenuators,etc.  I sourced it at Stormwise.com, it is Material "T" and you must look for the 2000 u(permeability).  They order it about once a month and then cut the lengths to order,  one week to one month wait time.   I agree hands on is the way to go, the math gives me a clue beforehand if the concept will work or not.....If the math does not make sense, then the pursuit is useless.  Actually, the Remanence is unimportant as this is used for an electromagnet, but I think the Remanence is low.

You're right, impure iron has low permeabilty, but very pure iron has high permeabilty.  Pure iron would boost the power 2000X, low power EM(1.5 watts) would see a tremendous boost in MAGNETIC power.  Permeabiltiy deals with "how easilty the domains align" offering a larger effect for the same power.  It does not normally effect saturation point as most magnetic materials saturate anywhere from .5 tesla to 1.5 tesla, however usually as a general rule the higher the permeability, the lower the saturation point.

I don't think that core and winding dimensions are a factor per se, however, the larger the cross-sectional area of the core, the stronger the magnetic field and also the more wire that is needed.  Hope this answers everything and sorry if I explained things you already know.  I'll try to get to my EM this weekend.

[capthook]

Well I've spent the last 4 hours searching on core materials.....

Sourcing pure iron is VERY expensive: $250 for a small rod ....(from www.goodfellows.com) or
$100 from http://www.surepure.com/products.php?ID=7&meas1_ID=41&subCat=23

1018 cold rolled steel is (relatively) easily sourced and reasonably priced.... is this a decent option?

BUT - the ferrite rods idea has peaked my interest the most.....

Found this supplier: https://www.amidoncorp.com/categories/6

The 77 is 2000u but limited sizes... the 33 is 800u with more selection... and cheap....
guess I'll order some to test........

How to mount an unthreaded rod securely? (can't thread brittle ferrite)
- - -

Winding a 'kiddie' electromagnet on a bolt from Lowe's is not the solution..........

Shout out!!! ->  What is THE material for EM core construction and where to source it?!?

Anyone else used ferrite rods as cores?