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Layers V.S. Length; Electromagnets ? Answered

Ok, so I am going to be working on a project that involves electromagnets and the on thing I have never gotten straight is this:

To make the most effective magnetic field possible do I make the (hypothetically) 100' of wire a long coil with only a couple of layers or 100' of wire a short coil with many layers?
I have always come across conflicting views on if length improve the fields or weaken them. Any insight would be helpful and if you could also provide a good reference site for these types of questions that would also be appreciated. 

Discussions

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Downunder35m

Best Answer 4 years ago

That depends on what you plan to do with it and what materials you have available.
Take a relay coil: It is about twice as long as the diameter.
This provides a good balance between forces generated and power required.
On the other hand lifting magnets, like those on cranes in scrap yards, are more flat and wide and in an enclosure that is only open to where the magnet is supposed to hold.
How many turns/layers depends on the power level, what lifting force is required and if it is suitable for the application.

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JayccobDownunder35m

Answer 4 years ago

I am going to be interacting with ferrofluid , with the goal to be able to vary the magnetic field across a grid sculpting the puddle of ferrofluid with peaks and valleys. Any thoughts on which one will be better for this application?

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Downunder35mJayccob

Answer 4 years ago

About twice the diameter than the height.
Check enclosed magnets from a speaker or these magnet hooks to check the pattern and size.
If you want to go small you will need to make the core and shielding yourself.
As an alternative check a small relay - take the thing apart to get just the coil with the shielding that holds the contact bar, remove the bar though.

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iceng

4 years ago

If I was going to sculpture ferrofluid I would wind my coil around a magnetically susceptible metal material that would concentrate initial flux and still allow for saturating the metal as current increases and permits a magnetic divergence to spread the flux to make unusual fluid formations..

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Jayccobiceng

Answer 4 years ago

I have marked this as answered already, but if you wouldn't mind could you elaborate what you mean (such as the type of metal, style of coil, etc.)? It could either be here or over a pm.

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kelseymh

4 years ago

I think it depends on what you mean by "effective."

If you want to create an enclosed region with a very uniform axial magnetic field, then you should wind your coil around a long tube (like a paper-towel tube or larger). Inside the tube, the field will be essentially uniform, and directed along the axis of the tube. This is what high-energy physics detectors (like mine) do.

If you want to create a very strong electromagnetic, with a high intensity external field, then wrap your coil around something relatively short, thick, and iron (like a heavy nail or spike).

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Jayccobkelseymh

Answer 4 years ago

I am going to be interacting with ferrofluid , with the goal to be able to vary the magnetic field across a grid sculpting the puddle of ferrofluid with peaks and valleys. Any thoughts on which one will be better for this application?

(A repeat of the above post so you can also get a notification)

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kelseymhJayccob

Answer 4 years ago

I think Downunder got it right. For your purpose, you will want a whole lot of small magnets filling your control space, each individually wired. Short and wide, with lots of turns, gets you the strongest external field You probably _don't_ want an iron core, because you will want the fields to turn on and off quickly (iron both saturates and has hysteresis).

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Jayccob

4 years ago

If you guys would like it I can make a quick sketch to give a better idea of what I am doing.