How to wire a STRONG electromagnet

[Undacuva]

Hi everyone,
I have a 12mm long hard ferrite core that I want to use as an electromagnet. I have wound it with 0.8mm copper as tightly as I can by hand, in a single layer, but the field is not strong enough. I have placed another coil over that first coil, and then a third coil, each in parallel - branching before the core, and then re-connecting afterward - wound concentrically in the same direction, to increase the number of windings. I'm still not getting the magnetic force I need. The electrical source is a car battery with 490 cold cranking amps (CCA) -- There is no overheating now that I have 3 branches.

Am I doing something wrong? Is there a winding method that will work better? Do I need higher voltage or just higher current?

 

[maajdl]

http://easycalculation.com/engineering/electrical/solenoid-force.php
http://www.ehow.com/how_5969962_calculate-force-electromagnet.html
http://www.byronacademy.org/knowledge-center/view/calculatiing-emf-in-solenoid/
http://www.electronics-tutorials.ws/electromagnetism/electromagnets.html
http://en.wikipedia.org/wiki/Permeability_(electromagnetism )

The mains factors are:

- the intensity of the current in the wires
- the number of turns
- the length
- the permeability of the material
- and also what your objective is: why is the field "not strong enough", how do you expect?

You need to check all of them.

 

[sophiecentaur]

Hi everyone,
I have a 12mm long hard ferrite core that I want to use as an electromagnet. I have wound it with 0.8mm copper as tightly as I can by hand, in a single layer, but the field is not strong enough. I have placed another coil over that first coil, and then a third coil, each in parallel - branching before the core, and then re-connecting afterward - wound concentrically in the same direction, to increase the number of windings. I'm still not getting the magnetic force I need. The electrical source is a car battery with 490 cold cranking amps (CCA) -- There is no overheating now that I have 3 branches.

Am I doing something wrong? Is there a winding method that will work better? Do I need higher voltage or just higher current?

There is a huge range of 'Ferrite' materials so you would need to specify what its permeability is. The original application it was used for would indicate what its permeability is likely to be. Basically, ferrets that are used for high frequency RF work have low permeability in order to have low loss in the material.
You may be better to use a piece of steel for your purpose - readily available in many shapes and sizes and easy to cut and shape.

 

[CWatters]

It would be interesting to know if the "strength" increased as expected when you added the extra windings? eg did it double then treble?

 

[NascentOxygen]

Am I doing something wrong? Is there a winding method that will work better? Do I need higher voltage or just higher current?

It all depends on amps, turns, and core material. Swap your ferrite core for a steel bolt and see how that works out.

EDITED
You have your 3 layers electrically connected in parallel? For a stronger magnet, either add more layers still, or replace what you have with thicker wire that can carry more current from your battery. Just watch that it doesn't overheat, though.

Good luck with your experimenting.

 

[Undacuva]

Hi everyone,
Thanks for the responses. It seems that no-one has any issues with my winding method. What about increasing the voltage? Is there any use in that? Or could I sacrifice voltage for higher current?

 

[jtbell]

What matters directly is the current. To increase the current, you can either decrease the resistance or increase the voltage (Ohm's Law).

 

[CWatters]

but how much stronger do you want? I mean if it needs to be 10x stronger you are looking at needing 120V which would be dangerous.

Did it get _any_ stronger when you added extra windings?

 

[sophiecentaur]

Hi everyone,
Thanks for the responses. It seems that no-one has any issues with my winding method. What about increasing the voltage? Is there any use in that? Or could I sacrifice voltage for higher current?

Unless you attend to the core material, you may not get anywhere. The core could have a very low permeability or you could be saturating it if you increase Ampere-Turns ad infinitum.

The Volts - Current compromise is always relevant. I think it will depend upon the power supply you have as to what is the best combination.