# electromagnet help

#### Dude22

Mar 30, 2012
66
hi everyone,

I am trying to build a pipe that will have a ball baring levitating inside it. It needs to be an electromagnet as I need to be able to turn it on an off. I have made one of the simple "coil around a nail" and it works as a magnet although it is weak.

What material should I use for the pipe... and what thickness of coil should I use... and what battery to power it... and how tight should the coils be wrapped...

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
How is the setup going to work?
Is the pipe the magnet? Or is the ball bearing floating within the pipe with an external magnet?
If the pipe's going to be the magnet, you should use steel or any other magnetically conducting material.
If the magnet is outside the pipe, you need to use magnetically inert material like PCV or copper (copper for DC or low frequency magnetic fields only).

The coil should be wound as tight as possible: The more magnetic energy you concentrate in a small volumen, the higher the magnetic force.
As to wire thickness, length and battery voltage: These depend on many factors, like the magnetic field strength you want to achieve, the type of core you use etc. In your setup some experiments may be needed.

Note that a coil typically has a comparatively small DC resistance. So if you connect it directly to a battery, a high current may flow. This, again, depends on the thickness and length of the wire. You can start with a small test coil, measure its DC resistance and extrapolate to a larger coil with more windings. If for a given battery voltage the current is too high, you could limit it by a series resistor, but this will burn some of the battery's energy in the resistor. A better way would be to use thinner wire or more windings (or both) for the coil so all of the battery's energy is available for the coil.

Note also that for the magnetic field the current is the controlling factor, not the voltage (in an ideal coil the resistance would be zero, thus no voltage drop at all for DC).

You can read up abit more here: http://en.wikipedia.org/wiki/Electromagnet

Harald

#### donkey

Feb 26, 2011
1,301
may I be so bold as to enquire the use of this item? is it rail gun in nature? or is it a level sensor? or an antigravity project? or is it to detect vibrations?
the reason I ask this is each project has different requirements, for example if it is to detect vibration then you would either want to detect a change in the magnetic field which is another circuit or make the pipe conductive and when the ball touches it it completes a circuit. a railgun experiment would need something with good heat dissapation. each project has its own requirements so a little more knowledge on the experiment might help us determine a better setup

#### Dude22

Mar 30, 2012
66
may I be so bold as to enquire the use of this item? is it rail gun in nature? or is it a level sensor? or an antigravity project? or is it to detect vibrations?
the reason I ask this is each project has different requirements, for example if it is to detect vibration then you would either want to detect a change in the magnetic field which is another circuit or make the pipe conductive and when the ball touches it it completes a circuit. a railgun experiment would need something with good heat dissapation. each project has its own requirements so a little more knowledge on the experiment might help us determine a better setup

Yes, it is of rail gun nature... more specifically... coil gun. I would like to use 2 coils... One around the whole barrel, to make the projectile levitate... and another high power coil near the front of the barrel... to provide motion.

Last edited:

#### Dude22

Mar 30, 2012
66
How is the setup going to work?
Is the pipe the magnet? Or is the ball bearing floating within the pipe with an external magnet?

If the pipe's going to be the magnet, you should use steel or any other magnetically conducting material.
If the magnet is outside the pipe, you need to use magnetically inert material like PCV or copper (copper for DC or low frequency magnetic fields only).

The coil should be wound as tight as possible: The more magnetic energy you concentrate in a small volumen, the higher the magnetic force.
As to wire thickness, length and battery voltage: These depend on many factors, like the magnetic field strength you want to achieve, the type of core you use etc. In your setup some experiments may be needed.

Note that a coil typically has a comparatively small DC resistance. So if you connect it directly to a battery, a high current may flow. This, again, depends on the thickness and length of the wire. You can start with a small test coil, measure its DC resistance and extrapolate to a larger coil with more windings. If for a given battery voltage the current is too high, you could limit it by a series resistor, but this will burn some of the battery's energy in the resistor. A better way would be to use thinner wire or more windings (or both) for the coil so all of the battery's energy is available for the coil.

Note also that for the magnetic field the current is the controlling factor, not the voltage (in an ideal coil the resistance would be zero, thus no voltage drop at all for DC).

You can read up abit more here: http://en.wikipedia.org/wiki/Electromagnet

Harald

I am looking for the best way to levitate a ball bearing (or other projectile) inside a metal barrel. I am open to any ideas.

#### BobK

Jan 5, 2010
7,682
A coil wrapped around the outside of a non-mangnetic tube would do that. There are plenty of coil gun sites on the web.

Bob

#### Dude22

Mar 30, 2012
66
Thanks

Thanks everyone, I will do some experimentation with levitating and will let you know how it works.

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