Building an Electromagnet

This document is complete, but still considered a draft. Email Douglas Moyes with any questions you have or comments. Last update: January 29,2007.

Things you'll need

Electromagnets work on the principle that current flowing through a wire will produce a magnetic Field. That magnetic field can then be transferred trough core made of ferrous material (iron, or other materials that interact well with magnetic fields). They were used in early research with electricity.

Building an electromagnet is easy:

  1. Wrap a wire around an iron core (a nail or a bolt works great)
  2. Make sure your wraps are all going in the same direction. The tighter the wraps, the closer they are together, and the more you have, the stronger your electromagnet will be.
  3. Have a 3 volt power supply or 6 volt lantern battery handy to connect your electromagnet to (you can use any power supply, but read the note below).

Pretty easy huh? Well, people sometimes have trouble with this, and mainly it's because they choose the wrong wire, or they forget that they need to have both ends of their wire outside of the coil so they can connect a power supply or battery to it.

The most common wire you'll find has rubber for insulation this isn't what you want to use. Wire used in electromagnets use a single solid piece of wire coated in an enamel (similar to paint) film for insulation. Take a look:

Normal wire with rubber insulation
Normal rubber insulated wire
Magnetic wire with very thin insulation
Magnetic wire
diagram showing
why magnetic wire is used instead of normal wire

As you can see, the rubber in the rubber insulated wire is about the same thickness as the radius of the wire. But in the magnetic wire, the insulation is so thin you can hardly see it when looking at the wire straight on. This means that more of the magnetic field is able to pass through our iron core making a much stronger electromagnet. The magnetic force closer to the conductor is much stronger than that the further out you go, so even being less than a millimeter closer to the conductor greatly increases the magnetic field strength.

The drawback to using magnetic wire is that the insulation can easily be removed by scraping it by accident (you'll have to gently scrape the wire to remove the insulation on both ends so you can connect a battery to your electromagnet).

You can get magnetic wire from many places, such as an old transformer, or from a electrical supplier. Some Radio Shack stores still carry electrical components, so you can shop there. You can also try www.AllElectronics.com, www.Jameco.com, www.Mouser.com, or me ;-).

Your friendly Electricity Merit Badge Counselor may even have some laying around (I have a 13 pound 22 gage magnetic wire, probably a few thousand feet worth). Though, for your electromagnet 13 feet of wire is more than enough-- we're building electromagnets here, not rail guns....

If you're going to be using anything other than a battery, remember: Your electromagnet is just a piece of wire, so you must add a resistor in series with your electromagnet or you could damage your power supply. You will want at least 2-10 amps going through your wire. Make sure the resistor you use is rated for your suspected power (not doing this could cause the resistor to burn):

	Power=Voltage X Current
	Current=Voltage/Resistance

   Or:  Power=Voltage X (Resistance)2

So, if we want 1 Amp running through our 6 volt power supply, we need a resistor rated for 6 watts or more, and it should have a resistance of 6 Ohms (or you could use 12 72 Ohm 1/2 watt resistors wired in parallel). If you try using a resistor that isn't rated for the current you're passing through it, it will burn up.

If you're using a 6 volt battery or 2 D cells (3 volts total if in series), then you don't need to worry too much about those equations above right now. The wire can get hot when left connected to your power source for too long. NEVER HOOK YOUR ELECTROMAGNET UP YOUR HOUSEHOLD ELECTRICAL OUTLET, DOING SO WILL BURN YOU, COULD ELECTROCUTE YOU, AND CAN CAUSE A FIRE!

Okay, let's build the electromagnet!

Get all your materials together: Wire, bolt (or a large nail or thick tent peg), tape, something to scrape or sand the thin insulation off with. You can also get a nut to add to the other end of the bold like I did at the end, but you don't need to.

You can click on most of the images below to see a larger version.

Step 1 -- Start your Electromagnet

beginning
	threading of the electromagnet

Start by winding the wire around your iron core. You should leave 2 or more inches of wire out on each end when finished. Always coil your wire in the same direction. If you're using a bolt, take extra care to avoid scraping the wire on the threads.

Step 2 -- Wind the wire around the iron core

Using a bolt Using a nail
Threading a
bolt with magnetic wire Pushing the
 threads closer together using a nail, or other
 smooth rod

After you have your bolt or nail partially threaded, put some tape on the threaded part to keep the wire from moving around as you make your coil. If you're using a threaded bolt, you can put your finger or thumb on the bolt just over where you have threaded, and turn. Your thumb will guide the wire into the groove. Be careful not to scrape the wire on the threads!

If you're using a nail or large tent peg, you will need to push your coil closer together every now and then. The nail that you see in the picture was actually too small. It became magnetized on the first use, and the paperclips wouldn't drop after power was dropped.

Keep your threads as tight as possible, and always wind your wire in the same direction.

Step 3 -- Add a second wrap (optional)

Start second wrap Finished Magnet
start of
second wrap electromagnet
with two wraps

This is an optional step. You can go back over the windings you just made to create an even stronger electromagnet. But it isn't really necessary. Just make sure that you continue to wind your coil in the same direction as before-- if you reverse it, your magnet will be made weaker!

You can see from the first picture that I have tape on the end that I stared on, and added a nut on the other end. Both are optional. The tape is there to help keep the wire from unthreadding its self as you wrap the wire.

You can lay down as many wraps as you want, but the first two will have the most effect.

First, start off by making one big "back wrap" with the wire moving around the core in the same direction as you were making the small wraps. Then, make a few small wraps at the top, and start making all the wraps again, trying to keep the coil as tight and as close as possible.

I also use that one last back wrap to move the other end from the bottom back to the top, making it easier to connect a battery.

Step 4 -- Remove the insulation

Sanding (safest method) Scraping
remove insulation
by sanding remove insulation
by sanding

Okay, now that you have finished winding, you need to cut the the excess wire off, leaving both ends 2 or more inches long.

Next, we need to remove the insulation at the ends so we can connect our battery. Now, on a normal wire with rubber insulation, we just use a wire stripper, here, we can't do that. We either need to sand the insulation off with sand paper, or gently scrape it off with a sharp knife.

When you are done, you should have about a half inch of exposed wire on each of the two ends (which we're going to call leads from now on). The wire should look like this:

Magnetic wire with part of insulation exposed

The red you see is the insulation, the copper color is the bare wire. If your magnetic wire uses green insulation rather than red, making it a lot easier to tell the bare wire apart from the insulation.

Final step, hook it up!

Electromagnet under power

If your magnet didn't work, or it was very weak, then here are the likely reasons why: Your battery doesn't have a good electrical contact wit the two wire leads of your electromagnet, or you scraped some of the insulation off wile winding, causing a short to the iron core (you can use a multimeter to find out if that has happened). A bad electrical contact is easy to fix, but if there is a short, you'll have to start all over from scratch with new wire (or spray paint your bolt, then rewind).

Right Hand Rule for Coils

This isn't something you're going to find in your merit badge book. But did you know you can tell which direction is north or south of your electromagnet by the direction of current and the way the coil is wound in your electromagnet? Yup, you can! It's called the Right Hand Rule for Coils (there's also one for motors and generators).

There is also a PDF version for printing as a reference card.

Here's the online version:

Right hand rule
 graphic, no text

Right Hand Rule for Coils

Place your right hand over the coil, with your fingers wrapped in the direction of current flow through the coil (not electron flow). Your thumb will then point to the magnetic north of your electromagnet

Remember:
You need to take care to note the direction the coil is wound. If the coil is wound in the opposite direction as shown in the diagram, then your magnetic poles would also be opposite as shown.

The parts to build this project can be obtained at your local hardware and electronics supply stores.

The other option is you can buy an Electricity Merit Badge Kit from me that has all the stuff you need to complete the electricity merit badge: batteries, battery holder, parts to build a SPDT switch (and show that it works), electromagnet wire, and a bolt.

All images and text are subject to copyright. Permission is granted to use this material in the course of a merit badge class, or in a public education setting. For all other uses, contact the author Douglas Moyes.