Electromagnet is a magnet made by running a flow of electric current through coil of wire on a core made of ferromagnetic material, usually iron.
To create a strong electromagnet, it is required very long of enamelled wire to make many windings, the more wire turns the stronger magnetic field. But enamelled wire price is quite expensive, for 0.3 mm diameter can reach US$ 0.1 per meter. The price may be cheaper if purchased in large quantities, and in units of kilograms with price about US$ 11/kg at retailers in Jakarta. Even if the enamelled wire has already available, there will be problem to make winding. It needs to have a special tool to make a good winding. Alternator and electric motor repair shop can help to make a good winding, but must spend some money for that service.
There is an easy yet inexpensive way to make an electromagnet, by using coil of ballast fluorescent lamp. Find an used ballast as the photo below, this ballast works with voltage 220 volts and power 20 watts. Check with ohmmeter whether both connectors are connected, if not connected means the inside coil was broken. That broken coil can still be used if the disconnected wire is in the top layer of winding, so that broken wire can be reconnected or just remove the remaining length of wire. If buy a new ballast, the price is about US$ 1.60 each.
Remove ballast cover plate, remove also magnet core plates that are mounted on the coil. Coil will be obtained as the photo below.
Connect both ends of the coil enamelled wire with a longer cable. Then wrap the coil with insulation to avoid damage and loose. Too much insulation will weaken magnetic field.
Cut two pieces of ballast housing plates as the photo below. Drill two holes of 3 mm diameter for bolts, make sure those two holes at the same position on each plate. Those holes will be used by bolts and pass through the empty space in the center of coil. Both plates will be fitted to clamp coil and hold by two bolts.
Prepare some pieces of small nails. Nails will be filled into the inside of the coil and serves as coil corel. Nails that I use are one-inch sized, the smaller the better because it makes a solid coil core thus strengthening the magnetic field generated. Please note that magnetic field of the iron core is stronger than steel core. Because iron is easily rusted, so I am looking for nails with a bit rusty, to make sure the nails are made of iron, not steel. The nail head should be cut off to reduce empty spaces inside the core and make it more solid. But since I will use those nails for other purposes, so I leave those nails in their original shape.
Plates of original ballast core can also be used for electromagnet core, but should be cut in order to be filled into the center of the coil.
Prepare two M3 sized screws with a length of about 20mm, complete with two washers and nuts on each bolt, as shown in the photo below.
Fit those two screws on one plate, with one washer on each bolt. Washer serves to widen the surface of bolt pressure to plate. Place the coil on the side of the plate where there are threads of bolts. Then fill some nails into the inside of coil.
Shown in the picture above the plate that has two bolts, coil is placed over the plate, and loaded nails inside the coil. Also can be seen plates with insulation layer, which aims to provide better protection to the coil. But that plate insulation is not very important and can be eliminated if we require a stronger magnetic field.
After fill in enough nails into the coil, fit the other plate to cover the coil. Tie the two plates to make them clamp the coil tightly by placing and tightening nuts on both bolts. Do not forget to install rings between plate and nut to distribute pressure of bolts and nuts on plates. Be sure not to have any nail stuck between coil and plates, pinched nail could damage enamelled wire.
Finished electromagnet will be look like below photo. Shown the coil is clamped by plates with nuts and bolts. Also shown two cables are connected to the coil.
This electromagnet is capable of lifting 120 grams load with voltage 12 volts, and will draw current of about 0.23 amperes, with about 2.8 watts of power. Coil resistance is 51.6 ohms. Video below shows the coil is lifting 3 pieces of small gears.
If powered by 30 volts, this electromagnet can lift loads weighing 340 grams, and requires current of 0.57 amperes, with a power of about 16.9 watts. Video below shows the coil lifts 1 piece of big gear plus 2 small pieces of small gears.
I made this electromagnet at no cost at all. Ballast was hiding for about 20 years in the garage, because the fluorescent light was replaced with compact fluorescent lamp (CFL) which is cheaper and more practical and using electronic ballast.
Magnetic force will be stronger with bigger current and more winding. I haven't tried to unravel glued ballast coil yet. If ballast coil enameled wire is rewinded with smaller diameter coil to get more winding, then we can get a much more powerful electromagnet.
This electromagnet can be used as component for: actuator, inductor, door bell, toy, experiment, relay, door lock / slot electromagnet, etc..