Introduction: Microwave Transformer Electromagnet
These instructions will guide you in creating an electromagnet capable of lifting over 50 lbs when powered by a single AA battery. This provides a great introduction to electricity and magnetism as well as an opportunity to learn about microwave ovens. It is also a much cheaper alternative to buying copper wire and creating an electromagnet from purchased parts.
Minimal skill is required. Basic hand tools including a Phillips and flathead screwdriver, a hammer, and a handsaw will be needed. Using these tools it should take approximately an hour and a half take a microwave, remove the transformer, and create the electromagnet. Additional power tools, such as an angle grinder, will greatly reduce the time required. While there are risks of electrocution when working with microwave ovens, simple precautions will be outlined to prevent injury.
Step 1: Get a Microwave
Find a used or broken microwave that can be taken apart. Look at local thrift shops, internet classified ad pages, or even on the side of the road. A working or broken microwave should work equally well for this project. I included screenshots of the search results for ‘microwave’ on craigslist and another classified ad site. Free microwaves are not difficult to find.
Step 2: Take the Microwave Apart
Microwave ovens supply potentially lethal amounts of electrical power when operating. Protect yourself from electrocution by unplugging the unit before exposing the electronics. After it is unplugged, remove the microwave casing using a 6 point security screwdriver and a Phillips screwdriver. One of the security screw is shown in the image above. You can also use pliers to remove the security screws if you don’t have a special 6 point screwdriver.
Step 3: Discharge the Capacitor
Discharge the capacitor before touching the internal wiring or removing anything from inside the microwave. Capacitors can hold large amounts of energy even when the microwave is not plugged in. Always assume that the capacitor is charged until you have made sure that it is not. While there are many safe ways to discharge a capacitor, doing it the wrong way can cause serious injury or death. Please, be careful.
With one arm behind your back, use an insulated screwdriver and touch both terminals of the capacitor at the same time, as shown in the video above. Make sure that your hand is only touching the screwdriver on the plastic insulation and that there are no cracks in the insulation or pieces of exposed metal in the handle. You may hear a sparking sound the first time you connect the terminals. You will not hear anything when the capacitor is fully discharged.
Richard Lloyd's video outlining how to discharge an AC capacitor is a great example of the process that should be followed for microwave capacitors. Gloves and safety glasses are recommended, though not required. The image of the internal components of a microwave is from the instructable “How to Take Apart a Microwave” by Plasmana (labels added).
Step 4: Remove the Transformer
With the unit unplugged and the capacitor discharged, it is now safe to remove the transformer. You will need the Philips screwdriver to remove components in the microwave to access the transformer. The transformer is the heavy piece of iron with copper wires wrapped inside of it, shown above.
Step 5: Gather the Required Hand Tools to Open the Transformer
At a minimum, you will need a hammer, a flat head screwdriver, and a hand saw to break open the transformer. If you have access to an angle grinder, chisel, vice, or pry bar they could also be used to speed up the process.
Step 6: Locate and Cut Along the Weld Lines
The transformer is held together by two welds near the base, one on each side. A close up of one of the welds is shown above. These welds attach the base and the E shaped core. Cut through these welds to open the transformer and access the copper windings. You will want to start slowly to ensure that the cut is directly above the seam between the transformer base and the E shaped transformer core. If the cut is not lined up correctly, like the one shown in the picture, you will need to cut at an angle until the cut reaches the intersection.
Step 7: Pry Apart As Necessary
As the cuts on each side get deeper, place a screwdriver or chisel in the cut and hit it with the hammer to try and separate the base from the core. If the transformer does not open, continue sawing, repeating this step periodically, until the transformer separates.
Step 8: Remove the Primary Coil
The primary coil is the winding of the thicker copper wire and is typically closest to the transformer. This coil, along with the iron transformer base, will be used for the electromagnet. Break off any visible insulation or glue holding the coil to the transformer. Drive the screwdriver or pry bar into the gap above the primary coil to slowly work it out. Repeat this on the left and right sides of the top and bottom. With the insulation and glue the wires will be very snug with the transformer core. Removing the winding might also require some creativity, such as using a vice when pressing down on the coil, as shown. Be careful not to cut the wires when removing the coil. The scratches shown on the wires did not have an impact on it's performance, but deeper cuts could ruin the winding.
Step 9: Remove Everything Else
Remove the other objects inside of the transformer using the same method as before. They will not be used for this project.
Step 10: Find a DC Power Supply or Battery and Connecting Wires
The electromagnet will need to be connected to DC power. If you don’t have a current limiting DC power supply, find a small battery, such as a AA. Solder or tape wires onto the positive and negative terminals of the battery as shown above. Find wire to connect the power supply or battery leads to the primary coil leads.
Step 11: Connect Power to the Coil and Have Fun
Place the primary coil back into the transformer core and connect the power supply. The electromagnet is now ready to be used. This electromagnet is a great way to explore the impact of magnetic core material and geometry, as the wires will not produce a strong magnetic field without a metal core in a complete loop around the wires, like the original transformer shape. Don't believe me? Try it for yourself. Happy testing!