How to Make a Transformer

By James McIlhargey

A transformer operates under the physical principle of mutual induction. When changing current and voltage is applied to a loop of wire, it will generate a magnetic field. A second loop placed in line with that field will generate a voltage and current. By changing the geometry of the loops, you can change the ratio between voltages and currents. Making your own transformer is a simple process, all it takes is a bit of math, wire, and a core material.

Things You'll Need

  • Two gauges of wire
  • Core material
  • Wire cutters
  • Pliers
  • Epoxy
  • Wax
  • Tape

Step 1

Decide upon your desired voltage or current ratio. A transformer works to convert between two voltages and two currents. The ratio describes the quantity of change. For example, a ratio of two means that taking a 10 volt, 1 amp can give either 5 volts at 2 amps or 20 volts at half an amp. This choice is important, because you need to also decide how much current will exist at both sides of the transformer. You will need to have wire for each side that is rated for at least the maximum current you believe you will use. It is safer to choose wire that is rated for one and a half to two times as much current.

Step 2

Determine a core material. Most applications will require a ferrite core, which is magnetic and will confine the magnetic field to within the coils. If you plan on strong voltages and currents, they will result in strong eddy currents, which will cause energy to escape as heat. To minimize this energy loss, ferrite transformer cores are available that are laminated. These cores are made up of many thin layers of iron or other ferrous material, minimizing eddy currents and energy loss. The size of your core should be proportionate to the energy you will put through the core. To illustrate, the large gray cylinders on power lines are transformers sized for the energy going to a neighborhood, while the black brick attached to your laptop will have two or three transformers. The type of core will also depend on application. Radio frequency transformers do not typically utilize cores, audio transformers are small and tight, some power control transformers are on toroidal, ferrite cores, and so on. Check out a library book or search the internet for transformer design. Unless you are trying to power very sensitive electronics, then you have leniency in the choice of core.

Step 3

Wind the wire. This step will take the most time, even more than research in design. To wind the wire, you should choose a high number of base turns. If you choose a two to one ratio, you could have two turns of one wire, and one of the other. However the large number of variables means that you could result in any variation of voltage ratios. If you chose 100 versus 200 and find that the ratio is off, it is easier to add or remove a turn to try and fine tune the ratio and make up for losses and other variables. When winding the wire, make sure that the wire is coated, and that the coating is solid with no damage. You do not want to risk a short in the transformer. Make your loops neat and tightly coiled, to minimize variation due to sloppy winding. Also make sure that you can access both ends of each coil.

Step 4

Seal and protect. Once the coils are wound, and the voltage or current ratio is right, you should use a sealer to keep the coils wound. You can soak the transformer in epoxy, which would bind the coils and act as an insulator. Wax also works, and can be more easily removed later if needed. Another option is to wrap the coils with tape to hold everything together.

Step 5

Use your new transformer.

Tips & Warnings

  • If you are dealing with high voltages, like from the wall, or high currents, any thing over 100 milliamps, make sure to work safely. Keep one hand away from the unit during testing, to avoid shorting a current over your heart. Also make sure to have someone nearby who can help in case of trouble.Build fuses into your circuits and make sure everything is properly grounded.