DIY 38-Volt Transformer

Take the iron core and wrap it with a thin layer of electrical tape. This will help keep the magnetic wire from shorting on the iron core.

Determine how many turns of primary wire and secondary wire are needed. A transformer has two field coils called the primary coil and the secondary coil. Power comes into the transformer on the primary side and power comes out the secondary side. The voltage level of the output depends on the turns ratio between the primary and secondary coil. For example, if the primary is 120 volts with 100 turns and the secondary has only 50 turns, then the secondary will have half of the voltage when compared to the primary. If the secondary coil had 200 turns, then the output voltage on the secondary would be 240 volts. The formula states that the turns on the secondary divided by the turns of the primary equals the voltage of the secondary divided by the turns of the primary.

Choose a number for the number of turns on the primary. For example, if the number of turns on the primary is 100 turns, then the number of turns on the secondary to achieve 38 volts with a 120 volt primary voltage is 32 turns.

Wrap the iron core with 32 turns of magnetic wire. This forms the secondary winding. Next, wrap the core with a second piece of magnetic wire using 100 turns. This forms the primary winding. Finally, wrap the primary winding with electrical tape to hold the coils in place.