Transformers are one of the basic, common, and important electrical components in use today. Transformers are tailored to a variety of applications, but all of them transmit electricity without a physical metallic connection between two coils that share a ferrous core. When the first coil is energized with alternating current, it creates a varying magnetic flux that energizes the second coil. By giving the second coil a different number of windings than the first, you can change the voltage. YouTuber GreatScott! wanted to find out if it’s possible to 3D print the core of a mains transformer, and made a video with his findings.