Below is a list of Transformer Coils manufacturers from San Diego, California. Transformer coils refer to both the primary and secondary coils used in the construction of electric transformers. A transformer is an electromagnetic component that is used to transfer energy between electrical circuits by means of a magnetic coupling without the requirement of moving parts. A transformer must have not only a primary coil, but a secondary coil as well in order to properly transfer the electrical energy, or the current flow. In addition, transformers may have multiple secondary coils in order to provide power to numerous electrical loads.