An ammeter is connected in series with the primary winding. The gap suddenly fires, allowing the charged tank capacitor to discharge into the primary winding. The primary winding is located on the upper electromagnet. The core and primary winding are represented by the gray-brown torus. The primary winding has relatively few turns of heavy wire. The Tesla coil primary winding, spark gap and tank capacitor are connected in series. The stator, containing four slots, contains both the primary winding and the two secondary windings. The primary winding is connected to the battery (usually through a current-limiting ballast resistor).