Part 3/9:
A critical part of the testing involves applying a 9-volt battery to the field windings. The technician notes the readings of voltage and millivolts to assess the magnetic state of the generator's core. During this process, an unexpected jolt occurs, hinting at residual magnetism within the generator. When the battery is disconnected and the rotor is spun, a small voltage appears—evidence of residual magnetism that can influence the generator’s behavior.
The technician explains that residual magnetism is common in old generators and can be used to prime the machine before actual operation. This magnetic remanence can cause the generator to produce a voltage even without external excitation, which is typical in vintage equipment.