The paper focuses on the modeling of iron losses for synchronous electric machines. Specifically, the paper describes the inclusion of iron-loss resistance parallel to the main inductance of a dual-voltage alternator model. Integration of the iron loss resistance is implemented in two different models: a quadrature direct (QD) axis model and a voltage behind reactance (VBR) model. Simulations with both models are performed and compared against measurements with a machine prototype. The measurements show that the usually made assumption of constant iron loss resistance does not accurately represent the iron losses of a claw-pole alternator. Therefore, the parallel resistance is implemented also as lookup table (LUT) and derived from measurements. The presented models can be parametrized as conventional 2 x 3-phase synchronous machine with one-voltage level.