The purposes of the research were; 1) to study the relative rotation of AC-generator 2) to study the angular velocities of magnetic coil and permanent magnetic influence generating voltage of AC-generator and 3) to construct predictive equations of generating voltage of AC-generator. By the 12-V 6-pole alternator of motorcycle Pearson’s correlation and regression analysis the findings revealed that: 1) At the lowest relative angular velocity of 376 rpm the generating voltage is 3.28 V. While the highest relative angular velocity of 2280 rpm the generating voltage is 22.98 V. 2) The angular velocity of permanent magnetic has great influences on generating voltage than the angular velocities of magnetic coil at the .01 level of significant and 3) function as below : Generating voltage = 0.806 (Velocity of permanent magnetic) + 0.634 (Velocity of magnetic coil)