3-phase Alternator Project, Part V - Pulley Drive System

In this follow-up video to a previous project from one year ago, I attempt to gain higher output by increasing the physical rotation speed (RPM) using a pulley drive system in place of the original gear system.

A pair of pulleys is selected for maximum allowable speed ratio within practical limits. The smaller pulley being 2.5" diameter and the larger one 16" diameter, a multiplier ratio of 1:6.4 is expected. In fact a slightly better ratio of 1:7 is achieved.

Maximum output RPM was measured using an oscilloscope which gave a minimum sine-wave peak separation of .014sec. Three sine-wave peaks is equivalent to one physical rotation of the rotor; hence a maximum speed of 60sec/(3x.014sec) = 1428 RPM.

Despite the fact that "no-load" voltage output increased by almost the same ratio as the speed (7/4 = 1.75, 85V/50V = 1.7), the same could not be said of output charging current. With gear drive, the maximum output current while charging a 12V battery was 600mA, while with the pulley system it increased to 750mA, a mere 1.25 gain while the expected linear gain at x1.75 would be 1050.

The conclusion is that maximum output current in an alternator system is more a function of inherent electrical parameters (magnetic flux of the rotor, inductance and related impedance, under load, of the coils) than simply a matter of rotor speed.
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