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Old 09-07-2012, 08:03 PM   #9 (permalink)
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Originally Posted by TheEnemy View Post
A pwm might use a stabilizing capacitor on the input, and output and there would be two ways of measuring the current and voltage. The results would depend on how exactly the pwm is built.
The results don't depend on the capacitors.

At 50% pulse width the motor sees 100V half the time, and approximately 0V half the time. It averages out to 50V, although the insulation and commutator still has to withstand 100V.

During the time the battery is being applied (the on pulse), the current comes from the battery. When the battery is not being applied the current flows through a "freewheel", either a diode or diode emulation. Thus the current is "multiplied" by 2x. In reality the current isn't multiplied, but with a high frequency PWM, some capacitors (see below) and a slow current meter you measure the average current from the battery rather than the pulsed current.

The capacitors are vital to avoid voltage spikes during the switching transitions, and help even out the current flow from the battery, but don't change the gross calculations.
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