PWM questions

When using PWM does the voltage ever change? For example say your using a motor driver and a 24v battery. If you PWM right 127, would the motor receive 12v or the full 24v, but just half the time?

Thanks!

Voltage will be 24V… at 127 it will just “less often” than if you set it to 255.

pwm.jpg

Motor driver usually scales the output voltage depending on the input voltage level. This allows it's speed to be controlled.

https://www.sparkfun.com/products/9457

So would that motor driver output half the input voltage or just the full input voltage half the time? PWM is really confusing!

I thought motor drivers, just pass the pwm to the motor (with more voltage/amps). The motor will run faster with a wider pulse width compared to a narrower pulse width. No actual VOLTAGE change. Am I wrong?

[quote author=Drew Davis ] So would that motor driver output half the input voltage or just the full input voltage half the time? PWM is really confusing! [/quote]

It will be half the time. That is why the value of such setting, called Duty Cycle, is in percents. As you are switching, voltage and current are influenced by this. Effectively you will be controlling current though. If you measure using a multimeter (which usually averages a measured value each second), you will see the voltage at about the value of the Duty Cycle times the supply voltage.

jackwp: I thought motor drivers, just pass the pwm to the motor (with more voltage/amps). The motor will run faster with a wider pulse width compared to a narrower pulse width. No actual VOLTAGE change. Am I wrong?

Yes and no. It depends on what type of motor you are controlling. And on the way you are measuring. Because PWM will influence voltage as well as current per time unit, there will be an effect to the speed of that motor. The strength or torque will be non linear to the Duty Cycle.