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Topic: PWM signals doubt with motor. (Read 205 times) previous topic - next topic

A3y4n

Jul 14, 2019, 05:45 pm Last Edit: Jul 14, 2019, 05:54 pm by A3y4n
I want to know if PWM signals vary current or voltage. On the net I see various places telling its voltage but if I am using a 5v motor then , wont using pwm signal of 2.5 V make it not rotate as opposed to rotate it slowly, as it requires a voltage of 5v to operate.

And does using PWM sacrifices Torque of the motor as compared to using geared reduction mechanism and is there any estimate to deduce that value.

Thanks in advance.

jremington

#1
Jul 14, 2019, 06:32 pm Last Edit: Jul 14, 2019, 06:33 pm by jremington
On a 5V Arduino, PWM signals are 5V pulses, with varying width (Pulse Width Modulation).

A DC motor will average the signal, so that the average voltage and average motor current are both reduced, as the pulse width is reduced.

Motor torque is proportional to motor current.
No PM's please.

slipstick

PWM varies the average voltage. Reducing voltage also reduces current. Most motors will run at much lower voltages than their recommended maximum voltage.

Since reducing speed with PWM reduces the power supplied to the motor then yes it does affect the torque. Gearing effectively multiplies torque while reducing speed. Reducing the power input to the motor with PWM reduces torque and speed.

Steve

A3y4n

#3
Jul 14, 2019, 08:35 pm Last Edit: Jul 14, 2019, 08:39 pm by A3y4n
slipstick and jremington thank you so much. I didn't knew that motors can run at a much lower voltage and about the torque being directly proportional to the current. Btw  any idea by how much would the torque reduce or would I have to use a multimeter to calculate it.

jremington

#4
Jul 14, 2019, 08:38 pm Last Edit: Jul 14, 2019, 08:42 pm by jremington
You have to measure the torque. It is a nonlinear function of the motor voltage, current and speed.
Example curves:
No PM's please.

MarkT

#5
Jul 16, 2019, 02:49 pm Last Edit: Jul 16, 2019, 02:51 pm by MarkT
I want to know if PWM signals vary current or voltage. On the net I see various places telling its voltage but if I am using a 5v motor then , wont using pwm signal of 2.5 V make it not rotate as opposed to rotate it slowly, as it requires a voltage of 5v to operate.

And does using PWM sacrifices Torque of the motor as compared to using geared reduction mechanism and is there any estimate to deduce that value.

Thanks in advance.
Depends on the mode, slow decay, fast decay, modified fast decay or synchronous rectification, and depends on the PWM frequency v. the motor inductance.  No simple answers I'm afraid, except that PWM switches the voltage, current is due to the load.  Many modes let the voltage float at parts of the cycle, which is where the complexity comes in.  Synchronous rectification never floats and is the easiest mode to analyze.

Gearing is a separate/independent issue.
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