controlling a motor - variable voltage or PWM?

Projects General Guidance
1

Hi,

I'm working with this motor....

Currently I just switch it on and off using a relay, however, I'd like to start controlling it more precisely. I believe I their are two basic options.

  1. Varying the DC voltage (up and down) to increase/decrease the speed of the pump.
  2. 'Chopping' the supply to the motor using PWM.

Any recommendations please on which method to use and why?

Thanks

2

PWM is basically varying the voltage. A PWM dutycycle woulf give 50% of the voltage.

3

PWM is basically varying the voltage

PWM is really just switching the motor on and off very fast - which can be equivalent to reducing the voltage.

I've worked with a PWM controlled motor many years ago, and from what I can remember the constant on-off cycling of the power caused a constant rattling vibration at the same frequency as the PWM signal, this is way I was asking about controlling the motor using a continuous voltage at a lower value, i.e. running a 12volt motor at 10, 9 or 8 volts.

4

Search the forum: there are some recent threads about some kind of filter on the PWM output to make it into a "real" lower voltage as opposed to the average, "pseudo" lower voltage.

Tobbera:
PWM is basically varying the voltage. A PWM dutycycle woulf give 50% of the voltage......

.... on average, but the voltage is still either all or nothing at any instant.

5

Wouldnt some capacitors take away the ratteling and smooth out the voltage?

6

Possibly but electrolytic capacitors would not last very long.
Large value film capacitors are bulky and expensive for the same values.

7

If your motor makes noise, increase the PWM frequency. Easier than a cap, and is usually just as effective.

http://playground.arduino.cc/Code/PwmFrequency