Spark Fun Vacuum Pumps

We are looking for something small and quiet to use on a vacuum chuck in a microscope type application, and would like to know if there are any constraints on a duty cycle?

Hi @David58017,

Thanks for dropping by! For anyone else following along either now or in the future, David’s inquiry was about this product:

As you likely know already, David, Pulse Width Modulation (PWM) is commonly used to control motor speed. You asked about limitations on Duty Cycle, so i’ll go back a step to help frame my suggestions below. The actual speed of the motor becomes related to the length of time the fast switching time has the voltage attached to the motor versus the length of time the voltage to the motor is switched off. This time relationship is referred to as the duty cycle of the signal. Change the duty cycle and the speed changes.

Duty Cycle is typically 50% (on time vs off time) - but there are constraints on the frequency side of things for motors.

  • The PWM Frequency needs to be fast enough to be “averaged out” by the motor. This is rarely a limiting factor as tens of Hz to hundreds+ Hz.
  • Using a frequency less than 25Khz can result in audible electronic noises as the motor harmonics are being driven by a signal that is within our audible range.
  • Transistor drivers will dissipate a lot more heat than MOSFET drivers at high frequencies. This is because the time a transistor takes to fully-turn-on is notably longer than a MOSFET. The transition state from ON-OFF is when heat is generated within the device.

There are some other, more advanced considerations that have little to no impact on most DIY projects. So I’ll leave it at that.

Choose a driver that is rated for whichever pump you go with, and works the way you need it to from whichever device is controlling the logic. Trial a PWM based on the above factors and you’ll be fine.