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Self-priming automatic electric pumps with helical gears, produced by Marco.

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Can these pumps be PWM controlled to vary output flow?

My question is specific to the UP3 series pumps and whether or not they can be PWM output controlled to vary output flow. The pressure is low (less than 15psi). Is there a recommend maximum PWM frequency? I was thinking 30Hz or less for this type of device. Also, I noticed on the 12VDC tag it says EMI filter not use with PWM, but the 24VDC version does not have this same warning. Can you please clarify?

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Dear Curtis,

the pump can be controlled with PWM, but you may want to check that the EMI filters inside do not interfere with your electronic driver: check with an oscilloscope that the rising edge of every pulse does not ring too much. This happens due to the fact that the motor is “an inductor” and the EMI filter is capacitive: this works perfectly with a steady voltage but resonates with a PWM applied to it. This is not an enormous issue, but it creates a fair amount of electric noise that can be unpleasant for commercial applications, in which you need to respect some standards. For bulk orders it’s possible to order PWM-compatible brush-holders that do not mount the capacitors, but the emi compliance has to be verified by the customer .

The switching frequency for the PWM is a compromise between:

  • Audible hiss/whistle of the frequency (higher frequencies are better, less audible)
  • Switching power dissipated at every switch-on switch-off (lower frequencies are better, less switching)
  • Current/torque smoothness (higher frequencies are better, less discontinuity)
  • Minimum and maximum duty cycle (if the frequency is too high and the duty cycle is too low, i.e. 30khz with 10% or 90% duty your electronic switch may not be able to turn on or off at all, thereby only heating up)
  • PWM resolution, if you use a microcontroller, you may want the frequency of the motor to be a multiple of the clock frequency, to be able to use the whole resolution (10bit or 16 bit) of your microcontroller. Using "custom" frequencies ends up in being forced to use less values than the maximum, thereby having less "steps" to have control with.

From my experience, good values are between 8kHz and 16kHz, whichever fits best the resolution of your pwm. For "DIY" applications I use this device:

It already fits some filtering, uses a half bridge configuration instead of the mosfet-diode configuration (way more efficient) and, if needed, it can be used also with both half-bridges to make the pump rotating in both directions.

If you're planning to design your custom board, I might suggest its "brother", the IFX007TAUMA1, that is way more powerful and reliable (especially if you're planning to use the pump at 24V), but doesn't have the demo board.

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Curtis zal eeuwig dankbaar zijn.

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