PWM of Diaphragm pump

Question

I'm pretty new in this area so sorry if this question seems foolish.

I have a 12V 20Lpm Diaphragm pump that draws around 18 Amps. I'm using it on a home built herbicide spray system to help deal with the Spanish Heath that has fully taken over a good portion of my 50 acres.

I am really happy with the pumps performance though it is a little bit of over kill at 20LPM. I am toying with the idea of making a PWM circuit to control the flow. I was wondering if anyone has had any experience with this type of idea on a Diaphragm pump? I'm going to make up a pulse generator circuit out of a couple of 555 timers just to get me started. I was thinking about making it run from 100Hz to 1Khz with the duty cycle adjustable from 10-100%. I haven't been able to Google much about controlling flow with this technique and was wondering if anyone had any ideas on the best frequency to drive the pump at or even advise if the idea is viable? Perhaps I am better off controlling the flow with a valve at the output in which case I have posted to the wrong forum.

Best regards

Adrian.

Answer 1

Raising the frequency will not help you. Even at 100 Hz, the mechanical inertia of the motor will make it run smoothly. The only difference will probably be slightly more heat being generated, as the power transistor is switching ON/OFF more frequently.

Duty cycle modulation seems quite doable. The only slight problem could be that the load on the motor is not constant - at the max excursion of the membrane, probably the pressure on the motor is higher. So, at low duty cycle, the motor might refuse to turn, while still consuming energy. You can probably avoid that with a minimum duty cycle.