Electronic – Controlling 12V 12A DC Pump using PIC

You should be able to test this yourself at home using household AC mains live as one of the phases L1, and something like a lamp as the load on T1. Keep the lamp neutral going to the wall. Leave L2, L3, T2 and T3 disconnected. This should be easier to troubleshoot.

Crucially check the Arduino control output is holding a voltage over 4V when you are sinking the 50mA 'holding current' in the contractor. You can measure this by turning on the output and checking the voltage at +terminal of the contractor control pins. The device has the 'indicator LED', zero-crossing logic and three opto-isolators sat on your supply. You may find a small logic level MOSFET is needed to drive it, rather than an Arduino pin.

If your drive is inadequate you may be in the position where some, but not all phases fire, (given the zero crossing detect will stagger the start-up) which is not great for the pump as it will stall but still be dissipating power. So until you fix this, don't leave it running for long periods.

Buck regulator is basically a PWM with a filter. If you use a PWM switch with a high temp low ESR cap. than can handle ripple current, you can provide DC control of speed easily to maybe 30% depending on stiction.

Without knowing the details of your pump, my guess 1HP 72V 10Amp, I assume you can reduce to 75% V+ to cut the flow and RPM in half but noise depends on brushes, gears and bearings. DC is more efficient but noisier. YOu could consider sound proofing but not thermal insulating the motor.

Once you provide more accurate requirements, there are many creative ways to reduce the DC voltage. PWM , buck reg., add 500W Halogen Lamp in series etc etc.