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Hedges

I See Electromagnetic Fields!
And NO deep well injection pumps cannot be soft started. Think about hauing a 5-gallon bucket of water up 200+ feet. It needs a high Amp start.

Why not?
We're talking about not having to deliver locked rotor amps while motor is at zero RPM, rather ramping up RPM more gradually.
If 3-phase it would be VFD. Grunfos makes well pumps like that. Constant current and torque at all RPM, rather than excessive current when slow.
Split-phase isn't as clean, but soft-start pulses some current to get motor turning, then ramp up to full is much less than a second. Peak current is significantly reduced compared to LRA.

Sure, if motor operates without an unloader the starting is more difficult. But with a turbine pump that allows some leakage, shouldn't be quite as bad as a piston type compressor for air or refrigeration (restarted without an unloader relieving pressure). At the least, power delivered lifting water is proportional to flow, so reduced at lower RPM but constant torque.

OK, could be because split-phase motors have low torque when stalled, need LRA to generate stronger magnetic field and get more torque. I think 3-phase motors have better stall torque. Like bicycle with 2 pedals vs. if it could have 3, one always at a decent angle.
 
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Hedges

I See Electromagnetic Fields!
The SQE line from Grundfos has soft start and variable speed capabilities built in on single phase.

Single phase input, but presumably VFD driving 3-phase motor.
I think that is superior to trying to soft-start a single-phase or split-phase motor. Those don't have any phase shift available from the two wires feeding them, but use a capacitor to produce a slight phase shift.

A soft-start that created a 3rd phase in the single phase motor's starting winding might work better. i.e. combine "hard start kit" larger capacitor with soft-start pulses. But that wouldn't be convenient for connecting to a motor down the well shaft, just above-ground.

An actual 3-phase motor would be best. Just undesirable to change existing deep well pump, but an option when considering cost of inverters and starting surge.
 

MPRanger

Beefield, GA 30461
Soft start is not a good thing for submersible pumps. They need to get up to speed very quickly to produce the film of water between the thrust bearing plates. The longer it takes to start, the more wear on the thrust bearing. The shorter the pump life.

A Cycle Stop Valve will give you a mechanical soft start and soft stop, which eliminates any water hammer without slowing the start-up RPM of the pump/motor. But then this does not solve the Inverter problem.
 

MPRanger

Beefield, GA 30461
Why not?
We're talking about not having to deliver locked rotor amps while motor is at zero RPM, rather ramping up RPM more gradually.
If 3-phase it would be VFD. Grunfos makes well pumps like that. Constant current and torque at all RPM, rather than excessive current when slow.
Split-phase isn't as clean, but soft-start pulses some current to get motor turning, then ramp up to full is much less than a second. Peak current is significantly reduced compared to LRA.

Sure, if motor operates without an unloader the starting is more difficult. But with a turbine pump that allows some leakage, shouldn't be quite as bad as a piston type compressor for air or refrigeration (restarted without an unloader relieving pressure). At the least, power delivered lifting water is proportional to flow, so reduced at lower RPM but constant torque.

OK, could be because split-phase motors have low torque when stalled, need LRA to generate stronger magnetic field and get more torque. I think 3-phase motors have better stall torque. Like bicycle with 2 pedals vs. if it could have 3, one always at a decent angle.
See my reply above please.
 

Hedges

I See Electromagnetic Fields!
Wonder if that's why some people report Grundfos pumps failing in a short time? Blamed on condition of the water, which didn't seem to affect conventional pumps.
 
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