How does that work?

[NiHaoMike]

http://www.hypereng.com/single_phase.html
Exact what do those do? They somehow reduce the inrush current without slowing down the starting process.

[David_AVD]

It doesn't say that it doesn't "slow down the starting process".  The "full torque" is only after it's finished the soft start I'd say.

[Marco]

In the literature you can see the oscilloscope waveform and they say they use thyristors, so we can make a guess ... it's a plain Triac type controller, it first lets through a small part of the wave for one or two cycles to determine the impedance of the motor at stall speed, it uses that to determine the phase angle at which to trigger the triacs to hit the current limit, when the motor drops below the current limit  the phase angle gets decreased until it hits 0 and the motor is in steady state operation.

[kaz911]

I seem to actually have one of them for my Dometic boat Air Condition - Box looks the same - just with Dometic label on it. Teardown on its way I have not installed it yet as I want to document the process and document inrush current changes etc.

[SeanB]

Simple triac phase controller that limits current to a level then increases it with time ( set by a pot) till it is at full power. It likely does this on the phase and the start winding, measuring the voltage across the start winding to determine when the motor is at near full running RPM then allowing full power to flow. Simple to do with a pair of triac controllers that are then switched to full power after a preset time or when the start voltage is over 200V. As well it disconnects the motor when the mains is low, and probably has a timer in it to limit the number of cycles per hour or just provides an on delay from power application to do the same.

3 phase ones do this on 2 of the phase windings, with the third being a pass through.