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Jim Pratten

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  1. Jim Pratten's post in EasyStarts on Original 2004 ACs? was marked as the answer   
    Soft starters limit motor inrush current on induction motor starting that commonly draw 6 to 8 times the running current.  The high inrush current may exceed the electrical source capacity (think Honda EU2000 generator) and does introduce stresses in the motor and load and arguably spikes the motor winding temperature.  Once the motor is at operating RPM, the soft starter should be out of the circuit.
    Whether the cost of the soft starter is recoverable with extended equipment service life is doubtful IMO. They are commonly a solution for those folks trying to run an air conditioner off a small 2kw generator. The much lower inrush allows the generator to successfully start the motor without the generator stalling at inrush currents in the 75 to 100 amp range.
    in my opinion, a better return on investment to extend our rotating equipment life is an autoformer (Hughes for one) designed to maintain adequate voltage at those parks with weak power distribution systems. We commonly see voltages hover around 100 to 110 volts during peak load conditions. If, say the voltage is reduced 20%, then the current must increase at least 20% to sustain the same load.  20% more current thru the windings results in much higher temperatures and consequently an increase in winding insulation breakdown with shorter motor life. An old rule of thumb was every 20F increase in winding temperature results in 50% loss of life. 
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