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Old 03-01-2017, 02:05 AM   #3034 (permalink)
oil pan 4
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I have been studying and testing soft starting single phase motors.
The only way to soft start a single phase motor with a load attached using constant frequency power is to reduce starting voltage down to around 220v with a transformer then quickly ramp up to full 240+ volts.
Using this sequence on an air compressor with an auto transformer I was able reduce starting amps by about 20%.
The only way to soft start a single phase motor on constant frequency is to completely unload it, resistor or transformer start with a clutch to engage the load after the motor is up to speed.

If you can reduce frequency and voltage you will likely have much better results starting the motor with load than I did.
But you have to get the motor up to speed quickly or the start circuit will burn up.
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