# Soft Starts



## besc (May 16, 2010)

They make single phase to three phase VFDs. I am looking for a single phase to three phase soft start. Having trouble finding one. Does such a critter exist?


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## gpop (May 14, 2018)

nope as a 3 phase motor will not run on single phase. (a vfd outputs 3 phase even with single phase input)

There are other ways to run a 3 phase motor using single phase like a rotary phase converter


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## tmessner (Apr 1, 2013)

nope. Use a vfd if you need soft/slow start.


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## just the cowboy (Sep 4, 2013)

First what size motor?
For most small motors the cost of a soft start vs a drive is not much.
If larger motor some drives will take single phase in but there is a trade up in that you almost double the size of the drive.

Let me guess someone else bought a three phase machine cheap and expect you to get it running cheap, it won't happen.

Cowboy


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## paulengr (Oct 8, 2017)

There are single phase soft starts but since it is only a reduced voltage starter you can’t create three phase power from a single phase...that’s an inverter (VFD).


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## besc (May 16, 2010)

Yap. I'll have to use the VFD method. Thanks.


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## JRaef (Mar 23, 2009)

VFDs work as phase converters because there is almost no relationship to input vs output. The input is just "raw material" to make DC, then the DC is recreated into what tricks the motor into thinking is AC. A soft start doesn't do anything like that, it just phases back the voltage on the AC, so it can only put out what was put in.


Your choices for going from single phase to 3 phase are a Rotary Phase Converter (RPC), a Motor-Generator Set (M-G Set), a Static Phase Converter or a VFD, twice the size of the motor (if over 3HP 230V). There are other "science experiment" methods that do or don't always work, steer clear of those.


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