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The simplest type of phase
converter is generically called a static phase converter and has
been in use for nearly one hundred years. This device typically
consists of one or more capacitors and a relay to switch between the
two capacitors once the motor has come up to speed. These units are
comparatively inexpensive. They make use of the idea that a
three-phase motor can be started using a capacitor in series with
the third terminal of the motor. It then runs with essentially two
of the three windings powered.
It is almost guaranteed that a
static phase converter will do a poor job of balancing the voltages
on the motor. Unless motors operated on
static converters run only for short periods or
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deliver
significantly less than half of their rated output, they will be
damaged from overheating. Some
manufacturers of static converters make a simplistic statement that
since two of the three windings are powered, the motor will be
capable of generating two-thirds its rated power. This is
misleading and could lead
to damage of the
motor. If the motor were loaded anywhere near two-thirds its
capacity, it would be permanently damaged in short order.
The only good thing that can be
said of static phase converters is that they are inexpensive. They
can only operate motors, and only single-motor loads. The motors
must be limited to light loads and intermittent use.
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