Industrial Engineer · phase 16 of 16 · noun
Soft Starter
Solid-state starter that limits motor starting voltage and current but does not provide continuous variable-frequency speed control.
The Explain card
- Plain English
- A soft starter ramps the voltage to a motor up gently at start using thyristors, then usually bypasses itself with a contactor. It limits inrush and mechanical shock and does nothing about speed once the motor is running.
- Example
- A 200 horsepower compressor starts on a soft starter to keep the line from sagging. Once up to speed it runs across the line at full speed, and the soft starter's work is done.
- Why it matters
- A soft starter is cheaper and simpler than a drive when the application only needs a gentle start and never needs speed control. Choosing one when the load would benefit from variable speed gives up the energy saving that would have paid for the drive.
- Hook
- A gentle start, then out of the way.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
During commissioning, the technician set the Soft Starter ramp time before testing the conveyor motor under load.
Why these words
- soft Old English sōfte, gently or mildly modifies starter by describing a gradual manner of starting
- starter start plus the agent-noun suffix -er names the device associated with initiating motor operation
Where it came from
- Origin
- English engineering compound formed from soft and starter
- Entered the language
- 1960s
- What changed
- Soft broadened from physical yielding to gentle or gradual action, while starter became a name for equipment that initiates machine operation.
How it is spelled
- Pattern
- The compound is normally written as two separate words.
- Pattern
- Starter keeps the doubled t of start before the suffix -er.
Spelled like
- motor starter
- soft start
- reduced-voltage starter
- automatic starter
Broken into chunks
-
soft
- soften
- software
-
start
- restart
- startup
-
-er
- controller
- breaker
What it sits beside
Same subject
- contactor
- overload relay
- variable frequency drive
- induction motor
Same shape
- motor starter
- manual starter
- combination starter
motor starting equipment
- across-the-line starter
- wye-delta starter
- autotransformer starter
- Soft Starter
Where it sits in the deck
Phase 16: VFD Related Drive Terms
The drive family's wider vocabulary, from soft starters and servo drives to the regenerative units people also call a drive.
