Therefore , when an application requires consistent speed adjustments and torque control throughout the motor ’ s operation , a VFD is the clear choice . However , for applications that do not need speed control beyond startup , a soft starter is a more efficient option .
Weighing the cost of simplicity versus advanced control Cost is another critical factor when deciding between a soft starter and a VFD . Soft starters are generally more affordable due to their simpler design and functionality . A soft starter uses silicon-controlled rectifiers ( SCRs ) to connect the AC input line to the motor . In contrast , VFDs incorporate more complex components including a diode front end , DC bus and insulated-gate bipolar transistors ( IGBTs ), which increase costs .
This additional complexity makes VFDs more expensive , often two to three times the price of a soft starter , especially for larger horsepower applications . However , the higher initial cost of a VFD can sometimes be justified by its potential to deliver long-term energy savings , particularly in applications where motors frequently run at partial loads or variable speeds .
Maximising space with compact solutions The next consideration should be size . Soft starters also offer substantial savings in physical size and volume compared to VFDs . The additional components in a VFD and its cooling system not only cost more but also take up more space . The volume savings with a soft starter depend on the power rating . In industries where space is limited , such as shipyards or small manufacturing facilities , the smaller footprint of a soft starter can be a crucial advantage . The reduced size and complexity also mean that soft starters are easier and quicker to install , further reducing operational costs .
Instant efficiency gains or long-term savings with speed control Finally , energy efficiency should be considered . Soft starters can achieve up to 99.5 per cent to 99.9 per cent efficiency . After the starting process , a soft starter with an integrated bypass activates an internal contactor , allowing current to flow through it efficiently . In contrast , VFDs are around 95 per cent efficient because active components like IGBTs are always on during start , run and stop phases , leading to lower efficiency . However , VFDs offer more opportunities for energy savings by controlling both voltage and frequency .
The motor starter market is poised to reach USD 13 billion by the end of 2026 , growing at a CAGR of five per cent during this period . While VFDs are versatile and suitable for almost all applications , soft starters are more specific in their use cases .
When operating at full speed and properly loaded , soft starters are more efficient than VFDs . Once up to speed and bypassed , the motor current flows across the bypass contactor in a soft starter , with no active solid-state components generating heat . Conversely , a VFD remains hotter due to its active components constantly managing voltage and frequency .
It ’ s clear that properly selected soft starters can yield significant cost , size and energy savings over VFDs . The latter can be two to seven times more expensive and
two to eight times larger than soft starters , but application characteristics are critical when choosing between the two options .
Both can start a motor with reduced voltage and current , but the unique aspects of your application will determine the best choice , allowing you to right-size either a soft starter or a drive . Regardless of the motor control method you choose , consider additional factors such as installation , commissioning and the need for extra filters or circuit protection when specifying a soft starter or a VFD .
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Issue 72 PECM 61