VFD vs Soft Starter — Which Should You Choose?

Choosing between a variable frequency drive (VFD) and a soft starter is one of the most common decisions in industrial motor control. Both devices reduce inrush current at motor start-up, but they work differently and suit different applications. This guide explains the key differences to help you select the right solution.

What Is a VFD?

A variable frequency drive controls motor speed by varying the frequency and voltage supplied to the motor. VFDs convert incoming AC power to DC and back to variable-frequency AC. This allows precise speed control from 0 Hz up to and beyond rated motor frequency.

Key VFD Advantages

Full speed control: Adjust motor speed continuously to match process demand.
Energy savings: Centrifugal fan and pump applications can save 30-60% on energy when running below full speed.
Smooth acceleration: Fully programmable ramp times for controlled starts and stops.
Process control: Integrate with PLC or SCADA for closed-loop pressure, flow or temperature control.
Braking capability: Dynamic or regenerative braking options available.

What Is a Soft Starter?

A soft starter reduces motor voltage during start-up using thyristors (SCRs), which limits inrush current and reduces mechanical shock to the drive train. Once the motor reaches full speed, the soft starter bypasses and the motor runs direct-on-line at full efficiency.

Key Soft Starter Advantages

Lower cost: Soft starters cost significantly less than equivalent-rated VFDs.
Simpler installation: Less wiring, no EMC filters required in most cases.
Smaller footprint: Compact units for panel space-constrained installations.
Bypass operation: Motor runs at full efficiency after starting — no drive losses.

VFD vs Soft Starter — Side-by-Side Comparison

Feature	VFD	Soft Starter
Speed control	Full variable speed 0 to 100%+	Full speed only (start and stop)
Energy savings at full speed	Minor — drive losses apply	Excellent — bypass mode
Energy savings at reduced speed	Excellent — 30-60% on fans and pumps	Not applicable
Initial cost	Higher	Lower
Installation complexity	Higher — EMC and harmonics to manage	Lower
Braking	Yes — dynamic or regenerative	Controlled stop only
Best for	Fans, pumps, conveyors needing speed control	Conveyors, compressors, fixed-speed loads

Which Should You Choose?

Choose a VFD if:

Your process requires variable speed control
You have a centrifugal fan or pump where running below full speed saves energy
You need precise acceleration and deceleration profiles
You want closed-loop process control integrated with a PLC

Choose a Soft Starter if:

Your motor only needs to start and stop at full speed
Budget is the primary constraint
Panel space is very limited
You have a high-inertia load that needs controlled acceleration to reduce mechanical shock

VFDs and Soft Starters at InstroDirect

InstroDirect stocks Allen-Bradley PowerFlex VFDs and Schneider Electric Altivar drives at parallel-import pricing — typically 25-40% below standard Australian distributor rates. We also carry soft starters for fixed-speed applications. Contact our team for selection assistance or visit the online store to browse current pricing and stock.