VFD vs. Softstarter vs. Direct-On-Line — Which One Do I Need?
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VFD vs. Softstarter vs. Direct-On-Line — Which One Do I Need?
When to use a simple contactor, when a softstarter is enough, and when you genuinely need a VFD. A decision tree for beginners with practical examples.
DATE: 2026-05-17
You have a motor. You need to start it. Three options — which is right?
Option 1: Direct-On-Line (DOL) — Simplest and Cheapest
Cost: lowest (€50-200 for contactor + overload).
Starting current: 6-8x full load current.
Starting torque: ~250%. Violent mechanical jerk.
Mechanical stress: high — belts snap, pipes get water hammer.
Best for: small motors (under 4kW), fans, pumps with check valves, compressors that unload before starting.
Option 2: Softstarter — Gentle Start
Cost: moderate (2-5x DOL).
Starting current: adjustable 2-4x full load current.
Speed control? NO. Only acceleration/deceleration.
Best for: conveyors, pumps (eliminates water hammer), fans, crushers — anywhere you need gentle start but not variable speed.
Option 3: VFD — Full Control
Cost: highest (3-10x DOL).
Starting current: ~1.1x full load. Minimal.
Speed control: YES — 0 to max RPM.
Torque control: YES — full torque at zero speed.
Energy savings: YES — especially for pumps and fans.
Best for: processes needing variable speed, precision control, or energy savings.
The Decision Tree
Need speed changes during operation? — VFD
Need energy savings from reduced speed? — VFD (especially pumps/fans)
Big motor on a weak power supply? — Softstarter or VFD
Need gentle start to protect equipment? — Softstarter or VFD
Simple fan or small pump? — DOL is fine
Cost Comparison (15kW Motor)
DOL: ~€100-150
Softstarter: ~€300-500
VFD: ~€800-1,200
A VFD on a pump running 8,000 h/year at 80% speed saves ~€2,000/year. Payback: 3-6 months.
Bottom line: DOL for simple and cheap. Softstarter for gentle start. VFD for speed control and energy savings. The VFD often pays for itself in energy alone.
