Choosing the wrong VFD causes overheating, tripped faults, and premature motor failure. This guide walks you through every selection step — voltage, load type, power rating, and application — so you get it right the first time.
For custom requirements beyond this range, contact SoftStarterPro's technical team for OEM/ODM solutions.
🔹 Quick VFD Selection Calculator
Enter your motor power and select the load type — the recommended VFD rating will appear automatically.
VFD Power Calculator
Step 1: Confirm Your Motor Voltage
Match your motor's nameplate voltage to the correct VFD input type:
| Motor Voltage | VFD Type | Typical Applications |
|---|---|---|
| Single-phase 220V supply → 3-phase output | Single phase to 3 phase VFD | Small pumps, fans, conveyors in single-phase locations |
| Three-phase 220V | 3-phase 220V VFD | Medium power motors, standard industrial equipment |
| Three-phase 380V | 3-phase 380V VFD | Medium to large motors, crushers, mixers, extruders |
Tip: Always check the motor nameplate — not the power supply. A 380V motor must be paired with a 380V VFD input, even if your facility runs on 220V single-phase (in which case you need a single-phase-to-3-phase VFD).
Step 2:Understand Load Type — Light Load vs Heavy Load
The load type determines how much headroom you need above your motor's rated power.
Light load (pumps, fans, centrifugal blowers, conveyors):
- Starting torque is low
- Choose a VFD rated equal to or one size above your motor's kW
Heavy load (crushers, extruders, mixers, hoists, compressors):
- High starting torque and inertia
- Choose a VFD two sizes above your motor's kW
Examples:
- 15 kW centrifugal pump (light load) → 15 kW or 18.5 kW VFD
- 45 kW extruder (heavy load) → 55 kW VFD
- 75 kW crusher (heavy load) → 90 kW VFD
Step 3: VFD Voltage and Power Range Reference
| Voltage Type | Power Range (kW) | Notes |
|---|---|---|
| Single-phase 220 V → Three-phase 220 V | 0.4 – 22 kW | For small motors such as pumps, fans, and conveyors. Custom 380V output available. |
| Three-phase 380 V | 0.4 – 500 kW | Standard industrial voltage, suitable for most medium to heavy-duty loads. |
| Three-phase 220 V (Custom) | 0.4 – 200 kW | Custom models available upon request. Please contact our technical team. |
Browse our VFD range: 3 Phase 380V VFD Inverter | Single Phase to 3 Phase VFD Inverter
Step 4: Power Factor (Selection Coefficient)
| Load Type | Selection Coefficient (Power Factor) |
|---|---|
| Pumps / Fans / Conveyors | 1.2 – 1.3 |
| Crushers / Mixers / Compressors / Hoists | 1.5 – 1.7 |
| Unknown or High Inertia Load | 1.5 – 1.7 (recommended) |
How to use this: Multiply your motor's rated kW by the selection coefficient to find the minimum VFD rating.
Example: 30 kW mixer × 1.6 = 48 kW → select the next standard size up, which is 55 kW VFD.
Step 5: Common Troubleshooting
| Symptom | Likely Cause | Action |
|---|---|---|
| VFD does not start | Input voltage fault or wiring error | Check supply voltage and motor connections |
| Overheating / OHT fault | VFD undersized or poor ventilation | Verify VFD rated power ≥ motor kW × selection factor; check cooling clearance |
| Vibration or noise | Carrier frequency setting too low | Increase carrier frequency (PWM) in parameter settings |
| Overcurrent fault (OC) | Acceleration time too short | Increase acceleration ramp time in parameters |
| Fault codes | Various | Refer to user manual or contact SoftStarterPro support |
Frequently Asked Questions
Q: Do I need to match the VFD power rating exactly to my motor?
A: Not exactly. For light loads (pumps, fans), select a VFD equal to or one size above your motor's kW. For heavy loads (crushers, extruders), select two sizes above. Never undersize.
Q: Can I use one VFD to control multiple motors?
A: Not recommended. Each motor should have its own dedicated VFD for proper protection and control.
Q: What happens if I select a VFD that is too small?
A: The VFD will overheat and trigger overcurrent or overload faults, leading to shutdowns and premature failure.
Q: Do I need a separate braking resistor?
A: For applications with fast deceleration or high inertia loads (hoists, centrifuges), a braking resistor is recommended. For standard pumps and fans, it is usually not required.
For more information, browse our VFD Drives or contact us for pricing and technical support.
