A variable frequency drive (VFD, also called an inverter or AC drive) controls motor speed. When one fails, the replacement has to match the motor and the supply — not just the old drive's model number. Here's what actually matters.
Match these to the MOTOR
- Power: the drive's HP/kW rating must meet or exceed the motor's.
- Output current (Amps): the single most important number — the drive's continuous output amps must be equal to or greater than the motor's full-load amps (FLA). Size on amps, not just HP.
- Overload rating: normal duty vs heavy duty, depending on the load (pumps/fans vs conveyors/hoists).
Match these to the POWER SUPPLY
- Input voltage: 120V, 230V, 480V, 575V — must match your incoming supply.
- Input phase: single-phase or three-phase in. (Note: most VFDs output three-phase to the motor even from a single-phase input — handy for running a 3-phase motor on 1-phase power.)
- Frequency: 50/60 Hz.
Enclosure, control and communication
- Enclosure: IP20 / NEMA 1 (in a cabinet) vs IP66 / NEMA 4X (washdown or outdoor).
- Control: keypad, analog 0–10V / 4–20mA, digital inputs, or fieldbus (Modbus, EtherNet/IP, PROFINET).
- Extras: built-in braking resistor, EMC filter, or bypass that the old setup relied on.
You don't always need the identical model
Drives from ABB, Siemens, Allen-Bradley (PowerFlex), Yaskawa, Danfoss, Schneider (Altivar) and WEG can often substitute for one another if the electrical specs match — though the wiring and parameters will differ. If the original is discontinued, a current-generation equivalent is usually the better buy.
Send us the drive and motor details
Give us the old drive's part number plus the motor's HP, voltage and FLA, and your supply voltage/phase. We'll quote a correctly sized replacement — exact model or a verified equivalent — with availability and lead time.