Frequency converter on a conveyor: when it is needed
When a conveyor needs a frequency converter: smooth speed control, energy saving, soft start and SCADA integration. We break down how to choose a converter.
A frequency converter (variable frequency drive, inverter) lets you smoothly change conveyor speed without touching the mechanics. Instead of the fixed speed of an asynchronous motor you get a control range, a soft start and real electricity savings. This article breaks down when a converter on a conveyor is genuinely needed, and when it is an unnecessary expense.
What a frequency converter does
An asynchronous motor on a direct start always runs at one speed, set by the mains frequency of 50 Hz. A frequency converter changes this frequency, and with it the motor’s rotation speed. Feeding the motor, say, 25 Hz gives you half the nominal conveyor speed. This opens four practical possibilities: speed control, smooth start and stop, energy saving and precise matching of line sections.
It is important to understand that a converter controls not only speed but also torque. On a direct start a motor develops a starting current 5–7 times the nominal — a shock to both the grid and the mechanics. The converter accelerates the motor smoothly over a set time, limiting the current. For a conveyor this means less wear on the gearbox, chains and belt, and for the plant’s electrical grid it means no voltage dips at every start.
When a converter is genuinely needed
Not every conveyor needs a converter. From our practice it is justified in the following cases:
- Variable throughput — the line runs different SKUs or flows, and speed has to be adjusted.
- Delicate product — a smooth jerk-free start saves berries, biscuits and eggs from damage at startup.
- Section matching — speeds of adjacent conveyors must be precisely synchronised to avoid jams.
- Hard start under load — the conveyor starts fully loaded, and a direct start gives a current surge.
- Automation integration — the line is controlled by a PLC or SCADA, speed changes on signal.
If the conveyor runs at one constant speed with a light, insensitive load, a converter becomes an unnecessary expense.
Energy saving: where the saving is real
A converter is often sold as a means of saving electricity, but the saving arises only where the motor genuinely runs at reduced speed. If the conveyor runs at 60–70% of nominal most of the time, the converter pays off. If always at 100%, there is no saving from control — only the gain from a soft start. Real saving on conveyor drives with a variable regime is 15–25% of consumption.
Choosing a converter for the motor
A converter is selected by motor power with a small margin and by operating conditions. Below are the benchmarks we design for conveyor drives.
| Parameter | Value | Comment |
|---|---|---|
| Power margin | +10–15% over motor | For conveyors with constant torque |
| Protection class | IP54–IP65 | For wet food zones — in a cabinet or IP65 |
| Control range | 5–50 Hz operating | Below 5 Hz torque and cooling drop |
| Braking resistor | as needed | For downward-inclined conveyors |
| Interface | Modbus RTU / RS-485 | For communication with the line PLC |
Engineer’s tip. On a downward-inclined conveyor the load “drives” the motor, which goes into generator mode. Without a braking resistor the converter trips on overvoltage on the bus. This is a typical mistake — to spec a converter but forget the resistor for inclined sections.
Integration with line automation
A modern converter is not just a speed regulator but a node of the control system. Via the Modbus interface it receives commands from the PLC: speed setpoint, start, stop, reverse, and reports back current, frequency and faults. This makes it possible to build a line where all conveyors are matched to each other and controlled from one panel. For automation projects we spec converters supporting industrial protocols and bring control onto a common mimic diagram.
The data the converter sends into the system is also useful for diagnostics. A rise in current at an unchanged load signals mechanical wear — a seizing bearing, an over-tightened belt, a clogged route. The PLC records these deviations and alerts the mechanic before an emergency stop. Thus the converter becomes not just an actuator but a source of data for the line’s predictive maintenance.
Converter installation and cooling
A converter is an electronic device that heats up during operation and is sensitive to dust and moisture. In a food workshop it is not placed openly next to the conveyor — the converter’s place is in an electrical cabinet with ventilation or air conditioning. The cabinet protects it from washing, condensation and food dust, and keeps the operating temperature within limits. Overheating is the main cause of premature converter failure, so when laying out the cabinet we leave space for air circulation around the heatsink and do not place converters tight against each other.
Conclusion
A frequency converter is a powerful tool but not a universal solution. It is justified where speed control, a soft start of a delicate product or automation integration is needed. For a simple conveyor with a steady regime it is an unnecessary expense. If you are unsure whether your drive needs a converter, get in touch — we’ll assess the line’s operating regime and select a solution.
