VFD for Conveyor: Constant Torque & Multi-Speed Setup

When you are standing on the production floor watching a 55kW belt conveyor struggle to start under a full load, you quickly realize why a properly configured VFD for conveyor applications is non-negotiable. We build and test the SHZK 300N series right here in our workshop, and I see firsthand how the right conveyor motor control parameters transform a jerky, belt-snapping startup into a smooth, controlled acceleration.

Solving the Constant Torque Challenge

Conveyors are constant torque loads. Unlike fans or pumps where torque drops off at lower speeds, a conveyor needs full holding torque even at 5 Hz. If your drive uses a variable torque V/F curve, the belt will stall under load.

On the SHZK 300N, we set P3-00 (VF curve setting) to 0 for a standard linear V/F curve. For heavy incline conveyors, you can bump up P3-01 (Torque increase) from the default 0.0% (automatic) up to 30.0%, with the cutoff frequency P3-02 set to 15.00Hz. This injects extra voltage at low frequencies to maintain magnetic flux without saturating the motor core.

Understanding the fundamentals of variable-frequency drives helps clarify why maintaining the V/F ratio is critical for low-speed torque production.

Dialing in Multi-Speed Profiles

Sorting systems and transfer conveyors rarely run at just one speed. You need a creep speed for indexing and a full speed for transit. Instead of relying solely on analog inputs, the 300N series handles multi-step speeds natively through the digital inputs.

We map the multi-speed terminals to trigger specific frequency commands. If you are integrating this into a larger PLC network, the Modbus RTU protocol allows you to write speed commands directly to the drive’s memory registers, bypassing the need for physical relay wiring for every speed step.

For applications requiring precise speed holding under fluctuating loads, switch to vector control. Parameter P2-10 lets you digitally set the maximum torque limit under speed control mode from 0.0% to 200.0% (default 150.0%), ensuring the motor doesn’t pull excessive current when a jam occurs.

Quick Parameter Reference for Conveyors

Real-World Testing: The 55kW Incline Belt

Just last week, we were bench-testing a 300N-055GB-T4 unit. The “B” in the model name means it includes the built-in braking unit, which is absolutely critical for incline conveyors where the load tries to overhauls the motor during stopping.

We wired it up with a 55kW motor, set the input to 380-480V (pulling 106A), and configured a multi-point V/F curve using P3-03 through P3-08 to give a slight voltage boost at 5Hz and 10Hz. The deceleration time was set to 15 seconds. Without the braking unit dissipating the regenerative energy, the DC bus would have tripped on overvoltage. Instead, the stop was buttery smooth, and the belt held perfectly at zero speed.

You can see our NEMA standard compliance testing protocols in action on the floor, ensuring every drive handles these regenerative loads safely before it leaves the building.

Conveyor Commissioning Checklist

Related Technical Guides

• V/F Curve and Torque Boost Explained
• Multi-Speed Control Wiring and Setup
• Complete VFD Wiring Guide
• Parameter Setup and Initialization
• Fault Codes and Troubleshooting
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