What Is Torque Boost in a VFD? Explained for Beginners
Have you ever wondered how a motor gets that extra “kick” during startup? That’s where Torque Boost comes in. This VFD (Variable Frequency Drive) function increases starting torque at low speeds—ideal for heavy-load applications like conveyors, mixers, and crushers.
In this guide, we explain what Torque Boost does, when to use it, and how to set it safely without damaging your motor or drive.
🔧 What Is Torque Boost?
Torque Boost (also called Voltage Boost) is a function in many VFDs that increases the output voltage at low frequencies. This helps compensate for voltage drop in the motor’s windings at slow speeds—improving starting torque.
It’s especially useful in:
- ✅ Applications with high breakaway torque (e.g., fans with static pressure)
- ✅ Machines that start under load (e.g., conveyors, grinders)
- ✅ Low-speed motor operations
⚙️ How Torque Boost Works
When a motor runs slowly, the back EMF (electromotive force) is low. A VFD typically reduces voltage to match frequency, which can result in weak torque. Torque Boost offsets this by adding more voltage at low speeds to maintain torque production.
There are two types:
- 🔹 Manual Torque Boost – User-defined % increase in voltage at low frequency
- 🔹 Automatic Torque Boost – The VFD adjusts boost dynamically based on load
📊 Example – Manual Torque Boost Curve
The graph below shows how voltage is increased at lower frequencies to provide more starting torque. Torque Boost tapers off as frequency rises to maintain efficiency.
As shown, Torque Boost is most effective in the 0–15 Hz range—especially helpful for loads that require a strong start from zero RPM.
⚠️ When to Use (and Avoid) Torque Boost
Use Torque Boost when:- 🔧 Starting heavy loads from standstill
- 🚚 Applications need high starting torque
- 🔁 Operating at slow speeds with load
- ⚠️ Your motor is lightly loaded
- ⚠️ You’re running close to full voltage/frequency curve
- ⚠️ Excessive heating may occur
💡 Pro Tip: Always monitor motor temperature if using high torque boost values!
🧪 How to Set Torque Boost on Your VFD
Most modern VFDs allow you to set torque boost via parameter programming:
- 🔸 ABB ACS355: Parameter 20.03 – Torque Boost
- 🔸 Delta MS300: Parameter 05-03 – Torque Compensation
- 🔸 Danfoss FC302: Parameter 1-71 – Torque Boost
- 🔸 PowerFlex 523: Parameter A081 – Torque Boost
📖 Always refer to your VFD’s manual before adjusting boost settings.
🛒 Buy VFDs with Torque Boost at Drive Outlet Megastore
- ✅ ABB ACS355 & ACS880 – Excellent torque control
- ✅ Delta MS300 – Built-in auto torque boost
- ✅ PowerFlex 4M & 523 – Rockwell performance with boost
- ✅ Danfoss FC Series – Adjustable boost with protection
🧮 Use our VFD Sizing Calculator or contact us for help choosing the right drive.
