🔢 HOW TO CALCULATE A SUITABLE BRAKING RESISTOR FOR YOUR INVERTER
The braking resistor is a crucial component for dissipating excess energy when the motor stops suddenly, preventing overvoltage (OV) faults. To select the correct resistor, two key factors must be determined: DC Bus voltage and desired dissipation power.
📘 1. Reference DC Bus Voltage
- Single-phase 220V inverter → DC Bus ≈ 310V
- Three-phase 380V inverter → DC Bus ≈ 540–600V
⚙️ 2. Braking Resistor Formula
Formula:
R = Vdc2 / P
Where:
– R: resistor value (Ω)
– Vdc: DC Bus voltage (V)
– P: desired dissipation power (W)
Example: For a 5.5kW inverter, DC voltage = 700V, desired dissipation ≈ 3000W:
R = 700² / 3000 ≈ 163.3Ω
👉 You can choose a resistor of 150–180Ω with a power rating of at least 3000W, depending on braking frequency.
💡 Selection Notes
- ✅ Choose a resistor power rating at least 1.5–2 times higher than the calculated value.
- ✅ For applications like cranes or uncoiling in cable/steel industries, choose higher power due to high inertia.
- ✅ Prefer aluminum-housed resistors for better heat dissipation.
📷 Example: AC10 Braking Resistor Selection
📌 Reference Table for Parker AC10 Inverter
📌 Real-World Braking Power Estimation by Application
- Standard Loads: ~10% of motor power
- Elevators: ~35–40%
- Unwinding systems: ~60%
- Cranes: >50%, depending on travel distance
Example: For a 15kW motor in continuous unwinding for cable production:
P = 15 × 60% = 9kW
✅ CONCLUSION
Choosing the right braking resistor improves braking performance, reduces overvoltage errors, and extends inverter lifespan. If you’re unsure about specs, refer to the manufacturer’s datasheets or contact a trusted provider like Kỹ Thuật Việt for proper consultation.
