Industrial Resistors (Braking / Load / Discharge)
Overview of braking, load and discharge resistors used in industrial automation and power electronics
Industrial resistors are used to safely dissipate electrical energy in automation systems, motion control and power electronics. They convert excess electrical energy into heat, protecting equipment and ensuring stable operation during braking, load testing or capacitor discharge. This page summarizes the three main resistor categories used in industrial environments.
Braking Resistors
Braking resistors are used with frequency inverters (VFDs) and servo drives to dissipate regenerative energy produced during motor deceleration. Without a braking resistor, the DC bus voltage rises and the drive may trigger an overvoltage fault.
Typical Applications
- Conveyors, cranes, elevators
- High‑inertia loads (centrifuges, flywheels)
- Servo systems with rapid acceleration/deceleration
- Emergency stop energy absorption
Characteristics
Braking resistors must handle short, high‑power pulses and repetitive duty cycles. Aluminum‑housed resistors are common for compact installations, while steel‑grid resistors are used for higher power levels. A typical example is a 35 Ω / 300 W / 800 V DC aluminum braking resistor.
Load Resistors
Load resistors simulate electrical loads during testing, commissioning or maintenance. They allow engineers to verify system behavior under controlled conditions without connecting real machinery.
Typical Applications
- VFD and inverter testing
- Generator and UPS load testing
- Power supply verification
- Laboratory and R&D environments
Characteristics
Load resistors provide stable resistance values and high continuous power capability. They may use natural or forced‑air cooling depending on the required load. Modular load banks allow adjustable load levels for precise testing and performance verification.
Discharge Resistors
Discharge resistors safely remove stored energy from capacitors, DC links and power electronics after shutdown. This prevents dangerous voltages from remaining in the system and ensures safe maintenance conditions.
Typical Applications
- DC bus discharge in VFDs and servo drives
- Capacitor banks
- Power supplies and rectifiers
- Energy storage systems
Characteristics
Discharge resistors are designed to provide controlled discharge times and high reliability. They must be selected according to the DC voltage level, capacitor size and required discharge time.
Comparison Table
| Resistor Type | Function | Typical Power Range | Common Applications |
|---|---|---|---|
| Braking Resistor | Dissipates regenerative energy | 100 W – 20 kW | VFDs, servo drives, cranes |
| Load Resistor | Simulates electrical load | 500 W – 100 kW | Testing, commissioning, R&D |
| Discharge Resistor | Discharges capacitors safely | 50 W – 5 kW | DC links, capacitor banks |
Safety Considerations
- Resistors generate significant heat — ensure proper ventilation
- Use thermal protection (PTC, thermostat, thermal switch)
- Maintain safe clearance around resistor enclosures
- Follow manufacturer wiring and grounding guidelines
- Avoid touching resistors during and after operation
Summary
Braking resistors dissipate regenerative energy, load resistors simulate electrical loads for testing, and discharge resistors safely remove stored energy from capacitors. Correct selection ensures system stability, protects equipment and improves operational safety.