Description:
The ABB NBRA-669C is a stand-alone Brake Chopper (Dynamic Braking) Module designed to work with ABB low-voltage AC drives — most commonly the ACS 400, ACS 510, and ACS 550 series — that lack an internal braking transistor or require higher braking duty than the drive’s internal chopper can handle. It monitors the DC-link voltage via a connection across the drive’s DC bus terminals (UDC+/UDC− or P+/N− on drives with brake option) and, when the bus exceeds the preset threshold, switches an external dynamic braking resistor (DBR) across the bus to dissipate regenerative energy from overhauling loads (cranes, hoists, centrifuges, down-hill conveyors). The NBRA-669C thus prevents “DC Overvoltage” trips and enables controlled rapid stopping or load-holding that would otherwise feed energy back into the drive.h2 Application Scenarios:A container-port gantry crane using an ABB ACS550 drive on the hoist frequently tripped “DC OVERVOLT” when lowering heavy loads — the motor acted as a generator, pushing energy back into the VFD’s DC bus faster than it could be returned to the mains. The drive had no internal brake chopper of sufficient rating. The integrator mounted an ABB NBRA-669C in the MCC bucket, wired its DC-sense leads across the drive’s DC bus, and connected a suitably sized external wire-wound braking resistor to the NBRA-669C’s B+/B− terminals. The chopper activated at the adjusted threshold (typically 760–780 V DC for 400 V class) and clamped the bus during every lower cycle. The NBRA-669C solved the core pain point — nuisance overvoltage trips on overhauling loads — and allowed the crane to hold and lower heavy containers smoothly with zero drive faults. This illustrates the module’s essential role in any application where the load regenerates more energy than the drive’s built-in capability or the supply can absorb.h2
Parameter:
| Main Parameters | Value/Description |
|---|---|
| Product Model | NBRA-669C |
| Manufacturer | ABB (ABB Drives / Low Voltage Products) |
| Product Category | External Brake Chopper Module / Dynamic Braking Unit (Stand-Alone) |
| Compatible Drives | ABB ACS400, ACS510, ACS550 (and select ACS350 / ACS800 w/o int. chopper) — verify drive DC-bus access |
| Rated Voltage (DC Bus Sense) | 400 V AC drive class — DC bus typical 570 V nom / 800 V max |
| Chopper Activation Voltage | Adjustable — typically 760 V DC (±20 V) default; range ~720–800 V DC |
| Max. Braking Resistor Current | Depends on external DBR ohmic value & duty — typical paired resistor 40–100 Ω, 2–10 kW continuous / higher peak |
| Control Supply | 24 V DC or 230 V AC (per variant — C-suffix typically 24 V DC control) |
| Mounting Method | DIN Rail (35 mm top-hat) or screw-fixed in MCC bucket |
| Connections | DC Bus sense (+UDC/−UDC), Brake Resistor (B+/B−), Control Voltage (A1/A2), Enable (optional) |
| Operating Temp. | -10 °C to +50 °C (derating may apply above 40 °C) |
| Protection Rating | IP20 (installed inside enclosed cabinet) |
| Certifications | CE, UL (check individual unit label) |
h2 Technical Principles and Innovative Values:
- Voltage-Threshold-Based DC-Bus Clamping: The NBRA-669C continuously compares the sensed DC-bus voltage against its internal adjustable threshold. When regeneration raises the bus above threshold, an IGBT inside the chopper switches the external braking resistor across the bus — dissipating the excess energy as heat — then turns off once the bus falls below the hysteresis band. This prevents overvoltage faults without affecting normal motoring operation.
- Decoupled from Drive Firmware — Works with Any Brand (with DC-bus access): Although optimized for ABB drives, the ABB NBRA-669C senses only the DC-bus potential and needs no communication with the VFD — meaning it can be applied to any VFD (ABB or third-party) that exposes the positive and negative DC-bus terminals, making it a versatile retrofit for older drives lacking internal braking.
- Adjustable Hysteresis Minimizes Resistor Cycling & EMI: The built-in hysteresis band (typically 10–20 V) prevents rapid on/off chattering of the chopper when the bus is hovering near the setpoint, reducing resistor thermal cycling and limiting high-frequency EMI — an important consideration in panels with sensitive analog instrumentation nearby.
h2 Application Cases and Industry Value:Case 1 – Wood-Products Band-Saw Down-Haul Conveyor (ACS510, 22 kW):A downhill belt conveyor regenerated heavily when loaded, causing intermittent “DC OVERVOLT 3210” trips on an ACS510 without the optional internal brake chopper. Installing the ABB NBRA-669C with a 60 Ω / 5 kW wire-wound resistor eliminated all overvoltage trips. The plant extended stopping-distance control by using the chopper to hold bus voltage steady during prolonged lower-haul cycles. No drive parameter changes were required — only the DC-bus and resistor wiring.Case 2 – Steel-Coil Uncoiler / Rewind Tension Stand (ACS550, 45 kW):An uncoiler mandrel driving a tension-closed-loop application occasionally regenerated during deceleration. The drive’s internal chopper was undersized for the duty cycle. Adding the NBRA-669C with a 30 Ω / 10 kW resistor (higher duty cycle) handled the peak braking energy. The line’s tension-control loop remained stable through deceleration ramps, and the drive logged zero overvoltage events over a 2-year review period.
