Size resistors for faster stopping and protected drives. Review energy, current, duty, and wattage needs. Use practical inputs, formulas, examples, exports, and clear results.
| Input | Example Value | Sample Result |
|---|---|---|
| Motor power | 15 kW | Reference motor size for comparison |
| Initial to final speed | 1500 rpm to 0 rpm | Full stop braking event |
| Total inertia | 1.80 kg·m² | 22,206.61 J per stop |
| Deceleration time | 8 s | 2,775.83 W peak mechanical braking power |
| Stops per hour | 20 | 123.37 W average braking power |
| Clamp voltage and current limit | 700 V and 20 A | 35.00 Ω minimum resistance |
| Safety factor | 25% | 43.75 Ω recommended resistance |
| Recommended resistor check | 43.75 Ω | 11,200.00 W pulse and 154.21 W continuous |
1. Total inertia: Jtotal = Jload + Jmotor
2. Angular speed: ω = 2π × rpm / 60
3. Braking energy: E = 0.5 × Jtotal × (ω12 − ω22)
4. Peak mechanical braking power: Ppeak = E / t
5. Average braking power: Pavg = E × stops per hour / 3600
6. Braking torque: T = Jtotal × (ω1 − ω2) / t
7. Minimum resistor value: Rmin = Vclamp / Ilimit
8. Pulse resistor power: Presistor = Vclamp2 / R
9. Suggested continuous rating: Pcont = Pavg × (1 + safety factor)
A VFD braking resistor helps control energy during fast deceleration. When a motor slows down, rotating energy flows back into the drive. The DC bus voltage rises. If the energy is not removed, the drive can trip on overvoltage. A braking resistor converts that energy into heat.
This calculator estimates braking energy, braking torque, peak mechanical braking power, average braking power, minimum resistor value, and suggested wattage. It also checks an entered resistor against the minimum safe resistance. That helps you compare a planned part with a safer design target.
Inertia is critical. Higher load inertia stores more rotational energy. Speed also matters because energy rises with the square of angular velocity. Shorter deceleration times increase braking torque and peak power. Frequent stops increase thermal loading. Clamp voltage and transistor current limit set the lowest safe resistance value.
Use the minimum resistance to avoid excessive current through the brake transistor. Use the recommended resistance for margin. Then review pulse power and continuous wattage separately. Pulse power describes short energy bursts. Continuous wattage reflects repeated stop duty over time. Both ratings matter for reliable operation.
Use this tool as a first-pass sizing method. Then compare the output with drive manuals and resistor manufacturer data. Verify brake chopper limits, overload duration, enclosure ventilation, ambient temperature, and duty class. A resistor that survives one stop may still overheat in repeated production cycles.
Fast stopping improves process control, machine uptime, and safety in many systems. Still, very aggressive ramps can demand high power dissipation. A realistic safety factor helps. So does reviewing stop frequency and total thermal duty. Better sizing reduces nuisance trips and improves resistor life.
It absorbs returned energy during deceleration. The resistor turns that electrical energy into heat. This prevents DC bus overvoltage trips and allows faster, more controlled motor stopping.
Minimum resistance protects the brake transistor. If resistance is too low, current rises too much. That can damage the braking circuit or trigger faults during heavy stopping.
Pulse power is the short burst during one braking event. Continuous wattage reflects average heat over time. A resistor must handle both conditions to work safely in repeated cycles.
No. Motor power helps as a reference. Inertia, speed change, deceleration time, stop frequency, and brake circuit limits are usually more important for resistor sizing.
Yes. Enter it in the optional field. The calculator compares it with the minimum safe resistance and shows the resulting current and pulse power.
Use kg·m². Keep both load inertia and motor inertia in the same unit. Mixed units will give wrong results and can mislead resistor selection.
A safety factor gives design margin. It helps cover estimation error, harsher duty, temperature rise, and practical operating differences between theory and the real machine.
No. It is a strong first estimate. Final selection should still follow drive documentation, resistor datasheets, thermal limits, enclosure design, and site-specific duty conditions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.