Formula Used
Angular speed: ω = 2πN / 60
Angular deceleration: α = |ω₁ − ω₂| / t
Inertia torque: Tᵢ = J × α
Net torque: Tₙ = Tᵢ + load effect − friction assistance
Required braking torque: Tᵦ = Tₙ ÷ efficiency × service factor
Brake power: Pᵦ = Tᵦ × average ω ÷ 1000
Energy per stop: E = 0.5 × J × |ω₁² − ω₂²|
The calculator assumes all inertia is reflected to the motor shaft.
How to Use This Calculator
Enter motor power and rated speed for reference torque.
Enter total reflected inertia at the motor shaft.
Add initial speed, final speed, and stopping time.
Choose whether the external load adds to braking demand.
Enter friction assistance if drag helps stop the motor.
Use brake efficiency and service factor for practical sizing.
Compare calculated torque with the selected brake rating.
Use CSV or PDF buttons to save the result.
Motor Brake Sizing Guide
A motor brake is selected to stop motion within a planned time. The task sounds simple, but the torque must cover stored kinetic energy, load torque, friction, efficiency losses, and a safety factor. Undersized brakes overheat. Oversized brakes can shock couplings, belts, shafts, and gearboxes.
Why Braking Torque Matters
Braking torque is the turning force applied against rotation. It is needed when a conveyor, fan, hoist, mixer, saw, or indexing table must stop predictably. The main driver is inertia. A heavy rotor or load stores more energy at the same speed. Higher speed also raises energy quickly. That is why a small speed change can alter brake duty.
Key Inputs
Start with total reflected inertia at the motor shaft. Include the motor rotor, gearbox, pulley, coupling, and driven load. Convert every rotating part to the motor shaft when ratios are used. Next, enter starting speed, ending speed, and required stop time. Shorter stop time means higher angular deceleration. That raises required torque.
Load and Service Conditions
Load torque may assist or resist stopping. A horizontal conveyor usually needs extra braking torque. A fan may have aerodynamic drag that helps stopping. A hoist can become critical because gravity may drive the load. Use conservative values when direction changes or loads vary. Apply a service factor for wear, heat, dust, and uncertain data.
Heat and Duty
Torque rating is not the only limit. Each stop turns kinetic energy into heat. Frequent stops can exceed the thermal capacity of the brake. Check energy per stop and hourly duty. Compare both values with the brake manufacturer's data. High cycle applications may need a larger brake or forced cooling.
Practical Review
Use the calculated torque as a sizing guide, not as the final approval. Review emergency stop rules, machine risk, holding torque, response time, voltage tolerance, and enclosure type. Confirm the result with measured stopping trials when possible. Good sizing gives repeatable stops, lower wear, and safer electrical motion control.
Document every assumption before buying hardware. Record inertia sources, gear ratios, brake voltage, ambient temperature, and expected stop frequency. This record helps maintenance teams troubleshoot drift later. It also makes future upgrades easier when motors, reducers, or driven masses change safely.
FAQs
What is braking torque in a motor?
Braking torque is the opposing torque needed to slow or stop motor rotation. It depends on inertia, speed change, stopping time, load behavior, friction, efficiency, and service factor.
Why does inertia affect braking torque?
Inertia stores rotational energy. Higher inertia needs more torque to decelerate within the same stopping time. Faster stopping also raises the required braking torque.
Should load torque be added or subtracted?
Add load torque when the load drives the motor during stopping. Subtract it only when drag or load resistance helps the motor stop.
What service factor should I use?
Use a higher service factor for uncertain data, harsh duty, shock loads, wear, high temperature, or frequent starts and stops. Many practical checks use values above 1.
Is brake power the same as motor power?
No. Brake power is the power absorbed during stopping. Motor power is the rated output during running. Both values are useful, but they mean different things.
Why is thermal load important?
Each stop creates heat. A brake may meet torque demand but fail thermally during frequent stops. Always review energy per stop and cycle rate.
Can this calculator size a holding brake?
It helps estimate stopping torque. Holding brakes also need static load checks, safety rules, mounting details, voltage limits, and manufacturer approval.
Do I need manufacturer data?
Yes. Use this tool for calculation support. Final selection should match brake torque, thermal rating, duty cycle, enclosure, response time, and safety requirements.