Electric Motor Stopping Time Calculator

1. Motor Parameters

Motor Power (kW)

Rated Speed (RPM)

Motor Inertia ($J_m$) [$kg \cdot m^2$]

Initial Speed ($N_1$) [RPM]

Final Speed ($N_2$) [RPM]

2. Load & Mechanical

Load Inertia ($J_L$) [$kg \cdot m^2$]

Gear Box Ratio ($i$)

Load Torque ($T_L$) [$N \cdot m$]

Friction Torque ($T_f$) [$N \cdot m$]

Mechanical Efficiency (%)

3. Braking & Electrical

Braking Mechanism

Braking Torque ($T_b$) [$N \cdot m$]

DC Injection Current (A)

Braking Resistance ($\Omega$)

Safety Factor

Formula Used

The stopping time ($t$) of an electric motor is governed by rotational dynamics and Newton's second law for rotation:

$$t = \frac{J_{total} \cdot \Delta \omega}{T_{net}} \cdot SF$$

Total Moment of Inertia ($J_{total}$): $J_{total} = J_m + \frac{J_L}{i^2}$ where $J_m$ is motor inertia, $J_L$ is load inertia, and $i$ is gear ratio.
Change in Angular Speed ($\Delta \omega$): $\Delta \omega = \frac{2 \pi (N_1 - N_2)}{60}$
Net Deceleration Torque ($T_{net}$): $T_{net} = T_b + T_f - T_L$ (where $T_b$ is braking torque, $T_f$ is friction torque, and $T_L$ is load torque).
SF: Safety factor accounting for system losses and thermal derating.

How to Use This Calculator

Enter Motor Specifications: Input your motor power, rated speed, base inertia, initial operating speed, and target final speed in Column 1.
Provide Load Data: Specify load inertia, gearbox reduction ratio, load torque, friction torque, and mechanical efficiency in Column 2.
Select Braking Mode: Choose the appropriate electrical braking type, braking torque, DC injection current or resistance value, and safety factor in Column 3.
Calculate: Click the "Calculate Stopping Time" button to instantly view precise deceleration duration and intermediate rotational metrics above the form.

Understanding Electric Motor Stopping Dynamics

Accurately determining the stopping time of an industrial electric motor is essential for maintaining operational safety, preventing mechanical wear, and programming programmable logic controllers (PLCs) or variable frequency drives (VFDs). When power is cut or an active braking command is issued, the kinetic energy stored in the rotating masses must be safely dissipated. This calculator integrates comprehensive electrical and mechanical parameters to deliver precise deceleration timings.

The Role of Inertia and Torque

System inertia is a combined measurement of both the motor rotor and the driven load. Because loads are frequently coupled through gearboxes or belt drives, calculating the referred inertia back to the motor shaft is crucial. Simultaneously, the braking torque—whether generated via DC injection, dynamic resistor braking, or regenerative methods—must overcome system friction and active load torque to bring the mechanism to a halt.

Frequently Asked Questions (FAQs)

The gear ratio directly scales the load inertia perceived by the motor shaft by the square of the ratio ($1/i^2$). A higher reduction ratio significantly lessens the effective load inertia the motor experiences during braking.