Electrical & Drives
VFD Dynamic Braking Resistor Calculator
Screen braking energy, power, current, resistance and thermal duty from inertia and stop profile—not motor kW alone.
This tool provides a preliminary engineering calculation for reference. Final equipment selection, design and commissioning decisions must consider manufacturer data, applicable standards, operating conditions and project-specific engineering requirements. It is not certified design output.
Preliminary result
Calculated outputs
Enter values and select Calculate. Results are estimates and do not replace nameplate data, applicable standards, or an engineering review.
Use this calculation
Only calculator parameters and results are transferred. Personal details are collected separately in the destination form.
Formula
Mechanical braking energy: E = ½J(ω₁² − ω₂²) + entered linear/gravitational energy
ω = 2πn/60
Pavg = E/tstop
Candidate electrical screen: PR ≈ VDC,chop²/R
IR = VDC,chop/R
Worked example
5 kg·m² decelerated from 1500 RPM to rest in 5 s.
Expected check: Mechanical braking energy per event = 61.69; Mean braking power during stop = 12.34.
Assumptions
- • Entered inertia is referred to the motor shaft
- • Energy recovery is not included unless represented in additional energy
Limitations
- • This separates mechanical braking-energy calculation from final DBR equipment selection
- • Final selection requires the exact VFD, DC-chopper threshold, manufacturer Rmin, chopper current capability, duty cycle, pulse-energy capability, resistor continuous rating, environmental/enclosure derating, and mechanical/gravitational energy where applicable
- • Motor kW alone never determines a recommended resistor
Frequently asked questions
Can this result be used for final equipment selection?
No. Use it for a preliminary check, then verify manufacturer data, site conditions, applicable standards and the complete system design.
What does formula version 1.0.0 mean?
It identifies the exact calculation logic used so a saved result can be traced when the formula register changes.
Can Elexorn review my calculation?
Yes. Transfer the result to Request a Quote or Talk to an Elexorn Engineer and add the relevant project or equipment details.