Engineering
Motor Design Calculator
Calculate a preliminary nameplate output from shaft duty, then reconcile electrical input, three-phase current, torque, starting current, and annual modeled losses.
Service-adjusted shaft requirement (kW)-
Calculated nameplate output (kW)-
Electrical input at duty point (kW)-
Three-phase duty current (A)-
Estimated starting current (A)-
Duty-point shaft torque (N·m)-
Annual electrical input (kWh)-
Annual modeled motor losses (kWh)-
Calculated nameplate spare output (kW)-
Duty output as share of calculated nameplate-
Decision view
Motor torque-speed operating point and electrical load path
Motor torque-speed operating point and electrical load pathThe duty torque sits on a live speed curve while input power divides into shaft output and losses and the start-current spike is compared with running current.
Exact scenario comparisonExpected operating load of nameplate (%) changes while all other entered assumptions remain constant.
| Expected operating load of nameplate (%) | Service-adjusted shaft requirement (kW) | Calculated nameplate output (kW) | Electrical input at duty point (kW) | Three-phase duty current (A) | Estimated starting current (A) | Duty-point shaft torque (N·m) | Annual electrical input (kWh) | Annual modeled motor losses (kWh) | Calculated nameplate spare output (kW) | Duty output as share of calculated nameplate |
|---|
How to use Motor Design Calculator
- Enter steady shaft output at the true duty point.
- Use a service factor appropriate to load shocks and duty.
- Set intended load fraction using actual motor efficiency curves and standard sizes.
Calculator guide
Understanding Motor Design Calculator
Motor sizing must serve the shaft load without turning every uncertainty into oversizing. This page separates application service factor, intended operating fraction, efficiency, power factor, current, torque, starting current, and energy loss.
Detailed calculation process
Detailed motor output, current, and torque calculation
The default duty needs 37 kW at 1,470 rpm with a 1.2 service factor, 85% intended nameplate loading, 93% efficiency, and 0.88 power factor.
General formula: P_s=P_L*K_sP_n=P_s/lP_in=P_L/etaI=P_in*1000/(sqrt(3)*V*PF)I_start=k_I*IT=9550*P_L/nE_in=P_in*hE_loss=(P_in-P_L)*h Mechanical duty and service sizing determine calculated nameplate. Electrical input and current are then reconciled at the entered efficiency and power factor.
What each symbol means
Worked substitution with the default inputs
The default calculated nameplate is 52.24 kW; the duty point draws about 65.3 A and produces about 240.4 N·m.
Worked situations
Practical examples
- A 37 kW duty with 1.2 service factor requires 44.4 kW before loading allowance.
- At 85% intended loading the calculated nameplate is 52.24 kW, while duty torque at 1,470 rpm is 240.4 N·m.
Better inputs
Useful tips
- Check the next standard rating rather than rounding down.
- Use the manufacturer curve at actual load and voltage.
- Coordinate starting method with driven inertia and supply voltage dip.
Before relying on the result
Limitations and common mistakes
- The model does not calculate acceleration time, load torque curve, thermal duty, enclosure, ambient, altitude, harmonics, or VFD effects.
- Starting current is a simple multiple.
- Efficiency and power factor are constant at the entered duty.
Reference
Key terms
- Service factor
- Application multiplier applied to required shaft output.
- Operating load fraction
- Duty output as a share of selected/calculated nameplate.
- Starting current
- Estimated current during starting based on the entered multiple.
Important note
Final motor and starter/VFD selection requires qualified engineering, load/inertia curves, duty and thermal class, environment, supply/fault studies, protection, efficiency standards, and manufacturer data.
Frequently asked questions
Why divide by intended load percentage?
A motor intended to run at 85% of nameplate needs nameplate output above the service-adjusted requirement.
Is the result a standard motor size?
No. Choose the next suitable standard rating and re-evaluate its manufacturer curve.
Does starting current predict voltage drop?
No. Supply impedance, starter/VFD method, and acceleration duration are also required.