Engineering purpose
Use the sequence below to establish a defensible starting point, then confirm the decision with model-specific performance, tolerances and test evidence.
Match Voltage to Required Speed
The drive must provide sufficient phase or armature voltage at the maximum loaded speed, allowing for supply tolerance, switching strategy, cable drop and winding resistance.
Match Current to Torque and Duty
Continuous current relates to sustainable torque and temperature; peak current relates to short events. Confirm both motor and drive limits with duration and cooling conditions.
Confirm Commutation and Feedback
BLDC, PMSM, servo and stepper motors require compatible phase arrangement, feedback type, alignment, signal level and control method. Encoder resolution alone does not guarantee system accuracy.
Manage Braking and Regeneration
Decelerating inertia can raise the DC-bus voltage. The system may require a braking resistor, regenerative supply, controlled deceleration or energy storage.
Coordinate Protection and EMC
Overcurrent, thermal protection, earthing arrangement, cable shielding, switching frequency and installation layout must be engineered together to protect the product and wider equipment.
Worked example
Check a 24 V BLDC speed requirement
Given
- Required loaded speed: 3,000 rpm
- Back-EMF constant: 6 V/krpm line-to-line, using the manufacturer’s stated measurement basis
- Estimated resistive and drive allowance: 3 V
Method
- Estimated line-to-line back EMF at 3 krpm = 6 × 3 = 18 V on the same measurement basis.
- Add the 3 V allowance: approximately 21 V is required at the motor before confirming modulation limits.
- A nominal 24 V supply may be viable, but minimum supply voltage, PWM utilisation, phase current and transient voltage drop must be checked.
Engineering result: Do not approve the combination from nominal voltage alone; confirm the back-EMF definition, winding, drive modulation and worst-case supply.
Common mistakes
What to Avoid
- Matching only nominal voltage
- Using drive peak current as continuous current
- Assuming any encoder works with any drive
- Ignoring regenerated energy and cable effects
Selection check
Confirm Before Selection
- Minimum and maximum supply voltage
- Continuous and peak current with duration
- Commutation, feedback and phasing
- Braking, protection, cable and EMC strategy
SDT engineering note
Apply General Knowledge with Product-Specific Evidence
This guide supports preliminary engineering. Final selection must be confirmed against the complete application, selected motor and drive data, declared operating conditions, applicable standards and agreed validation criteria.