Rated Input Power vs Shaft Output: What to Check Before Specifying a Small BLDC Motor

1. Define the quantities before comparing watts

Rated electrical input power, W

Specified electrical power entering the stated boundary at rated conditions, not constant consumption at every load.

Mechanical shaft output power, W

Rotational power: shaft torque multiplied by angular speed at the same load point.

Efficiency, %

Shaft output divided by corresponding electrical input, multiplied by 100, for a defined boundary.

Tektronix describes these measurement relationships. A headline wattage alone is also a poor basis for comparing suppliers whose rating definitions differ; maxon explicitly highlights this limitation.

2. Agree where input power is measured

A-to-C efficiency includes controller losses; B-to-C describes the motor boundary. Record included electronics. For PWM phases, request an appropriate real-power measurement rather than simply multiplying voltage and current readings. See Tektronix, sections 4–5.4.

On a steady DC supply, voltage × current is a useful input-power check. With fluctuating signals, use the average of instantaneous voltage × current over a defined interval. Do not combine a startup current peak with a steady-running voltage to claim a continuous power rating.

3. Use a calculation to check consistency, not to invent a specification

If a supplier gives torque and speed, calculate their implied output and compare it with the stated output at that exact point. An inconsistency is a reason to clarify units, measurement location or operating conditions. Even a consistent calculation does not establish continuous thermal capability or validate a different load.

4. Compare the evidence in one operating-point sheet

Ask each supplier to complete the same rows. Keep an unanswered row marked “not confirmed”; do not fill it by copying a value from another model.

Scroll the table horizontally to compare all three columns.

This worksheet is a procurement review aid, not a claim that every requested report is already available. maxon's terminology reference illustrates why rated voltage and continuous-operation conditions need separate definitions; its numerical limits are not specifications for HONGQU motors.

5. Send a brief that the supplier can check

Copy the following into your project inquiry and fill only what you know. For fan equipment, include the impeller and the required airflow/pressure point in the assembled air path; motor input watts alone cannot establish airflow. For drone propulsion, provide the propeller, battery, controller and required thrust/duty information for a dedicated review.

Separate your requirements from supplier-confirmed data in the reply. Before ordering, agree the exact configuration and drawing revision; record unresolved fields explicitly rather than turning them into assumed specifications.

6. Apply the checklist to the two featured HONGQU families

• HQ-OR48-P15: 48 mm outer diameter; 15 W rated electrical input power.
• HQ-OR61-P30: 61 mm outer diameter; 30 W rated electrical input power.

Here, 48 mm and 61 mm describe outer diameter, not shaft diameter or a complete mounting envelope. DC ≤48 V is the product-family ceiling, not either configuration's rated voltage and not a universal 0–48 V operating range.

Shaft output, efficiency, speed, torque, rated voltage, operating range, controller and mechanical details remain subject to configuration-specific engineering confirmation. A higher input rating does not establish greater airflow or suitability for your equipment. Application inquiries are welcome; compatibility, including drone propulsion, is not a blanket promise.

Use the existing inquiry form to share your requirements. Available drawings, test information, samples, price, minimum order and lead time are confirmed after reviewing the proposed configuration.