Many customers have limited understanding of motor characteristics and often worry that operating a motor outside its rated voltage will cause it to malfunction or suffer from reduced efficiency. There is also a lack of clear awareness regarding how performance changes under different voltages. To address this, this article selects the same brushless DC motor and conducts a comparative analysis of its TI-TN curves at multiple voltages—6V, 7.4V, 9V, and 12V—to provide an in-depth examination of the correlation patterns among speed, current, and efficiency. Through intuitive data and curve interpretation, we aim to help users eliminate application concerns, accurately grasp the voltage adaptation characteristics of the motor, and achieve more flexible and efficient engineering applications.

From the TI-TN curve above, for the same brushless DC motor operating at 6V, 7.4V, 9V, and 12V, speed and output power change significantly with voltage, while the current-torque curves almost completely overlap. When efficiency is evaluated using the motor body current (after deducting the driver bias), the overall efficiency levels are similar across voltages.

1. Speed Variation

Speed is primarily determined by voltage. As voltage increases, speed increases proportionally or approximately proportionally. As load torque increases, speed decreases linearly.

2. Torque / Stall Torque Variation

The motor's output torque and stall torque are determined by voltage. The higher the voltage, the greater the output torque and stall torque, increasing proportionally or approximately proportionally.

3. Current Variation

In the graph, the current curves for 6V, 7.4V, 9V, and 12V almost coincide. This means that at the same output torque, the total current is essentially the same for 6V, 7.4V, 9V, and 12V. Torque determines current; voltage has minimal effect on the current curve.

Note: The curves include the current consumed by the driver itself, approximately 20–30 mA. When analyzing motor body efficiency, this fixed bias should be deducted.

4. Output Power Variation

Output mechanical power:

Pout​=2πNT/60

As voltage increases, the motor's output power increases. The output power is proportional to the square of the voltage ratio. For example, going from 6V to 12V, the speed doubles and the torque doubles, meaning the output power at 12V is four times that at 6V.

5. Efficiency Pattern

Motor body input electrical power:

Pin​=U×Imotor​

If the driver's static current of approximately 20–30 mA is deducted and the motor body current is used, the "torque-current" curves are nearly identical across voltages, while output power increases with speed/voltage. Therefore, the motor body conversion efficiency is approximately the same at different voltages. The optimal efficiency point is generally in the light-to-medium load range, but its exact position varies slightly with voltage.