Measuring the actual power output of an electric motor on a dynamometer

The power rating listed on a motor or scooter specification sheet is rarely the actual power you will experience. It can be a peak power value measured for a few seconds, an electrical power rather than mechanical power, or a marketing figure. The only way to know what a motor is truly capable of is to measure it. This is the role of a dynamometer (or "engine bench"), which we use to fine-tune our drive systems.

What does a dynamometer measure?

A dynamometer applies a load to the motor, which can be adjusted, and measures its performance continuously. This load can be provided by a brake, a second motor acting as a counterforce, or a similar mechanism

• torque, with a sensor placed between the motor and the load;
• rotational speed, using a speed sensor;
• The voltage and current at the controller's input, on the battery side;
• The temperatures of the motor and the controller.

Calculating power

Mechanical power is the product of torque and rotational speed, expressed in radians per second. In practice: power in watts = torque in Newton-meters × speed in revolutions per minute × 2π ÷ 60. A motor that delivers 10 N·m at 3,000 revolutions per minute, for example, would produce approximately 3,140 W.

Electrical power is the product of voltage and battery current. It is always greater than mechanical power; the difference is dissipated as heat in the motor and the controller. The ratio between the two is the efficiency of the system. Our guide on motor overheating details where these losses originate.

The curves to be analyzed

• The torque curve as a function of speed: it remains flat up to a certain speed, then decreases when the battery voltage is no longer sufficient. Field weakening allows you to push this limit.
• The power curve that results from this.
• The performance map, which shows in which areas of torque and speed the motor performs best.
• Warm-up duration: This setting determines the power level that can be sustained over time.

Peak power and sustained power

A motor can deliver a lot of power for a few seconds, but then needs to reduce its output to avoid overheating. A reliable specification sheet will provide both figures, along with the duration for which each can be sustained. On a test bench, we measure the peak power, and then maintain a constant load until the temperature stabilizes, allowing us to determine the continuous power output.

Why a test bench saves time

On a test bench, the conditions are reproducible: the same load, the same starting temperature, the same settings. You can use it to adjust the controller, compare two motors, verify motor parameter detection, or troubleshoot a stutter, all without risking the machine or the rider. See our guide on motor detection.

What Rage does:

We validate our powertrains on test benches and on the track, recording data. For manufacturers, schools, or laboratories, our engineering department offers these tests and provides the controllers and telemetry for a test bench. Also, see our page for engineering schools and research.

For the general methodology of a project, please refer to our guide on how to electrify a machine: where to start.