DIY Electric Car Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
244 Posts
Discussion Starter #1 (Edited)
Electric motor suppliers often claim up to 98% electromechanical efficiency. I need a way to measure the output shaft torque/power of a motor. The motor is rated continuous 20 kW.

The torque (or power) is to be measured at continuous RPMs - from 1,000 to 4,000 RPM.

Are reasonably priced torque meters commercially available? Or do I need to build my own? What kind of torque sensor is needed? How to generate such loads for testing?

Thanks to all.

Solarsail
 

·
Registered
Joined
·
98 Posts
There are commercially available, but very expencive. Build your own are often cheaper. Strain Gauges are cheap.
 

·
Registered
Joined
·
4,577 Posts
The normal approach is to use the motor to drive a generator. You control the load by controlling the generator. To reduce the problem of needing a massive DC power supply to run the motor, you can charge the battery from the generator output while powering the motor, so the battery only provides some smoothing and makes up the energy loss of the inefficiencies of the all of the components.

Ideally the generator characteristics are well known so that you can infer the torque from the current and voltage produced by the generator, but for accuracy you need a more direct measurement of torque.

In theory you can mount the motor or the generator on bearings to allow it to rotate about the shaft, and restrain it with a lever with a load cell measuring the restraining force (torque = force x lever arm length), and that might be okay at constant speed. the load cell can be just a hydraulic cylinder with a pressure gauge on it. This is the principle of basic dynamometers, which is why the power measured by them is called "brake" power... and it's not how accurate modern dynos work.
 
1 - 3 of 3 Posts
Top