How to Calculate Motor Efficiency
What is Motor Efficiency?
Calculates electric motor efficiency comparing input power to useful mechanical output. Identifies opportunities for energy savings.
Formula
Efficiency = output ÷ input × 100%
Step-by-Step Guide
- 1Measure input power (watts)
- 2Determine shaft load and speed
- 3Calculate output mechanical power
- 4Efficiency = output ÷ input × 100%
- 5Typical industrial motors 85-95% efficient
Worked Examples
Input
Input 746W, output 0.5hp
Result
89% eff
Common Mistakes to Avoid
- ✕Assuming all motors equal efficiency across speed range
- ✕Not considering part-load efficiency (motors inefficient at low load)
Frequently Asked Questions
Why do motor speeds vary if efficiency is similar?
Motor slip determines actual speed; typical slip 1-10%; affects torque and efficiency.
How do I improve motor efficiency?
Match motor size to load (oversized motors run inefficient), reduce friction, improve cooling.
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