Motor Power Calculator — Input Power from Shaft Power
Free online motor power calculator for dairy plant engineers. Calculate electrical input power from shaft power, motor efficiency, and power factor for energy audits.
Understanding Motor Power in Dairy Plants
Electric motors are the largest electricity consumers in dairy processing plants. Understanding the relationship between shaft power and electrical input power is essential for:
- Energy audits — calculating actual power consumption for each motor
- Electricity billing — checking if motors are running efficiently
- Motor selection — choosing the right motor size for a new application
- Variable speed drive sizing — determining drive capacity requirements
Power Relationships
Shaft Power (kW) → What the motor delivers to the load (pump, conveyor, agitator)
Electrical Input Power (kW) → What the motor draws from the electrical supply
The difference is due to motor losses (heat, friction, magnetic losses).
Formula
Electrical Input Power (kW) = Shaft Power (kW) / (Efficiency% / 100 / Power Factor)
Or more precisely: Apparent Power (kVA) = Shaft Power / (Efficiency × Power Factor)
Typical Motor Parameters
| Motor Size | Typical Efficiency | Typical Power Factor |
|---|---|---|
| 0.37–1.5 kW | 72–82% | 0.72–0.82 |
| 1.5–7.5 kW | 82–89% | 0.82–0.87 |
| 7.5–22 kW | 89–92% | 0.85–0.90 |
| 22–75 kW | 92–94% | 0.87–0.92 |
| 75+ kW | 94–96% | 0.88–0.94 |
Use nameplate values when available — they are more accurate than these typical ranges
Energy Cost Calculation
Once you have the electrical input power:
Annual Energy Cost = Input Power (kW) × Hours/Year × Electricity Rate (₹/kWh)
Example: A 15 kW motor running 8 hours/day, 330 days/year at ₹8/kWh:
- Annual energy = 15 × 8 × 330 = 39,600 kWh
- Annual cost = 39,600 × 8 = ₹3,16,800/year