Synchronous Speed of AC Motors
The Synchronous Speed Calculator computes the theoretical no-load speed of AC induction and synchronous motors. Actual speed is slightly lower due to slip.
Formula
N_s = (120 × f) / P
Where:
- N_s = synchronous speed (RPM)
- f = frequency (Hz)
- P = number of poles
Common Speeds
| Poles | 60 Hz (RPM) | 50 Hz (RPM) |
|---|---|---|
| 2 | 3600 | 3000 |
| 4 | 1800 | 1500 |
| 6 | 1200 | 1000 |
| 8 | 900 | 750 |
| 10 | 720 | 600 |
| 12 | 600 | 500 |
Slip
Induction motors run at 2–5% below N_s:
Slip (%) = (N_s - N_actual) / N_s × 100
Applications
- Pumps, fans (4-pole, ~1750 RPM)
- Conveyors (6-pole, ~1150 RPM)
- High-speed tools (2-pole, ~3450 RPM)
Examples
- 60 Hz, 4 poles → 1800 RPM
- 50 Hz, 6 poles → 1000 RPM
Motor Nameplate
Check rated RPM (e.g., 1750 RPM for 1800 RPM sync). Difference = slip.
Conclusion
Use with Slip Calculator and Torque tools for complete motor analysis.