Speed Regulation
The difference between a motor's no-load speed and its full-load speed, expressed as a ratio to the full-load speed and given as a percentage. It states numerically how much the speed will sag when the load changes. In brushed DC motors driven in open loop this value is noticeably high.
The calculation is simple: subtract the full-load speed from the no-load speed, divide by the full-load speed and multiply by a hundred. If a motor running at 3000 rpm with no load drops to 2600 rpm at full load, the regulation is about 15 percent.
The source of the sag is winding resistance. As the load increases the current increases, the drop across the winding resistance grows and the voltage left for the back-EMF decreases; as a result the speed falls.
- In open loop: The driver only keeps the average voltage constant, it does not measure speed. As the load changes the speed changes too.
- In closed loop: The duty ratio is corrected according to the speed measured by an encoder or similar feedback, and the regulation drops to the level of a few percent.
Evaluate this value in the application: in jobs such as doors, barriers and curtains, 10–20 percent sag is not a problem. In dosing that requires a constant travel speed, or in mechanisms requiring synchronous motion, a feedback solution is needed. A supply voltage that collapses under load also makes the regulation look worse than it is; take the measurement at the driver terminal.
The context in which this term is used: DC Motor Driver Selection Guide