Ramp Time
The time it takes for the output to rise gradually from zero to the target value. On a direct start the pulse reaches typically 5–8 times the rated current; with a ramp applied it drops to 2–4 times, which reduces blown fuses, battery voltage sag and mechanical jolting. On the PT500 this time is set with the RMP pot.
A ramp means the driver increases its duty cycle along a defined slope instead of all at once. As the motor speeds up, back-EMF rises and naturally limits the current; the job of the ramp is to give back-EMF time to build.
- Short ramp (0.3–0.5 s): Suitable for light, low-inertia loads that need a fast response.
- Long ramp (2–5 s): Preferred for heavy loads, loads that can swing, or loads hanging on a rope; it reduces swinging and mechanical shock.
Making the ramp longer than necessary has its own cost: the motor stays at low voltage and low speed for a long time, and during that period it keeps drawing current to produce torque. In terms of heating this is the most demanding region.
In systems that use current-sensing stop, a ramp also prevents the starting pulse from tripping the threshold by mistake. If you have to choose between lengthening the ramp and raising the threshold, try the ramp first; that way you do not give up any protection margin.
Where this term is used: DC Motor Driver Selection Guide