I'm designing a motor speed control circuit as part of a larger system for a one-off project. Specs are :
- The motor is an existing PM brush type with an integrated reduction gear, and is also coupled to an optical tachometer. The name plate has faded until it's no longer legible, but it was originally powered from a 24V, 90VA transformer via a controller card. DC resistance is about 1 ohm.
- It drives a timed process that lasts a few minutes per session. Load is fairly constant. Speed regulation has to be fairly precise.
- The original (damaged) controller card has the current limit set at 3.5A. I have not yet measured the current under normal load.
If the motor is stalled or significantly slowed down, the process is ruined and has to be repeated. So, instead of just limiting the current, I thought I'd have the motor shut off until it's restarted. I intend to introduce a time delay so that the motor won't shut down during normal start-up.
My question is : How long should the delay be ? It's probably not possible to give an accurate answer without knowing details about the motor and the load. But can anyone give a ball-park figure - something like 3 secs, 5 secs ... ? TIA for any input.