Drive a DC Motor

DC motor mode

In DC motor mode the Seletek drives a brushed DC motor using PWM (Pulse Width Modulation) to control speed, and reverses the direction by switching polarity. Unlike a stepper motor, a DC motor has no defined step position — the Seletek uses a virtual encoder to track position based on time and speed. This gives approximate but usable positioning for focusers that do not require sub-step precision.

The main practical advantage of DC mode is compatibility with motors already installed on older focusers — many Crayford and rack-and-pinion focusers came with a small DC motor and a proprietary controller, and the Seletek can replace that controller without changing the motor.

Video guide — DC motor wiring and configuration

Celestron focus motor coupling

The Celestron focus motor is a popular DC motor used on SCT telescopes. The Seletek can control it directly using DC motor mode. The following video shows how to build the coupling cable between the Seletek and the Celestron motor connector:

Software settings for DC mode

In the Seletek software, select the motor port and choose DC motor as the motor type. Key settings:

• PWM frequency: Usually 1–5 kHz. Lower frequencies may cause audible whine; higher frequencies may run cooler. Start with the default.
• Max duty cycle: Limits the maximum speed. Start at 50% and increase carefully — DC motors at full duty cycle can move too fast for reliable positioning.
• Steps per revolution (virtual): Calibrate by running the motor for a known number of turns and adjusting until the software's position count matches the real focuser movement.