What the thread found

• The RS port on the Alexa has a maximum current output of 2 amps total across both ports, which may be insufficient for powering motorized focus systems depending on the motor and lens resistance.
• When the available current is exceeded, motorized focus systems may fail mid-calibration or enter recalibration loops during moderately fast focus movements.
• Using an external D-tap power source instead of the RS port resolved motorized focus system failures in multiple cases.
• The camera must upconvert lower battery voltage to 24V for the RS port output, and the total current draw from the camera itself plus all accessories connected to the RS port can collectively exceed the port's current limit.
• Using a dedicated power cable with a Y-split breakout to external batteries bypasses the camera's internal power management and is recommended practice for high-current accessories.

Depends on

• The voltage specification of the RS port was uncertain to participants; some thought it 12V, others 24V.
• Testing with 24V power was not completed by the original reporter.
• Current draw specifications for different motorized focus motors were not comprehensively documented across the discussion.
• The relationship between lens stiffness and current draw was not fully explored.
• Participants used different motorized focus systems and batteries, making direct comparison difficult.

Gear in this thread

BFD

Same gear or parts

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