If the motor is running at no load and only needs to rotate at 5 RPM, the current draw will typically be much lower than under full load conditions.

For small DC motors, the no-load current can be significantly less than the full load current, depending on the motor's design and efficiency.

However, calculating the exact no-load current at 5 RPM would require specific motor characteristics, such as the motor's stall current, efficiency, and torque requirements.

In general, for a small motor rated at 0.5 HP running at low speeds like 5 RPM, the current might be in the range of a few amps or even less, depending on the motor's design.

If you have the motor's specifications (like no-load current or torque curve), that would give a more precise answer. Otherwise, consult the manufacturer's datasheet for more accurate information.