Calculating Resistor Value for 12V DC Motor on 120V AC with Rectifier Bridge

A 12V DC motor rated around 6 watts and 1.2 amps under load is being powered from a 120V AC source through a diode bridge rectifier. The user initially assumed a resistor was needed to protect the motor but experienced motor damage and tripped breakers when connecting the motor directly after the rectifier. Responses clarify that a resistor is generally unnecessary unless current limiting or torque estimation is required. Instead, a capacitor is recommended to filter the rectified output. To safely power the motor from 120V AC, options include using an AC-to-DC adapter with appropriate voltage output or implementing capacitive AC voltage dropping with film capacitors in series before the rectifier. The capacitor value depends on the desired current; starting with around 0.05 to 1.0 µF rated for 250V or higher is suggested. Inductors can also be used for current limiting but require large values. The motor wiring resembles a hairdryer motor, implying it may be in series with other circuit elements, necessitating a detailed circuit diagram for precise advice. Safety precautions include isolating the high voltage side with capacitors and avoiding direct contact with 120V AC lines. The discussion emphasizes the importance of proper voltage reduction and filtering rather than simple resistive current limiting to prevent motor damage and circuit breaker trips.
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