Component Ratings for Adjustable AC Power Supply for 100VDC 21A Motor from 120VAC

The discussion centers on designing an adjustable AC power supply using a triac-based phase control circuit to power a 100VDC, 21A brushed DC motor from a 120VAC source, with possible adaptation to 220VAC. Key components considered include triacs (BTA41-600, BTA-800B), a potentiometer (100-500K), a DIAC (DB3), resistors (~500KΩ), and capacitors (~100nF). Emphasis is placed on selecting a triac with a current rating exceeding the motor's 21A load, ideally 25A or higher, and ensuring sensitivity to avoid overloading control circuits. The circuit type discussed is a phase angle controller commonly used for speed regulation in resistive or brushed motor loads, not suitable for induction motors or heavily inductive/capacitive loads. Full bridge rectifiers can be added after the AC control stage to supply DC to the motor, improving performance for brushed motors such as treadmill motors. Component values, especially potentiometers, resistors, and capacitors, often require empirical adjustment for proper operation at 120VAC. Inductors in series serve to limit radio frequency interference generated by rapid switching of thyristors. The discussion references a classic thyristor project book for deeper understanding. Testing with resistive loads like incandescent lamps is recommended to verify circuit functionality before connecting motors. The use of high-wattage resistors and appropriate component ratings is critical to avoid circuit failure. Capacitor values can be increased without harm but may affect circuit timing. The overall approach is a cost-effective, experimental method rather than a pure adjustable AC power supply, with limitations in waveform quality and load compatibility.
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