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Original fan voltage: 12V Original fan current: 1.8A V=IR (Ohm's Law), so 12 = 1.8R => R = 12 / 1.8 = 6.667 Fan resistance: 6.667 Ohms Target voltage: 8V V=IR (Ohm's Law), so 8 = 6.667I => I = 8 / 6.667 = 1.2 Target current: 1.2A Voltage drop across resistor: 12V - 8V = 4V V=IR (Ohm's Law), so 4 = 1.2R => R = 4 / 1.2 = 3.333 Target resistance: 3.333 Ohms Power dissipated by resistor: 4V * 1.2A = 4.8W |