Why J1939 Common-Mode Noise Follows Alternator Ripple Frequency, Not Engine Load
A few winters ago, a test-cell engineer at a powertrain integrator sent me a capture he could not explain. His J1939 bus was dropping frames on a stationary engine run-in stand—not under load, not during acceleration, but at a specific RPM band that appeared whenever the engine was dragged by the dyno in motoring mode. […]