Alternator Charging Load Balance
Whether the alternator keeps up with the electrical load at idle and cruise: it makes only ~50% of its rated output at idle and ~90% at cruise, so balance = output - total continuous load. A 65 A load on a 120 A alternator runs a 5 A deficit at idle (battery drains at stoplights) but a healthy +43 A at cruise; a 160 A alternator turns the idle balance to +15 A. A screening aid; the alternator's actual output curve and the real duty cycle govern.
Formula and source
idle_out = alternator x idle_frac; cruise_out = alternator x cruise_frac; balance = output - total_load; idle_frac ~0.5, cruise_frac ~0.9.
Automotive/marine alternator charging-balance practice (alternator output-vs-RPM curves) by name; first-principles load balance.
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