Electrical Load Management: Notes
Power mode master calculates battery temperature, voltage and charging rate at all times while engine is running. Body Control Module (BCM) calculates battery temperature by factoring in:
- Current intake manifold air temperature compared to last temperature recorded when ignition switch was turned to OFF position.
- Current battery voltage compared to last battery voltage recorded when ignition switch was turned to OFF position.
- Length of time since last battery temperature calculation.
Power mode master calculates discharge rate, or draw, on battery by making constant measurements and using measurements to calculate discharge rate in amp/hours. If power mode master detects a high current draw from battery, power mode master institutes steps to control load.
One of highest loads on an electrical system is resistance load of heating elements. Power mode master controls heating elements in outside rear view mirrors and rear window, as well as heated seats, by controlling relay coil controlling power to these devices.
Power mode master will either request an increase in engine idle speed from Powertrain Control Module (PCM) or power mode master will turn off loads, called load-shed function, in order to preserve vehicle electrical system operation. Each load management function, either idle boost or load-shed, is discrete. No two functions are implemented at same time. During each load management function, power mode master checks battery temperature, battery voltage and amp-hour calculations and determines if power mode master should implement a different power management function.