Skip to content

1.8.2 START Battery Load Analysis

Scenario-based load analysis for START battery circuits (alternator-supplied).

START Battery Circuit Summary

All circuits powered by START battery (alternator charging):

Source Circuit Typical Peak Duty Cycle Notes
PMU Outputs
OUT1+10 iBooster 0.25A 40A Seconds during braking Non-adjacent combined
OUT2+3+4 Radiator Fan 20A 53A Variable PWM 3× combined outputs
OUT5 HVAC Blower 10A 20A Continuous when on Speed-dependent
OUT6 GMRS Radio 1A 15A Brief TX bursts Standby vs transmit
OUT7 Oil Cooler Fan 0A 15A Temp-triggered Off unless hot
OUT8 PS Cooler Fan 0A 15A Temp-triggered Off unless hot
OUT9 Dakota Digital 25A 25A Continuous Gauges always on
OUT11 Wiper Controller 0A 15A Intermittent Rain only
OUT13 CT4 Controller 10A 10A Continuous Street lighting
OUT15 Winch Trigger 0A 1A Recovery only Control signal only
OUT17 A/C Clutch 0A 5A Summer only Seasonal
OUT18 Horn 0A 5.4A Seconds Emergency only
OUT19 iBooster Ignition 5A 5A Continuous Ignition signal
OUT20 STX Intercom 1A 5A Brief TX bursts Standby vs transmit
OUT21 Brake Lights 0A 3A Seconds during braking Traffic-dependent
OUT22 Reverse Lights 0A 3A Seconds in reverse Parking only
OUT23 DRL 2.6A 2.6A Daytime only Auto-off at night
BCDC Charger
- BCDC to AUX 30A 50A Continuous Charges AUX battery
Direct Loads
- Starter 0A 400-600A 3-5 seconds Cranking only
- ECM ~2A ~5A Continuous Engine management
- Grid Heater 0A 250A 3-5 seconds Cold start only

Scenario Analysis

Scenario 1: Daily Highway Driving

Conditions: Highway cruising, moderate temps (70°F), radio on standby, climate control on

Circuit Load Reason
iBooster (OUT1+10) 0.25A Idle - no braking
Radiator Fan (OUT2+3+4) 16A Low speed - highway airflow
HVAC Blower (OUT5) 10A Medium speed
GMRS Radio (OUT6) 1A Standby
Oil Cooler Fan (OUT7) 0A Temp normal
PS Cooler Fan (OUT8) 0A Temp normal
Dakota Digital (OUT9) 25A Always on
Wiper (OUT11) 0A Dry weather
CT4 (OUT13) 10A Running lights
iBooster Ignition (OUT19) 5A Always on
STX Intercom (OUT20) 1A Standby
DRL (OUT23) 2.6A Daytime
BCDC Charger 30A Maintaining AUX
TOTAL 101A

Alternator Load: 101A of 270A capacity = 37% utilization Excellent

Scenario 2: Hot Day City Driving (Stop-and-Go)

Conditions: City traffic, hot day (95°F), A/C on, frequent braking

Circuit Load Reason
iBooster (OUT1+10) 5A Average - frequent braking
Radiator Fan (OUT2+3+4) 42A High speed - no airflow, hot
HVAC Blower (OUT5) 20A Max speed for A/C
GMRS Radio (OUT6) 1A Standby
Oil Cooler Fan (OUT7) 15A Hot - active
PS Cooler Fan (OUT8) 15A Hot - active
Dakota Digital (OUT9) 25A Always on
Wiper (OUT11) 0A Dry weather
CT4 (OUT13) 10A Running lights
A/C Clutch (OUT17) 5A A/C on
iBooster Ignition (OUT19) 5A Always on
STX Intercom (OUT20) 1A Standby
Brake Lights (OUT21) 1A Average - traffic
DRL (OUT23) 2.6A Daytime
BCDC Charger 40A Higher rate
TOTAL 188A

Alternator Load: 188A of 270A capacity = 70% utilization Good

Scenario 3: Offroad Trail (Slow Speed, Hot Engine)

Conditions: Technical trail, slow speed (<10 mph), engine working hard, radio use

Circuit Load Reason
iBooster (OUT1+10) 2A Occasional braking
Radiator Fan (OUT2+3+4) 53A Max speed - no airflow
HVAC Blower (OUT5) 15A Moderate
GMRS Radio (OUT6) 5A Occasional TX
Oil Cooler Fan (OUT7) 15A Hot - active
PS Cooler Fan (OUT8) 15A Hot - active
Dakota Digital (OUT9) 25A Always on
Wiper (OUT11) 0A Dry
CT4 (OUT13) 10A Running lights
iBooster Ignition (OUT19) 5A Always on
STX Intercom (OUT20) 3A Occasional TX
DRL (OUT23) 2.6A Daytime
BCDC Charger 50A Full rate - supporting SwitchPros
TOTAL 201A

Alternator Load: 201A of 270A capacity = 74% utilization Good

Note: Offroad lighting (SwitchPros) draws from AUX battery, not alternator.

Scenario 4: Emergency Braking in Rain

Conditions: Highway, sudden hard braking, wipers on, headlights on

Circuit Load Reason
iBooster (OUT1+10) 40A Peak braking assist
Radiator Fan (OUT2+3+4) 20A Normal - highway airflow
HVAC Blower (OUT5) 15A Defrost
GMRS Radio (OUT6) 1A Standby
Oil Cooler Fan (OUT7) 0A Temp normal
PS Cooler Fan (OUT8) 0A Temp normal
Dakota Digital (OUT9) 25A Always on
Wiper (OUT11) 15A High speed
CT4 (OUT13) 10A Headlights
iBooster Ignition (OUT19) 5A Always on
STX Intercom (OUT20) 1A Standby
Brake Lights (OUT21) 3A Braking
DRL (OUT23) 0A Off - headlights on
BCDC Charger 30A Normal rate
TOTAL 165A

Duration: iBooster peak lasts 2-5 seconds only

Alternator Load: 165A of 270A capacity = 61% utilization Excellent

Scenario 5: Parked with Engine Idling (Engine Warm)

Conditions: Stationary, engine idling, waiting, moderate accessories

Circuit Load Reason
iBooster (OUT1+10) 0.25A Idle
Radiator Fan (OUT2+3+4) 35A Moderate - no airflow
HVAC Blower (OUT5) 10A Comfortable
GMRS Radio (OUT6) 1A Standby
Oil Cooler Fan (OUT7) 0A Temp stable
PS Cooler Fan (OUT8) 0A Temp stable
Dakota Digital (OUT9) 25A Always on
Wiper (OUT11) 0A Off
CT4 (OUT13) 10A Parking lights
A/C Clutch (OUT17) 5A If summer
iBooster Ignition (OUT19) 5A Always on
STX Intercom (OUT20) 1A Standby
DRL (OUT23) 0A Off - parked
BCDC Charger 30A Normal rate
TOTAL 122A

Alternator Load: 122A of 270A capacity = 45% utilization Excellent

Summary

Scenario Total Load Alternator Utilization Status
Highway Driving 101A 270A 37% Excellent
Hot City Driving 188A 270A 70% Good
Offroad Trail 201A 270A 74% Good
Emergency Braking 165A 270A 61% Excellent
Parked Idling 122A 270A 45% Excellent

Worst Realistic Case: 201A (offroad with hot engine) = 69A margin

Key Insight: All realistic scenarios stay well within alternator capacity. The 270A alternator provides adequate margin for all operating conditions.

Load Exclusions (Not Alternator Loads)

The following high-current loads are NOT supplied by the alternator:

Load Current Source Why Not Alternator
SwitchPros (all outputs) 127A max AUX battery BCDC-fed, isolated
ARB Compressor 90A AUX battery Via SafetyHub on AUX
Winch 400A peak AUX battery Direct connection
BODY PDU circuits 56A max AUX battery CONSTANT bus fed
Starter 400-600A START battery Cranking only, engine off
Grid Heater 250A START battery 3-5 sec cold start only

Architecture: The dual battery system isolates high-current accessory loads (AUX battery) from engine/safety loads (START battery). The BCDC charger (50A max) is the only connection between batteries during normal operation.