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1.2 START battery Distribution (Driver Rear Wheel Well)

Odyssey PC1500 Battery Terminals

Overview

The START battery (driver rear wheel well) provides power for critical engine and safety systems:

  1. Direct high-current → Starter (no CB), alternator charging input (no CB)
  2. Circuit breaker protected → PMU (250A CB), BCDC (80A CB)
  3. START+ Forward Distribution Bus (150A master CB → single feed → engine-bay busbar) → radiator fan (60A), iBooster main (50A), TCU (25A) — relocated off the PMU
  4. Direct low-current → ECM, grid heater (fusible link protection)

See Circuit Breakers for complete CB specifications. All CBs mounted in rear wheel well within 7" of battery (code compliant).

Single Source of Truth

This page is the authoritative source for all START battery wire specs (gauge, distance, voltage drop). Component pages reference here. For battery specs see Section 1.1. For ground bus bars see Section 1.5.

START battery Positive Terminal (7 connections)

Circuit Destination Wire Gauge Distance Current Voltage Drop Protection
Alternator Engine bay 2/0 AWG 8 ft 270A 2.81% @ 60°C None
Starter Engine bay 2/0 AWG 6 ft 400-600A 1.9-3.9% @ 20°C None
PMU24 Engine bay 2/0 AWG ~7 ft 250A max 2.4% @ 60°C 250A CB
START+ Forward Dist Bus Engine bay 2 AWG ~8 ft ~108A peak 1.3% @ 60°C 150A master CB
ECM Engine bay Per Cummins Short <5A Negligible Fusible link
Grid Heater Engine bay Per Cummins Short ~80A Negligible Fusible link
BCDC Alpha 50 Passenger rear wheel well 4 AWG ~6 ft 50A 0.94% @ 20°C 80A CB

All circuit breakers mounted within 7" of battery (ABYC/NEC compliant). See Circuit Breakers.

START+ Forward Distribution Bus

The radiator fan, iBooster, and TCU were relocated off the PMU onto START-direct power. All three sit forward (engine bay / transmission) while the START battery is in the rear wheel well, so — mirroring the AUX forward-feed architecture — a single master-protected feed runs forward to an engine-bay busbar that fans out to the three loads on short local feeds. This keeps the long rear-to-front run to one heavy cable instead of three, and places each load's breaker near its load.

Busbar: Blue Sea 2105 MaxiBus (250A), engine bay, insulated cover — recommended; confirm with ⚠️ TBD #135 Master feed: 2 AWG, ~8 ft, 150A CB at battery post (<7")

Load Feed (from bus) Wire Gauge Distance Current Voltage Drop Breaker
Radiator Fan Radiator shroud 4 AWG short 53A continuous <1% @ 60°C1 60A
iBooster main Firewall 8 AWG short 40A peak / 0.25A idle <0.5%1 50A
Turbolamik TCU Transmission 12 AWG short 15A continuous <0.5%1 25A

The master feed carries the combined load (~68A continuous, ~108A brief peak); voltage drop and breaker sizing are set on that single cable.1 The iBooster's separate ignition enable (~5A) is sourced from the Ignition Signal bus, not this bus. Fan speed is set by a dedicated fan controller (⚠️ TBD #134) with its own coolant sensor, independent of the PMU and J1939.

Shared forward feed — intentional tradeoff

The three loads share one master feed + busbar (a passive cable, breaker, and bus bar — no active electronics), versus three independent runs from the battery. This is the same tradeoff the AUX side accepts, and is far more robust than their former shared dependency on the PMU module. Each load keeps its own breaker. See Standards Exceptions.

START battery Negative Terminal (6 connections)

Circuit Destination Wire Gauge Distance Current Voltage Drop
Engine Bay Ground Bus Engine bay 2/0 AWG ~8 ft 600A+ peak <0.1V @ 60°C
ECM Engine bay 12 AWG Short <5A Negligible
Grid Heater Engine bay Per Cummins Short ~80A Negligible
AUX Battery Passenger rear wheel well 1/0 AWG 5-6 ft 75A max <0.05V @ 20°C
G1 GMRS Radio Dashboard 10 AWG ~8 ft 15A TX 1.2% @ 20°C
STX Intercom Dashboard 10 AWG ~8 ft 5A 0.4% @ 20°C

Radio grounds direct to battery for RF noise isolation. ECM/grid heater via Cummins harness to isolate from starter spikes.

START− intentionally has no local chassis bond — its chassis reference is the 2/0 AWG run to the Engine Bay Ground Bus (the rear frame chassis bond lives on the AUX− side). The 6 connections above are the complete, final set; an earlier "7 connections" count was an error.

  1. Master feed 2 AWG @ ~108A brief peak (~68A continuous), ~8 ft, 60°C-derated (×1.2) ≈ 1.3% — sized on the combined load. Load feeds are short from the engine-bay bus, so per-load drop is negligible: fan 4 AWG @ 53A, iBooster 8 AWG @ 40A brief, TCU 12 AWG @ 15A. Final master-feed length and breaker selective-coordination pending ⚠️ TBD #136 and ⚠️ TBD #135. ↩↩↩↩