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2.9 Grid Heater System

Type: Cold-start air intake heater

Model: Grid Heater Relay

Part Number: Cummins 5467024

Manufacturer: Cummins

Mounting: Engine bay near intake manifold

Power Source: START battery+ direct (via fusible link, 40-80A)

Control: Direct ECM control (pins 46/21)

System Architecture

  1. ECM Control (Direct):
  2. ECM triggers grid heater relay directly via pins 46/21 (~0.5-1A)
  3. ECM manages timing, temperature thresholds, and duty cycle

  4. No PMU involvement - ECM knows engine temperature better than external controller

  5. Grid Heater Relay (Cummins 5467024):

  6. Coil Power: ECM pins 46/21 (~1A) - direct connection
  7. Main Power: Direct from START battery+ via fusible link (bypasses all bus bars and PMU)
  8. Main Ground: START battery- or NEGATIVE bus
  9. Output: 80A to grid heater element (design value - verify via resistance measurement during installation)

  10. Protection: Integrated fusible link

  11. Grid Heater Element:

  12. Location: Intake manifold
  13. Power: 80A from relay (design value)
  14. Duty Cycle: 3-5 seconds during cold start (ECM controlled)

Wiring Summary

Two-Stage Design: ECM pins 46/21 (1A) → relay coil → relay switches high current (40-80A) directly from battery to element.

flowchart LR
    ECM["Cummins ECM<br/>Pins 46/21"]
    RELAY["Grid Heater Relay<br/>Cummins 5467024"]
    BATT["START battery+<br/>(Direct Connection)"]
    GND["START battery-"]
    ELEMENT["Grid Heater Element<br/>40-80A"]

    ECM -->|"~1A coil control"| RELAY
    BATT -->|"Fusible Link<br/>40-80A"| RELAY
    RELAY -->|"40-80A switched"| ELEMENT
    ELEMENT --> GND

    style ECM fill:#d1d5db,color:#000
    style RELAY fill:#d1d5db,color:#000
    style BATT fill:#ffd93d,color:#000
    style GND fill:#ffd93d,color:#000
    style ELEMENT fill:#d1d5db,color:#000

Why Direct ECM Control

  • ECM has accurate engine temperature data
  • ECM knows optimal grid heater timing for cold starts
  • Eliminates unnecessary complexity of PMU passthrough
  • Frees PMU output slots for other critical systems

Power Distribution

Bypasses all distribution systems:

  • Does NOT use CONSTANT bus bar
  • Does NOT use PMU outputs
  • Direct battery connection with fusible link protection

Reason: High current draw (40-80A) for very short duration (3-5 seconds). Direct connection minimizes voltage drop and connection complexity.

Outstanding Items

None - design complete. See installation checklist for build tasks.