BOOM GP 1191215 - Caterpillar

Illustration 1 g01019048
Typical example
(1) Terminal box
(2) Wiring harness
(3) Magnetic switch
(4) Starting motor solenoid
(5) Starting motor When the Electronic Control Module (ECM) in terminal box (1) receives an input for start-up, the ECM supplies +Battery voltage to two magnetic switches (3). The magnetic switches are located in a junction box on the side of the engine. The +Battery voltage is provided via wiring harness (2).The two magnetic switches are connected in a secondary electrical circuit to two starting motor solenoids (4). The +Battery voltage closes the contacts of the magnetic switches in order to complete the secondary electrical circuit. This energizes the starting motor solenoids.Note: The contacts of the two magnetic switches are protected by a circuit breaker in the junction box.The energizing of the starting motor solenoids causes the starting motors' pinions to engage with the flywheel ring gear.The starting motor solenoids are also connected in another electrical circuit between the starting motors and a source of +24 VDC for cranking the starting motors. After the starting motor's pinions are engaged with the flywheel ring gear, the starting motor solenoids' contacts complete the other electrical circuit for cranking of the starting motors.The starting motors crank the engine until the ECM detects the crank terminate speed. Then, the ECM removes the +Battery voltage from the magnetic switches. The contacts of the magnetic switches open and the +Battery voltage is removed from the starting motor solenoids. The starting motor solenoids' contacts open and the +24 VDC for cranking is removed from the starting motors. The starting motors' pinions are disengaged from the flywheel ring gear.Illustration 2 is a schematic of the electrical starting circuit.
Illustration 2 g00998859
Schematic of the electrical starting circuit