E N G I NEE L E C T R I C A L S Y S T EMTM 5-3805-258-24-1S Y S T E M S O P E R A T I O NT Y P I C A L S O L E N O I D S C H E M A T I CThe solenoid switch is made of an electromagnet(one or two sets of windings) around a hollow cy-linder. There is a plunger (core) with a spring loadinside the cylinder that can move forward and back-ward. When the start switch is closed and electricityis sent through the windings, a magnetic field is madethat pulls the plunger forward in the cylinder. Thismoves the shift lever (connected to the rear of theplunger) to engage the pinion drive gear with the ringgear. The front end of the plunger then makes con-tact across the battery and motor terminals of thesolenoid, and the starter motor begins to turn theflywheel of the engine.When the start switch is opened, current no longerflows through the windings. The spring now pushesthe plunger back to the original position, and, at thesame time, moves the pinion gear away from theflywheel.When two sets of windings in the solenoid are used,they are called the hold-in winding and the pull-inwinding. Both have the same number of turns aroundthe cylinder, but the pull-in winding uses a largerdiameter wire to produce a greater magnetic field.When the start switch is closed, part of the currentflows from the battery through the hold-in winding,and the rest flows through the pull-in windings tomotor terminal, then through the motor to ground.When the solenoid is fully activated (connectionacross battery and motor terminal is complete), cur-rent is shut off through the pull-in windings. Nowonly the smaller hold-in windings are in operation forthe extended period of time it takes to start theengine. The solenoid will now take less current fromthe battery, and heat made by the solenoid will bekept at an acceptable level.Starter MotorThe starter motor is used to turn the engine fly-wheel fast enough to get the engine to start running.The starter motor has a solenoid. When the startswitch is activated, the solenoid will move the starterpinion to engage it with the ring gear on the flywheelof the engine. The starter pinion will engage with thering gear before the electric contacts in the solenoidclose the circuit between the battery and the startermotor. When the circuit between the battery and thestarter motor is complete, the pinion will turn theengine flywheel. A clutch gives protection for thestarter motor so that the engine can not turn thestarter motor too fast. When the start switch is re-leased, the starter pinion will move away from thering gear.STARTER MOTOR CROSS SECTION1. Field. 2, Solenoid. 3. Clutch. 4. Pinion. 5, Commuta-tor. 6. Brush assembly. 7. Armature.OTHER COMPONENTSCircuit BreakerThe circuit breaker is a switch that opens thebattery circuit if the current in the electrical systemgoes higher than the rating of the circuit breaker.A heat activated metal disc with a contact pointmakes complete the electric circuit through the cir-cuit breaker. If the current in the electrical systemgets too high, it causes the metal disc to get hot. Thisheat causes a distortion of the metal disc which opensthe contacts and breaks the circuit. A circuit breakerthat is open can be reset (an adjustment to make thecircuit complete again) after it becomes cool. Pushthe reset button to close the contacts and reset thecircuit breaker.CIRCUIT BREAKER SCHEMATIC1. Reset button. 2. Disc in openposition. 3. Contacts. 4.Disc.5. Battery circuit tarminals.3-19
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