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Transcript of Starter Motors
Windings are energised drawing the solenoid plunger in
This makes the pinion lever move the pinion into contact with the flywheel ring gear
The plunger then closes the contacts which allows current to flow to the motor
Current flows through the brushes into the commutator and sets up a magnetic field in the armature
This interacts with the permanent magnets causing rotation
As the armature turns a new segment comes into contact with the brushes allowing correct alignment of the two magnetic fields for maximum torque
To prevent over speeding of the armature when the engine fires up a one way clutch (roller type) is used. This allows torque to be transmitted from the armature to the ring gear but not the other way around
Check between this terminal and earth when cranking for battery voltage
Check between these two terminals when cranking for 0.2V max
Check between this terminal and the battery positive (multimeter + on the battery) when cranking for 0.3V max
Check betweenthe starter body and the battery negative (multimeter - on the battery) when cranking for 0.3V max
May also have reduction gearing for extra torque
But don't forget to check the battery!!
And if it's Auto - make sure it's not in gear!
One of the characteristics of an electric motor is that it draws maximum current at zero rpm and so generates maximum torque at zero rpm
This and the gear ratio (about 12-14:1) allows the starter to turn the engine easily
Copy this diagram of the solenoid & starter wiring
The gearing may use step-down gears...
...Or planetary gearing
Whilst series and series-parallel starter motors have been used (pure electro-magnetic devices), these days they are much more lightly to be of the permanent magnet type.
This is where the field (outer) magnets are actual magnets
This makes the starter motor lighter ( about 15%) and more compact