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42 Cards in this Set
- Front
- Back
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How do you make an electromagnet? |
Apply current thru a coil of wire |
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How do you increase the field of strength in an electromagnet? |
Apply more current Add more coils Wrap around an iron core |
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What is the principle of induction? |
Moving a conductor thru a magnetic field or a magnetic field past a conductor to induce voltage in the conductor |
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What 4 factors affect induction? |
Speed at which the conductor or field is moved Number of conductors Strength of the magnetic field Angle of intersection |
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What 2 types if magnets are used in electric motors? |
Permanent magnets Electromagnets or field coil magnets |
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What is the commutator? |
2 halves of a split copper ring attached to the windings. Allows current to charge the windings as the motor rotates. |
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What are the brushes in a starter made of and why? |
Copper as a conductor and carbon for lubrication |
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What is CEMF? |
Counter electromagnetic force is the voltage induced in the windings which opposes battery voltage |
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What are the causes and products of CEMF? |
The higher the speed of the armature the more CEMF is produced. As CEMF increases torque and current decreases |
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How are field coil magnets and brushes connected? |
Magnets are in series with the brushes, brushes are in parallel with each other. |
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What limits the maximum speed of a starter motor? |
CEMF and load |
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What is the target crank speed on an engine? |
between 100 and 200 RPM |
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What is the minimum battery voltage required to power a starter? |
9.6 V |
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How many brushes are on a typical starter motor and how do they differ? |
4 brushes in total 2 insulate (+) and 2 Grounded (-) |
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When does a starter motor achieve maximum torque? |
When the armature just starts to turn |
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How do you reverse the direction of a permanent magnet motor? |
Reverse direction of current in the brushes |
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Why is it more difficult to reverse the direction of a field coil motor? |
Reversing the direction of current in the brushes will also reverse the direction of current in the field coil magnets causing the motor to turn in the same direction. Extra switches and wiring are needed to reverse the current flow in the armature OR the field coil magnets. |
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What are 3 types of safety interlocks that can prevent the starter motor from engaging? |
Park/ Neutral position switch Clutch start switch Theft prevention |
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What is the typical gear reduction between a starter drive pinion and the ring gear? |
20:1 |
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What are 4 factors that can disable the starter on modern vehicles? |
Engine already running Automatic transmission in gear Clutch pedal not depressed Theft alarm activated |
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Why are permanent magnet motors better than field coil motors? |
Lighter weight Smaller size Reduced current requirements |
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What is the starter motor housing made of and why? |
The housing is made of steel to concentrate the magnetic field of the magnets |
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What are the drive housing and end cover made of and why? |
Aluminum because it is light weight |
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How is the armature supported in the motor? |
needle bearings or bushings in the end cover and drive end housing |
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What are electromagnets made of? |
Heavy copper ribbon wire wound around pole shoes |
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What does the plunger on a starter solenoid operate? |
Moves the shift fork to engage the drive mechanism with the ring gear and pushes the contact disc to complete the circuit from batter + to the starter motor |
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How many terminals are on a starter motor and what are their functions? |
Battery terminal supplies operating current for the motor Motor terminal connects to the motor and receives supply voltage when solenoid is energized Solenoid terminal energizes solenoid coils when current is supplied |
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What is the pull in winding of a starter solenoid? |
Heavy gauge high current winding generates a strong magnetic field to engage the drive. Connected between S terminal and M terminal it grounds thru the armature so when the solenoid contact closes both ends of the winding are connected to + thus de-energizing the winding. |
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What is the hold in winding of a starter solenoid? |
Finer gauge and lower current than the pull in winding the hold in winding grounds directly to the case of the starter or solenoid. The hold in winding assists the pull in winding in engaging the drive and then holds the drive engaged when the pull in winding is de-energized. |
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How do the solenoid windings work together during engagement? |
Both coils work together in parallel to create a strong magnetic field to move the plunger |
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How do the solenoid winding work together during cranking? |
The Pull in winding is de-energized, the hold in winding works alone to keep the plunger engaged |
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How do the windings work together during disengagement? |
Both windings oppose each other in series cancelling the magnetic field and allowing the plunger spring to disengage the starter |
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What is the purpose of the mesh spring on the drive end of the starter motor? |
Allows the shift fork to move to its full travel position event if drive teeth jam against the ring gear. In this situation the mesh spring compressing sliding the shift collar along the drive. As soon as the motor rotates the mesh spring forces the drive the rest of the way into mesh with the ring gear |
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What is the purpose of the overrunning clutch? |
Allows the starter to drive the ring gear but prevents the starter to be driven by the ring gear at excessively high speeds |
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How is torque increased at the drive pinion? |
Gear reduction |
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What are the first 3 things you should check when diagnosing starter motor faults? |
Battery voltage Clean and tight battery terminals Clean and tight battery connection at the starter |
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What is the purpose of a starter motor draw test? |
Measure the actual current flow required to crank over the engine. |
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What are the general specifications for maximum current draw limits when testing the starter motor on a gasoline engine? |
4 cylinder: 175 amps 6 cylinder: 225 amps 8 cylinder: 250 amps Always follow manufacturer specifications when available |
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What is the general rule for voltage drop on a starter motor circuit when manufacturer specifications are not available? |
no more than .2 V drop per 100 amps current draw total on the positive and ground side of the starter motor |
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How can you test the condition of the contact disc in a starter solenoid? |
Voltage drop across terminals B and M must not exceed .2 V |
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What are the 2 main causes of solenoid chatter? |
Low battery voltage or open in the hold in winding |
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What is the maximum operating time and minimum cool down time for a starter motor? |
30 seconds operating time, 2 minutes cool down time |
