Electronics

the magnitude of the voltage is to constant and the carbon brushes are worn out by friction and sparks

Use more than one winning => more windings, the higher the output voltage of the generator

The magnetic field of the stator can be produced either by a permanent magnet or by coils with an iron core => An electromagnet with coils consume current as opposed to a permanent magnet => permanent magnet has a higher output at low RPM

The permanent magnet which produces the magnetic field turns inside the stationary induction loop. Rectification is performed by a diode => The function is to allow a current flow only in one direction => Max. current through a diode is limited

both sine half-waves are guided in the same direction through the load by passing different diodes depending on the AC polarity

a) alternator has a larger AC output than a generator at the same RPM and the current is more constant

b) power/weight ratio is better by the Alternator

c) all the current generated in a gnerator has to flow through the carbon bruhses = a lot of heat is produced by the generator

d) operating life by a alternator is longer 

1. Permanent Magnet Excited Generator

2. Battery Excited Generator

3. Residual Magnetism or Remance Excited Generator

4. Exciter Generator Type Generator 

permanent magnet induces a voltage in the stator coils => depends on the RPM and on the power consumption of the connected loads

the magnetic field is built from the battery => the output voltage becomes controllable => Disadvantage: extra power must be available for building up the magnetic field

teh residual magnetism inside an iron core after a magnetic field was excited => after Shutting down a generator, the romance inside the iron core of the coil will supply a small magnetic field => this type of generator requires a voltage regulator

producing current within the exciter coil is to use another generator excited by a permanent magnet connected to the main generator shaft

a) generator RPW

b) connected loads

c) magentic field strength

=> teh increasing current and the increasing voltage over the internal resistance, the generator heats up and consumes increasingly more energy  ==> The regulator must be regulate to obtain a constant voltatge 

1.) Variable resistance type voltage regulator: If the voltage is too high, a higher current flows through the solenoid which increases teh resistance of the variable resistor

2.) Switching Type Voltage Regulator: a relay opens or close a bypass around a consant resistor depending on the voltage in the circuit 

A) first and second generation alternator: have large volatge variations at small RPM variations => a battery must be connected to teh alternator all teh times whiel alternator is running

b) thirs generation alternator: at the same RPM their output is lower than of the 1 and 2. => a constant voltage is guaranteed by the voltage:

=> Disadvantage: the batter is charged at approx. 1000 RPM and not at idle.

==> the current flow through the field windings of the alternator 

The slips rings and the carbon brushes

to keep the generator output voltage constant, a voltage regulator is needed. The voltage regulator measures the output voltage and varies the field strength of the generator, so that the output voltage stays constant

The Induction principle

by a fan located on the alternator shaft

The rotor is an electromagnet with three stator coils . The stator consists of three coils separated by 120 Grad => Every revolution of the magnet produced three full sine waves of induced voltage, shifted about 120

converts electrical energy into mechanical energy

The magnetic field lines of the conductor together with the fields lines of the permanent magnet increases the field strength on one side of the conductor and decrease it on the other side => The distorted magnetic flux causes the conductor to move to one side

If the polarity of the current in the rotor didn't change, the rotor would stop turning when a north/south pole reached ==> a commutator is used to change the direction of the current through the conductor loop at that moment

loop rotates inside the magnetic field, a voltage is induced which is directed opposite to its cause = counter induced voltage = reduces the voltage across the rotor coil => through he rotor with increasing RPM leads to decreasing motor torque

the field is connected in series ( constant current) to the rotor => The resistance of the field coil must be very low Disadvantage: decreasing torque at higher speeds

a high resistance field coil is connected in parallel with the rotor coil = constant voltage => the change of RPM with a changing mechanical load is less extreme

=> other hand: switch on the current field coil is nearly zero , since at first all current flows though the rotor coil

=> Has a lower torque than the series field motor 

two exciter => one connected in series with the rotor coil and the other in parallel ===> Series and Shunt field Motor in combination

uses the reverse effect of generators => the stator coils are separated by 120 degrees and are supplied with three phase AC voltage => a rotating magnetic field is produced inside the stator and this is used to turn the rotor

1. Synchronous AC Motor can't start by itself

2. Asynchronus AC Motor can start by itself 

a permanent magnet or an electromagnet ==> the rotor RPM must be proportional to the frequency of the AC voltage, it depends furthermore on the number of pole pairs

only with two of three phases must be changed

position of the rotor is exactly known Disadvantage: cannot start by itself and synchronous motor is unable to support high mechanical load => use only for special aircraft applications

The squirrel cage rotor consists of aluminium or cooper conductors => The strength of the induced voltage /strength of the rotor magnetic field depend on the change of the stator magnetic field over time ==> the motor produces high torque at low RPM

the rotor always lags behind the stator => the difference in speed between rotor and stator field is called slip

High starting torque and no electrical connection between the rotor and stator Disadvantage: the slip itself