Dynamo Configuration

Dynamo Configuration

Two brush dynamos can be wired in several different configurations but as far as automotive applications are concerned, the vast majority of them are wired in one of two different ways referred to as 'shunt' and 'series' configurations. Some manufacturers such as Lucas preferred 'shunt' and others, notably Bosch, chose to use 'series' so both configurations are common place.  

In the pictures below, only the parts involved in wiring up the required configuration are shown. Along the bottom of each picture are the  field coils. In this case there are four field coils wired in series so that the end of one coil is connected to the start of the next. This means that , however many field coils there are, there will be two field coil connections - shown as two brown wires. Above the field coils are the two brushes which would bear on the commutator on the rotating armature (not shown).  Each brush has its own tag wire. So we have two field coil connections and two brush connections.
SHUNT CONFIGURATION
Here, one end of the field coil exits the dynamo as the 'F' terminal - brown wire on the left. The other end of the field coil and one brush are both connected to the metal body of the dynamo - shown by the nut and bolt - and for this reason is sometimes referred to as the  'internally grounded field' configuration. This is the 'earth'  or 'E' connection. The remaining brush exits the dynamo as the 'D' terminal - yellow wire. (Lucas terminology - other manufacturers use other descriptions). This is the 'shunt' configuration also sometimes known as 'parallel' configuration as both the armature and field coils each have one end connected to earth.
SERIES CONFIGURATION
Here, one end of the field coil exits the dynamo as the 'F' terminal as before. The other end of the field coil is connected to one brush and this field/brush connection exits the dynamo via the yellow wire as the 'D' terminal. The second brush is connected to earth. This is the 'series' configuration, sometimes referred to as the 'externally grounded field' configuration.

This all looks straightforward but be careful! A few points to finish off with:
  • Yes, a field coil only has two ends, but getting them the wrong way round will stop the dynamo working correctly.
  • Similarly, a row of individual field coils such as is shown in the pictures above will need to be wound in the correct direction so that each pole has the correct polarity and although they usually alternate N S N S as you go round the dynamo body, some do have N N S S...... 
  • And on some two field coil dynamos, the coils are not wired in series at all......
  • The brushes must not be swapped either!
  • It is important to remember that many dynamos have been worked on over the years and may well have been changed to a configuration different to the one it had when it left the factory. This is especially true if the charging system has been fitted with an electronic regulator as these devices will have been designed for use with one particular configuration rather than the other. So, just because it's a Lucas dynamo, don't assume it's wired in the 'shunt' configuration!
  • 'Motoring' is one way of checking a dynamo - not a conclusive test on it's own but a good starting point. Be aware that how the motor test is carried out is different for the two configurations.  See the dynamo motor test page for details.
Sometimes answering one question creates a lot more......
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