9
Brush Holder / Bridge Rectifier Assembly
The brush holder is mounted to the rear bearing carrier. The
positive (+) brush contacts the slip ring nearest the rotor
bearing.
The bridge rectifier is made up of four diodes and a varistor,
shown schematically in Figure 2. The diode (rectifier) permits
current flow in one direction only. Stator excitation winding
(AC) output leads connect to the two terminals labeled J1 and
J2 (
C
, Figure 1) located on top of the bridge rectifier. Direct
current (DC) is taken from the bridge rectifier and applied
to the rotor via the brush and slip rings. The varistor is a
“variable resistor” which protects the diodes against high
voltage surges.
This generator is equipped with a bridge rectifier (
A
, Figure 1)
attached to the brush holder assembly (
B
).
How it Works
Figure 3 is an operating diagram of a revolving field
alternator with a bridge rectifier.
Figure 3
Figure 1
B
C
A
Figure 2
A
- Rotor
B
- Magnetic Lines of Flux
C
- Excitation Winding
B
B
C
E
F
G
NOTICE:
The brushes are made of a carbon material and
can easily break. Use care when removing and installing the
brushes.
D
- Bridge Rectifier
E
- Power Winding
F
- Receptacle
G
- Slip Ring
The brush rectifi er acts to supply direct current (DC) fl ow to
the rotor winding. The increase in current fl ow through the
rotor results in a proportional increase in the rotor’s magnetic
fi eld strength, which induces alternating currect (AC) in the
windings of the stator.
1. The rotor (
A
) may be considered a permanent magnet
since some residual magnetism is always present in the
steel laminations.
2. The rotor (
A
) is rotated at a pre-determined speed.
3. Residual or “stored” magnetism in the rotor winding
creates magnetic lines of flux (
B
) which cut through
stator excitation winding (
C
) and power winding (
E
), to
induce Electro Motive Force (EMF) into both windings.
4. Winding
(
C
) is the excitation winding. The EMF induced
into this winding produces an alternating currect (AC)
flow, which is applied to a bridge rectifier (
D
).
5. The bridge rectifier changes alternating current (AC)
into direct current (DC).
6. Direct current (DC) from the bridge rectifier is applied
to the rotor windings (
A
) via the slip rings (
G
) and
brush assembly, to create a magnetic field that is
stronger than that created by the residual magnetism of
the rotor.
7. This stronger magnetic field induces a greater EMF
(and resulting current flow) into both stator windings
(
C
and
E
).
8. The cycle then repeats itself until a predetermined
(AC) output is reached. Any load(s) connected to the
receptacle (
F
) completes circuit.
D
A
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