Charging Circuit; Amp D.c. 5 Amp A.c. Alternator; Diode Replacement - Tecumseh V-twin Technician's Handbook

CHARGING CIRCUIT

The charging system works independently of any manual
controls. The engine needs to be running to produce an
electric current flow. When a conductor (alternating coils)
cuts the magnetic field generated by the magnets in the
flywheel, a current is induced in the alternator coil. The
permanent magnets in the flywheel have a magnetic field
in which the lines of magnetic force run from the North
Pole to the South Pole. As the flywheel rotates and the
position of the magnets change, the direction of the
magnetic field changes or alternates. The alternating coils
are wound in different directions to allow current to flow
as an A.C. waveform. (Illust. 5-5)
ROTATION OF FLYWHEEL
CHARGING CIRCUIT
The charging systems used on the TVT engine is best
identified by obtaining the engine model and specification
number from the engine. Consult a Tecumseh dealer or
a parts manual to correctly identify the charging system.
Many of the tests require running the engine and
measuring alternator output with a voltmeter. When
making voltage tests with the engine running, it is not
necessary to take readings at all of the listed R.P.M.'s.
Checking at one of the speeds is sufficient.
In some cases an open circuit D.C. check cannot be
made. A SCR (Silicon Controlled Rectifier) is located in
the circuit which requires a minimum "turn on" voltage
to allow it to conduct. Without the battery in the circuit
this "turn on" voltage is not present. The SCR "senses"
this and there will be no D.C. output from the regulator/
rectifier.
Each charging system has its own testing procedure.
Test the charging system using the applicable procedure
found on the following pages.

3 AMP D.C. 5 AMP A.C. ALTERNATOR

This unit combines a 3 Amp D.C. system used to charge
a battery with a 5 Amp A.C. system used for lighting.
Located in the red wire of the harness is a diode, which
converts the alternating current to direct current for
charging the battery. The yellow wire provides the A.C.
voltage for the lighting circuit.
5-4
A wire harness (part 36588) may be added to the 3 Amp
D.C. / 5 Amp A.C. charging system to power an electric
clutch without the use of a battery. Test the charging
system using the applicable "Checking the System"
procedure listed in this section. Test the diode in the
harness by using a continuity test. (Illust. 5-6) Continuity
should exist in one direction only. Replace the diode if
continuity exists after reversing tester leads or no
continuity is found.
IF BULB DOES NOT LIGHT OR LIGHTS WHEN
POLARITY IS REVERSED, DISCARD DIODE.
5-5

DIODE REPLACEMENT

To replace the diode, disconnect at the plug (spade
terminal) and cut the wire on the opposite end of the
diode at the solderless (crimped) connector. Remove
1/4" (6.35 mm) of insulation from the cut end of the wire
and twist the strands together. Place the solderless
connector from the new diode onto the exposed 1/4" (6.35
mm) wire and crimp the connector with a standard
electricians pliers. Reconnect the plug end or spade
connector.
NOTE: DO NOT USE ACID CORE SOLDER. BE
CAREFUL NOT TO APPLY HEAT DIRECTLY TO THE
DIODE. USE HEAT SHRINK.
New heat shrink tubing can be installed by slipping over
the wires and heating with a heat gun. If this is not
available, tape the diode and connections with electrical
tape.
5-6