BSA D14/4 BANTAM SUPREME D14/4 BANTAM SPORTS, Workshop Manual

Page: 91 / 120

D14/4 ELECTRICAL SYSTEM G5
FIG. G2. Generator testing.
A low reading on one group of coils would indicate
coil failure and low readings on both groups of coils
will, in all probability, be due to a low flux density in
the magnetic rotor. No readings from both groups of
coils indicates an open circuit in the green supply lead.
Winding resistance between:—
Yellow/green 0·25 ohms
Orange/green 0·4 ohms
NOTE:—It is essential that bulbs of the correct
wattage be used throughout the system, as any
deviation will seriously upset the charge rates. See
page GD6 for correct specification of each bulb.
If the meter readings are unsatisfactory, proceed as
follows.
(3) Check the alternator output by disconnecting the
yellow, orange and light green leads from the
five-way connection, into which the alternator
harness is plugged. It will be seen from the
appropriate wiring diagram, on page G14 and
from Fig. G2, that the light green lead from the
alternator is common to all coils, whilst the
yellow connects two coils only and the orange
the remaining four. Connect one side of the
Wilkson test meter (A.C. volts with 1 ohm load)
or the A.C. voltmeter with 1 ohm load paralleled
across it, to the green lead and the other side of
the meter to the yellow and orange leads in turn.
Check with the table below:—
Check
between
Revolutions
per minute
Volts
output
Yellow/
green
Orange/
green
2,000—3,000
2,000—3,000
4—4·75
7·5—8·5
NOTE:—During these series of tests, the importance
of correct battery connections cannot be over-
emphasised. The translucent lead should always be
connected to the battery positive terminal, and the
brown lead to the negative terminal. Reversal of these
connections will invariably burn out the rectifier and,
if the engine is run under these conditions, the
generator rotor will become demagnetised.
(4) A further cause of low or no charge may be due
to the alternator short-circuiting to earth. To
check this, it is necessary to construct a simple
continuity check circuit,
viz., a six-volt battery
introduced in series with the D.C. voltmeter will
amply suffice. Connect one end of the circuit to
the green lead and the other end to the machine
frame earth. If a reading is obtained on the
voltmeter then the alternator is short-circuit to
earth. It is desirable to carry out this check with
both the generator stator rotor in position on the
machine, the reason being that in isolated cases,
careless handling of the stator may have caused
one or more of the soldered coil link connections
to have become displaced, thus making contact
with the circumference of the rotor and short-
circuiting all coils. Before condemning the
alternator, therefore, it is wise to check that all
connections are well clear of the rotor, gently
easing back any which look a possible cause of
future trouble.