d. When CB4 of the 0-28VDC supply is closed and the battery charger timer
has been properly activated, closing S2, AC power is applied from the T1 secondary
to DS3 and T4. The illumination of DS3 indicates that AC power is available in
this part of the circuit. The AC power from T4 to the primary of T5 is controlled
by the setting of the battery charger control located on the front panel. When the
control is fully counterclockwise, the wiper arm of T4 has been moved down and no
power is applied to the T5 primary. When the control is rotated clockwise, the AC
power to the T5 primary is increased. The available AC power coupled to the
secondary of T4 is rectified by bridge rectifier CR2. The output of CR2 ranges
from 0-28VDC as T4 wiper is moved from the counterclockwise position. The voltage
output of the rectifier is between P20 and P73 when CB5 is closed. To provide a
charging current to the batteries, the voltage output of the rectifier must be
slightly higher than the voltage output of the batteries.
e. Meter movement M4 and associated circuitry is used to monitor the
voltage being applied to the batteries. The 50VDC range is used for 24VDC battery
charging. To make the measurement a small current is drawn from the CR2 rectifier.
This current flows from the negative side of the rectifier through connection P20
to the B- battery regulator terminal. A bus bar link (not shown on the electrical
wiring diagram) connects the B-battery regulator terminal to the G- armature
regulator terminal. The current, therefore, flows from B- to G- and along P68.
You should note that P68 and the negative side of the CR2 rectifier were placed at
case ground when relay K9 energized and closed contacts K9-1. The current flowing
in P68 flows to S13, the DCVM range selector. With S13 set to the 50V range, the
current is directed through R25 and the M4 meter movement. The voltmeter circuit
selector S14 is in the BAT position so the current from the meter will flow through
the switch and along P21. The current then flows through closed contacts K11-1 and
K7-1, along P4 to R42, through R42 to P73, CB5, and P74. This monitoring current
exists only when the output of the 0-28VDC supply is set to an output slightly
higher than the battery voltage. When the 0-28VDC supply output is set too low,
the current to deflect the meter is drawn from the battery.
f. The current in the voltage monitoring circuit is less than 1mA, while
the battery charging current is normally several amperes. This current from the
negative side of CR2 flows along P20 to R35, R33, and R31. P1 provides the
connection from R31 to the negative side of the batteries. This charge current
flows from negative to positive through the batteries reversing the normal chemical
reaction and restoring the batteries to full charge. From the positive terminal of
the battery the charge current flows along P4, through R42, along P73, through CB5,
and along P74 returning to the positive side of rectifier CR2.
g. The charge current is monitored by two ammeter circuits. The load and
starter DC ammeter (M1 and associated circuits) monitors the current to the
negative battery terminal. It is set to the 50A range during the charging process.
The field and battery charger DC ammeter (M2 and associated circuits) measures the
charge current coming from the positive battery terminal plus the small monitoring
current used by the DC voltmeter circuit. The field current range selector (S10)
is set to the 30A DC position during the charging process. It was mentioned before
that the DC voltmeter monitor current is extremely small; therefore, both ammeters
will indicate the same current flow, for all practical purposes. When a noticeable
difference in meter readings exists, there is something wrong. Usually the problem
can be traced to the battery compartment. The spillage of electrolyte or the
accumulation of dirt and grime in this area can cause undesirable paths for current
flow.
h. Organizational maintenance personnel should be able to give a general
explanation of all test stand functions. The discussion of 24VDC battery charging
is an example of the type of explanation you, as a supervisor, should expect from
these personnel. Remember, they are highly skilled
OS 010, 7-P17
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