ARR Series Three Phase, Six Pulse SCR Charger
Corrective Maintenance
RS-420, Rev. 7
5-8
5.5.3
Checking the Current Transformer
First make sure all the leads and cables connected to the current transformer are making good contact. If the
connections are good, then disconnect the outer leads (terminals may be marked 1 and 3 on the transformer itself),
and with an ohmmeter check the resistance between terminals 1 and 3. You should get a reading of 150 ohms
±
15%. Next, check the resistance between terminals 1 and 2 and then 2 and 3; the readings here should be one half
the readings between the terminal 1 and 3. If these readings are not obtained, the current transformer is defective
and should be replaced.
Check also for shorts between the coils, and from the coils to the ground (cabinet is the ground).
5.5.4
Checking the Auxiliary Transformer
To check the auxiliary transformer, place the AC circuit breaker in the “ON” position, energizing the charger.
Use an AC voltmeter to check the voltages at the auxiliary transformer secondary. Voltage between terminals 5
and 6 and terminals 5 and 7 should be 45 volts
±
15%. If these voltages are not found, the auxiliary transformer is
defective and should be replaced.
CAUTION: Connect voltmeter probes before placing the AC breaker in the “ON” position.
5.5.5
Checking DC Filter Capacitors
Capacitor trouble can be spotted by a ruptured or broken can. Open capacitors will look normal. However, to
check capacitors, first, open the AC circuit breaker and disconnect the battery from the charger. All capacitors in
the charger will then bleed to zero voltage or discharge the capacitors with a resistor.
Second, isolate the capacitor to be tested and apply the test probes of an analog ohmmeter to the capacitor
terminals. If the capacitor is good, it will show a defection to zero resistance, then a steady increase toward
infinite resistance. If, however, the capacitor is shorted, it will show zero resistance. If the capacitor is open it
will read infinite resistance.
Replace faulty capacitors with ones which have the same rating as the original. See parts list.
Filter capacitors are connected in parallel and correct polarities must be observed. When connecting a filter
capacitor, if the red dot on the terminal end of the capacitor is to be right of center, the positive(
+
) terminal
