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7. MAINTENANCE
This charger requires a minimum of maintenance. There are no rotating parts and most components have an indefinite
life with no expected aging effect. Large electrolytic capacitors (C1, C2) have a 20-year expected service life. They should be
replaced when the output ripple voltage exceeds 500 mVrms, measured with a resistive load. If necessary, dry air may be used to
blow dust out of the interior. In the event of any irregular operation, examine, and tighten if necessary, all internal and external
connections. The unit is designed to be mobile. However, do not drop or slam the equipment down. If the charger is dropped,
inspect interior for damage or loose components.
8. INTERNAL PROTECTION
When operating normally, the OUTPUT CURRENT LIMIT ADJUST control (R12) will limit the maximum output
current to approximately 110 percent of the rated charge current. In case of a high dc current demand, the current limit control
will keep the charger output within safe values without tripping the dc circuit breaker (CB2) or the ac breaker (CB1). The
connection of the 120V input needs to have the current limit control reduced to 50%. The input circuit breaker (CB1) is designed
to protect the equipment at the 208/240 Vac connection. The input current for 120Vac is two (2) times the rating of the ac input
circuit breaker (CB1). In the 480 Vac input connection, the UMC is protected by ac fuses (F3/F4) in addition to the ac circuit
breaker (CB1). The dc circuit breaker (CB2) will trip if over current occurs or battery is connected in reverse polarity. Metal-
Oxide Varistors (SS1/SS2) are used on the ac input and dc output for surge protection.
9. DESCRIPTIONS OF COMPONENT OPERATION
The Universal Maintenance Charger (UMC) uses an SCR phase-controlled ac-to-dc isolated power circuit. The
following is a basic description of the main components, from input to output.
1. AC Input Power Section: This section includes the input terminals, CB1, F3 and F4, SS2 and T1. Its purpose is
to supply an ac voltage of the proper magnitude and capacity to the rectifier section. It also supplies various other voltages used
by the control unit and meters. It is connected to an ac source by means of a circuit breaker for most inputs and fuses and breaker
in the 480 Vac input connection. The power transformer (T1) is an isolation type to prevent any currents from flowing into the
dc bus from the ac line.
2. Rectifier Section: The Silicon-Controlled Rectifier (SCR) bridge accepts the ac voltage from the power
transformer (T1), rectifies this voltage to dc, and controls the voltage's magnitude so that the charger's output voltage remains
constant. The firing angle of the SCRs (Q1/Q2) is controlled by the action of the control module pc board (A1). The SCRs are
protected from ac and dc voltage surges by means of Metal-Oxide Varistor (MOV) surge suppressors (SS1, SS2).
3. The Control Module: This printed circuit board (A1) generates a signal which phase-fires the gates of the SCRs
(Q1/Q2). The output voltage of the charger is monitored by the voltage feedback circuit and advances or retards the phase angle
of the trigger pulses so that the output voltage is maintained essentially constant.
4. The Filter Section: The eliminator-filter assembly (L2/C1/C2/CR1) minimizes the ac ripple voltage at the
battery terminals. To accomplish this, the charger includes a low pass filter consisting of inductors (L1, L2) and capacitors (C1,
C2). The filter section also includes a diode (CR1) placed across the output to prevent a reverse polarity battery connection from
damaging the capacitors (C1, C2).
5. Meters: The dc ammeter (M1) uses a shunt (R13) to measure output current. The ac ammeter (M3) uses a
current transformer (CT1) to measure ac input. The dc voltmeter (M2) and dc ammeter (M1) operate from a 10 Vdc supply
powered by the transformer (T1) and a small rectifier circuit pc board (A2).
6. DC Output: The dc output circuit breaker (CB2) allows the user to disconnect the dc bus or battery from the
charging circuit. The voltmeter can be switched from the dc bus to the battery charger's internal voltage using the selector switch
(SW2). This allows the user to inspect setup prior to final connection.
7. Controls: The output adjustment knobs on the front panel control the output voltage (R5) and the output current
(R12). These controls allow the user to adjust the charger for many charging applications. The voltage adjustment will be
overridden by the current limit adjustment. The voltage adjustment is the fine adjustment of the output voltage. The current limit
adjustment controls the maximum current allowed to be transferred to the load or battery.
...NOTICE...
The warranty does not cover damage due to dropping.
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