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EnForcer™ SCR Service Manual I.B. 1561
7
THEORY OF OPERATION
INTRODUCTION
EnerSys™ EnForcer™ SCR Battery Chargers are three phase 50 or 60 Hz, and SCR/Diode Block-controlled. EnForcer™
SCR chargers use the control board known as “ES3”. See Replacement Parts Lists for complete part numbers.
SCR/Diode Blocks are used to control the output and yield tight regulation over the whole operating curve. Line variations
of ±10% will have almost no effect on the operating curve.
All chargers are designed for convection cooling with no de-rating, up to an ambient temperature of 40°C, 104°F (if
properly installed per the Installation and Operating Instructions manual).
All models have an Equalize cycle that can be started manually or automatically.
While charging, the information about the state of charge is provided through the control board LEDs and LCD display.
Batteries with cell size and amp hour ratings less than or equal to the charger nameplate values can be charged.
Charging batteries that have higher cell size and amp-hour ratings above of the charger nameplate is strongly
discouraged.
Refer to the schematic diagrams in the back of this manual as you read the following description.
The 3-phase SCR-controlled battery chargers are available with several operating voltage ranges and come in 50 or 60
Hz models. The voltage, current, and frequency ratings are specified on the nameplate located on the lower-left corner in
the front of the charger.
It is important not to exceed any of these nameplate ratings.
The charger power circuitry contains a transformer that provides full isolation from the primary source to the secondary.
In the transformer secondary there is a 3-phase bridge rectifier made up of 3 SCR/Diode Blocks that converts AC to DC
for charging.
The AC voltage of the secondary is connected directly to the SCR/Diode Blocks.
For increased reliability there is a snubber assembly connected across each SCR/Diode Block to limit the gate firing noise
and high voltage spikes. Each snubber assembly consists of an MOV (Metal Oxide Varistor), which is a device used to
clamp positive or negative voltage spikes at a given level and a capacitor (used to limit DV/DT of the SCR) in parallel.
The magnitude of the secondary AC voltage can be measured across the inputs of the SCR/Diode Blocks, and the values
are listed in the troubleshooting section of this manual.
Each primary input line is individually fused, and in some cases, the charger may have been provided an optional AC
fused Disconnect Switch. This switch, when it is on, prevents the front door from opening. The secondary DC cable is
fused on the negative lead.
Chargers rated at 36 cells and higher will have a different style fuse designed to operate with higher voltages. This will
typically be a FWA style semiconductor fuse.
If the charger has been provided with optional parallel DC cables, each of the two negative leads will be individually fused
with a size ½ of the rating of a single-cabled charger of similar rating.
PRINTED CIRCUIT BOARDS
All charger functions, features, and controls are handled by one printed circuit board (PC Board) under microprocessor
control. Because of its flexible design, this PC board model is capable of being used on an entire range of chargers.
If changes are required on a board that is already installed, then all adjustments, calibrations, and settings are made
through the front panel using the pushbuttons and the display. The specific operation of all adjustments through the front
panel is described in detail in later parts of this manual. The adjustments are permanently stored in on-board FLASH