APPENDIX F
92
FORCED LOAD SHARING
INTRODUCTION
Multiple battery chargers are sometimes employed in dc power systems to provide
redundancy. Two or more chargers of the same voltage rating can be connected in parallel, each of
them capable of powering the connected dc load and charging the battery. If a battery charger
should fail during normal operation, the parallel charger can continue to supply the entire required
dc load current, and maintain charge on the battery.
When two AT30s operate in parallel, they normally will not share the load current equally.
Since any two chargers will have slightly different characteristics, one of the two chargers in a
system will have a slightly higher dc output voltage, and will therefore assume more of the burden of
providing necessary load current. This section describes an optional accessory for the AT30 battery
charger that system operators can use to force units to share load equally. The accessory consists of
an interconnecting cable to provide such communication.
SYSTEM REQUIREMENTS
•
The forced load sharing feature is designed only to work with two AT30 Series battery chargers.
You cannot force load sharing with three or more chargers.
•
The units must have the same dc voltage and current rating, and have the same dc filtering level.
•
Both chargers must have the same ac input source and the same phase rotation.
•
Both chargers must feature
Rev. 6
(or higher) builds of the main control circuit boards (A1), and
corresponding (Rev. 6 or higher) software programs.
•
We recommend that both chargers use the same program version, since the load sharing option
has not been tested using a different program version in each charger. To view the program
version, press the
LAMP TEST
button on the front panel of the charger. When you release the
button, the version number is shown on the front panel display for two seconds.
•
The interconnecting signal cable length should be no more than 50ft (15m).
INSTALLING THE INTERCONNECTION CABLE
The AT Series forced load sharing accessory is normally supplied by the factory with a
standard 15ft (4.6m) interconnection cable (EH5041-00). A 25ft (7.6m) long cable (EH5041-01)
and a 50ft (15.2m) long cable (EH5041-01) are also available. The interconnection cable is
terminated at each end with a 6-pin connector that mates with the plastic connector (J4) on lower-
right corner of the main control circuit board (A1). One end of the cable features an extra jumper in
the connector, and should be identified for use with the
Secondary
charger. The other end of the
cable connects to the
Primary
charger. Either charger may be selected as Primary or Secondary, but
you may wish to choose the charger that is more accessible to be the Primary. The Primary charger
controls the dc output voltage of both chargers.
You may run the interconnection cable through conduit if necessary. However, do not run
the cable through the same conduit with power wiring. Do not remove the connectors in order to
"fish" the cable through the conduit. Maximum pulling tension is 46 lb. (20.9kg). The cable has a
plenum-rated outer jacket, and passes the NFPA 262 flame propagation test. Install the cable
between the chargers, and anchor it in place at both ends before connecting. Connect each end to the
main control circuit boards, inserting the connector into J4 until it is completely seated.
NOTE:
DC power cabling for the battery charger, battery, and load interconnection is not
supplied with the AT Series Forced Load sharing option. All user-supplied system wiring should
meet National Electric Code (NEC) standards, as well as local/site codes. Confirm polarity of all dc
cabling before making connections.
Summary of Contents for AT30 SERIES
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