24VDC Li Expander Pak 1300 Operator Manual
June 2020
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Solar Stik® Inc.
26
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• The cell maintenance circuit manages the cell voltages, and actively balances voltages across the
cells as the battery cycles. It calculates for parity across all eight (8) Super Cells, ensuring long
operational life.
The Li Expander Pak 2400 offers a BATTERY STATUS LED located on the outside of the
Expander Pak case
The BATTERY STATUS LED circuit monitors and reports the output of the battery. If the STATUS LED
controller senses the output has been disabled for any reason, it turns the LED to red. BATTERY
STATUS LED is not connected to the BMS-computed SOC; it is only monitoring the output of the
battery and indicating to the user if the terminals of the battery are active or not.
The Li Expander Pak 1300 battery BMS has only one control board for protection and cell
management There is no display or STATUS LED on the case
Without the BMS protection circuit, there would be a significant safety risk. For example, if charging
voltage and current are applied to a battery with dead or damaged lithium cells and no BMS, the
remaining (functioning) cells would be exposed to higher individual voltages in order to compensate
for the loss of dead cells in the battery. The external charging circuits would attempt to function by
keeping the battery at its prescribed operating voltage, completely unaware that individual cells in
the battery were being overcharged. With a BMS installed, however, the failure of a cell will trigger
the protection circuit; thus the battery will protect itself and the operator.
Charging mechanisms used with ANY Li Expander Pak do not have the ability to recognize when a
cell in a battery module has failed or, by extension, when a battery has removed itself from service.
In any lithium battery that is made of multiple cells, that is the exclusive role of the BMS. External
charging sources such as solar, vehicular, and the AC circuit will continue to attempt to charge at
their set charging voltage values (in this case, at about 28 V) regardless of an individual cell’s health
or SOC. If one battery drops out of service, the system voltage is not affected, and the loss of one
battery will have minimal impact on the overall system performance. If this situation is amplified,
and multiple Expander Paks are removed from the system, then the system’s performance will
progressively degrade.
Additional Notes about BMS operation:
• The BMS is the key feature enabling the battery to handle high charge and discharge rates (up to
35 A each) and also allows multiple batteries to be used in concert (in a scaled configuration).
• In order for a scaled battery bank (multiple Li Expander Paks in a parallel connection) to function
properly, the individual battery BMSs must be synchronized with each other. This is accomplished
by fully cycling the bank 2–3 times after the batteries are connected.
Li Expander Pak in an Overdischarged State
It takes only ONE (1) supercell reaching a voltage of 2.5 VDC in an Li Expander Pak to cause an
overdischarged condition. If the BMS senses that one cell has breached this low-voltage threshold,
the protection circuit will immediately deactivate the battery terminals. This is also considered 0%
SOC for the whole battery. This will protect the cell from going into a deeply discharged state, which
can cause damage to the individual cell.