Charge in parallel, discharge in series
For a low voltage charger and a high voltage load
To handle a low voltage charger and a high voltage load, you may split the battery pack in two, charging in parallel and discharging is series.
The Elithion Lithiumate Pro BMS is the only off-the-shelf BMS that allows this operation.
Connect as shown here.
Configure the BMS:
When the AC is available, the charger is on and the contactor opens the series connection between the half packs. The rectifier diodes are forward biased, effectively connecting the two half packs in parallel. The charger charges both half-packs (first just the lower voltage one, and then both).
When the AC is gone, the contactor closes, and the packs are connected in series. The rectifier diodes are reverse biased, disconnecting the charger from the half-packs. Current flows through each half pack in series, and into the load.
The BMS monitors how it is powered (through VS when AC powered, or VL when the load is on), to determine which current sensor to monitor, and to determine whether the pack voltage is the sum of all cell voltages (load on, half packs in series) or half as much (AC power on, half packs in parallel).
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