Overcoming the Achilles’ heel of the multi-cell battery pack
Typically, in multi-cell batteries, individual cells may have somewhat different capacities and may be at different levels in terms of their state of charge. Without cell balancing, the cell of smallest capacity is a ‘weak point’. It can be easily overcharged or over-discharged, while cells with higher capacities undergo only a partial cycle.
For the higher capacity cells to undergo a full charge/discharge cycle of the largest amplitude, a balancing mechanism is needed to ‘protect’ the weaker cells, allowing the cell with the largest capacity to be filled without overcharging any other cell, and it can be emptied without over-discharging any other cell.
Battery balancing is done by transferring energy from or to individual cells, until the state of charge of the cell with the lowest capacity is equal to the battery's state of charge.
Batteries such as those used for modern energy storage systems – either linked to solar photovoltaic systems or used in conjunction with commercial grade, long run uninterruptible power supply (UPS) systems - are usually made up from strings of cells in series in order to achieve the higher operating voltages required.
They are particularly vulnerable to premature failure. The problem can be compounded if parallel packs of cells are required to achieve the desired capacity or power levels.
With a battery made up from n cells, the failure rate for the battery will be n times the failure rate of the individual cells.
Significantly, the potential failure rate is even worse than this due to the possibility of interactions between the cells. Because of production tolerances, uneven temperature distribution and differences in the ageing characteristics of particular cells, it is possible that individual cells in a series chain could become overstressed leading to premature failure of the cell.
During the charging cycle, if there is a degraded cell in the chain with a diminished capacity, there is a danger that once it has reached its full charge it will be subject to overcharging until the rest of the cells in the chain reach their full charge. The result is temperature and pressure build up and possible damage to the cell. With every charge/ discharge cycle the weaker cells will get weaker until the battery fails.
Providing a solution to this problem is the Powermode-supplied Q-on LR Battery Pack. It represents a ‘first’ for the energy storage industry in that it is backed by a comprehensive three-year, on-site guarantee.
Underpinning Powermode’s guarantee is the ‘smart’ battery balancing/equalising technology built into the pack. This includes a computerised harness that automatically monitors and reports - via a ‘cloud-based’ portal to the Powermode Management Centre - on a range of parameters associated with individual battery cells in the pack.
Data streams containing information critical to the well-being of these cells, including temperature, state of charge and depth of discharge, are monitored and a tally of the number of discharge/charge cycles is recorded.
As the growing number of Q-on users confirm, the key to battery longevity lies in a thorough understanding of the status of individual battery cells in terms of their duty cycles and load factors.
In addition to a return on investment (ROI) boost, this knowledge gives users the peace-of-mind that comes with having Powermode in charge of the management and regular servicing of their Q-on LR Battery Packs.
Importantly, the incremental investment in a Q-on LR Battery Pack is more than offset by the savings associated with the escalating costs of early battery replacement.
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