Li-Ion batteries are highly sensitive to over voltage (catastrophic failure and fire hazard), as well as under voltage (severe loss of capacity). For this, every battery pack requires a protection circuit to ensure cell voltages are kept between these thresholds. Aside from the voltage level limits, protection circuits also prevent over current and over temperature. Since the voltage of each cell directly relates to its state of charge, ability to set these thresholds accurately is key in getting maximum capacity, while maintaining safety. Common low cost protection circuits have high tolerances, resulting in much broader threshold settings than desired.
No two batteries are identical, mainly due to the manufacturing tolerances, as well as temperature variation among cells. These variations will result in different state of charge in multi-cell packs that will show as differences in cell voltages. Since Li-Ion batteries are sensitive to over voltage and under voltage, the protection function will cut off charge and or discharge to the entire pack prematurely, when any single cell reaches a maximum or a minimum voltage threshold. Forced cell balancing is the only way to assure longevity and full capacity of a battery pack throughout its life. The error due to the difference in capacity will accumulate over charge and discharge cycles, resulting in severe out of balance cells. The more unbalanced the cells become, the lower the battery pack capacity. This is how a notebook computer battery, as an example, can exhibit a few minute of charge capacity, sometimes after only a short few months of operation.
One of the most challenging tasks in battery management is accurately estimating the state of the charge. This estimation has high dependency in accuracy of cell balancing, voltage and current measurements, as well as considering temperature for its effect on these measurements. The industry has come up with multiple algorithms, but nonetheless, the accuracy of the measurement and having a balanced battery pack are key elements in making the best estimate possible. Inaccurate estimation will result in prematurely alarming the user when the battery is not empty, or not alarming the user when the battery is almost depleted. In both case, the user experience is adversely affected, and depending on the end equipment, severe and undesirable outcomes are possible.
Clearly, the measurement accuracy is the most important element in all aspects of battery management. For various reasons, including the flat curve of Li-Ion cell voltage vs. state of charge, ~5mV has become the standard accuracy target. A simple math puts this target at about 0.1%, which is extremely difficult to achieve, especially when done using brute force approaches. To make things even more challenging, for best performance, this accuracy needs to be maintained throughout the entire temperature, as well as cell voltage range. Brute force approaches have historically failed to make this possible!
Nova’s patented technology provides a breakthrough solution to this old problem. Instead of brute force approaches, a new digitally assisted analog provides an unprecedented 1mV accuracy or 0.02% overall operating conditions, but most importantly this is done with elegance and therefore at low cost. Lack of effective and affordable balancing solutions, has pushed many low-cost consumer products to shy away, and not implement such important and necessary functions, leading to severe short life of battery packs. Often a dead battery results in end of life for the whole unit, creating unnecessary waste, affecting the consumer and the environment alike. We have set out to change this by providing true solutions to these old problems. No battery pack should lose capacity before its time!