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Tech Tips: Smart Batteries
Download this as a PDF.What is a Smart battery? A smart battery is a battery that is, to a large extent, "self aware" and is able to communicate information back to its host or user. These batteries are typically equipped with microchips that monitor the battery for parameters such as: state of charge, temperature, battery status, etc. Smart batteries communicate back to the user or system host through single or two wire protocols. What are the advantages of using a Smart battery? A smart battery is "self-aware" and communicates specific information to its system host or end user. If the system host is capable of processing the information that a smart battery transmits, it will be aware of the status of the battery and will be able to adjust its operation to save power or extend run-times. Conserving power and extending run-times are crucial for many mission critical operations. In addition, a smart battery will have levels of primary and secondary protection. If a safety condition in the battery is violated, it will be reported to the system host or end user through the communication channel making them aware of a potential failure. Therefore, using a smart battery enables the system to better understand the capabilities of the battery in real time. What is Smart charging? Smart charging is the process by which a smart battery is charged either by acknowledging and responding to charging requests from the battery or by probing the battery for charge parameters and by providing adequate charging voltage/current. A system that works in this manner, adjusting the charging profile based on communications with the battery is called a Smart charger. Based on how the charger interacts with the battery it can be classified as either a Level 2 charger or Level 3 charger. Is a Smart charger better than a non-Smart charger? It depends on what is meant by "better". For some customers a charger that can charge a battery in 2 hours is "great"...for others, one that charges overnight is "just as great". It is difficult to predict what works best for a customer without knowing what the use case is. Rather than using "good" as a measurement to gauge chargers, the better question would be: Which charger is better for my application? Is there an accuracy advantage to a smart charger and a smart battery? In terms of charging accuracy (a charger has nothing to do with battery state-of-charge computation accuracy), you will get better accuracy, i.e., control, when using a smart battery/charger combination. This is because charging is done either because the battery requested it or because the charger probed the battery, found out its state-of-charge (and temperature, state-of-health, etc.), then charged based on what the battery can handle. Thus, charging using a smart battery - smart charger combination is a perfect marriage as both products understand each other really well. Will this translate to better accuracy for charging? Absolutely! Because in this relation the charger can respond to the battery in real time and adjust outputs accordingly. In non-smart systems, the charger is forced to rely on pre-determined algorithms, look-up tables, etc. This is not an ideal marriage because, ultimately, one product is over imposing. Will I get more cycle life with smart batteries and chargers vs. non-smart batteries and/or chargers? Conceivably, yes. A smart charger and smart battery will work together to ensure proper charge and proper conditioning (if required). Charging using smart techniques will never be an abusive process to the battery, so there could be long-term cycle life benefits of when using a smart charger/battery combination. Is it true that a smart battery and charger can provide charge capacity accuracy up to 1% of actual capacity, while non-smart batteries or chargers could be off by 20%? State-of-charge is computed by the battery. The charger has nothing to do with the state-of-charge computation. This is a common misunderstanding, which can be explained with the following example. Take the Ultralife LI-145 battery...if the user is depending just on the 5 segment LED display to communicate state-of-charge, then the margin of error could be within 20%. If, however, the end user is using the SMBus to read state-of-charge, he/she can get fuel gauge measurement numbers like 99% or 95%, narrowing the margin to within 1 - 5%. Ultimately the accuracy you get is dependent on the way you use the smart battery. Non-smart batteries, on the other hand, have no fuel-level reporting systems. So the user is left guessing, where the margin of error can be up to 100%. Can I get more capacity out of a smart battery vs. a same-sized non-smart battery? Capacity is a chemistry function and "smarts" is an electronics function. The best the electronics can do is to keep battery impedance (measured from the outside world) as low as possible through good design, good board layout and good pack assembly practices so that energy in the cells can be transferred to the external world with minimal loss. After all, we are trying to contain energy into a "boundary" and save it for "future" use - another definition of a battery. So in a way it is incorrect to say that we can get more capacity from a smart battery than from a non-smart battery. But, if the user is using a smart battery and the system is probing the battery to get battery information, then the battery will report (for example) run-time-to-empty. If the user is using this information then he can continue using his smart battery until he has to shut down (based on use case). This way he is maximizing battery usage, which translates to more capacity. On the other hand, a non-smart battery user will not have this privilege. He will have to guess or use crude measurements (mostly inaccurate) to gauge battery energy level and then abort his activity, which translates to less capacity. A concept that often gets overlooked is SoH: State-of-Health. A non-smart battery can never compete with the state-of-health maintenance systems that are in place within a smart battery. A smart system will have a layered safety architecture - starting from the cell level, then at the board level and then at the pack level. As more energy gets compressed within limited space it only makes sense to have a tiered safety structure - something a smart battery can provide. And, if the host equipment supports it, this information can be sent to the system for corrective action. This is a huge advantage over non-smart systems. |
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