Many new technologies not only improve performance, but also increase
system power consumption. For chemical companies that produce batteries,
substantial progress in battery production technology is difficult,
time-consuming, and costly.
So one must look for ways to optimize power conservation. Smart battery
systems (SBS) are the most promising technology to emerge and can significantly
improve battery pack performance. In the computer industry, lithium-ion
batteries are really loved and feared. Accidents that occurred in the early days
of lithium-ion batteries are still fresh in the minds of the companies involved.
They learned an impressive lesson: Under no circumstances should the rated
parameters of a lithium-ion battery be exceeded, otherwise it would definitely
cause an explosion or fire.
In addition to the chemical composition or electrode parameters of the
battery, there are several certain parameters for lithium-ion batteries. If
exceeded, the battery will enter an out-of-control state. In the diagrams
explaining these parameters (refer to the Lithium Ion Parameters Chart), any
point outside the corresponding threshold curve is a runaway condition. As the
battery voltage increases, the temperature threshold decreases. On the other
hand, anything that causes the battery voltage to exceed its design value will
cause the battery to overheat.
Beware of Charger Hazards Battery pack manufacturers put in several layers
of battery and packaging protection to prevent dangerous overheating conditions.
However, there is a component in the use of batteries that may cause these
measures to fail and cause harm. This component is the charger.
There are three ways in which rechargeable lithium-ion batteries can cause
harm:
The battery voltage is too high (the most dangerous situation); the
charging current is too large (excessive charging current causes lithium plating
effect, thereby causing heating); the charging process cannot be terminated
correctly, or charging is performed at too low a temperature. Designers of
lithium-ion battery chargers take extra precautions to avoid exceeding the
allowable ranges of these parameters. To absolutely ensure that the relevant
parameters of the system work within a safe range. For example, the smart
battery charger specification allows a negative voltage deviation of -9%, but
emphasizes that the positive deviation must not exceed 1%. Compliance with smart
battery safety standards is guaranteed. Of course, in an actual design, the sign
of the deviation is random. Therefore, designs that comply with this
specification often set the charger's target voltage value near -4% of the rated
value. Due to the inaccuracy of the charging voltage (whether it is -4% or -9%),
the battery is always undercharged. Fear of the potential dangers of lithium-ion
batteries results in low utilization of battery pack capacity.
According to the experience of industry experts, even if the voltage after
charging is only 0.05% lower than the rated value, the capacity drop is as high
as 15%. The principle of smart battery technology with a built-in computer in
the battery is very simple. A small computer is built into the battery to
monitor and analyze all battery data to accurately predict the remaining battery
capacity.
The remaining battery capacity can be directly converted into the remaining
operating time of the portable computer. Compared with the original capacity
measurement method that only relies on voltage monitoring, the operating time
can be immediately extended by 35%. Unfortunately, smart battery technology can
only go so far. Unless they can communicate with the charger circuitry, they
cannot determine their operating environment or control the charging
process.
In the context of an "intelligent battery system", the battery requests a
smart charger to charge it under specific voltage and current conditions. The
smart charger is then responsible for charging the battery based on the
requested voltage and current parameters. The charger relies on its own internal
voltage and current references to adjust its output to match the values
requested by the smart battery. Since these benchmarks have inaccuracies of up
to -9%, the charging process may end with the battery only partially
charged.
A more detailed understanding of the charging environment can reveal more
issues that affect the charging efficiency of lithium-ion batteries. Even in the
best-case scenario, assuming the charger is 100% accurate, the resistive
elements in the charging path between the cells of the charger introduce
additional voltage drops, especially during the constant current charging phase.
These additional voltage drops cause the charging process to transition from
constant current to constant voltage phase prematurely. Since the voltage drop
introduced by the resistor gradually weakens as the current decreases, the
charger will eventually complete the charging process. But the charging time
will be extended.
The energy transfer efficiency is higher during constant current charging.
Eliminating Resistor Drop The most ideal situation is when the charger's output
accurately eliminates the effect of resistor drop. One might propose a solution
where a smart charger monitors and corrects its own output using smart
in-battery monitoring circuit data at all stages of the charging process. This
is feasible for a single battery system, but less so for a dual or multi-battery
system. In a dual-battery system, it is best to charge and discharge both
batteries at the same time, if possible.
Although battery charging is parallel, the typical charger with only one
SMBUS port is not up to the job. Because if there is only one SMBUS port, the
charger or other SMBUS device can only communicate with one battery at the same
time. Therefore, an ideal system should provide two or more SMBUS ports so that
both batteries can communicate with the charger at the same time. In addition to
providing multiple SMBUS ports, the Smart Battery System (SBS) manager
technology can also significantly improve the performance of lithium-ion smart
batteries. The SBS Manager is part of SBS and is defined by the SBS1.1
specification. It replaces the SmartSelector defined in the previous
version.
On the one hand, the SBS manager provides an interface with the driver and
vibration system, and on the other hand, it manages the smart battery and
charger. The driver can read and request information about the battery, charger
and the manager itself. The interfaces related to this information transfer are
defined in the specification. In a multi-battery system, the SBS manager is
responsible for selecting the system power source and deciding which battery to
charge or discharge at a specific moment.
In short, the SBS manager determines which battery to charge, which to
discharge, and when. A well-implemented SBS management has several major
advantages: a more complete and faster charging process, efficient charging and
discharging simultaneously, and the ability to detect and respond quickly to
dangerous situations (such as potential voltage over-limits). An SBS manager
that monitors the voltage of the battery itself can charge the battery to its
true capacity. It can avoid insufficient charging caused by smart chargers due
to inaccurate monitoring voltage (as mentioned above, generally -4% to -9%).
Furthermore, this process does not require a particularly accurate voltage
reference (accurate voltage references are expensive).
The strategy to avoid using a precise voltage reference is to use the
measurement circuitry inside the smart battery to measure the battery voltage
with an accuracy of up to 1%. In this way, the SBS manager can command the
charger to increase the voltage appropriately until the monitored voltage
reaches the appropriate value. A well-implemented SBS manager can make the
battery charging process 16% faster than traditional chargers. Safely increase
the charger's output voltage above the battery's rated voltage to compensate for
voltage drops due to the battery's internal resistance and loop resistance. This
is accomplished by monitoring the battery's internal voltage and quickly
adjusting the charger voltage. The SBS manager can decide when to charge the
battery pack simultaneously.
Simultaneous charging allows better utilization of the charger's current
for charging. In a single-battery system, when entering constant voltage
charging mode, the charging current provided by the charger decreases as the
battery is fully charged. Unused current is wasted. This is not the case in a
dual-battery system that utilizes an SBS manager. Current that is not utilized
when charging one battery can be utilized by the other. Moreover, the SBS
manager can determine which battery's condition allows for faster energy
transfer. Batteries that can increase system capacity the fastest are charged
first, and batteries that can charge more energy are quickly discharged
first.
This speeds up the charging process by up to 60%. The SBS manager can also
decide when to enable simultaneous discharge functionality. Proper simultaneous
discharge can increase system capacity by as much as 16%. Of course, all these
improvements must be safe for battery performance. As discussed earlier,
lithium-ion batteries have a rated voltage. When the voltage applied to the
battery reaches its maximum value, the charging process switches from constant
current to constant voltage mode.
The detection of this transition point is performed by the smart charging
SBS manager based on the measured battery voltage. But the SBS Manager's huge
advantage over smart chargers is that it constantly monitors and corrects
charger and battery voltages. This ensures safety while reaching the maximum
capacity of the battery.
As the performance of computers and other equipment continues to improve,
energy needs are growing rapidly, and improvements in chemical batteries have
not been able to keep up with this growth rate. Although SBS technology is very
helpful, there will come a time when SBS technology alone cannot provide the
power required by high-performance systems, and more intelligent power
management solutions will be needed. If that OEM can make a laptop work for 6
hours without significantly affecting performance, it will quickly capture the
market. SBS Manager takes a big step towards this goal.
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