Coulomb counting amount of battery capacity

"Coulomb Counting" method for capacity measurement of Li-Ion battery

Li-ion battery capacity measurement of "Coulomb Counting" method;
Always wanted to write an article about battery capacity Coulomb counting, you can fully explain
Coulomb counting's working principle is quite troublesome, because this capacity measurement method involves the
The knowledge of the battery is too much and too complicated, and there is a part of the Integrated IC knowledge.
In order to "popular tastes", I will divide this article about Coulomb counting into four ministries.
Score of.
1. Introduction of basic concepts, that is, why to use Coulomb counting to measure the battery capacity
Amount.
2. Coulomb counting simple explanation, speaking relatively shallow for the general user.
3. Coulomb counting advanced instructions, in detail to supplement the working principle of Coulomb counting.
4. Explanations of the various phenomena used by Coulomb counting on mobile phones, especially the possession of love
Li Xin Mobile phone machine friends, may wish to refer to
☆☆☆ the first part. Introduction to Basic concepts
; MAh: The unit of measurement of battery capacity is actually the battery can be released as an external
The total number of electrons used.
The unit of physical standard is the Coulomb that everybody is familiar with.
; The Coulomb's International standard unit is the ampere-second of the current multiplied by the time.
; 1mah=0.001 Amp * 3,600 sec = 3.6 Ampere Second =3.6 coulomb
Mah is not a standard unit, but this unit can be conveniently used for metering and
Calculation.
, for example, a 900mAh battery can provide 300mA constant current for 3 hours of
Power supply capability.
In the article "voltage method for capacity measurement of lithium-ion battery", I described in detail
The battery voltage approximates the aspect of the battery capacity. But this method is rather rough.
To obtain the correct use of lithium-ion battery power, only use Coulomb counting. Like
The function principle of water meter used in our house. To calculate the charge that flows through
To get the power usage of the lithium-ion battery.
How to get the amount of charge that flows through, only through the test unit time within the loop
The size of the current flowing through.
If the measured current is constant, the measured current can be multiplied by the time
To simply get the charge amount. This clock is usually only in the lab.
A constant current is used to calculate the capacity of the battery and the measured
More precise.
If the measured current changes over time, then it is necessary to change the
The current is integral to get the charge, the battery on the phone is the case, the current
It's changing all the time.
How do you measure the current?
Simply by measuring the voltage at each end of a specific resistor (unit volt
Voltage (ohm ohm or milli-ohms), and the Resistance
Mohm) to get an instantaneous current value (in amperes A or MA).
☆☆☆☆
The second part, the working principle and simple application of Coulomb counting
Coulomb Counting working principle
Current cell phone battery capacity measurement (like Ericsson cell phone battery), is in the battery
A power metering chip is connected in series on the protection line, in which an integrated
Resistance, the resistance value is generally 20~30 between Europe and the EU.
The basic principle is that a sample resistor is integrated on the chip when the current is flowing through different
The chip has a different dropout voltage (actually converted to current) and time
To get the correct amount of power when used by the user (note that the unit of charge is
MAH).
;; Many chips can achieve this function, TI's, Maxim's several semiconductors
Chip companies have similar products produced. After the battery increases this chip, the cost increases, the
Mobile phones also put forward "communication" requirements. So many phones do not have this feature.
Then the chip through real-time integration to obtain capacity, the capacity (unit is mah)
The data is stored in the EEPROM of the chip and transmitted via the communication line according to the demand of the handset.
to the phone. Then the cell phone gets the exact capacity of the battery.
The Coulomb counting chip, the power metering chip, is installed in the cell phone battery,
It is usually designed with a protective circuit for lithium-ion batteries.
;　;
In the memory of the Coulomb counting chip, there is usually a basic battery information
▲ the initial capacity of the battery (mAh), that is, the rated capacity, after a fully charged battery
The resulting capacity
▲ the current capacity of the battery (mAh), in use is the battery capacity
Current current flowing through (MA), i.e. the current loss of the cell phone
Coulomb Counting Simple Application
But the average phone does not show capacity (such as "550mAh" or "left
345mAh "This is a bad value for the user to understand.
There are two types of capacity display, which is calculated to convert capacity mah to
Another unit that is well understood.
1. Percentage of capacity (in%)
Each battery has an initial capacity or is known as rated capacity.
The current battery capacity in addition to the rated capacity of the current capacity can be obtained
Percentage
A battery with a nominal capacity of 600mAh, if the current battery capacity is only
456mAh, the phone will show 456/600=76%.
2. Standby time and talk time (unit time: h)
The phone itself according to its own standby or call current loss, the corresponding built-in a
Calculation formula, see this capacity converted to user-understandable standby time and call
Time.
The calculation formula for the standby time is:
Current capacity of the battery/current flowing through =*** hours
The calculation formula for talk time is
Current capacity of the battery/average current =* hours during call
☆☆☆☆
Part III Coulomb counting advanced instructions
1. Circuit
There are two types of design circuitry to get the capacity of the battery
One is a/d analog-to-digital conversion, typically 12-bit precision, converting a voltage value to 12-bit
The precision of the 16 digits is multiplied by the sampling interval.
One is the integrated mode, which uses the RC integral circuit to obtain the voltage-to-time integral
Value.
Both end up with the capacity of the battery.
2. The return of the capacity
The voltage method has a very short time to measure a voltage. The return of the capacity is not required.
Since the capacity of the Coulomb counting must be an integral to the time to obtain. So
To obtain the rated capacity of the battery, the battery must be fully
To get the correct battery capacity information.
At the beginning of the use of Coulomb counting, manufacturers will give Coulomb counting a battery initial capacity
The volume. But each use is not always completely exhausted or fully charged. So often shallow
The error of capacity is accumulated when the charge is shallow.
Therefore, the use of Coulomb counting lithium-ion batteries must be regularly fully
To regain the correct battery rating capacity.
3. Adjustment of rated capacity
The actual capacity of the Li-ion battery will follow the cycle, and the usable capacity will gradually
The attenuation of the Coulomb counting. If the initial capacity stored in the
Errors caused by the capacity display.
For example, the initial capacity is 600mAh of the battery, after 100 cycles, its actual capacity
The volume has become 500mAh, if the capacity display is still in accordance with 600MAH this
Number to calculate, it is bound to cause the battery will never fill the problem.
So there's an algorithm for the number of usage adjustments in the Coulomb counting,
The actual capacity is adjusted based on the number of battery cycles.
The capacity of the lithium-ion battery will also vary with the temperature
Amount.
For example, at 25 degrees, the battery can get almost 100% of usable capacity
At 0 degrees, the battery can only emit 80% of the usable capacity.
If the capacity is not temperature adjustment, it is bound to cause the use of low-temperature environment,
Clearly show the remaining 20% of the capacity, but early shutdown this phenomenon.
So there's a capacity-to-temperature adjustment algorithm in the Coulomb counting, based on
The actual temperature of the battery is adjusted for usable capacity.
4. Battery Identification Code
Many Coulomb counting chips have been integrated with a battery identification code recording area.
Its role is to give the cell phone battery A serial number, this serial number is saved in
The inside of the chip, using the phone with the communication port to pass to the mobile phone. Verify this sequence
If it is correct, the battery will be judged as genuine. If the serial number is verified incorrectly, the phone
The prompt is non-genuine battery even refused to work.
Do not underestimate the Coulomb counting chip, careful of a chip, not only to carry out high-precision
The power metering, but also to carry on the complex operation adjustment. But also with the host (cell phone) into the
Communication links.
☆☆☆☆
Part IV: Explanation of the phenomenon of the use of Coulomb counting on mobile phones
The above describes in detail the working principle of the Coulomb counting chip itself.
But as a user-oriented application, getting capacity (MAH) This data is far
Far from enough. So how to convert capacity into standby time is the phone's software
Work out.
Mobile phone through the communication, get the following information
▲ the initial capacity of the battery (mAh), that is, the rated capacity, after a fully charged battery
The resulting capacity
▲ the current capacity of the battery (mAh), in use is the battery capacity
Current current flowing through (MA), i.e. the current loss of the cell phone
Note that the current flowing through is a very irregular value. Obviously, Xu
Many factors have affected this current.
Local signal strength, will affect the phone's standby current
Phone add-ons, such as Bluetooth, will increase or change the
Flow
Phone backlight (when operating the phone), will greatly increase the standby current.
These factors can cause deviations in the following standby time calculation formula
▲ current capacity of the battery/current flowing through =*** hours
If the standby current is stable or small, this standby time will
Play a very good role in computing
This is why the phone is fixed in one place, the standby time is very accurate original
Because
Local signal quality also directly affect the phone's standby time display.
Would have shown a 180-hour standby on the same phone to get B to the right
Became a 240-hour standby. This is because the denominator of the calculation formula has changed.
But the change of standby time and the emergence of a strong contrast do not mean that the battery appears
Problem, the actual capacity of the battery is still unchanged. It's not meant to explain
Is the reason for the bad battery.
Although the lithium-ion battery does not have the memory effect, does not need the specialized discharge treatment, does not need
To fill the battery can be used, this does not affect the performance of lithium-ion battery.
However, for mobile phone users with Coulomb counting batteries, one thing must be
Emphasize.
¡ï ★ Please regularly on the battery you used to carry out a full,
In order to Coulomb counting for capacity adjustment and normalization. Make sure Coulomb counting is working
In the best state. ★