How does coulomb counter work

Mon-Fri, 9am to 12pm and 1pm to 5pm U. Mountain Time:. If you've worked with circuits a bit, you probably know that you can measure the current a circuit is using by using an ammeter or more likely a multimeter on the amps setting , and that this is useful information to know. Odometers are extremely useful for cars, they tell you how far you have gone, wouldn't it be nice if you were able to have a ….

Check out the product showcase at Instantaneous current consumption is definitely useful, but sometimes you'd like to keep track of cumulative current use, especially when you're trying to determine how much power is left in a battery. Battery life is easy to predict for a circuit that uses a constant amount of current, but things get a lot harder when the circuit is doing different things at different times, like lighting up LEDs.

Consider the speedometer and odometer in a car. The speedometer is like an ammeter - it shows you your instantaneous speed, which is good to know, but it can't tell you how far you've gone unless you're constantly keeping track of it.

This is the odometer's job; it constantly monitors your speed, accumulates it over time, and tells you how far you've traveled. A coulomb counter is like an odometer for current. It constantly monitors the current your circuit is using, adds it up, and gives you a pulse each time a given amount of amp-hours have been used.

With each pulse, you'll also get a "polarity" signal, which tells you which direction the current is flowing great for rechargeable batteries! By counting the pulses and direction, you can maintain an accurate count of how much power your circuit is removing from or putting back into your battery. If you start with a full battery, you'll always know exactly how much of it is left! Neat, huh? When you buy a battery from SparkFun or anywhere else , you'll decide which one you want based on two important numbers:.

One of these is how many volts the battery provides. You'll of course want to pick a battery that matches your project's requirements too much or too little voltage isn't good. Usually we'll recommend a specific battery, such as two 1.

The other number is the capacity of the battery, or how "big" it is. The higher the capacity, the longer your project will run. Higher capacity batteries are larger and heavier than smaller ones, so you'll need to trade off size and weight vs.

We measure battery capacity in milliamp-hours mAh for small batteries, or amp-hours Ah for large ones. This number indicates the theoretical amount of current a battery can provide for one hour before running out of juice. For example, all of these alkaline batteries have the same voltage 1. The AAA battery above has a capacity of mAh, which means it could provide 1.

But that's just the current it could provide for one hour. It could just as easily provide:. In reality, the chemicals in a battery can only react at a certain rate, so you can't get unlimited amounts of power even for a short amount of time. However, high-discharge LiPo batteries without protection circuitry CAN discharge breathtaking amounts of power for a few minutes, and are used in model aircraft for exactly this reason.

To determine the current a full battery can provide for a given number of hours, divide the total capacity by hours:. To determine how long a full battery will last at a given current draw, divide the total capacity by your project's current draw:. A coulomb like most units named after people , the name is written out in lowercase unless you're specifically referring to that person , is defined as one amp for one second :.

The LTC has an output pin called interrupt, or INT for short the line above the name indicates that this is an "active low" signal. This line is normally high, but will pulse low each time 0. Or to look at it another way, you will get INT "ticks" for each amp-hour:. As you know, battery capacity is measured in mAh milliamp-hours or Ah amp-hours. If your battery holds 1 amp-hour when it's full, you can continuously draw one amp from it for one hour before it's empty.

Because it measures amp-hours as you're using them, the coulomb counter makes it very easy to keep track of your battery's state-of-charge how full it is :. First, assuming you're starting with a full battery, set a variable to your battery's initial state-of-charge e. Listen for the "tick" low signals from the INT pin. Each time you detect a tick, check the direction signal, and add or subtract the above per-tick mAh value 0. As we saw in the last section, one "tick" from the device is equal to 0.

Conversely, it takes ticks to equal one amp-hour. The amount of loss varies depending on the type of battery, charge rate, age of the battery, temperature, etc. You can account for this by providing a manual "reset" input when the battery is fully charged, or doing some calibration to see how many more ticks you get when charging vs. We've written example code that shows you how to do all this, see the Example Code section for more information.

An additional and entirely optional trick is that if you keep track of the time delay between "ticks", you can back out the average current used over that period. The equation is very simple:. Note that because this number is the average current use over the time period, the instantaneous current could be higher or lower. This is also covered in the example code. It has an INT interrupt output that is normally high, but will go low when a given amount of current has passed through the device.

There is also a POL output that tells you which direction current is flowing. The Coulomb Counter can accommodate power sources up to 8. It works particularly well for single-cell 3. On the interface side, the Coulomb Counter can be attached to systems running at either 3.

There are three solder jumpers on the Coulomb Counter board that configure it for different situations. Please read this section carefully and make any necessary changes before using your Coulomb Counter. To close a solder jumper, melt a small blob of solder onto the jumper so that it bridges both pads, shorting them together.

To open or "clear" a solder jumper, use some solder wick and a hot iron to remove the solder blob bridging the two pads. Place the wick over the blob, and heat the blob through the wick. When the solder melts, the wick will absorb it.

When you're done, ensure that the two pads are fully separated no solder bridging them. As you would when using an ammeter, you will need to install your Coulomb Counter between your power source usually a battery and your circuit.

All the current your circuit uses needs to pass through the Coulomb Counter to be measured. You could also add a 2-pin JST pigtail or adapter to your own battery or other power source and plug it into this connector.

This is a simple two wire cable. Great for jumping from board to board or just about anything else. There is a 2-pin JST conn…. Great for jumping from board to board. Two pin JST connector to a 2. We use this cable to adapt from a wall power ….

Note that if you'll be using both the Coulomb Counter and a Lipo charger, connect the Coulomb Counter not the charger directly to your battery. This way the Coulomb Counter can monitor both charging and discharging:. If you need to charge LiPo batteries, this simple charger will do just that, and do it fast! If you need to charge LiPo batteries, this simple charger will do just that.

It is designed to charge single-cell Li-Ion or L…. The PowerCell board is a single cell LiPo boost converter to 3. The board comes with…. At the other end of the Coulomb Counter, you'll find a header with six pins.

These are the pins you'll need to connect to your microcontroller. Depending on what you want to do, you'll need at least the first four pins:.

PROTIP: When you see a signal name that contains an asterisk or has a line over it, that's an indication that this signal uses "negative logic". In negative logic, a low logic level means the signal is asserted or active.

Thus, if you see a signal named RESET , you must provide a low signal to reset the part, and keep it high at other times. Note that the Coulomb Counter is powered by the IN header usually your battery and not by the VIO pin, which is used only as a voltage reference for the output pins.

This is so that the small amount of power used by the Coulomb Counter itself is included in its measurements for maximum accuracy. The Coulomb Counter uses under 1mA when it's running, and you can use the SHDN shutdown input to reduce its power consumption further though it will not be able to keep track of current use while shut down. Before plugging your Coulomb Counter into your microcontroller, see the Solder Jumpers section above for instructions on setting up the board for a 3. Our Arduino Example Code has been written so that you can plug the Coulumb Counter board directly into Arduino digital pins 2 through 7 as shown below.

Speaking of which:. These diagrams show the use of a single-cell Lipo battery powering the system. Note that you should also connect 3. You can do this with the Arduino's VCC 3. Note that you will need to connect 5V to VIO for the logic level reference. The SVM has also been applied for regression problem, even the regression problem inherently more difficult than classification problem. The SVM used as a nonlinear estimation system is more robust than a least-squares estimation system because it is insensitive to small changes [ 29 ].

Fuzzy neural network FNN has been used in many applications, especially in identification of unknown systems. In nonlinear system identification, FNN can effectively fit the nonlinear system by calculating the optimized coefficients of the learning mechanism [ 30 ].

The soft computing approach uses a fusion of an FNN with B-spline membership functions and a reduced-form genetic algorithm. Using real-time measurement road data to estimate the SOC of battery would normally be difficult or expensive to measure. In [ 32 ], application of the Kalman filter method is shown to provide verifiable estimations of SOC for the battery via the real-time state estimation.

Yatsui and Bai [ 33 ] presented a Kalman filter based SOC estimation method for lithium-ion batteries. Experimental results validate the effectiveness of Kalman filter during the online application. Barbarisi et al. Sun et al. The adaptive adjustment of the noise covariance in the SOC estimation process is implemented by an idea of covariance matching in the UKF context. The object of hybrid models is to benefit from the advantages of each method and obtain a globally optimal estimating performance.

Since the information contained in the individual estimating method is limited, hybrid method can maximize the available information, integrate individual model information, and make the best use of the advantages of multiple estimating methods thus improving the estimation accuracy. The literatures show that the hybrid methods generally produce good SOC estimating results compared to individual methods [ 37 — 39 ].

The hybrid methods combine different approaches such as direct measurement method and book-keeping estimation method. A new SOC estimation method that combines direct measurement method with the battery EMF measurement during the equilibrium state and book-keeping estimation with Coulomb counting method during the discharge state has been developed and implemented in a real-time estimation system [ 37 ].

Any battery will lose capacity during cycling. In order to calculate SOC and remaining run-time RRT accurately and to improve the SOC estimation system capability to cope with the aging effect, a simple Qmax adaptation algorithm is introduced. In this algorithm the stable conditions of the charge state are exploited in order to adapt Qmax with the aging effect.

Since a battery loses capacity during cycling, it is concluded that the Qmax adaptation algorithm will increase substantially the SOC and the RRT estimation accuracy. Wang et al. In KalmanAh method, the Kalman filter method is used to make the approximate initial value converge to its real value. Then the Coulomb counting method is applied to estimate the SOC for the long working time. The SOC estimation error is 2. This compares favorably with an estimation error of Kim and Cho [ 39 ] described the application of an EKF combined with a per-unit PU system to the identification of suitable battery model parameters for the high accuracy SOC estimation of a lithium-ion degraded battery.

To apply the battery model parameters varied by the aging effect, based on the PU system, the absolute values of the parameters in the equivalent circuit model in addition to the terminal voltage and current are converted into dimensionless values relative to a set of base value. The converted values are applied to dynamic and measurement models in the EKF algorithm. Since the energy storage systems have been highlighted in portable electronics and hybrid electric vehicle applications, the estimate accuracy of SOC becomes increasingly important.

In recent years, many scholars have done a lot of research on SOC estimation. The estimate accuracy has improved constantly, and it can be expected that intense research and development efforts are already on track. In order to further improve SOC estimates, combined with some literatures, anticipated improvements for the further research include the following areas.

Do further research on the practical universal application of the methods. In addition, new methods on complex terrain are the focus of future research. The models have the ability to automatically adapt to various kinds of batteries, various discharging conditions, and the different aged batteries.

This paper presented a review on estimating of battery SOC under different discharging conditions. Four categories of estimating mathematical methods, which have their own characteristics, were discussed.

Papers were selected to emphasize the diversity of estimating mathematical methods. Some of these methods have good performances at fixed discharging current condition, while others perform better in varied discharging current condition.

It is difficult to evaluate the performance of various methods, as the existing applications were in different discharging condition and different size of battery. The developments of various SOC estimate methods are expected to be valuable in battery applications such as BMS in hybrid electric vehicles. Based on the development history of SOC estimation, the future development directions of SOC estimating are proposed in the end.

NSC E This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Academic Editor: E.

Di Nardo. Received 12 May Accepted 05 Jul Published 23 Jul Abstract An overview of new and current developments in state of charge SOC estimating methods for battery is given where the focus lies upon mathematical principles and practical implementations.

Introduction Rising crude oil prices and worldwide awareness of environmental issues have resulted in increased development of energy storage systems. The SOC can be defined as follows: The various mathematical methods of estimation are classified according to methodology. Categories Mathematical methods Direct measurement i Open circuit voltage method ii Terminal voltage method iii Impedance method iv Impedance spectroscopy method Book-keeping estimation i Coulomb counting method ii Modified Coulomb counting method Adaptive systems i BP neural network ii RBF neural network iii Support vector machine iv Fuzzy neural network v Kalman filter Hybrid methods i Coulomb counting and EMF combination ii Coulomb counting and Kalman filter combination iii Per-unit system and EKF combination.

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