We would also like to pay our gratitude to instructor Worthy Dr.Asim Samejo(Assistant Professor) of Electrical Engineering Department at Sukkur IBA University and Sir Nadir for guiding us in our project Lithium-ion Battery Management System.
The Electric Vehicle (EV) is seems to be the roadmap of every important car manufacturer and is seen as the modern solution to a more sustainable transport system, contributing to a reduction of the Greenhouse Gas Emissions. Our project is about a Lithium-ion Battery Management system
Li-ion batteries are able to be recharged hundreds of times and are more stable. They tend to have a higher energy density, voltage capacity and lower self-discharge rate than other rechargeable batteries. This makes for better power efficiency as a single cell has longer charge retention than other battery types.Today, lithium-ion is one of the most successful and safe battery chemistries available. Two billion cells are produced every year. Some of the most common applications of lithium-ion batteries are: Power backups/UPS. Mobile, Laptops, Electric vehicles EVs and other commonly used consumer electronic goods, electric mobility. Whereas Battery Management System BMS, is an electronic device that acts as a brain of a battery pack, monitors the output, and protects the battery from critical damages.It is a circuit combined with an algorithm that monitors the voltage, current and temperature of the cells in a battery pack and ensures performance and safety of the individual cells in a battery pack. It is also responsible for balance charging, State of Charge (SoC) and State of Health (SoH) measurement of the cells and much other important functionalities.The Smart Battery Management System (BMS) is an important component that not only reliably tests battery conditions but also ensures safe operation and extends battery life. Thus we conclude that A battery management system (BMS) is any electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside and helps in balancing.
Cellular batteries are considered original (non-renewable) or seconds (renewable), depending on their ability to charge electronically. Within this category, other categories are used to identify specific buildings or designs. For this, we have two types
Since these batteries lack the ability to recharge electrically or efficiently, they are discharged once and then discarded. The main battery is a low-cost option, heavy source of healthy integrated energy on the shelf, high power output at low to moderate output levels
Primary cells
These batteries can be electrically recharged in their original state after being discharged by passing them on the other side of the current discharge. Depending on the type of battery and its quality, the replacement process can be repeated hundreds or thousands of times. They are also known as "storage batteries" or "accumulators" and are the final component of the power supply. The second set of batteries has been charged by high power capacity, high rate of discharge and flat charging, while their power capacity is usually lower than that of main batteries
Secondary cells
Some key words to highlight the electrical characteristics of batteries, are shown in the next section.
The type of active substances present in a cell defines the cell's normal capacity. The following formula can be used to measure general power from normal electrode strength: anode (oxidation potential) + cathode (reduction potential) = standard cell potential
The number of active substances in the cell determines the cell's volume. It is calculated in coulombs or ampere-hours and reflects the sum of electricity used in electrochemical reactions.
By taking both energy and quantity of electricity, the volume of a cell can also be determined on the basis of energy (watt-hour). The highest value that a specific electrochemical system can produce is the amount of thought capacity.
In the following pages, we will go through some main terms that will help you understand how batteries work and what they're good for.
The voltage between direct and indirect electrodes when a load is attached to the battery is referred to as the closed voltage or circuit closed. The operating power varies depending on the state of charge (SOC) and the current discharged / charged.
The percentage of battery discharge expressed as a percentage of full capacity is referred to as this. A deep discharge is described as a withdrawal of at least 80% DOD.
Present battery capacity expressed as a percentage of full capacity. To detect changes in battery capacity over time, SOCs are usually measured using current integration.
SOH is a term that describes the current state of a battery's health in comparison to its initial health calculation. In other words, the SOH is supposed to tell you how long the battery will last before it dies. In a nutshell, it's a measurement of internal resistance, capacity, electrical strength, self-discharge, battery charging capacity and the total number of battery discharge cycles completed by that time.
More about Charging and discharging of batteries
MORE Advantages of BMS BY NASA
Lithium-ion (li-ion) batteries are the best option for e-bikes.As for its self-charging feature, the bike integrated lithium-ion battery can be completely recharged just by pedaling or braking.An electric-vehicle battery (EVB, also known as a traction battery) is a battery used to power the electric motors of a battery electric vehicle (BEV) or hybrid electric vehicle (HEV). These batteries are usually rechargeable (secondary) batteries, and are typically lithium-ion batteries. These batteries are specifically designed for a high ampere-hour (or kilowatt-hour) capacity
The battery management system's aim is to preserve the battery in good working order. During discharge, the BMS should protect the cell from any occurrences. Otherwise, the cell is unrestricted in its activity.
Improper charging may be more dangerous to batteries than any other factor. As a result, charging power is an important feature of the BMS. A fixed-voltage charging system for lithium-ion batteries is also regarded as a two-stage charging system (CC-CV). The charger generates a steady current that increases the battery capacity during the first charging process (current continuous phase). The battery enters the voltage (CV) process on a regular basis when the voltage reaches a constant value and the battery is almost completely charged. As the current battery decomposes further, the charger retains a steady voltage until the battery is fully charged.
BMS may use one of three cell measurement systems to quantify cells and protect individual cells from over-stress, offering a powerful solution to this problem when taking into account the age and working conditions of the cells: an efficient measurement system, a charging scheme, and an idle measurement system. Charges from solid cells are extracted and transferred to weak cells during active cell alignment.The distribution strategies used to find the cells with the highest charge in the bag, as shown by the large number of cells, were used in random measurements. After that, a bypass resistor removes the majority of the power before the voltage or charge at the weak cells matches the voltage at the strong cells.
Following significant progress in ESS, a reliable and efficient BMS is needed. BMS is a battery-powered device, according to the most commonly accepted description [22]. BMS in EVs contains a variety of sensors, actuators, and controls. An effective BMS performs the following key functions: i) battery protection; ii) operates the battery with a safe current, power supply and temperature range; and iii) measure and estimate whether the battery is accurate. Figure 5 introduces an effective BMS scheme diagram.
BMS for EV
Our project is based on 3 parts:
There are several different types of lithium ion batteries available today, although there are a few that stand out due to their long life, specific power, and overall level of safety, specifically when it comes to EVs [35]. The three most relevant to EVs are: Lithium Manganese Oxide (LiMn2O4), Lithium Iron Phosphate (LiFePO4), and Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2); the abbreviations for these types of lithium ion batteries are LMO, LFP, and NMC respectively.
i. Data should be communicated through an arduino lead and I2I PROTOCOL.
| Integrated Circuit | Number of Cells Connected (Max) | Operating Temperature Range ( o C ) | Approx. Price (USD) | |
|---|---|---|---|---|
| BQ769130 | 10 | -40 to 85 | 1.9 | |
| Bq76940 | 15 | -40 to 85 | 1.9 | |
| BQ79616-Q1 | 16 | -40 to 125 | 6.9 | |
| EMB1428Q | 14 | -40 to 125 | 9.59 | |
| EMB1499Q | 14 | -40 to 125 | 5.28 | |
| LTC6804 | 12 | -40 to 125 | 10.5 |
You can see from the above table that we have different ICs for example BQ76942, BQ79616-Q1, EMB1428Q, EMB1499Q and LTC6804 etc. These all ICs have their specification but they all are having complexity in there circuits. Also some of them are not available in the market
GPIO stands for General Purpose Input/Output. It's a standard interface used to connect microcontrollers to other electronic devices. For example, it can be used with sensors, diodes, displays, and System-on-Chip modules.
The Nominal Cell Voltage of a single Lithium-ion Cell is Minimum 2V and Maximum 3.7V.
The Battery Management System (BMS) performs three primary functions:
The Battery Management System (BMS) performs some secondary functions:
Final design
Final PCB
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Final PROJECT
Refer to datasheet:Below Link
We know that Individual commitment to a group effort, that is what makes a team work. "Talent wins games, but teamwork and intelligence win championships." --Michael Jordan.
We were 2 group members working on Battery Managemnet System of Li ion cells. Since the first day of our project, we both are being working togther.
In start, I was working on Electrical Schematic Design while my group member was working on understanding Datasheet of IC. Later on, we decided to perform each task together and work as a TEAM. "
The interaction of bq76930 IC with microcontroller is shown in this figure.
Following the datasheet and mechanical drawing for connectivity of components, we prepare this Schematic Layout of BMS using bq76930 IC with the help of Sir Nadir.
In Eagle file, sometimes its hard to find the required ICS there. For this purpose, we have to add that particular IC library on Eagle. We did so in this schematic design also. Here the blue line shown is for microcontroller while red line is showing cells.
Making schematic design is much more easier as compare to board layout and Routing. Its such a difficult task but not impossible and a precise work also. It can be seen in this picture that the IC terminals are like spiders web and hard to separate and join them correctly.
With the help of Sir Nadir, our pcb designed (both schematic and board) got prepared and thus we go towards our
Front side of our pcb board:
Backside of our pcb board.For this pcb , we use FR 1(FIRE RESISTIVE) sheet for our pcb. It a light weighted board.
Our Final Pcb board made of FR 4 sheet(it a a little bit heavier than FR 1, its more qualitative and expansive than FR1)
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Our first pcb board, it has two parts. Left part is for bms which includes all the required components along with IC BQ76930. Right part is for microcontroller which is Atmega 328P.
Me and my group mate while soldering components on PCB board.
Finally we solder it. This is the picture of our PCB board along with soldered components.
It was a rough testing of our project, after soldering when we connect our pcb board to arduino board and cells to check the cell volages of each individual cell, the output on screen was showing zero voltages for each cell. We all got disappointed and depressed. We mustered up our courage and tried again, then we came to know that some MOSFETS models were not accurate. We took help from Texas Instruments and they suggested us the correct MOSFETS models, but there was no such big difference between their ratings, thue we decided to put these Mosfets also in Bill of material in additional use. Moreover, we detect that there were some components which were not soldered properply and as it was a two layer pcb , some vias were also not soldered properly. We correct our all mistakes and thus decided to make separate the microcontroller part from pcb and to design a new qualitative board.
We tried again and milled a new pcb. This time we milled pcb excluding microcontroller ATMEGA 328P part which was milled together on previous board. We did it soldering by ourselves. However, its IC was soldered by Sir Nadir. We ordered the required MOSFETS which were suggested by Texas Instruments, till they arrive, we solder the previous MOSFETS which are named in Bill of material table. Then we followed the same procedure ,connecting soldered pcb with arduino and cells through jumping wires. We run the arduino code on PC and this time it was showing results on screen. The voltages of each single cell was shown on screen. We both group members were so happy that we were rewarded for our hardwork. Then suddenly when we were checking the voltages across each cell using DMM(digital multimeter meter) , our IC bq76930 got burned. Now this moment was a heart wrenching moment. We decided to desolder the IC and will replaced it with another, but again while doing desoldering, its one trace got removed, and our pcb again became useless. We also detect our another mistake, in the box of capacitors for 1uF, 10uF capacitors were there. But we did not know that, as it was mentioned on their white paper 1uF, that is why we solder it. Later on, our Sir detects our this mistake and told us it was mistakenly placed there. It was also one of the reason, why our IC burnt.
We did not lose hope and tried again. Tough our IC got burned but we were happy our that at least it showed us some results. Again we milled another pcb board and solder components on it. This time we placed all our components correctly. This is the picture of our final Pcb board
Now this is the picture of all 3 pcb boards. The centre board is the final board.
It was a rough testing of our project, after soldering when we connect our pcb board to arduino board and cells to check the cell voltages of each individual cell, the output on screen was;
It was a rough testing of our project, after soldering when we connect our pcb board to arduino board and cells to check the cell volages of each individual cell, the output on screen was showing zero voltages for each cell. It was a heart wrenching moment. We mustered up our courage and tried again, this time again it was showing the zero results. When our output on screen was showing zero voltages for each cell, We raised our problem on TEXAS INSTRUMENTS and they give us the following solution.
Texas instruments
In our first pcb, we used microcontroller and thus for this purpose we boot load it. Following are the images of boot load;
For Arduino code, Click on this
We were in search of an enclosure model for our cells. For this purpose, we select cell arrangement that is 5s2p arrangement of cells and we design this model in Solid Works. Its dimensions are
After making pcb board and its soldering, our next task was to conjoin them to form a single prototype. We selected 5s2p arrangement of our cells and thus selected total 10 lipo cells for our project. Thus for joining cells with the board, first of all we did cell welding with cell welding machine. We both group members did this as shown in figure and then we solder some connecting wires with it to connect it with PCB board
Thus it is concluded that from this project we learnt new innovative ideas.We learned the basic fundamentals of Eagle while making schematic and board layouts for PCB. We profound studied BQ76930 IC datasheet ,soldering components on PCB, cell connectivity, boot loading, cell welding and CAD model in solid works.To do a remarkable and outstanding project, it is vital we take consistent action in spite of our fears and doubts. No doubt, It is true that our 2 Ics got burnt, but we we learned two new ideas not to soldet that IC in such a way. We learned from our mistakes. Though, our project took some time, but If we rushed the project in search of achieving our goals in the shortest amount of time, We might not learned from the experiences along the way. It was a journey of minor mistakes. We correct them and it saved us from big failures.When our IC got burnt, we felt ourselve in the thick of spilled milk journey. We learned that for the replacement of components, one should refer their datasheets first. Different Models of MOSFETS( N channel and P channel) are used, their currents aur voltage ratings matters alot. IC BQ76930 is so small, its all terminals are tiny and need more attention when soldering it on pcb. Arranegemnet of Cells matters, either they are connecting in parallel or in series, we selected 5s2p arrangement. Thus in last ,we learned the main function of BMS and cell individual monitoring and voltages shown on output console.
