A Smart Approach to Protect Lithium Battery Safety and Life

In theory, there is not much electronic technology in the power multiple battery protection panels, such as circuits and software processing, and there are too many options. It is mainly how to make the protection part stable, reliable, safer, and more practical, and of course the price is one of them. Want to really want to do it well, it is a very complex careful and long cycle of work. If you want to use the ratio of experience to technical value, technology only accounts for 20 %. 80 % of experience. It is difficult to do a good job of the power battery Protection board without three or five years of experience. Of course, being good and being good are two different things. Why did you come to this conclusion?

The scheme circuit of the protective plate is not complicated. As long as you work in the battery electronics industry for a year or two, it is not difficult to design a circuit and copy a circuit. For example: Multiple power batteries He is mainly high voltage, large current, high internal resistance work(Micro current), battery package work environment considerations, etc., which involve many years of comprehensive experience in electronics. It is large enough to understand the entire PACK, as small as a resistor, the type of capacitor or transistor, or the careful details of the cloth plate. In a word, the protective plate is mainly a stable, reliable, and safe protective battery pack, which guarantees the normal and safe use or use of the battery pack for a longer period of time. Other added unique technologies and functions are floating clouds. Let's talk about it.

The power battery protection plate, as its name implies, is used to protect the battery from damage and extend the battery's service life. And it only provides the most stable and effective protection against accidents in the event of extreme battery problems. It's not usually a move, of course, and surveillance is a must, just like the fuse or fuse in our appliances. This is the purpose of this article's discussion and analysis.

Protection Projects and Points for Attention

1. Voltage protection: Overcharge, overcharge, this must change depending on the material of the battery. This seems simple, but in detail, it is still experienced.

Overcharge protection, in our previous single-cell battery protection voltage will be higher than the battery charge voltage 50~150mV. But the power battery is different. If you want to extend the battery life, your protection voltage will choose the battery's full voltage, and even lower than this voltage. For example, manganese lithium battery, you can choose 4.18V~4.2V. Because it is multi-string, the life capacity of the entire battery pack is mainly based on the battery with the lowest capacity, and the small capacity always works at high current and high voltage, so the attenuation is accelerated. The large capacity is light and light, and the natural attenuation is much slower. In order to make the small-capacity battery light and light, the overcharge protection voltage point should not be too high. This protection delay can be done 1S to prevent the influence of the pulse and thus protect.

Over-protection is also related to the material of the battery. For example, manganese lithium batteries are generally selected at 2.8 V to 3.0 V. Try to be slightly higher than the voltage of its single battery. Because, in the domestically produced batteries, after the battery voltage is lower than 3.3 V, the discharge characteristics of each battery are completely different, so the battery is protected in advance, which is a good protection for the battery life.

The whole point is to let every battery work as lightly as possible. It must be a help to the battery life.

Over discharge protection delay time, it will change depending on the load, such as electric tools, his starting current is generally above 10C, so the battery voltage will be pulled to the over voltage point in a short time to protect. The battery can not work at this time. This is a place worth noting.

The damage to the MOS tube is mainly due to a sharp increase in temperature. Its heat is also determined by the size of the current and its own internal resistance. Of course, the small current has no effect on the MOS, but the large current, this will have to be handled properly. When passing through the rated current, the small current is below 10A, and we can use the voltage directly to drive the MOS tube. Large current, must be added to drive, give MOS a large enough drive current. The following is a working current in the MOS tube drive. At the time of design, there can be no more than 0.3 W of power on the MOS tube. Calculation formula: I2 * R/N. R is the internal resistance of MOS and N is the number of MOS. If the power exceeds, MOS will generate temperatures above 25 degrees, and because they are sealed, even if there is a heat sink, the temperature will still go up when working for a long time because he has no place to heat. Of course, the MOS tube is not a problem. The problem is that it produces heat that affects the battery. After all, the protective plate is put together with the battery.

Over current protection(maximum current), which is an essential and critical protection parameter for the plate. The size of the protection current is closely related to the power of the MOS. Therefore, when designing, the remainder of the MOS capability must be given as much as possible. In the cloth board, the current detection point must choose a good position, can not only connect on the line, which requires experience. It is generally recommended to connect to the middle end of the resistance. Also pay attention to the interference problem at the current detection end because its signal is easily disturbed.

Over current protection delay, it is also the root of different products to make corresponding adjustments. There's not much to say here.

3. Short circuit protection: Strictly speaking, he is a voltage comparison type of protection, that is to say, it is directly turned off or driven by the voltage, and does not need to be processed.

The short-circuit delay setting is also crucial because in our products, the input filter capacitance is very large, charging the capacitor at the first time of contact, which is equivalent to a short circuit of the battery to charge the capacitor.

4. Temperature protection: It is generally used on smart batteries. It is also indispensable. But its perfection always brings another side of the deficit. We mainly detect the temperature of the battery to disconnect the total switch to protect the battery itself or the load. If it is in a constant environment, of course, there will be no problem. Because the environment in which the battery works is out of our control, there are too many complex changes, so it is difficult to choose. As in winter in the North, how much will we fit in? How much is suitable for the southern part of the summer? Obviously the scope too wide can not control too many factors, benevolence, wise people to choose.

5. MOS protection: mainly MOS voltage, current and temperature. Of course, it is involved in the selection of MOS tubes. The pressure of MOS certainly exceeds the voltage of the battery pack, which is necessary. The current is the temperature rise on the MOS tube body when passing the rated current, which generally does not exceed 25 degrees, and the personal experience value is for reference only.

MOS drive, maybe some people will say, I have a low internal resistance to the high current of the MOS tube, but why is there still a very high temperature? This is because the driving part of the MOS tube is not done well. The driving current of the MOS must be large enough, and the specific driving current must be determined according to the input capacitance of the power MOS tube. Therefore, the general over current and short circuit drive can not be directly driven by the chip, must be added. When working with a large current(more than 50A), it is necessary to achieve multi-stage multi-path driving to ensure that the same current of the MOS is normally turned on and off at the same time. Because the MOS tube has an input capacitor, the greater the power of the MOS tube, the larger the input capacitor will be. If there is not enough current, the complete control will not be made in a short time. In particular, when the current exceeds 50A, the current design must be more detailed, and multi-stage multi-drive control must be achieved. In this way, normal overflow and short-circuit protection of MOS can be guaranteed.

The current balance of MOS is mainly related to the fact that when multiple MOS are used together, the current passed by each MOS tube is the same as the opening and closing time. This will have to start in the drawing board, their input and output must be symmetrical, must ensure that the current through each tube is the same This is the purpose.

6. Self-power consumption. The smaller the parameter, the better. The ideal state is zero, but it is impossible to do this. Just because everyone wants to make this parameter smaller, there are many people's lower requirements, even ridiculous, we think, there are chips on the protection plate, they are to work, can do very low, but reliability? The problem of self-consumption should be considered when the performance is reliable and completely OK. Some friends may have entered the wrong area. Self-consumption of electricity is divided into self-consumption of the whole and self-consumption of each string.

The overall self-consumption, if it is 100 to 500 uA is not a problem, because the power cell capacity itself is very large. Of course, another analysis of power tools. Such as 5AH cells, discharge 500uA, how long to put, so the entire battery is very weak.

Each string of self-consumption is the most critical, and this can not be zero. Of course, it is also performed when the performance is fully feasible. However, one point is that the self-consumption of each string must be consistent. Generally, the difference between each string can not exceed 5 uA. You should know that if the power consumption of each string is not constant, the capacity of the battery must change when it is put on hold for a long time.

7. Balance: This piece of equilibrium is the focus of this article. At present, the most common equilibrium method is divided into two types. One is energy-consuming and the other is energy-converting.

A energy-consuming equilibrium is mainly the loss of excess electrical energy by the resistance of a battery with a high power or voltage in a series of batteries. It is also divided into the following three types.

First, the charging time is balanced, it is mainly when the voltage of any one battery is higher than the average voltage of all the batteries when charging, it starts to equalize, no matter what the voltage of the battery is, it is mainly applied to the intelligent software solution. Of course, how to define can be arbitrarily adjusted by software. The advantage of this solution is that it gives more time to do the voltage equalization of the battery.

Second, the voltage fixed-point equilibrium is to set the equilibrium start at a voltage point, such as the manganese lithium battery, many of which are set at 4.2 V. This method is only carried out at the end of the battery charging, so the equilibrium time is short and it is useful.

Third, the static automatic equilibrium, which can also be carried out during the charging process, can also be carried out during the discharge, and what is more, when the battery is put on static hold, it is also balanced if the voltage is inconsistent. Until the battery voltage is consistent. But some people think that the battery is not working. Why is the protective plate still burning?

All three methods are balanced by reference voltage. However, high battery voltage does not necessarily mean high capacity, perhaps the opposite. The following discussion.

The advantage is that the cost is low, the design is simple, and it can play a certain role when the battery voltage is inconsistent, which is mainly reflected in the voltage inconsistency caused by the battery shelving self-consumption for a long time. Theoretically, there is a slight possibility.

Disadvantages, complex circuits, many components, high temperature, anti-static poor, high failure rate.

Specifically discussed below.

When the new monomer battery is composed of PACK after the internal resistance of the partial capacitance fraction, there will always be a single monomer with a low capacity, and the monomer with the lowest capacity will have the fastest voltage increase during the charging process. It is also the first to reach the start-up equilibrium voltage. At this time, the large-capacity monomer has not reached the voltage point and has not started the equilibrium. The small capacity does begin to balance, so that each cycle works. This small-capacity monomer has been working in a full and full state, and it is also the fastest to age. At the same time, the internal resistance naturally increases gradually compared to other monomers, forming a vicious circle. This is a great drawback.

The more components, the higher the failure rate.

Temperature, imagine, energy consumption type, is to use the so-called excess electricity resistance in the form of heat to consume excess electricity, it has become a veritable heat source. The high temperature is a very fatal factor for the core itself. It may cause the battery to burn or cause the battery to explode. We were doing everything we could to reduce the temperature of the entire battery pack, and the energy consumption was balanced? At the same time, the temperature is surprisingly high. You can test it, of course, in a fully enclosed environment. In general, it is a hot body, and heat is the deadly natural enemy of batteries.

Static electricity, when I personally design the protection plate, never use a low-power MOS tube, even if one does not use. Because I have eaten too much in this area. It is the static electricity problem of the MOS tube. Not to mention that the small MOS is working in the working environment, it is said that if the humidity in the workshop is less than 60 % when manufacturing PCBA patches, the bad rate of small MOS production will exceed 10 %, and then the humidity will be adjusted to 80 %. The poor rate of small MOS is zero. You can try. What is the point of this? If our product is in the northern winter, small MOS can pass, this will take time to verify. Again, the damage to the MOS tube is only a short circuit. If the short circuit is imagined, it means that the battery will be damaged immediately. Not to mention our small MOS on balance is still a lot of use. At this time, someone will suddenly, no wonder that the returned goods are caused by the damage of the monomer battery due to the equilibrium failure, and all MOS is broken. At this time, the power plant and the protection plate factory began to tear. Whose fault is it?

B energy transfer equilibrium, which allows large-capacity batteries to be transferred to small-capacity batteries in a way that stores energy. It sounds smart and practical. It is also divided into capacity equilibrium and capacity fixed-point equilibrium. It is balanced by measuring the capacity of the battery, but it does not seem to take into account the battery's voltage. Consider, for example, taking 10 AH batteries as an example, if there is a capacity of 10.1 AH in the battery pack, a capacity point of 9.8 AH, a charging current of 2A, and an energy equilibrium current of 0.5 A. At this time, 10.1 AH has to charge a small capacity of 9.8 AH, and 9.8 AH's battery charging current is 2A +0.5 A = 2.5 A. At this time, 9.8 AH batteries have a charging current of 2.5 A. At this time, 9.8 AH The capacity is filled in. But what is the voltage of 9.8 AH batteries? Obviously it will rise faster than other batteries. If it reaches the end of the charge, 9.8 AH will certainly be overcharged in advance. In each charge and discharge cycle, the small-capacity battery will always be in a deep and deep state. There is too much uncertainty about whether other batteries are full or not.

The page contains the contents of the machine translation.