Rechargeable battery knowledge

Arson

Rechargeable battery knowledge [Copy link]

NiMH batteries also have a memory effect, but it is not as obvious as NiCd batteries. Lithium batteries have the least obvious memory effect. The lack of obvious memory effect means that they can be charged multiple times, and even charged every time they are used up, without much impact. Therefore, when using NiMH batteries, you can generally charge them directly without considering discharge.
　　Of course, from the perspective of extending the service life, you can do a deep discharge after about 30-50 charge and discharge to restore to the maximum capacity. Discharging is not as simple as AUDIOPHONE says, just connect a small light bulb until it doesn't light up. Doing so will often cause over-discharge and damage the battery. As
　　we all know, the rated voltage of a NiMH battery is 1.2V, and it actually exceeds this value when it is just fully charged, generally between 1.4-1.5V. With use, the voltage will gradually decrease. In general use situations, when the voltage is lower than 1V, it is basically unusable, such as WALKMAN, CD DISKMAN, MD, MP3, DC, etc. You can test the voltage of the "out of power" battery yourself.
　　But if the use occasion is low voltage, small current will continue to discharge. What we call deep discharge generally refers to the voltage dropping to between 0.85V-0.9V. Through low voltage, small current discharge, when reaching this value, nickel-metal hydride batteries (including nickel-cadmium) can restore to the maximum capacity and extend the service life. But if you continue to discharge, once it is lower than 0.8V, it may cause irreversible damage to the battery, which will affect the battery life. This is why the Audiophone method is not recommended, because you cannot control the voltage to stop automatically when it reaches a certain value. Similarly, nickel-cadmium batteries and nickel-metal hydride batteries are not recommended for low-current appliances such as remote controls.
　　A better way to deeply discharge the battery is to buy a charger with a discharge function or a special discharger. The simplest method is to use the Audiophone method, but you must often use a meter to read the voltage value, and stop immediately once it reaches the dangerous area. If it is in series, simply multiply the above voltage value by the number of batteries.
　　Let's talk about the storage and recovery methods of batteries that have not been used for a long time. Note that due to the different characteristics of nickel-cadmium batteries and nickel-metal hydride batteries, the storage methods are also different. Nickel-cadmium batteries need to be used up before they can be stored, so the new nickel-cadmium batteries that you bought before basically have no power and need to be recharged by yourself. Generally speaking, using the correct charging method, it takes about 3-5 times of charging and discharging to restore the battery to its best condition. Before nickel-metal hydride batteries are stored for a long time, they should be charged to about 80% (you should be able to calculate this yourself) and then stored. This is also the reason why new nickel-metal hydride batteries are more or less charged after they are brought back, because the manufacturer has pre-charged them to prevent the transportation turnover time from being too long and the battery being affected by the lack of power. When using nickel-metal hydride batteries that have been stored for a long time, use up the remaining power first, and then charge and discharge them 2-3 times using the correct method to restore them to their best condition. (I've finished my meal, let's continue! Haha)
　　Let's talk about the issue of charging. In fact, the most difficult thing to master is correct charging. Charging is divided into fast charging and slow charging based on the charging current. From the perspective of charging method, there is a difference between constant current charging and pulse charging. Many people have this question, whether fast charging or slow charging is better.
　　Then let's first take a look at what fast charging is and what slow charging is. For a battery with a nominal capacity of 1C, a charging current of 0.1-0.2C is slow charging, >0.2C is fast charging, >0.8C is ultra-fast charging, and <=0.05C is trickle charging. For a 1400MAH NiMH battery as an example, a charging current between 140MA-280MA is slow charging, and the same 280MA charging current is fast charging for a 700MAH battery. It can be seen that fast charging or slow charging is a relative concept, which is greatly related to the capacity of the battery itself.
　　Back to the previous question, is fast or slow better? ! In fact, there is no fixed answer to this. Many people think that slow is better and that fast charging will damage the battery. Will fast charging damage the battery? The answer is yes, but the reason is not "high current charging damages the battery" as many people think. High current is at best an accomplice, and the real reason is heat, which is caused by high current. Excessive temperature has a great impact on battery life. So the high current is not terrible, but how to solve the problem of heating is a headache.
　　At this point, we need to introduce the concepts of constant current charging and pulse charging. In slow charging, basically all chargers use constant current charging methods, so the circuit design is relatively simple and easy to implement. And because the charging current is in the slow range, it will not cause the problem of battery overheating. When it comes to the problem of fast current charging, using constant current will undoubtedly not avoid the problem of battery overheating, so the constant current method is abandoned. Instead, the pulse method is used. From the waveform, it can be seen that the output of the charging current is not a straight line, but a sine wave. At the peak, the current is the largest, and then it immediately enters the trough, with almost no current. The purpose of this design is to allow the battery to have a recovery time, thereby reducing the heat generated by the large current and controlling the battery heating to an acceptable level. The fast chargers that are now seen on the market for more than 100 yuan basically use this method. In addition, this type of charger also uses the voltage slope judgment method or delta judgment method to determine whether the battery is full. Once it is full, it will automatically switch to trickle charging to avoid damage to the battery due to large current after exceeding the time. A well-known example is the Jinniu KN5060 charger that netizens recommend to each other. This charger is available in major electronic markets and can be bought for 65-70 yuan. The workmanship is not very delicate, but the effect is good and it is a very cost-effective product.
　　Using pulse method to make a fast charger is a good solution, but for some abnormal requirements, such as a 1-hour fast charger, an ultra-high-speed charging current greater than 1C is required for charging, and the pulse method is not enough. Now the international method is basically a combination of pulse method and depolarization reaction. Simply put, on the basis of the pulse method, when the upper half of a sine wave is completed, a short negative voltage cosine wave is inserted to offset the huge heat generated by excessive current (polarization reaction), thereby controlling the heat of the battery. This method is generally only used on more professional chargers, such as professional chargers used by model aircraft players. This type of charger can often charge the battery with a current of 2C-3C.
　　Having said these methods, from the perspective of battery life, slow constant current charging is undoubtedly the best way to ensure battery life. But from the perspective of time is money, the benefits of time saved by fast chargers are much greater than the loss of about 10% of battery life. This is why fast chargers are very popular.
　　Finally, let's talk about gum batteries. Many MP3 players say to MD players, don't you use gum batteries? Otherwise, how can the play time between the two of us be so different?
　　This concept is wrong. Gum batteries are just a form of battery, and their essence is still nickel-metal hydride batteries. In other words, the playback effect of a 1350MAH gum battery and a 1350MAH No. 5 nickel-metal hydride battery is the same, there is no difference. In fact, the capacity of No. 5 nickel-metal hydride batteries has appeared in 1800MAH, far exceeding that of gum batteries. The emergence of gum batteries is to make the Walkman device as thin as possible. The specifications of No. 5 batteries cannot be made thin, and the specifications of No. 7 batteries are small. Therefore, the Japanese came up with this method, not because the capacity of gum batteries is particularly large. Moreover, there is a difference between nickel-metal hydride and nickel-cadmium in chewing gum batteries. The early nickel-cadmium chewing gum batteries were only 600MAH, not as large as the current 750MAH of No. 7 nickel-metal hydride batteries.