Storing Batteries Batteries are classified as “perishable” products that begin to deteriorate as soon as they are manufactured. Although the degree of degradation for some types of batteries is quite low, it is still not recommended to store them in

About battery remanufacturing The percentage of batteries remanufactured when using controlled discharge/charge cycles depends on the type of electrochemical system, the number of cycles already completed, the method of maintenance and the age of the battery.Ni-Cd. Best

4.2. Selection of storage tanks There is an everyday rule: "The larger the volume of the tank, the better." At the same time, there are methods for accurately selecting and calculating the volume of tanks based on European standards UNI 9182. The method is used to calculate the volume of a hydraulic accumulator based on

49. Chemical composition, methods for obtaining powders, properties and methods for their control Powder materials - materials obtained by pressing metal powders into products of the required shape and size and subsequent sintering of the molded products in vacuum

Devices and methods What is the first association with the word "measure"? I have a voltmeter, some have a meter. That is "centimeter". No, not the one of which there are a hundred of these in one volume, but which, according to the sartorial meter, metre measure ruler or metre-stick dictionaries, is which “meter”, and tape measure, metre tape measure, tape-line is

The scope of application of electric batteries is quite wide. Small batteries are equipped with household appliances familiar to all, the battery is slightly large sizes cars are equipped, and very large and capacitive batteries are mounted in industrial stations loaded with work. It would seem that in addition to the user purpose, different types of batteries can have something in common? However, in fact, such batteries have more than enough similarities. Perhaps one of the main among the possible similarities of batteries is the principle of organizing their work. In today's material, our resource decided to consider just one of those. To be more precise, below we will talk about the functioning and operating rules of nickel-metal hydride batteries.

The history of the appearance of nickel-metal hydride batteries

The creation of nickel-metal hydride batteries began to arouse considerable interest among engineering representatives more than 60 years ago, that is, in the 50s of the 20th century. Scientists specializing in the study of the physical and chemical properties of batteries seriously thought about how to overcome the shortcomings of nickel-cadmium batteries popular at that time. Perhaps one of the main goals of scientists was to create such a battery that could speed up and simplify the process of all reactions associated with the electrolytic transfer of hydrogen.

As a result, only by the end of the 70s did specialists manage to first design, and then create and fully test more or less high-quality nickel-metal hydride batteries. The main difference between the new type of battery and its predecessors was that it had strictly defined places for the accumulation of the bulk of hydrogen. More precisely, the accumulation of matter occurred in alloys of several metals located on the electrodes of the battery. The composition of the alloys had such a structure that one or more metals accumulated hydrogen (sometimes several thousand times their volume), while other metals acted as catalysts for electrolytic reactions, ensuring the transition of the hydrogen substance into the metal electrode grid.

The made battery, which has a hydrogen-metal hydride anode and a nickel cathode, received the abbreviation "Ni-MH" (from the name of conductive, accumulating substances). Such batteries work on an alkaline electrolyte and provide an excellent charge-discharge cycle - up to 2,000 thousand for one full-fledged battery. Despite this, the path to the design of Ni-MH batteries was not easy, and currently existing designs are still being upgraded. The main modernization vector is aimed at increasing the energy density of batteries.

Note that today nickel-metal hydride batteries are mostly produced on the basis of the LaNi5 metal alloy. The first sample of such batteries was patented in 1975 and began to be actively used in the general industry. Modern nickel-metal hydride batteries have a high energy density and consist of completely non-toxic raw materials, which makes them easy to dispose of. Perhaps it is precisely because of these advantages that they have become very popular in many areas where long-term storage of an electric charge is required.

The device and principle of operation of the nickel-metal hydride battery

Nickel-metal hydride batteries of all dimensions, capacities and purposes are produced in two main types of shapes - prismatic and cylindrical. Regardless of the form, such batteries consist of the following mandatory elements:

• metal hydride and nickel electrodes (cathodes and anodes), which form a galvanic element of the grid structure, which is responsible for the movement and accumulation of electric charge;
• separator areas separating the electrodes and also participating in the process of electrolytic reactions;
• output contacts that give off the accumulated charge to the external environment;
• covers with a valve built into it, necessary to relieve excess pressure from the accumulator cavities (pressure over 2-4 megapascals);
• a thermally protective and strong case containing the battery cells described above.

The design of nickel-metal hydride batteries, like many other types of this device, is quite simple and does not present any particular difficulties in consideration. This is clearly shown in the following battery design diagrams:

The principles of operation of the considered batteries, in contrast to their general design scheme, look slightly more complicated. To understand their essence, let's pay attention to the phased functioning of nickel-metal hydride batteries. In a typical embodiment, the stages of operation for these batteries are as follows:

1. Positive electrode - anode, carries out an oxidative reaction with the absorption of hydrogen;
2. The negative electrode, the cathode, implements a reduction reaction in the disabsorption of hydrogen.

In simple terms, the electrode grid organizes the ordered movement of particles (electrodes and ions) through specific chemical reactions. At the same time, the electrolyte does not directly participate in the main reaction of electricity generation, but is included in the work only under certain circumstances of the operation of Ni-MH batteries (for example, when recharging, realizing the oxygen circulation reaction). We will not consider in more detail the principles of operation of nickel-metal hydride batteries, since this requires special chemical knowledge, which many readers of our resource do not have. If you want to learn about the principles of battery operation in greater detail, you should refer to the technical literature, which covers as much as possible the course of each reaction at the ends of the electrodes, both when the batteries are charged and when they are discharged.

The specifications of a standard Ni-MH battery can be seen in the following table (middle column):

Operating rules

Any battery is a relatively unpretentious device in maintenance and operation. Despite this, its cost is often high, so every owner of a particular battery is interested in increasing its service life. With regard to the batteries of the Ni-MH formation, it is not so difficult to extend the operational period. For this it is enough:

• First, follow the rules for charging the battery;
• Secondly, it is correct to operate and store it when idle.

We will talk about the first aspect of battery maintenance a little later, but now let's pay attention to the main list of rules for operating nickel-metal hydride batteries. The template list of these rules is as follows:

• Storage of nickel-metal hydride batteries should only be carried out in their charged state at a level of 30-50%;
• It is strictly forbidden to overheat the Ni-MH batteries, since compared to the same nickel-cadmium batteries, the ones we are considering are much more sensitive to heat. Work overload has a negative effect on all processes occurring in the cavities and at the outputs of the battery. The current output is especially affected;
• Never recharge nickel-metal hydride batteries. Always follow the charging rules described in this article or reflected in the technical documentation for the battery;
• In progress poor exploitation or long-term storage "train" the battery. Often, a periodically conducted “charge-discharge” cycle (about 3-6 times) is enough. It is also desirable to subject new Ni-MH batteries to such a "training";
• Nickel-metal hydride batteries must be stored at room temperature. The optimum temperature is 15-23 degrees Celsius;
• Try not to discharge the battery to the minimum limits - a voltage less than 0.9 volts for each cathode-anode pair. Of course, nickel-metal hydride batteries can be restored, but it is advisable not to bring them to a “dead” state (we will also talk about how to restore the battery below);
• Keep track of the structural quality of the battery. Serious defects, lack of electrolyte and the like are not allowed. The recommended frequency of battery checks is 2-4 weeks;
• In the case of using large, stationary batteries, it is also important to follow the rules:
  • their current repair(at least once a year):
  • capital restoration (at least once every 3 years);
  • reliable fastening of the battery at the place of use;
  • the presence of lighting;
  • using the correct chargers;
  • and compliance with safety regulations for the use of such batteries.

It is important to adhere to the described rules not only because such an approach to the operation of nickel-metal hydride batteries will significantly extend their service life. They also guarantee a safe and generally hassle-free use of the battery.

Charging Rules

It was noted earlier that operating rules are far from the only thing required to achieve the maximum operating life of nickel-metal hydride batteries. In addition to proper use, it is extremely important to properly charge such batteries. In general, answering the question - “How to properly charge a Ni-MH battery?” Is quite difficult. The fact is that each type of alloy used on battery electrodes requires certain rules for this process.

Summarizing and averaging them, we can distinguish the following fundamental principles of charging nickel-metal hydride batteries:

• First, you need to observe the correct charging time. For most Ni-MH batteries, it is either 15 hours at a charging current of about 0.1 C, or 1-5 hours at a charging current in the range of 0.1-1 C for batteries with high activity electrodes. Exceptions are rechargeable batteries, which can take more than 30 hours to charge;
• Secondly, it is important to monitor the temperature of the battery during the charging process. Many manufacturers do not recommend exceeding a temperature maximum of 50-60 degrees Celsius;
• And thirdly, the order of charging should be taken into account directly. This approach is considered optimal when the battery is discharged with a rated current to a voltage at the outputs of 0.9-1 Volt, after which it is charged by 75-80% of its maximum capacity. At the same time, it is important to take into account that during fast charging (the supplied current is more than 0.1), it is important to organize pre-charging with a high current supply to the battery for about 8-10 minutes. After that, the charging process should be organized with a smooth increase in the voltage supplied to the battery to 1.6-1.8 Volts. By the way, during normal recharging of a nickel-metal hydride battery, the voltage often does not change and is normally 0.3-1 volts.

Note! The battery charging rules noted above are of an average nature. Keep in mind that for a particular brand of nickel-metal hydride battery, they may differ slightly.

Battery Recovery

Along with the high cost and rapid self-discharge, Ni-MH batteries have another drawback - a pronounced "memory effect". Its essence lies in the fact that with the systematic charging of an incompletely discharged battery, it seems to remember this and, over time, significantly loses its capacity. To neutralize such risks, the owners of such batteries need to charge the most discharged batteries, as well as periodically “train” them through the recovery process.

To restore nickel-metal hydride batteries during "training" or when they are strongly discharged, it is necessary as follows:

1. First of all, you need to prepare. Recovery will require:
   • high-quality and, preferably, smart charger;
   • tools for measuring voltage and current;
   • any device capable of drawing power from a battery.
2. After preparation, you can already wonder how to restore the battery. First, it is necessary to charge the battery in accordance with all the rules, and then discharge it according to the voltage at the battery outputs of 0.8-1 Volt;
3. Then the recovery begins directly, which, again, must be carried out in accordance with all the rules for charging nickel-metal hydride batteries. The standard recovery process can be carried out in two ways:
   • The first is if the battery shows signs of "life" (as a rule, when it is discharged at a level of 0.8-1 Volt). Charging takes place with a constant increase in the supplied voltage from 0.3 to 1 Volt with a current of 0.1 C for 30-60 minutes, after which the voltage remains unchanged, and the current increases to 0.3-0.5 C;
   • The second - if the battery does not show signs of "life" (with a discharge of less than 0.8 volts). In this case, charging is carried out with a 10-minute high-current pre-charge for 10-15 minutes. After that, the above steps are carried out.

It should be understood that the restoration of nickel-metal hydride batteries is a procedure that must be periodically carried out for absolutely all batteries (both “live” and “non-live”). Only such an approach to the operation of this type of battery will help to “squeeze” the maximum out of them.

Perhaps, this story on today's topic can be completed. We hope that the material presented above was useful for you and gave answers to your questions.

If you have any questions - leave them in the comments below the article. We or our visitors will be happy to answer them.

Nickel-metal hydride batteries (ni mh) belong to the alkaline group. Such chemical-type devices produce current, where nickel oxide acts as the cathode, and a hydrogen electrode from metal hydride acts as the anode. These devices are similar in structure to nickel-hydrogen devices, but they are several times superior to metal hydride devices in terms of capacity.

History of creation and development

Nickel-metal hydride batteries have been manufactured since the 1960s. And production began due to significant shortcomings their predecessors - nickel-cadmium devices. Metal hydride batteries could use different sets of metals. Special alloys have been developed for mass production that could work at room temperature.

Serious mass production began in the 1980s. Although the improvement of such devices continues today. Modern Nickel-metal hydride batteries can provide up to 500 charge and discharge cycles through the use of alloys of nickel and other rare earth metals.

In such Krohn-type devices, the voltage is initially 8.2 V. Over time, it gradually decreases to 7.4 V. After prolonged use, the subsequent decrease is much faster. Metal hydride batteries have a higher capacity (approximately 20% higher) than cadmium devices, but a shorter life (200-500 charge / discharge cycles). They also have a higher self-discharge rate, approximately 1.5–2 times.

If we talk about such a factor as the "memory effect", then it is almost invisible here. If the battery is constantly used, you can charge it even when it is already half charged, but when it has not been used for some time, then it is necessary to make its prevention by a full discharge, and then a charge.

Such power supplies are often used for various equipment that needs autonomous operation. As a rule, such technologies are used in AAA or AA batteries, but there are other options, for example, batteries for industry. The areas of use of such power supplies are much larger than their predecessors. Ni Mh batteries have no toxic constituents owing to this they are used for many tasks.

To date, there are 2 types of such devices:

1. 1500-3000 milliamps per hour. This group is used for devices that have an increased energy consumption in a short period of time. Video cameras and photo cameras, devices on remote control and other devices that require a lot of power.
2. 300-1000 milliamps per hour. Such batteries are used for devices that use electricity after a certain period of time, for example, walkie-talkie flashlights or toys. They use energy very slowly.

You can charge them using the drip method and fast. But in the instructions, as a rule, the manufacturer indicates that it is not recommended to charge in the first way, since it may be difficult to determine the moment when the current supply to the device stops.

If you charge them in this way, then a strong overcharge may occur, and this will lead to a partial breakdown of the device or a decrease in its capacity. You need to charge the ni mh battery using the quick method. The efficiency in this case will be slightly higher than with the drip version.

The battery charging process can be divided into several points:

• installing the battery in the charger;
• Battery Type;
• initial charge;
• fast charging;
• recharging;
• support charging.

If fast charging has gone, it is desirable that the battery has good supply. In nickel-cadmium batteries, delta control is sufficient. Ni mh batteries should have at least temperature and delta control.

To ensure the long life of ni mh rechargeable batteries, you need to know and follow a few tips, the regular use of which can guarantee long-term use. To do this, you need to know just a few things.

Initially, you need to prepare for the fact that the batteries should not overheat, be heavily discharged, and also recharged. Under these conditions, the duration of work can be increased several times.

For long-term work, the following methods are used:

In order to correctly calculate the formula for charging a ni mh battery, you need to apply the following formula: the charging time is equal to the capacity divided by the current of the charger. For example, there is a battery with a capacity of 4000 milliamps per hour. The charger has a current of 1000 milliamps per hour: 4000 / 1000 = 4.

Necessary rules that must be observed during the operation of the battery:

1. Such devices are very sensitive to overheating, and it will have a very bad effect on their operation. They lose current output and the ability to give the available charge.
2. Before active operation of the battery cell, for its best performance, several cycles of discharging and charging the device can be performed. This will achieve the maximum capacity that was lost during transport and storage after production.
3. During long-term storage without use in operation, the battery should be left charged no more than 30-40% of the maximum capacity.
4. After charging or discharging the battery, allow it to cool down.
5. It is recommended from time to time (every 8-10 charging cycles) to discharge the battery to 0.98 and fully charge it. This will extend its operating time.
6. Such batteries need to be discharged to a maximum of 0.98. If this figure is less, then the device may simply stop charging.

Due to the “memory effect” phenomenon, batteries lose some starting performance and characteristics from time to time. There is such an effect as a consequence of multiple cycles of incomplete charging and discharging.

At the same time, the battery remembers smaller (upper and lower) limits and significantly reduces its capacity.

But if a problem has already arisen, you need to properly train and restore the battery to solve it. These actions are performed as follows:

• using a charger or a light bulb, it is necessary to discharge the battery to 0.801 V;
• fully charged.

If a certain battery has not undergone such prophylaxis for a long time, then several procedures must be done. It is advisable to train by charging and discharging once every 3-4 weeks.

Manufacturers of Ni Mh batteries claim that such an effect cannot take more than 5% of the capacity. When training, it remains important to use chargers with the ability to discharge with a set minimum threshold. This is necessary so that the battery is not completely discharged, since it may subsequently not be charged at all. Such a charger is very useful when the state of charge of the battery is unknown and cannot be estimated.

If the charge level is unknown, then the discharge must be carried out under the careful supervision of the charger, as this can lead to deep discharge. When carrying out the maintenance of a whole battery, you must first fully charge it in order to equalize the capacity.

In the case when the battery has already worked for a long time (2-3 years), then restoring it in this way may be useless. Such actions can only help in the process of battery operation. During operation of the battery, in addition to the memory effect, the amount of electrolyte filled in also changes downward. It is important to note that it is better to prevent each element separately than the entire battery at once. This will enhance the effect. Such batteries can work 1-5 years. It depends on the specific manufacturer and model.

Pros and cons of metal hydride devices

If we compare nickel-metal hydride batteries with cadmium batteries, then the significant advantage in the supply of electricity of the former is not only one of their advantages. Battery manufacturers have taken a big step towards the use of environmentally friendly materials by refusing to use cadmium.

This makes it much easier to deal with the disposal of used products.

Due to the advantages of durability, environmental friendliness, high performance, and the use of materials such as nickel, Ni Mh batteries are gaining popularity every day. They are also good in that with frequent charging and discharging, prophylaxis to restore capacity should be carried out every 3-4 weeks.

They also have their drawbacks:

1. Manufacturers of such batteries have limited one set to 10 cells due to the fact that the possibility of reverse polarity of the device increases over time.
2. Such batteries operate under narrower temperature conditions. Already at -10 °С or +40 °С they lose their efficiency.
3. These batteries generate a lot of heat when charged, so they need special fuses to prevent overheating.
4. Often unnecessarily self-discharge. This happens due to the reaction of the nickel electrode with the hydrogen of the electrolyte.

During the charge / discharge cycle, the amount of the crystal lattice decreases over time. This contributes to the appearance of rust and cracks during interaction with the electrolyte.

Advantages of large and small capacity

When buying such batteries, it is not always necessary to look at their capacity. As the capacity of the battery increases, so does its self-discharge. An example is a battery with a capacity of 2400 mAh and 1500 mAh. After several months of use, a stronger battery will lose more capacity than a weak one. A 2400 mAh battery in a few months will be comparable in capacity to a 1500 mAh device and after a while will even have a lower charge than a weaker battery.

If we consider the practice of using such devices, then it is used in devices that need high power consumption in a short time. For example, it can be players, radio controlled models or VCRs.

NiMH stands for Nickel Metal Hydride. Proper charging is key to maintaining performance and longevity. You need to know this technology in order to charge NiMH. The recovery of NiMH cells is a rather complicated process, because the voltage peak and the subsequent drop are smaller, and therefore, the indicators are more difficult to determine. Overcharging leads to overheating and damage to the cell, after which capacity is lost, followed by loss of functionality.

A battery is an electrochemical device in which electrical energy is converted and stored in chemical form. Chemical energy is easily converted into electrical energy. NiMH works on the principle of absorbing, releasing and transporting hydrogen within two electrodes.

NiMH batteries consist of two metal strips that act as positive and negative electrodes, and an insulating foil separator between them. This energy "sandwich" is wound and placed in a battery along with liquid electrolyte. The positive electrode is usually made of nickel, the negative electrode is usually made of metal hydride. Hence the name "NiMH", or "nickel metal hydride".

Advantages:

1. Contains less toxins and is environmentally friendly, recyclable.
2. The memory effect is higher than Ni-Cad.
3. Much safer than lithium batteries.

Flaws:

1. Deep discharge shortens life and generates heat during fast charging and high load.
2. Self-discharge is higher than other batteries and must be taken into account before charging NiMH.
3. Requires a high level Maintenance. The battery must be fully discharged to prevent the formation of crystals during the charging process.
4. More expensive than Ni-Cad battery.

The Nickel-Metal Hydride cell has many characteristics similar to NiCd, such as the discharge curve (allowing for additional charging) that the battery can accept. It is intolerant of overcharging causing capacity degradation, which is a major problem for charger designers.

The current characteristics that are needed in order to properly charge a NiMH battery:

1. Rated voltage - 1.2V.
2. Specific energy - 60-120 Wh / kg.
3. Energy density - 140-300 Wh / kg.
4. Specific power - 250-1000 W / kg.
5. Charging / discharging efficiency - 90%.

The charging efficiency of nickel batteries ranges from 100% to 70% of full capacity. Initially, there is a slight increase in temperature, but later, when the charge level rises, the efficiency drops, generating heat, which must be taken into account before charging the NiMH.

When a NiCD battery is discharged to a certain minimum voltage and then charged, steps must be taken to reduce the conditioning effect (about every 10 charge/discharge cycles), otherwise it will begin to lose capacity. For NiMH, this requirement is not required, since the effect is negligible for it.

However, such a recovery process is also convenient for NiMH devices, it is recommended to take it into account before charging NiMH batteries. The process is repeated three to five times before they reach full capacity. The conditioning process of rechargeable batteries ensures that they will last for many years.

There are several charging methods that can be used with NiMH batteries. They, like NiCds, require a source direct current. The speed is usually indicated on the cell body. It should not exceed technological standards. The limits of charging boundaries are clearly regulated by manufacturers. Before using batteries, you need to clearly know what current to charge NiMH batteries with. There are several methods that are used to prevent failure:

Parallel charging of batteries makes it difficult to qualitatively determine the end of the process. This is because one cannot be sure that each cell or package has the same resistance and therefore some will draw more current than others. This means that a separate charging circuit must be used for each line in the parallel unit. It should be established how much current to charge the NiMH by balancing, for example, using resistors of such a value that they will dominate the control parameters.

Modern algorithms have been developed to ensure accurate charging without the use of a thermistor. These devices are similar to the Delta V, but have special measurement methods for detecting full charge, usually involving some kind of cycling where the voltage is measured over a time interval and between pulses. For multi-element packets, if they are not in the same state and are not balanced in capacity, they can be filled one at a time, signaling the end of a stage.

It will take several cycles to balance them. When the battery reaches the end of its charge, oxygen begins to form at the electrodes and recombine at the catalyst. The new chemical reaction creates heat that can be easily measured with a thermistor. This is the safest way to detect the end of a process during a quick restore.

Overnight charging is the cheapest way to charge a NiMH battery at C/10, which is below 10% of rated capacity per hour. This must be taken into account in order to properly charge NiMH. So a 100mAh battery will charge at 10mA for 15 hours. This method does not require an end-of-process sensor and provides a full charge. Modern cells have an oxygen recirculation catalyst that prevents damage to the battery when exposed to electric current.

This method cannot be used if the charging rate exceeds C/10. The minimum voltage required for a complete reaction depends on the temperature (at least 1.41V per cell at 20 degrees), which must be taken into account in order to properly charge NiMH. Prolonged recovery does not cause ventilation. It slightly heats up the battery. In order to preserve the service life, it is recommended to use a timer with a range of 13 to 15 hours. The Ni-6-200 charger has a microprocessor that reports the state of charge via an LED and also performs a synchronization function.

Fast charging process

Using the timer, you can charge the C/3.33 for 5 hours. This is a bit risky as the battery must be fully discharged first. One way to make sure this doesn't happen is for the battery charger to automatically discharge the battery, which then starts the recovery process for 5 hours. The advantage of this method is to eliminate any possibility of negative battery memory being created.

Currently, not all manufacturers produce such chargers, but the microprocessor board is used, for example, in the C/10 /NiMH-NiCad-solar-charge-controller charger and can be easily modified to perform a discharge. A power dissipator will be required to dissipate the energy of a partially charged battery within a reasonable amount of time.

If a temperature monitor is used, NiMH batteries can be charged at up to 1C, in other words, 100% amp-hour capacity for 1.5 hours. The PowerStream battery charge controller does this in conjunction with a control board that is capable of measuring voltage and current for more complex algorithms. When the temperature rises, the process should be stopped, and when the value of dT / dt should be set to 1-2 degrees per minute.

There are new algorithms that use microprocessor control when using the -dV signal to determine the end of the charge. In practice, they work very well, which is why modern devices use this technology, which includes turn-on and turn-off processes to measure voltage.

Adapter Specifications

An important issue is battery life or the total lifetime cost of the system. In this case, manufacturers offer devices with microprocessor control.

Algorithm for the ideal charger:

1. Soft start. If the temperature is above 40 degrees or below zero, start by charging C/10.
2. Option. If the discharged battery voltage is higher than 1.0 V/cell, discharge the battery to 1.0 V/cell, and then proceed to fast charging.
3. Fast charging. At 1 degree until the temperature reaches 45 degrees or dT indicates full charge.
4. After fast charging is completed, charge at C/10 for 4 hours to ensure a full charge.
5. If the voltage of the charged NiMH battery rises to 1.78V/cell, stop operation.
6. If the fast charging time exceeds 1.5 hours without interruption, it is stopped.

In theory, trickle charge is a charge rate that is fast enough to keep the battery fully charged, but low enough to avoid overcharging. Determining the optimal recharging rate for a particular battery is a little difficult to describe, but it is generally accepted that it is about ten percent of the battery capacity, for example, for Sanyo 2500 mAh AA NiMH, the optimal recharging rate is 250 mA or lower. It must be taken into account in order to properly charge NiMH batteries.

The most common cause of premature battery failure is overcharging. The types of chargers that most often cause it are the so-called "fast chargers" for 5 or 8 hours. The problem with these instruments is that they don't really have a process control mechanism.

Most of them have simple functionality. They charge at full speed for a fixed period of time (usually five or eight hours) and then turn off or switch to a lower "manual" speed. If they are used properly, then everything is in order. If they are applied incorrectly, battery life is reduced in several ways:

1. If fully charged or partially charged batteries are inserted into the device, the device cannot sense this and therefore fully charges the batteries it was designed for. So, the battery capacity drops.
2. Another common situation is to interrupt a charge cycle in progress. However, this is followed by a reconnection. Unfortunately, this leads to the restart of a full charge cycle, even if the previous cycle is almost completed.

The easiest way to avoid these scenarios is to use a microprocessor-controlled smart charger. It can detect when the battery is fully charged, and then - depending on its design - either turn off completely or switch to trickle charge mode.

In order to charge the NiMH iMax, you will need a dedicated charger, as using the wrong method can render the battery useless. Many users consider iMax B6 the best choice for charging NiMH. It supports the process of up to 15 cell batteries, as well as many settings and configurations for different types batteries. The recommended charging time should not exceed 20 hours.

As a rule, the manufacturer guarantees 2000 charge / discharge cycles from a standard NiMH battery, although this number may vary according to operating conditions.

Work algorithm:

1. Charging NiMH iMax B6. It is necessary to connect the power cord to the outlet on the left side of the device, taking into account the shape at the end of the cable to ensure that the correct connection is made. We insert it all the way and stop pressing when a sound signal and a welcome message appear on the display screen.
2. Use the silver button on the far left to scroll through the first menu and select the type of battery to be charged. Pressing the leftmost button will confirm the selection. The button on the right will scroll through the options: charge, discharge, balance, fast charge, storage and others.
3. Two central control buttons will help you select the desired number. By pressing the far right button to enter, you can go to the voltage setting by scrolling again with the two center buttons and pressing enter.
4. Use multiple cables to connect the battery. The first set looks like lab wire equipment. It often comes bundled with crocodile clips. Connection sockets are located on right side devices near the bottom. They are easy enough to spot. This is how you can charge NiMH with iMax B6.
5. Then you need to connect the free battery cable to the end of the red and black clamps, creating a closed loop. This can be a little risky, especially if the user makes the wrong settings for the first time. Press and hold the enter button for three seconds. The screen should then inform that it is testing the battery, after which the user will be asked to confirm the mode setting.
6. While the battery is charging, you can scroll through the various display screens using the two central buttons that provide information about the charging process in different modes.

The most standard advice is to completely drain the batteries and then recharge them. Although this is a treatment for the "memory effect", care must be taken in nickel-cadmium batteries, as it is easy to damage them due to over-discharging, which leads to "pole reversal" and irreversible processes. In some cases, battery electronics are designed to prevent negative processes by shutting down before they happen, but simpler devices such as flashlights do not.

Necessary:

1. Be ready to replace them. Nickel-metal hydride batteries don't last forever. After the end of the resource, they will stop working.
2. Buy a "smart" charger that electronically controls the process and prevents overcharging. Not only is this better for batteries, but it also uses less power.
3. Remove the battery when recharging is complete. Unnecessary time on the device means that more "jet" energy is used to charge it, so wear and tear increases and more energy is wasted.
4. Do not fully discharge batteries to prolong their life. Despite all the advice to the contrary, a complete discharge will actually shorten their life.
5. Store NiMH batteries at room temperature in a dry place.
6. Excessive heat can damage batteries and cause them to drain quickly.
7. Consider using a low battery model.

Thus, a line can be drawn. Indeed, nickel-metal hydride batteries are more prepared by the manufacturer to work in modern conditions, and properly charging batteries using a smart device will ensure their performance and longevity.

Since 1932, attempts have been made to resume experiments. At that time, the idea was proposed to introduce a porous plate nickel electrode made of active metals inside, which would provide better charge movement and significantly reduce the cost of battery production.

But only after the Second World War (in 1947), the developers came to an almost modern scheme of sealed Ni-Cd batteries.

What you need to know about Ni-MH batteries

With this design, the internal gases released during the charge were absorbed by the unreacted part of the cathode, and were not released outside, as in previous versions.

If for some reason (exceeding the charging current, lowering the temperature) the rate of anodic oxygen formation is higher than the rate of its cathodic ionization, then a sharp increase in internal pressure can lead to an explosion of the battery. To prevent this, the battery case is made of steel, and sometimes there is even a safety valve.

Since then, the design of Ni-Cd batteries has not changed significantly (Figure 2).

Figure 2 - The structure of the Ni-Cd battery

The basis of any battery is the positive and negative electrodes.

In this scheme, the positive electrode (cathode) contains nickel hydroxide NiOOH with graphite powder (5-8%), and the negative electrode (anode) contains metallic cadmium Cd in powder form.

Batteries of this type are often called roll batteries, since the electrodes are rolled into a cylinder (roll) together with a separating layer, placed in a metal case and filled with electrolyte. The separator (separator), moistened with electrolyte, isolates the plates from each other. It is made of non-woven material, which must be resistant to alkali. The most common electrolyte is potassium hydroxide KOH with the addition of lithium hydroxide LiOH, which promotes the formation of lithium nickelates and increases the capacity by 20%.

Figure 3 - The voltage on the battery during charging or discharging, depending on the current level of charge.

During discharge, active nickel and cadmium are transformed into hydroxides Ni(OH)2 and Cd(OH)2.

The main advantages of Ni-Cd batteries include:

- low cost;

- work in a wide temperature range and resistance to its differences (for example, Ni-Cd batteries can be charged at a negative temperature, which makes them indispensable when working in the Far North);

- they can deliver much more current to the load than other types of batteries;

- resistance to high currents of charge and discharge;

- relatively short charge time;

- a large number of "charge-discharge" cycles (with correct operation they withstand more than 1000 cycles);

— are easily restored after long-term storage.

Disadvantages of Ni-Cd batteries:

- the presence of a memory effect - if you regularly put an incompletely discharged battery on charge, its capacity will decrease due to the growth of crystals on the surface of the plates and other physical and chemical processes. So that the battery does not “give up” ahead of time, it must be “trained” at least once a month, as discussed below;

- Cadmium is a very toxic substance, so the production of Ni-Cd batteries is bad for the environment.

There are also problems with the recycling and disposal of the batteries themselves.

— low specific capacity;

- large weight and dimensions compared to other types of batteries with the same capacity;

- high self-discharge (after charging, in the first 24 hours of operation they lose up to 10%, and in a month - up to 20% of the stored energy).

Figure 4 - Self-discharge of Ni-Cd batteries

Currently, the number of Ni-Cd batteries produced is rapidly declining, they have been replaced, in particular, by Ni-MH batteries.

3. Nickel-metal hydride batteries

For several decades, nickel-cadmium batteries have been used quite widely, but the high toxicity of production forced the search for alternative technologies. As a result, nickel-metal hydride batteries were created, which are still produced today.

Despite the fact that work on the creation of Ni-MH batteries began in the 1970s, stable metal hydride compounds capable of binding large volumes of hydrogen were found only ten years later.

The first Ni-MH battery, which used LaNi5 as the main active material of the metal hydride electrode, was patented by Will in 1975. In early experiments with metal hydride alloys, nickel-metal hydride batteries were unstable, and the required battery capacity could not be achieved. Therefore, the industrial use of Ni-MH batteries began only in the mid-80s after the creation of the La-Ni-Co alloy, which makes it possible to absorb hydrogen electrochemically reversibly for more than 100 cycles. Since then, the design of Ni-MH batteries has been continuously improved in the direction of increasing their energy density.

Nickel-metal hydride batteries in their design are analogous to nickel-cadmium batteries, and in electrochemical processes - nickel-hydrogen batteries. The specific energy of a Ni-MH battery is much higher than the specific energy of Ni-Cd and Ni-H2 batteries (Table 1).

Table 1

A significant scatter of some parameters in Table 1 is associated with different purposes (designs) of batteries. Distinctive features NM batteries are high capacity, high power (critical) characteristics (the ability to charge and discharge with high currents), the ability to withstand overcharge and ultra-deep discharge (polarity reversal), and the absence of dendritic formations. A very important advantage of the NM battery over the NK battery is the absence of an environmentally very harmful element - cadmium. In terms of voltage, size, design and technology, the NM battery corresponds to the NK battery, and they can be interchanged both in production and in operation.

The replacement of the negative electrode made it possible to increase the load of active masses of the positive electrode by 1.3-2 times, which determines the capacity of the battery. Therefore, Ni-MH batteries have significantly higher specific energy characteristics compared to Ni-Cd batteries.

As a result, the field of application of NM batteries is close to the field of application of NK batteries, NM batteries are used in cell phones, pagers, cordless phones, scanners, flashlights, radio stations, electric bicycles, electric vehicles, hybrid cars, electronic timers and decade counters, backup storage devices ( MBU) and central processing units (CP) of computers and laptops, fire and smoke detection devices, burglar alarms, water and air environmental analysis devices, memory units of electronically controlled processing machines, radios, voice recorders, calculators, electric shavers, hearing aids, electric toys, etc.

Unlike Ni-Cd, Ni-MH batteries use an alloy of metals that absorb hydrogen as an anode. The alkaline electrolyte still does not take part in the reaction based on the movement of hydrogen ions between the electrodes. During charging, nickel hydroxide Ni(OH)2 is converted into oxyhydrite NiOOH, donating hydrogen to the negative electrode alloy. The absorption of hydrogen is not an isothermal reaction, therefore, metals for the alloy are always selected in such a way that one of them releases heat when binding the gas, and the other, on the contrary, absorbs heat. In theory, this was supposed to provide thermal balance, however, nickel-metal hydride batteries heat up significantly more than nickel-cadmium.

The success of the distribution of nickel-metal hydride batteries was ensured by the high energy density and non-toxicity of the materials used in their production.

4. Basic processes of Ni-MH batteries

Ni-MH batteries use a nickel-oxide electrode as the positive electrode, like a nickel-cadmium battery, and a hydrogen-absorbing nickel-rare-earth alloy electrode instead of the negative cadmium electrode.

Detailed Description of Nickel-Metal Hydride Batteries

We are all used to the fact that cars are mainly used lead batteries.

AA element holders. An attempt to restore the capacity of used NiCd and NiMh batteries.

But there are other types of batteries that make a car start and move, and one of them is a nickel-metal hydride battery, the advantages and disadvantages of which we will talk with you today.

They are mainly used in hybrid cars or electric cars. So, what do you need to know about the properties of this type of battery?

Benefits of Nickel-Metal Hydride Batteries

• high power batteries (compared to nickel-cadmium batteries). The difference is up to 40%. At the same time, this battery is lightweight.
• For nickel-metal hydride batteries very low memory effect, which means that the user can easily recharge the batteries without waiting for them to be completely discharged
• NiMH battery has high mechanical reliability
• Complete charge-discharge cycles of such a battery are carried out much less frequently than NiCd batteries
• Nickel metal hydride batteries do not require special transportation conditions
• These batteries environmentally friendly, after the expiration of their service life, they can be disposed of without problems

Disadvantages of Nickel Metal Hydride Batteries

Unfortunately, this type of battery also has disadvantages. And the most important of them is very high self-discharge. In other words, even if the car is stationary and not in use, the battery is discharged.

To prolong battery life, if the battery has not been used for an extended period of time, it should be fully discharged before charging. Thus, you will extend its service life.

The next disadvantage of a nickel-metal hydride battery is a relatively small (about 600) charge cycles.

The battery described above does not tolerate high temperatures (from 25 degrees of heat), so store it in a cool environment. Here it is also necessary to take into account the fact that keeping the battery in a discharged state accelerates its aging. The average shelf life is 3 years.

It is also important to consider the type of charger you are going to use to charge your NiMH battery. It should be with a staged charge algorithm, so you avoid overheating and overcharging the battery, which negatively affect its quality characteristics.

Another factor to consider when exploitation nickel metal hydride batteries - very important here do not exceed the maximum allowable loads recommended by the manufacturer.

And finally: subject to all the rules and regulations for the use, as well as storage of nickel-metal hydride batteries, they will serve you for a very long time.

FONAREVKA.RU — All about flashlights and lighting equipment > Power supplies and chargers > Secondary batteries (batteries) > Proper recovery of NI-MH batteries

View Full Version: Proper recovery of NI-MH batteries

Good afternoon.
The title came out a little yellow, yes. The content is rather the opposite - a question, not a narrative, as you would expect. But as the topic fills in, I think it may be useful to readers later.

Actually, I got such a zoo of batteries (Appendix 1), which people threw away.
Something tells me that almost all of them were charged with stupid cheap chargers for 50 rubles, they were not charged on time and stored incorrectly, and from this they lost a lot in capacity.
And this something also tells me that almost all of them can be reanimated and safely used in all sorts of non-high-current devices, such as weak flashlights, players, watches, remote controls, etc.

I have a LaCrosse charger that can train cans, and as everyone probably already knows, it works. There is also imax.
From personal experience- I found the oldest nickel-cadmium battery (app. 2), I bought it more than 10 years ago for an mp3 player, then it was the most capacious. So, after a year of use and 9 years of wallowing in the lacrosse table, it showed a capacity of mad 120 mAh. After 7 charge-discharge cycles in recovery mode, the capacity at a discharge of 250 mA is 650 mAh. Not bad, right?

So, in fact, what I had a snag in: charging nickel with currents of more than 0.7C and below 0.2C is harmful. And what kind of current to drive them to discharge-charge for optimal, let's say, recovery?

The principle of operation of nickel-metal hydride batteries and the possibility of their replacement

The Internet is full of conflicting information: someone advises 1C, someone 0.1.

I would be grateful for the advice of knowledgeable people.

05.03.2014, 19:20

And what kind of current to drive them to discharge-charge for optimal, let's say, recovery?
Duc lyakruza does not have such a wide choice 🙂 Charge / discharge: 200/100mA, 500/250, 750/350, etc.
If they are completely dead, I would start with 200/100, then 500/250. Well, you need to make sure that they do not overheat and there is no overcharging, if Cruz does not catch the delta, this can happen with half-dead ones.

Well, as I said, there is also an imax, they can blow much larger currents.
But the question is mostly about lacrosse, yes.

05.03.2014, 20:59

they can blow much larger currents.
My opinion is that you should not blow high currents into half-dead batteries, they heat up and swell from this: LaughOutLoudBulb: But, perhaps, there are people who think otherwise.

If completely dead, I would start with 200/100, then 500/250
Exactly.
750/350 is suitable only for fresh modern batteries, such as Enelups. You can, of course, blow such a current into this trash (how it will affect the batteries - xs, it’s already individual here), but charging will be cut down due to overheating - there will be no gain in time.

if they are heated by currents above 0.2-0.3C, it's time to add water (http://forum.ixbt.com/topic.cgi?id=20:29955:1018#1018).
or throw away already nafik, and not engage in necrophilia.

charging nickel with currents over 0.7C and below 0.2C is harmful
God bless him with 0.7, but why is below 0.2C harmful? if recommended 0.1C?

Not bad, right?
by the way, most likely, you will not achieve such a wonderful result as with cadmium, with metal hydride. simply because the memory effect they have is weaker than degradation.

07.03.2014, 14:05

but why is below 0.2C harmful?
I think because charging most likely ΔV will not catch and stop charging. But at such currents, this is already drip charging.

I think because charging most likely will not catch ΔV
then less than 0.3C
and less than 0.2С the delta is no longer needed, it doesn’t matter there

I once thought about topping up water but didn’t try :)), but the trainings didn’t give any sense, but yes, the capacity was restored, but not for a long time. With the transition to lithium, I abandoned this whole topic. Fujicell 2800mA has probably been living in the mouse for more than a year, the memory integrated into the mouse is charging while I sleep with a 1.39V spring current at the end drops to 20mA.

thought but didn't try
I tried. capacity of course is not restored, why would it recover.
but the internal resistance of the dramatic falls 🙂
8 pieces from 0.5-1 (!) Ohm fell to an average of 60-100 mOhm

But the water consumption for aqueous electrolytes is the way it should be, all batteries suffer from this. Yes, the autopsy showed that all the Ni-Mhs were very dry.

I know that the electrolyte was changed in Ni-Ca liquid tanks before and they worked for 15 years.

Nickel-cadmium batteries

Sealed Ni-Cd batteries are characterized by a horizontal discharge curve, high speeds discharge and the ability to operate at low temperatures. They are used to power portable equipment, power tools, household appliances, toys, etc. This is a type of battery that is able to work in the harshest conditions.

For nickel-cadmium batteries, a full periodic discharge is necessary: ​​if it is not done, large crystals form on the cell plates, significantly reducing their capacity (the so-called "memory effect").
The nominal voltage of sealed Ni-Cd batteries is 1.2 V.
Nominal (standard) charge mode - current 0.1C for 16 hours.
The nominal discharge mode is with a current of 0.2C up to a voltage of 1 V.

Immediately after charging, nickel-cadmium batteries can have a voltage of up to 1.44 V., but it drops quite quickly and reaches stationary 1.2 V. Such batteries can withstand 1000 charge-discharge cycles, but only with the correct charge mode. Advantages of Ni-Cd batteries:

• the possibility of quick and easy charging, even after long-term storage of the battery;
• a large number of charge / discharge cycles: with proper operation - more than 1000 cycles;
• good load capacity and the ability to operate at low temperatures;
• long periods of storage at any degree of charge;
• preservation of standard capacity at low temperatures;
• operating temperature range from -40 to +60 ?C.
• the greatest suitability for use in harsh operating conditions;
• low cost;

Disadvantages of Ni-Cd batteries:

• relatively low energy density compared to other types of batteries;
• the memory effect inherent in these batteries and the need for periodic works to eliminate it;
• the toxicity of the materials used, which adversely affects the environment, and some countries restrict the use of batteries of this type;
• relatively high self-discharge - after storage, a charge cycle is necessary.

Modern cylindrical Ni-Cd batteries with rolled electrodes allow high discharge currents, for some types of batteries the maximum long-term current is 7-10C.

The performance of sealed Ni-Cd during operation is determined by the gradual changes that occur in batteries during cycling and lead to an inevitable decrease in discharge capacity and voltage. Ambient temperature is one of the most significant factors of external influence, which determines the duration of the working state of sealed batteries. The aging processes of batteries are most affected by high temperatures, at which all chemical reactions are accelerated (2-4 times for every 10 ° C), including those leading to battery damage. At low temperatures during charging, the risk of hydrogen evolution increases. The operating mode has a strong influence: the mode and depth of discharge, the charge mode, the duration of the pause between charge and discharge during continuous cycling, periods of operation and storage.

Nickel-metal hydride batteries

The specific capacity and energy of nickel-metal hydride batteries is 1.5-2 times higher than the specific energy of nickel-cadmium batteries, in addition, they do not contain toxic cadmium, which allows them to significantly replace nickel-cadmium batteries in many areas of technology. They are manufactured in hermetically sealed cylindrical, prismatic and disc shapes. They are used to power portable devices and equipment, both domestic and industrial.
The rated voltage of the batteries is 1.2-1.25 V.
Rated (standard) charge mode - current 0.1C for 15 hours.
The nominal discharge mode is with a current of 0.1-0.2C up to a voltage of 1 V.
Ni-MH batteries do not have the "memory effect" of Ni-Cd, but the effects associated with overcharging are retained. Decrease discharge voltage, observed with frequent and long recharges in the same way as with Ni-Cd batteries, can be eliminated by periodically performing several discharges up to 1 V. It is enough to carry out such discharges once a month. Depending on the type of Ni-MH batteries, operating mode and operating conditions, the batteries provide from 500 to 1000 discharge-charge cycles at a discharge depth of 80% and have a service life of 3 to 5 years.

However, nickel-metal hydride batteries are inferior to nickel-cadmium batteries in some performance characteristics:

• Ni-MH batteries work effectively in a narrower range of operating currents.
• Ni-MH batteries have a narrower operating temperature range: most of them are inoperable at temperatures below -10 °C and above +40 °C, although in some battery series the temperature limits are extended.
• during the charge of Ni-MH batteries, more heat is released than when charging Ni-Cd batteries, therefore, in order to prevent overheating of the battery from Ni-MH batteries during fast charging and / or significant overcharging, thermal fuses or thermal relays are installed in them, which are located on the wall of one of the batteries in the central part of the battery.
• Ni-MH batteries have a high self-discharge.
• the risk of overheating when charging one of the Ni-MH batteries of the battery, as well as reversal of the battery with a lower capacity when the battery is discharged, increases with the mismatch of the battery parameters as a result of long cycling, so the creation of batteries from more than 10 batteries is not recommended by all manufacturers.
• more stringent requirements for the selection of batteries in the battery and the control of the discharge process than in the case of using Ni-Cd batteries.

The discharge curve of a Ni-MH battery is similar to that of a Ni-Cd battery.

The operating time (number of discharge-charge cycles) and service life of a Ni-MH battery are also largely determined by operating conditions. The operating time decreases with an increase in the depth and speed of the discharge. The operating time depends on the speed of the charge and the method of controlling its completion. The greatest attention should be paid to the temperature regime, to avoid overdischarges (below 1V) and short circuits. It is recommended to use Ni-MH batteries for their intended purpose, avoid mixing used and unused batteries, and do not solder wires or other parts directly to the battery. During storage, the Ni-MH battery self-discharges. After a month at room temperature, the loss of capacity is 20-30%, and with further storage, the loss decreases to 3-7% per month.

Charging nickel batteries

When charging a sealed battery, in addition to the problem of recovering the expended energy, it is important to limit its overcharging, since the charging process is accompanied by an increase in pressure inside the battery.

How should a Ni─MH battery be refurbished and why is it important?

A significant factor in the external influence on the electrical characteristics of batteries is the ambient temperature. The capacity that can be obtained from a battery at 20°C is the largest. It almost does not decrease even when discharging at a higher temperature. But at temperatures below 0 ° C, the discharge capacity decreases, and the more, the larger the discharge current.

The nominal (standard) charge mode is the mode in which the battery, discharged to 1V, is charged with a current of 0.1C for 16 hours (for Ni-Mh 15 hours). Batteries can be charged at temperatures from 0 to +40°C, most effectively in the temperature range from +10 to +30°C. Accelerated (in 4 - 5 hours) and fast (in 1 hour) charges are possible for Ni-MH batteries with highly active electrodes. With such charges, the process is controlled by changes in temperature? T and voltage? U and other parameters. A three-stage charging method is also recommended: the first stage of a fast charge (current up to 1C), a charge at a rate of 0.1C for 0.5-1 h for the final recharge, and a charge at a rate of 0.05-0.02C as a compensation charge. The charging voltage Uz at Iz=0.3-1C lies in the range of 1.4-1.5V. To prevent overcharging of batteries, the following charge control methods can be used with appropriate sensors installed in batteries or chargers:

• charge termination method by absolute temperature Tmax.
• charge termination method based on temperature change rate?T/?t.
• charge termination method by negative voltage delta -?U.
• method of termination of the charge by the maximum charge time t.
• method of termination of the charge by the maximum pressure Pmax. (0.05-0.8 MPa).
• method of termination of the charge by the maximum voltage Umax.

Constant voltage charging is not recommended for Ni-MH batteries as "thermal failure" of the batteries can occur. Heat dissipation in a sealed Ni-Cd battery depends on the level of its charge. By the end of the charge in standard mode, the battery temperature may rise by 10-15 °C. With a fast charge, the heating is greater (up to 40-45 ° C).

Rules for operating NiCd/NiMh batteries

• Try to use only standard chargers
• When using non-automatic chargers, do not charge the battery for more than the time specified in the instructions. Overcharging greatly speeds up the aging process of the battery.
• Do not leave a discharged battery in the switched on equipment. Further uncontrolled discharge* completely disables the battery.
• Avoid charging an incompletely discharged battery.
• Completely discharge* the battery in the equipment every 3-4 weeks
• Observe operating temperature range
• The NiCd battery must be discharged* before storing for more than 1 month. NiMh battery store at 30-50% charge level. Store at +5°С…+20°С. Shelf life - up to 4 years.
• Every 6 months for NiMh and 12 months for NiCd storage, it is recommended to do at least 3 charge-discharge cycles in standard mode.

*Note: A battery is fully discharged when its voltage drops to 83% of its nominal voltage. For example, a 1.2V battery will be completely discharged when the voltage across the battery reaches 1V while the equipment is running. Typically, this voltage level coincides with the shutdown threshold of the equipment.

ATTENTION! During operation, DO NOT:

• use of chargers not designed to charge batteries of this chemical system
• short circuit between battery contacts
• external heating above 100°С and exposure to open fire
• any physical damage to the battery case
• charging a cold battery (below 0°C)
• liquid penetration into the battery case.