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

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. Recycling NiMH cells is a rather complex process because the voltage peak and subsequent drop are smaller, and therefore the indicators are more difficult to determine. Overcharging causes the cell to overheat and become damaged, leading to loss of capacity and subsequent 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 a principle based on the absorption, release and transfer of 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 the battery along with liquid electrolyte. The positive electrode is usually made of nickel, the negative electrode is made of metal hydride. Hence the name NiMH, or nickel metal hydride.

Advantages:

1. Contains fewer toxins and is environmentally friendly and 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 compared to other batteries and must be taken into account before charging NiMH.
3. Required high level Maintenance. The battery must be completely discharged to prevent crystal formation during charging.
4. More expensive than Ni-Cad battery.

The NiMH cell has many characteristics similar to NiCd, such as the discharge curve (subject to additional charging) that the battery can accept. It is intolerant of overcharging, which causes capacity degradation, which poses a serious problem for developers chargers.

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

1. Rated voltage - 1.2V.
2. Specific energy - 60-120 W-hour/kg.
3. Energy density - 140-300 W-hour/kg.
4. Specific power - 250-1000 W/kg.
5. Charge/discharge 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 as the charge level rises, the efficiency drops, generating heat, which must be taken into account before charging NiMH.

When NiCD battery discharges to a certain minimum voltage and then charges, measures must be taken to reduce the conditioning effect (about every 10 charge/discharge cycles), otherwise it will begin to lose capacity. NiMH does not require such a requirement because the effect is negligible.

However, this recovery process is also convenient for nickel-metal hydride devices and is recommended to be taken 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 constant current source. The speed is usually indicated on the cell body. It should not exceed technological standards. Charging limits 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 you cannot be sure that each cell or stack has the same resistance, and so some will draw more current than others. This means that a separate charging circuit must be used for each line in the parallel bank. It is necessary to establish what current to charge the NiMH by determining the balancing, for example, using resistors of such resistance that they will dominate the control of the parameters.

Modern algorithms have been developed to provide accurate charging without the use of a thermistor. These devices are similar to Delta V, but have special measurement methods to detect full charge, usually involving some kind of cycling where the voltage is measured over time and between pulses. For multi-element packs, 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 the 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, which is easily measured by a thermistor. This is the safest way to detect the end of a process during a fast recovery.

Overnight charging is the cheapest way to charge a NiMH battery at C/10, which is less than 10% of rated capacity at one o'clock. This must be taken into account in order to charge NiMH correctly. So a 100mAh battery will charge at 10mA for 15 hours. This method does not require an end-of-process sensor and ensures a full charge. Modern cells have an oxygen recirculation catalyst, which 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 full reaction depends on temperature (at least 1.41 V per cell at 20 degrees), which must be taken into account in order to properly charge NiMH. Prolonged recovery does not cause ventilation. It warms up the battery slightly. To maintain 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 timing function.

Fast charging process

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

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 the discharge. A power dissipator will be required to dissipate the energy of a partially charged battery for a reasonable amount of time.

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

There are new algorithms that use microprocessor control 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 involves switching on and off processes to measure voltage.

Adapter Specifications

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

Algorithm for an ideal charger:

1. Soft start. If the temperature is above 40 degrees or below zero, start with charging C/10.
2. Option. If the voltage of the discharged battery 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 a charged NiMH battery rises to 1.78 V/cell, stop working.
6. If the fast charging time exceeds 1.5 hours without interruption, it is stopped.

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

Most common cause premature failure of the battery is overcharging. The types of chargers that most often cause it are the so-called “fast chargers” of 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 switch off or switch to a lower "manual" speed. If they are used properly then everything is fine. If they are applied incorrectly, battery life will be reduced in several ways:

1. If fully charged or partially charged batteries are inserted into the device, it cannot sense this, so it fully charges the batteries for which it is intended. So, the battery capacity decreases.
2. Another common situation is when the charging cycle is interrupted while it is in progress. However, after this, a reconnection follows. Unfortunately, this causes the full charging cycle to start again, even if the previous cycle is almost complete.

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 shut down completely or switch to recharging mode.

In order to charge the NiMH iMax you will need a special charger as using the wrong method can render the battery useless. Many users consider iMax B6 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 depending on operating conditions.

Work algorithm:

1. Charging NiMH iMax B6. You must connect the power cord to the outlet on the left side of the device, taking note of the shape at the end of the cord to ensure the correct connection is made. We insert it all the way and stop pressing when it appears sound signal and a welcome message on the display screen.
2. Use the silver button on the far left to view the first menu and select the type of battery to charge. 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 rightmost button to enter, you can move to the voltage setting by scrolling again using the two center buttons and pressing enter.
4. Use several cables to connect the battery. The first set looks like lab wiring equipment. It often comes complete with alligator clips. Connection sockets are located on the right side of the device near the bottom. They are fairly easy to spot. This is how you can charge NiMH with the 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 bit risky, especially if the user makes the wrong settings the first time. Press and hold the enter button for three seconds. The screen should then inform you that it is checking 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 different display screens using the two central buttons, which provide information about the charging process in different modes.

The most standard advice is to completely discharge the batteries and then charge them. Although this is a treatment for the "memory effect", care must be taken in NiCad batteries as they are easily damaged by over-discharging, resulting in "pole reversal" and irreversible processes. In some cases, the battery electronics are designed in such a way that they prevent negative processes by turning off before they happen, but more simple devices, for example, for flashlights, this is not done.

Necessary:

1. Be prepared to replace them. Nickel-metal hydride batteries do not last forever. After the resource expires, they will stop working.
2. Buy a “smart” charger that electronically controls the process and prevents overcharging. This is not only better for batteries, but also uses less energy.
3. Remove the battery when recharging is complete. Unnecessary time on the device means more "trickle" energy is used to charge it, therefore increasing wear and tear and wasting more energy.
4. Do not completely discharge batteries to extend their life. Despite all the advice to the contrary, completely discharging them actually shortens their lifespan.
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 model with low level charge.

Thus, we can draw a line. Indeed, nickel-metal hydride batteries are better prepared by the manufacturer for operation in modern conditions, and proper charging of batteries using a smart device will ensure their performance and durability.

Nimh batteries are power sources that are classified as alkaline batteries. They are similar to nickel-hydrogen batteries. But the level of their energy capacity is greater.

The internal composition of ni mh batteries is similar to the composition of nickel-cadmium power supplies. To prepare a positive output, use the following chemical element, nickel, minus - an alloy that includes hydrogen-absorbing metals.

There are several typical designs of nickel metal hydride batteries:

• Cylinder. To separate the conductive terminals, a separator is used, which is given the shape of a cylinder. An emergency valve is located on the lid, which opens slightly when the pressure increases significantly.
• Prism. In this nickel metal hydride battery the electrodes are concentrated alternately. A separator is used to separate them. To accommodate the main elements, a housing made of plastic or a special alloy is used. To control the pressure, a valve or sensor is inserted into the lid.

Among the advantages of such a power source are:

• The specific energy parameters of the power source increase during operation.
• Cadmium is not used in the preparation of conductive elements. Therefore, there are no problems with battery disposal.
• Absence of a kind of “memory effect”. Therefore, there is no need to increase the capacity.
• In order to cope with the discharge voltage (reduce it), specialists discharge the unit to 1 V 1–2 times a month.

Among the restrictions that relate to nickel metal hydride batteries are:

• Compliance with the established range of operating currents. Exceeding these values ​​leads to rapid discharge.
• Operation of this type of power supply in very coldy not allowed.
• Thermal fuses are introduced into the battery, with the help of which they determine overheating of the unit and an increase in the temperature level to a critical value.
• Tendency to self-discharge.

Charging a nickel metal hydride battery

The charging process of nickel metal hydride batteries involves certain chemical reactions. For their normal operation, part of the energy supplied by the charger is required from the network.

The efficiency of the charging process is the portion of the energy received by the power source that is stored. The value of this indicator may vary. But it is impossible to achieve 100 percent efficiency.

Before charging metal hydride batteries, study the main types, which depend on the magnitude of the current.

Drip charging type

This type of charging for batteries must be used carefully, as it leads to a reduction in service life. Since this type of charger is turned off manually, the process requires constant monitoring and regulation. In this case, the minimum current indicator is set (0.1 of the total capacity).

Since when charging ni mh batteries in this way, the maximum voltage is not set, they focus only on the time indicator. To estimate the time interval, use the capacity parameters that a discharged power source has.

The efficiency of a power supply charged in this way is about 65–70 percent. Therefore, manufacturing companies do not recommend using such chargers, since they affect the performance parameters of the battery.

Fast charging

When determining what current can be used to charge ni mh batteries in fast mode, the manufacturers' recommendations are taken into account. The current value is from 0.75 to 1 of the total capacity. It is not recommended to exceed the set interval, as the emergency valves are activated.

To charge nimh batteries in fast mode, the voltage is set from 0.8 to 8 volts.

The fast charging efficiency of ni mh power supplies reaches 90 percent. But this parameter decreases as soon as the charging time ends. If you do not turn off the charger in a timely manner, the pressure inside the battery will begin to increase and the temperature will increase.

To charge the ni mh battery, perform the following steps:

• Pre-charge

This mode is entered if the battery is completely discharged. At this stage, the current is between 0.1 and 0.3 of the capacitance. It is prohibited to use high currents. The time period is about half an hour. As soon as the voltage parameter reaches 0.8 volts, the process stops.

• Switching to accelerated mode

The process of increasing the current is carried out within 3–5 minutes. The temperature is monitored throughout the entire period. If this parameter reaches a critical value, the charger is turned off.

When fast charging nickel metal hydride batteries, the current is set at 1 of the total capacity. In this case, it is very important to quickly disconnect the charger so as not to harm the battery.

To monitor the voltage, use a multimeter or voltmeter. This helps eliminate false positives that adversely affect the performance of the device.

Some chargers for ni mh batteries operate not with constant, but with pulsed current. Current is supplied at specified intervals. The supply of pulsed current promotes uniform distribution of the electrolytic composition and active substances.

• Additional and maintenance charging

To replenish the full charge of the ni mh battery, at the last stage the current indicator is reduced to 0.3 of the capacity. Duration – about 25–30 minutes. It is forbidden to increase this time period, since this helps to minimize the period of operation of the battery.

Fast charging

Some models of chargers for nickel-cadmium batteries are equipped with a fast charging mode. To do this, the charging current is limited by setting the parameters at 9–10 of the capacity. You need to reduce the charge current as soon as the battery is charged to 70 percent.

If the battery is charged in accelerated mode more than half an hour, the structure of the conductive terminals is gradually destroyed. Experts recommend using this type of charger if you have some experience.

How to properly charge power supplies, and also eliminate the possibility of overcharging? To do this, you must follow these rules:

1. Temperature control of ni mh batteries. It is necessary to stop charging NIMH batteries as soon as the temperature level rises rapidly.
2. For nimh power supplies, time limits are set that allow you to control the process.
3. Ni mh batteries must be discharged and charged at a voltage of 0.98. If this parameter decreases significantly, then the chargers are turned off.

Remanufacturing of Nickel Metal Hydride Power Supplies

The process of restoring ni mh batteries is to eliminate the consequences of the “memory effect”, which are associated with loss of capacity. The likelihood of this effect increasing if the unit is often incompletely charged. The device fixes the lower limit, after which the capacity decreases.

Before restoring the power source, prepare the following items:

• Light bulb of required power.
• Charger. Before use, it is important to clarify whether the charger can be used for discharging.
• Voltmeter or multimeter to determine voltage.

A light bulb or a charger equipped with the appropriate mode is connected to the battery with your own hands in order to completely discharge it. After this, charging mode is activated. The number of recovery cycles depends on how long the battery has not been used. It is recommended to repeat the training process 1-2 times during the month. By the way, I restore in this way those sources that have lost 5–10 percent of their total capacity.

To calculate the lost capacity, a fairly simple method is used. So, the battery is fully charged, after which it is discharged and the capacity is measured.

This process will be greatly simplified if you use a charger, with which you can control the voltage level. It is also beneficial to use such units because the likelihood of deep discharge is reduced.

If the charge level of nickel metal hydride batteries has not been established, then the light bulb must be installed carefully. Using a multimeter, the voltage level is monitored. This is the only way to prevent the possibility of a complete discharge.

Experienced specialists carry out both the restoration of one element and the entire block. During the charging period, the existing charge is equalized.

Restoring a power source that has been in use for 2–3 years, with a full charge or discharge, does not always bring the expected result. This is because the electrolytic composition and conductive terminals are gradually changing. Before using such devices, the electrolytic composition is restored.

Watch a video about restoring such a battery.

Rules for using nickel-metal hydride batteries

The service life of ni mh batteries largely depends on whether the power source is allowed to overheat or be significantly overcharged. Additionally, experts advise taking into account the following rules:

• Regardless of how long the power supplies will be stored, they must be charged. The charge percentage must be at least 50 of the total capacity. Only in this case there will be no problems during storage and maintenance.
• Batteries of this type are sensitive to overcharging and excessive heating. These indicators have a detrimental effect on the duration of use and the amount of current output. These power supplies require special chargers.
• Training cycles are not necessary for NiMH power supplies. With the help of a proven charger, lost capacity is restored. The number of restoration cycles largely depends on the condition of the unit.
• Be sure to take breaks between recovery cycles and also study how to charge a used battery. This time period is required for the unit to cool down and the temperature level to drop to the required level.
• The recharging procedure or training cycle is carried out only in an acceptable temperature range: +5-+50 degrees. If you exceed this figure, the likelihood of rapid failure increases.
• When recharging, make sure that the voltage does not drop below 0.9 volts. After all, some chargers do not charge if this value is minimal. In such cases, it is possible to connect an external source to restore power.
• Cyclic restoration is carried out provided that there is some experience. After all, not all chargers can be used to discharge a battery.
• The storage procedure includes a number of simple rules. It is not allowed to store the power source outdoors or in rooms where the temperature level drops to 0 degrees. This provokes solidification of the electrolytic composition.

If not one, but several power sources are charged at the same time, then the degree of charge is maintained at the set level. Therefore, inexperienced consumers carry out battery restoration separately.

Nimh batteries are effective power sources that are actively used to complete various devices and units. They stand out with certain advantages and features. Before using them, it is necessary to take into account the basic rules of use.

Video about Nimh batteries

It is no secret that at any moment you can find yourself in such conditions when there is a need to recharge “dead” batteries. For example, Ni-MH batteries are widely used in everyday life and in production - how to charge them correctly? Of course, you can use the simplest charger included with any item. household appliances. However, their strength is very low, so such a charge will “hold” for a very short time. The use of more complex types of chargers helps ensure that the battery not only works “on full power”, but also used all her possible resources. In addition, batteries are different. Their names directly depend on the composition from which they are made.

Common types of nickel batteries, their similarities and differences

There are many, which contain various chemical compounds. For household consumption, it is optimal to use nickel-metal hydride, cadmium and nickel-zinc elements. Of course, any battery needs some care, so it is always important to follow the operating and charging rules.

Ni-MH

Nickel-metal hydride batteries are secondary chemical current sources with a much higher capacity than their predecessors - but have a shorter service life. One of the popular areas of application for nickel cells is model building (except for aviation, due to the fact that the battery is quite heavy in weight).

The first development of these cells began in the 70s of the twentieth century with the goal of improving CD batteries. 10 years later, in the late 80s, it was possible to ensure that the chemical compounds used to create Ni-MH batteries became more stable. In addition, they are much less susceptible to the “memory effect” than Ni-Cd: they do not immediately “remember” the charge current remaining inside if the element was not completely discharged before use. Therefore, they do not need a full discharge so often.

Ni-Cd

Despite the fact that Ni-MH have a number of obvious advantages over Ni-Cd, it is worth noting that the latter do not lose their popularity. Mainly because they don’t heat up as much when charging due to greater energy conservation inside the element. As you know, there are different types of chemical processes that occur between substances.

If you charge Ni-MH, the reactions will be exothermic, and if you charge cadmium batteries, they will be endothermic, which provides a higher efficiency. Thus, Cd can be charged at a higher current without fear of overheating.

Ni-Zn

IN Lately Much attention is paid to discussions on the Internet about batteries that contain zinc. They are not as well known to consumers as the previous ones, but are ideal for use as batteries for digital cameras.

Their main feature is high voltage and resistance, due to which even at the end of the charge-discharge cycle there is no sharp drop in voltage, like with a Ni charge. If the camera contains metal hydride batteries, it will turn off even if the battery is not completely discharged, but Ni-Zn does not have this even at the end of the discharge.

Due to the specifics of these batteries, they may require an individual charger, or they can be charged on any universal “smart” charger, for example, ImaxB6. Ni-Zn batteries are also excellent for use in electric children's toys and blood pressure monitors.

Fast charging of NiMH batteries and other power sources

It is better to charge the battery using more complex models of the corresponding devices. Their current algorithms have a more complex sequence. Of course, doing this is a little more complicated than simply inserting the battery into the basic charger included in the package. But the quality of charging when using a “smart” device will be much higher. So how to charge Ni-MH batteries?

First, the current is turned on and the voltage at the battery terminals is checked (current parameters are 0.1 battery capacity, or C). If the voltage exceeds 1.8 V, this means that the battery is either missing or damaged. In this case, the process cannot be started. You need to either replace the damaged element with a intact one, or insert a new one into the device.

After checking the voltage, the initial discharge of the battery is assessed. If U is less than 0.8 V, then you cannot immediately proceed to fast charging, but if U = 0.8 V or more, then you can. This is the so-called “pre-charge phase”, used to prepare cells that are very discharged. The current value here is 0.1-0.3 C, and the duration is half an hour, no less. It should immediately be noted that At all stages it is important to constantly monitor the temperature . Especially when it comes to what current and how to properly charge a Ni-MH battery. Such batteries heat up much faster, especially towards the end of the process. Their temperature should not exceed 50°C.

Fast charging is only carried out if the previous checks have been carried out correctly. How to charge the battery correctly? So, the initial voltage is 0.8 V or a little more. Current flow begins. It is carried out smoothly and carefully for 2-4 minutes until the desired level is reached. Optimal current level for Ni-MH and Ni-Cd batteries - 0.5-1.0 C, but sometimes it is recommended not to exceed more than 0.75.

It is important to determine in time the end of the fast phase in order to avoid damaging the battery. The most reliable, in this case, is the dv method, which is used differently when charging nickel-cadmium and Ni-MH batteries. For Ni-Cd, the voltage becomes increasingly higher and falls towards the end of charging, so the signal for its end is the moment when U drops to a level of 30 mV.

Since in Ni-MH the drop in U of the charged elements is much less pronounced, in this case the dv=0 method is used. A period of time of 10 minutes is detected, during which the battery U remains stable - that is, with a zero voltage fluctuation threshold set.

Finally, there is a short recharging phase. Current - within 0.1-0.3 C, duration - up to half an hour. This is necessary to ensure that the battery is fully charged, as well as to equalize the charge potential in it.

An important point (this also applies to charging Ni-Cd batteries): if it is carried out immediately after fast charging, be sure to cool the battery for several minutes: the heated element is unable to accept the charge properly.

In addition to fast charging, there is also drip charging, which is produced by low currents. Some people believe that it “extends the life” of batteries, but this is not true. In essence, trickle charging is no different from the effect of a standard charger without “serious” adjustment of the current indicators. Any battery, if it is not used, sooner or later loses its accumulated energy, and it will still need a full charging process, regardless of its duration and “labor intensity”. This charging process is also attractive for many because the current indicators here do not need to be recorded due to their smallness. However, only a serious approach to the use of “smart” chargers can “extend the life” of batteries. As well as their proper storage, taking into account the characteristics of a particular type of battery.

Temperature factor and storage conditions

Modern chargers are equipped with a special system for “evaluating” conditions environment, including temperature factors. Such a “charger” can determine for itself whether to charge under certain conditions or not. It has already been mentioned that the efficiency level inside the battery is highest at the beginning of the process, when hydride batteries do not heat up so much. At the end of the charging process or closer to it, the efficiency drops sharply, and all the energy turns into heat due to exothermic chemical reactions, stands out. It is important to stop charging the Ni-MH battery in time. And, if possible, get the latest charger that will accurately control this process.

Currently, all chargers, including CD batteries, can be charged with a current of up to 1C with the establishment of air cooling standards. The optimal temperature of the room in which charging is carried out is 20°C. It is not recommended to start the process at temperatures less than +5 and more than 50°C.

The unique thing about Ni-Cd is that it is the only type of cell that will not suffer if stored completely discharged, unlike Ni-MH. For better current delivery, it is recommended to charge nickel-cadmium batteries immediately before use. Also, after long-term storage, they require a “boost”: the Ni-Cd battery should be fully charged and discharged within 24 hours for optimal operation.

Nickel-metal hydride cells, unlike their predecessors, can easily fail when deeply discharged. Therefore, they should only be stored charged. In this case, the voltage should be checked regularly every two months. Its minimum level should always remain 1 V, and if it drops, recharging is necessary.

A new Ni-MH battery must be fully charged and discharged three times before use, then immediately placed on the “base” for 8-12 hours. Later, there will be no need to keep it on charge for a long time - remove it immediately after indicating a special indicator on the charger.

Although all these batteries have long been replaced by more capacious ones based on lithium, they are still actively used today. This is both more familiar and much cheaper. In addition, lithium batteries low temperatures they work much worse.

Nickel-metal hydride batteries are gradually spreading on the market, and their production technology is being improved. Many manufacturers are gradually improving their characteristics. In particular, the number of charge-discharge cycles increases and the self-discharge of Ni-MH batteries decreases. This type of battery was produced to replace Ni-Cd batteries and is gradually pushing them out of the market. But there remain some applications where nickel-metal hydride batteries cannot replace cadmium batteries. Especially where high discharge currents are required. Both types of batteries require proper charging. We have already talked about charging nickel-cadmium batteries, and now it’s the turn to charge Ni-MH batteries.

During the charging process, a series of chemical reactions take place in the battery, which uses part of the supplied energy. The other part of the energy is converted into heat. The efficiency of the charging process is that part of the supplied energy that remains in the “reserve” of the battery. The efficiency value may vary depending on charging conditions, but is never 100 percent. It is worth noting that the efficiency when charging Ni-Cd batteries is higher than in the case of nickel-metal hydride batteries. The charging process of Ni-MH batteries generates a lot of heat, which imposes its own limitations and features. Read more about this in the article at the given link.

The charging speed depends most on the amount of current supplied. What currents to charge Ni-MH batteries is determined by the selected type of charge. In this case, the current is measured as a fraction of the capacity (C) of Ni-MH batteries. For example, with a capacity of 1500 mAh current 0.5C will be 750 mA. Depending on the charging rate of nickel-metal hydride batteries, there are three types of charging:

• Drip (charge current 0.1C);
• Fast (0.3C);
• Accelerated (0.5-1C).

By and large, there are only two types of charging: drip and accelerated. Fast and accelerated are practically the same thing. They differ only in the method of stopping the charging process.

In general, any charging of Ni-MH batteries with a current greater than 0.1C is fast and requires monitoring of some criteria for the end of the process. Trickle charging does not require this and can continue indefinitely.

Types of charging nickel-metal hydride batteries

Now, let's look at the features different types charging details.

Trickle charging of Ni-MH batteries

It is worth saying here that this type of charging does not increase the service life of Ni-MH batteries. Since trickle charging does not turn off even after a full charge, the current is selected very small. This is done to ensure that the batteries do not overheat during long-term charging. In the case of Ni-MH batteries, the current value can even be reduced to 0.05C. For nickel-cadmium, 0.1C is suitable.

With drip charging, there is no characteristic maximum voltage and the only limitation for this type of charging can be time. To estimate the required time, you will need to know the capacity and initial charge of the battery. To calculate charging time more accurately, you need to discharge the battery. This will eliminate the influence of the initial charge. The efficiency of trickle charging of Ni-MH batteries is 70 percent, which is lower than other types. Many nickel-metal hydride battery manufacturers do not recommend trickle charging. Although recently more and more information has appeared that modern models of Ni-MH batteries do not degrade during the trickle charging process.

Fast charging of nickel-metal hydride batteries

Manufacturers of Ni-MH batteries in their recommendations provide characteristics for charging with a current value in the range of 0.75-1C. Focus on these values ​​when you choose what current to charge Ni-MH batteries. Charge currents higher than these values ​​are not recommended as this may cause the safety valve to open to relieve pressure. It is recommended to quickly charge nickel-metal hydride batteries at a temperature of 0-40 degrees Celsius and a voltage of 0.8-.8 volts.

The efficiency of the fast charging process is much greater than that of drip charging. It is about 90 percent. However, by the time the process is completed, the efficiency decreases sharply, and the energy turns into heat release. The temperature and pressure inside the battery rise sharply. have an emergency valve that can open when the pressure increases. In this case, the properties of the battery will be irretrievably lost. And the high temperature itself has a detrimental effect on the structure of the battery electrodes. Therefore, we need clear criteria by which the charging process will be stopped.

We will present the requirements for a charger (charger) for Ni-MH batteries below. For now, we note that such chargers charge according to a certain algorithm. The stages of this algorithm are general view the following:

• determining the presence of a battery;
• battery qualification;
• pre-charge;
• transition to fast charging;
• fast charging;
• recharging;
• maintenance charging.

Let's look at these stages in more detail.

At this stage, a current of 0.1C is applied and the voltage at the poles is checked. To start the charging process, the voltage should be no more than 1.8 volts. Otherwise the process will not start.

It is worth noting that checking for the presence of a battery is carried out at other stages. This is necessary in case the battery is removed from the charger.

If the memory logic determines that the voltage value is greater than 1.8 volts, then this is perceived as the absence of a battery or its damage.

Battery qualification

Here you can determine an approximate estimate of the battery charge. If the voltage is less than 0.8 volts, then fast charging of the battery cannot be started. In this case, the charger will turn on pre-charging mode. Under normal use, Ni-MH batteries rarely discharge below 1 volt. Therefore, pre-charging is activated only in the case of deep discharges and after long-term battery storage.

Pre-charge

As mentioned above, pre-charging is activated when Ni-MH batteries are deeply discharged. The current at this stage is set at 0.1-0.3C. This stage is limited in time and lasts somewhere around 30 minutes. If during this time the battery does not restore the voltage to 0.8 volts, then the charge is interrupted. In this case, the battery is most likely damaged.

Transition to fast charging

At this stage there is a gradual increase charging current. The current increases smoothly over 2-5 minutes. At the same time, as at other stages, the temperature is controlled and the charge is turned off at critical values.

The charge current at this stage is in the range of 0.5-1C. The most important thing at the fast charging stage is to turn off the current in a timely manner. To do this, when charging Ni-MH batteries, control is used according to several different criteria.

For those who are not aware, the delta voltage control method is used when charging. During the charging process it constantly grows, and at the end of the process it begins to fall. Typically, the end of the charge is determined by a voltage drop of 30 mV. But this control method does not work very well with nickel-metal hydride batteries. In this case, the voltage drop is not as pronounced as in the case of Ni-Cd. Therefore, to trigger the shutdown, you need to increase the sensitivity. And with increased sensitivity, the likelihood of false alarms due to battery noise increases. In addition, when charging several batteries, the operation occurs at different times and the whole process is blurred.

But still, stopping charging due to a voltage drop is the main thing. When charging with a current of 1C, the voltage drop to turn off is 2.5-12 mV. Sometimes manufacturers set detection not by a drop, but by the absence of a change in voltage at the end of the charge.

In this case, during the first 5-10 minutes of charging, the voltage delta control is turned off. This is because when fast charging starts, the battery voltage can change greatly as a result of the fluctuation process. Therefore on initial stage control is disabled to eliminate false alarms.

Due to the not very high reliability of switching off charging based on the voltage delta, control is also used based on other criteria.

At the end of the charging process of the Ni-MH battery, its temperature begins to rise. This parameter is used to turn off the charge. To exclude the value of the OS temperature, monitoring is carried out not by absolute value, but by delta. Typically, a temperature increase of more than 1 degree per minute is taken as a criterion for stopping charging. But this method may not work at charge currents less than 0.5 C, when the temperature rises quite slowly. And in this case, the Ni-MH battery can be recharged.

There is also a method for monitoring the charging process by analyzing the voltage derivative. In this case, it is not the voltage delta that is monitored, but the rate of its maximum increase. The method allows you to stop fast charging slightly before the charge is complete. But such control is associated with a number of difficulties, in particular, more accurate voltage measurement.

Some chargers for Ni-MH batteries are used to charge not D.C., but pulsed. It is delivered for a duration of 1 second at intervals of 20-30 milliseconds. Experts cite a more uniform distribution of active substances throughout the battery volume and a reduction in the formation of large crystals as the advantages of such a charge. In addition, more accurate voltage measurements are reported between current injections. As a development of this method, Reflex Charging was proposed. In this case, when applying a pulsed current, the charge (1 second) and discharge (5 seconds) alternate. The discharge current is 1-2.5 times lower than the charge. The advantages include a lower temperature during charging and the elimination of large crystalline formations.

When charging nickel-metal hydride batteries, it is very important to monitor the end of the charging process using various parameters. Emergency termination methods must be provided. For this purpose, the absolute temperature value can be used. Often this value is 45-50 degrees Celsius. In this case, the charge must be interrupted and resumed after cooling. The ability of Ni-MH batteries to accept a charge at this temperature is reduced.

It is important to set a charge time limit. It can be estimated by the battery capacity, the charging current and the efficiency of the process. The limit is set at the estimated time plus 5-10 percent. In this case, if none of the previous control methods work, the charge will turn off at the set time.

Recharge phase

At this stage, the charging current is set to 0.1-0.3C. Duration about 30 minutes. Longer recharging is not recommended as it will shorten battery life. The recharging phase helps equalize the charge of the cells in the battery. It is best if, after fast charging, the batteries cool down to room temperature, and then recharging starts. Then the battery will restore its full capacity.

Chargers for Ni-Cd batteries often switch the batteries into trickle charging mode after the charging process is complete. For Ni-MH batteries, this will only be useful if a very small current is supplied (about 0.005C). This will be enough to compensate for battery self-discharge.

Ideally, the charger should have the function of enabling maintenance charging when the battery voltage drops. Maintenance charging only makes sense if a sufficiently long time elapses between charging the batteries and using them.

Ultra-fast charging of Ni-MH batteries

And it’s also worth mentioning fast charge batteries. It is known that when charged to 70 percent of its capacity, a nickel-metal hydride battery has a charging efficiency close to 100 percent. Therefore, at this stage it makes sense to increase the current to speed up its passage. In such cases, currents are limited to 10C. The main problem here is determining those 70 percent of the charge at which the current should be reduced to normal fast charging. This greatly depends on the degree of discharge at which the battery began charging. High current can easily lead to overheating of the battery and destruction of the structure of its electrodes. Therefore, the use of ultra-fast charging is recommended only if you have the appropriate skills and experience.

General requirements for chargers for nickel-metal hydride batteries

It is not practical to disassemble any individual models for charging Ni-MH batteries within the framework of this article. It is enough to note that these can be narrowly targeted chargers for charging nickel-metal hydride batteries. They have a hard-wired charging algorithm (or several) and constantly work according to it. And there are universal devices that allow you to fine-tune charging parameters. Eg, . Such devices can be used to charge various batteries. Including for, if there is a power adapter of appropriate power.

It is necessary to say a few words about what characteristics and functionality a charger for Ni-MH batteries should have. The device must be able to adjust the charging current or its automatic installation depending on the type of batteries. Why is it important?

Now there are many models of nickel-metal hydride batteries, and many batteries of the same form factor may differ in capacity. Accordingly, the charging current should be different. If you charge with a current higher than normal, there will be heating. If it is below normal, the charging process will take longer than expected. In most cases, the currents on chargers are made in the form of “presets” for standard batteries. In general, when charging, manufacturers of Ni-MH batteries do not recommend setting the current to more than 1.3-1.5 amperes for type AA, regardless of capacity. If for some reason you need to increase this value, then you need to take care of forced cooling of the batteries.

Another problem involves the charger cutting off power during charging. In this case, when the power is turned on, it will start again from the battery detection stage. The moment at which fast charging ends is determined not by time, but by a number of other criteria. Therefore, if it has passed, it will be skipped when turned on. But the recharging stage will take place again, if it has already happened. As a result, the battery receives unwanted overcharging and excess heating. Among other requirements for the charger of Ni-MH batteries is a low discharge when the charger is turned off. The discharge current in a de-energized charger should not exceed 1 mA.

It is worth noting that the charger has another important function. It must recognize primary current sources. Simply put, zinc-manganese and alkaline batteries.

When installing and charging such batteries in a charger, they may well explode, since they do not have an emergency valve to relieve pressure. The charger is required to be able to recognize such primary current sources and not initiate charging.

Although it is worth noting here that determining batteries and primary current sources has a number of difficulties. Therefore, memory manufacturers do not always equip their models with similar functions.

Some tips for using nickel-metal hydride batteries

As you understand, the basic rules for using Ni-MH batteries are to avoid overheating and overcharging. Below are additional tips for using nickel-metal hydride batteries to help you extend their life:

• If you leave Ni-MH batteries for long-term storage, then the charge in them should be 30-50 percent of the rated capacity;
• Nickel-metal hydride batteries are much more sensitive to overcharging and heat than nickel-cadmium batteries. These things negatively affect the battery life and current efficiency. Remember that a Ni-MH battery charger can be used to charge Ni-Cd batteries, but not vice versa;
• Nickel metal hydride can be subjected to training cycles, but is not necessary. A high-quality charger allows the battery to gain capacity lost during storage and transportation in a few charges. For products from different manufacturers, the number of cycles to fill a container varies. For some batteries, 3-4 cycles are enough, while for others, fifty may not be enough;
• After completing the charge or discharge cycle, leave the battery to cool. Charging should not be carried out at temperatures below 5 and above 50 degrees Celsius. This shortens the life of Ni-MH batteries;
• Try not to discharge a Ni-MH battery below 0.9 volts. In such cases, many inexpensive chargers simply will not be able to start charging. When charging cannot recognize such a discharged battery, you can connect the battery to an external power source (current 90-160 mA) and increase the voltage to 0.9 volts;
• When using the same battery of cells in recharging mode, it is recommended to discharge the battery to 0.9 volts and then fully charge it in the charger. It is advisable to repeat this process once every ten times the Ni-MH batteries are recharged.

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Charging parameters for the most common Ni-MH batteries

In conclusion, we present the charging parameters for the most common types of nickel-metal hydride batteries. The characteristics are selected for completely discharged batteries. They are summarized in the table below.

11. Storage and operation of Ni-MH batteries

Before you start using new Ni-MH batteries, it is worth remembering that they must first be “boosted” for maximum capacity. To do this, it is advisable to have a charger capable of discharging batteries: set the charger to the minimum current and charge the battery, and then immediately discharge it by pressing the appropriate button on the charger. If you don’t have such a device at hand, you can simply “load” the battery to full capacity and wait.

2-5 such cycles may be required, depending on the duration and temperature of storage in warehouses and stores. Very often, storage conditions are far from ideal, so repeated training will come in handy.

For the most efficient and productive operation of the battery for the longest possible time, it is necessary to further, if possible, completely discharge it (it is recommended to charge the device only after it has turned off due to battery discharge) and charge the battery in order to Avoid the appearance of the “memory effect” and shortening the battery life. To restore the full (as far as possible) battery capacity, it is also necessary to carry out the training described above. In this case, the battery discharges to a minimum permissible voltage on the cell and crystal formations are destroyed. You need to make it a rule to train your battery at least once every two months. But you shouldn’t go too far either - frequent use of this method wears out the battery. After discharge, it is recommended to leave the device on charge for at least 12 hours.

The memory effect can also be eliminated by discharging with a high current (2-3 times higher than the rated current).

“We wanted the best, but it turned out as always”

The first and simplest rule correct charging any battery - use the charger (hereinafter referred to as the charger) that was sold in the kit (for example, mobile phone), or where the charging conditions comply with the requirements of the battery manufacturer (for example, for AA Ni-MH batteries).

In any case, it is better to purchase batteries and chargers recommended by the manufacturer. Each company has its own production technologies and operating features of batteries. Before using batteries and chargers, you must carefully read all included instructions and other information materials.

As we wrote above, the simplest memory devices are usually included in the package. Such chargers, as a rule, give users a minimum of concern: phone manufacturers try to coordinate the charging technology with all possible types of batteries designed to work with a given brand of device. This means that if the device is designed to work with Ni-Cd, Ni-MH and Li-Ion batteries, this charger will equally effectively charge all of the above batteries, even if they are different capacities.

But there is one drawback here. Nickel batteries, which are susceptible to the memory effect, must be completely discharged periodically, but the “device” is not capable of this: when a certain voltage threshold is reached, it turns off. The voltage at which automatic shutdown occurs is higher than the voltage to which the battery must be discharged to destroy the crystals that reduce the battery capacity. In such cases, it is still better to use a charger with a discharge function.

There is an opinion that Ni-MH batteries can only be charged after they are completely (100%) discharged. But in fact, completely discharging the battery is undesirable, otherwise the battery will fail prematurely. A discharge depth of 85-90% is recommended - the so-called surface discharge.

In addition, you need to take into account that Ni-MH batteries require special charging modes, unlike Ni-Cd, which are the least demanding on the charging mode.

Although modern nickel-metal hydride batteries can handle exceeding their rated charge, the resulting overheating reduces battery life. Therefore, when charging, you need to consider three factors: time, amount of charge and battery temperature. Today, there are a large number of chargers that provide control over the charging mode.

There are slow, fast and pulse memories. It’s worth mentioning right away that this division is quite arbitrary and depends on the battery manufacturer. The approach to the charging problem is approximately the following: the company develops various types of batteries for various applications and sets recommendations and requirements for the most favorable charging methods for each type. As a result, the same appearance(size) batteries may require various methods charge.

“Slow” and “fast” chargers differ in the speed at which batteries are charged. The first ones charge the battery with a current equal to approximately 1/10 of the nominal current, the charging time is 10 - 12 hours, and, as a rule, the condition of the battery is not monitored, which is not very good (completely and partially discharged batteries must be charged in different modes).

“Fast” charges the battery with a current in the range from 1/3 to 1 of its nominal value. Charging time - 1-3 hours. Very often this is a dual-mode device that responds to changes in voltage at the battery terminals during charging. First, the charge accumulates in the “high-speed” mode, when the voltage reaches a certain level, high-speed charging stops and the device is switched to slow mode"jet" charging. These devices are ideal for Ni-Cd and Ni-MH batteries. Nowadays, the most common chargers are those using pulse charging technology. As a rule, they can be used for all types of batteries. This charger is especially suitable for extending the life of Ni-Cd batteries, since this destroys crystalline formations active substance(the “memory effect” that occurs during operation is reduced. However, for batteries with a significant “memory effect”, using only a pulsed charging method is not enough - it is necessary deep discharge(recovery) using a special algorithm to destroy large crystalline formations. Conventional chargers, even with a discharge function, are not capable of this. This can be done at the service center using special equipment.

For those who spend a lot of time driving, a car charger is definitely a must. The simplest one is made in the form of a cord connecting cellular telephone with a car cigarette lighter socket (all “old” options are intended only for charging Ni-Cd and Ni-MH batteries). However, you should not abuse this charging method: such operating conditions negatively affect the battery life.

If you have already chosen a charger that suits you, read the following recommendations for charging Ni-Cd and Ni-Mh batteries:

Charge only completely discharged batteries;

You should not place a fully charged battery for additional charging, as this significantly shortens its service life;

You should not leave Ni-Cd and Ni-MH batteries in the charger for a long time after the end of charging, since the charger continues to charge them even after a full charge, but only with a much lower current. Long-term presence of Ni-Cd and Ni-MH batteries in the charger leads to their overcharging and deterioration of parameters;

Batteries must be at room temperature before charging. Charging is most effective at ambient temperatures from +10°C to +25°C.

During the charging process, the batteries may heat up. This is especially true for a series of high capacity with intensive (fast) charging. The maximum heating temperature for batteries is +55°C. The design of fast chargers (from 30 minutes to 2 hours) provides temperature control for each battery. When the battery case heats up to +55°C, the device switches from the main charging mode to the additional charging mode, during which the temperature decreases. The design of the batteries themselves also provides protection against overheating in the form of a safety valve (preventing destruction of the battery), which opens if the electrolyte vapor pressure inside the case exceeds permissible limits.

Storage

If you bought a battery and do not intend to use it immediately, then you better familiarize yourself with the rules for storing Ni-MH batteries.

First of all, the battery must be removed from the device and protected from moisture and high temperatures. The voltage on the battery must not be allowed to drop significantly due to self-discharge, that is, during long-term storage, the battery must be periodically charged.

Do not store the battery in high temperature, this accelerates the degradation of the active materials inside the battery. For example, continuous operation and storage at 45°C will reduce the cycle rate of a Ni-MH battery by approximately 60%.

At low temperatures, storage conditions are the best, but we note that it is specifically for storage, since the energy output of any batteries at sub-zero temperatures drops, and they cannot be charged at all. Storing at low temperatures will reduce self-discharge (for example, you can put it in the refrigerator, but never in the freezer).

In addition to temperature, the battery life is significantly affected by the degree of its charge. Some say that it should be stored in a charged state, others insist on completely discharging it. The best option is to charge the battery by 40% before storage.

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