Features of charging Ni─MH batteries, charger requirements and basic parameters
Nickel-metal hydride batteries are gradually spreading in the market, and their production technology is improving. Many manufacturers are gradually improving their performance. 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 little by little they are pushing them out of the market. But there are still some uses where nickel metal hydride batteries cannot replace cadmium batteries. Especially where high discharge currents are required. Both types of batteries require competent charging to extend their service life. We have already talked about charging nickel-cadmium batteries, and now it's time to charge Ni-MH batteries.
In the process of charging, a series of chemical reactions takes place in the battery, to which part of the supplied energy goes. Another 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. Efficiency 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 process of charging Ni─MH batteries is accompanied by a large release of heat, which imposes its own limitations and peculiarities. For more information, read the article at the specified link.
The charging speed depends most of all 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 in fractions of the capacity (C) of Ni-MH batteries. For example, with a capacity of 1500 mAh, the 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 tracking some criteria for the end of the process. Drip charging does not require this and can continue indefinitely.
Charging options for nickel-metal hydride batteries
Now, let's take a closer look at the features of different types of charging.
Drip charging Ni─MH batteries
It should be said here that this type of charging does not increase the life of Ni-MH batteries. Since trickle charging does not turn off even after a full charge, the current is chosen very small. This is done so that the batteries do not overheat during prolonged 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 trickle charging, there is no characteristic maximum voltage and only time can act as a limitation of this type of charging. To estimate the time required, you need to know the capacity and initial charge of the battery. To calculate the charging time more accurately, the battery must be discharged. This will eliminate the influence of the initial charge. The efficiency with trickle charging of Ni─MH batteries is at the level of 70 percent, which is lower than other types. Many manufacturers of nickel metal hydride batteries do not recommend the use of trickle charging. Although recently there is more and more information that modern models of Ni─MH batteries do not degrade in the process of trickle charging.
Fast charging nickel metal hydride batteries
Manufacturers of Ni─MH batteries in their recommendations give characteristics for charging with a current value in the range of 0.75─1C. Focus on these values when choosing what current to charge Ni─MH batteries with. Charge currents above these values are not recommended as this could cause the safety valve to open to relieve pressure. It is recommended to carry out quick charging of 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 higher than that of drip charging. It is about 90 percent. However, by the end of the process, the efficiency drops sharply, and the energy goes into heat release. Temperature and pressure rise sharply inside the battery. have an emergency valve that can open when the pressure rises. 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, clear criteria are needed by which the charging process will stop.
The requirements for a charger (charger) for Ni─MH batteries are presented below. For now, we note that such chargers conduct a charge according to a certain algorithm. Generally, the stages of this algorithm are as follows:
- determination of the presence of a rechargeable battery;
- battery qualification;
- pre-charge;
- transition to fast charging;
- fast charging;
- recharging;
- maintenance charging.
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 also carried out at other stages. This is necessary in case the battery is removed from the charger.
If the logic of the charger determines that the voltage is greater than 1.8 volts, then this is perceived as the absence of a battery or its damage.
Battery qualification
A rough estimate of the battery charge is determined here. If the voltage is less than 0.8 volts, then the fast battery charge cannot be started. In this case, the charger will activate the pre-charge mode. During normal use, Ni-MH batteries are rarely discharged to a voltage below 1 volt. Therefore, pre-charging is only activated in the case of deep discharges and after long-term storage of the batteries.
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 is somewhere around 30 minutes. If during this time the battery does not restore the voltage of 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 in the charging current. The current build-up occurs smoothly within 2-5 minutes. At the same time, as in other stages, the temperature is monitored 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 in the fast charging stage is the timely disconnection of the current. For this, when charging Ni─MH batteries, control is used according to several different criteria.
For those who are not in the know, the voltage delta control method is used when charging. During the charging process, it constantly grows, and at the end of the process it begins to fall. Usually, 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 increases due to battery noise. In addition, when multiple batteries are charged, the triggering occurs at different times and the whole process is smeared.
But still, stopping charging due to a voltage drop is the main one. When charging with a current of 1C, the voltage drop for shutdown is 2.5-12 mV. Sometimes manufacturers set detection not by a drop, but by the absence of a voltage change at the end of the charge.
In this case, during the first 5-10 minutes of charging, the voltage delta control is disabled. This is because at the start of fast charging, the battery voltage can vary greatly as a result of the fluctuation process. Therefore, at the initial stage, control is disabled in order to exclude false alarms.
Due to the not too high reliability of disconnecting charging by the voltage delta, control is also used by other criteria.
At the end of the Ni─MH battery charging process, its temperature begins to rise. This parameter is used to turn off the charge. To exclude the OS temperature value, monitoring is carried out not by the absolute value, but by the delta. Usually, a temperature rise of more than 1 degree per minute is taken as a criterion for terminating a charge. But this method may not work at charge currents of less than 0.5C, when the temperature rises rather slowly. In this case, the Ni-MH battery may be overcharged.
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 growth. The method allows you to stop fast charging a little earlier than the end of the charge. But such control is fraught with a number of difficulties, in particular, a more accurate voltage measurement.
Some chargers for Ni─MH batteries use pulsed rather than direct current for charging. It is fed for 1 second at intervals of 20-30 milliseconds. As the advantages of such a charge, experts call a more uniform distribution of active substances over the volume of the battery and a decrease in the formation of large crystals. In addition, a more accurate voltage measurement in the intervals between current applications is reported. As a development of this method, Reflex Charging was proposed. In this case, when a pulse current is applied, charge (1 second) and discharge (5 seconds) alternate. The discharge current is 1-2.5 times lower than the charge. The advantages are lower charging temperatures and elimination of large crystalline formations.
When charging nickel-metal hydride batteries, it is very important to control the end of the charging process according to various parameters. Provision should be made for emergency termination of the charge. For this, the absolute value of the temperature can be used. Often this value is 45-50 degrees Celsius. In this case, the charge must be interrupted and resumed after cooling down. Ni─MH batteries are less able to take charge at this temperature.
It is important to set a time limit for charging. It can be estimated by the capacity of the battery, the magnitude of 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 stage
At this stage, the charging current is set to 0.1-0.3C. Duration about 30 minutes. Longer recharging is not recommended as this will shorten the battery life. The recharge phase helps to equalize the charge of the cells in the battery. It is best if, after a quick charge, the batteries cool down to room temperature, and then recharge starts. Then the battery will restore full capacity.
Chargers for Ni-Cd batteries often put the batteries in trickle charging 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 the self-discharge of the battery.
Ideally, the charger should have the function of turning on float charge when the battery voltage drops. Trickle charging only makes sense when a sufficiently long time has elapsed between charging the batteries and using them.
Ultra-fast charging of Ni-MH batteries
And it is also worth mentioning the super-fast charging of batteries. It is known that when charged up 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 for its accelerated passage. Currents in such cases are limited to 10C. The main problem here is determining the very 70 percent of the charge at which the current should be reduced to normal fast charging. This greatly depends on the degree of discharge from which the battery started charging. High current can easily lead to overheating of the battery and destruction of the structure of its electrodes. Therefore, the use of an ultra-fast charge is recommended only with the appropriate skills and experience.
General requirements for chargers for nickel metal hydride batteries
It is inappropriate to disassemble any separate models for charging Ni─MH batteries within the framework of this article. Suffice it to say that these can be narrowly targeted chargers for charging nickel-metal hydride batteries. They have a wired charging algorithm (or several) and they constantly work on it. And there are universal devices that allow you to fine-tune the charging parameters. For example, . Such devices can be used to charge various batteries. Including, if there is a power adapter of appropriate power.
I need 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 automatically set it depending on the type of batteries. Why is it important?
There are many models of nickel metal hydride batteries now, and many batteries of the same form factor may differ in capacity. Accordingly, the charging current must be different. If charged with a current above normal, there will be heating. If it is below the norm, then the charging process will take longer than expected. In most cases, the currents on the chargers are made in the form of "presets" for typical batteries. In general, when charging, the manufacturers of Ni-MH batteries do not recommend setting a current of 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 the forced cooling of the batteries.
Another problem has to do with disconnecting the power to the charger while charging. In this case, when the power is turned on, it will start again from the battery detection stage. The end of fast charging is not determined by time, but by a number of other criteria. Therefore, if it passed, then it will be skipped when turned on. But the recharge stage will take place again, if it has already been. As a result, the battery receives unwanted overcharging and unnecessary heating. Among other requirements for the charger of Ni-MH batteries - low discharge when the charger is disconnected from the power supply. The discharge current in a de-energized charger should not exceed 1 mA.
It is worth noting the presence of another important function in the charger. It must recognize primary power sources. Simply put, zinc-manganese and alkaline batteries.
When installing and charging such batteries in the 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 activate charging.
Although it is worth noting here that the definition of batteries and primary current sources has a number of difficulties. Therefore, memory manufacturers do not always equip their models with such functions.
The main difference between Ni-Cd batteries and Ni-Mh batteries is their composition. The base of the battery is the same - it is nickel, it is the cathode, and the anodes are different. For a Ni-Cd battery, the anode is metal cadmium, for a Ni-Mh battery, the anode is a hydrogen metal hydride electrode.
Each type of battery has its own pros and cons, knowing them, you can more accurately select the battery you need.
| pros | Minuses | |
| Ni-Cd |
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| Ni-Mh |
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Will the old charger fit the new battery if I change from Ni-Cd to Ni-Mh or vice versa?
The principle of charging for both batteries is absolutely the same, so the charger can be used from the previous battery. The basic rule of thumb for charging these batteries is that they can only be charged after they have been completely discharged. This requirement is due to the fact that both types of batteries are subject to the "memory effect", although with Ni-Mh batteries this problem is minimized.
How to properly store Ni-Cd and Ni-Mh batteries?
The best place to store the battery is in a cool dry place, as the higher the storage temperature, the faster the battery will self-discharge. The battery can be stored in any condition other than full discharge or full charge. The optimal charge is 40-60 %%. Once every 2-3 months, additional charge should be carried out (due to the self-discharge present), discharge and again charge up to 40-60 %% of the capacity. Storage for up to five years is acceptable. After storage, the battery should be discharged, recharged and then used normally.
Can I use batteries with a larger or smaller capacity than the original set?
Battery capacity is the amount of time your power tool has been running on battery power. Accordingly, for a power tool, there is absolutely no difference in battery capacity. The actual difference will only be in the charging time of the battery and the operating time of the power tool on battery power. When choosing a battery capacity, you should start from your requirements, if you need to work longer using one battery - the choice is in favor of more capacious batteries, if the complete batteries are completely satisfactory, then you should stay on batteries of equal or similar capacity.
Nickel-cadmium and nickel-metal hydride batteries are two main types of alkaline chemical current sources for autonomous power supply of various equipment. They are similar in structure. An alkali is used as an electrolyte, and nickel oxide is used as a cathode.
Ni-cd was invented first. This technology is over a hundred years old. NI-MH is widely used in household devices, began only in the 90s of the twentieth century. The massive appearance on the market of more capacious (NI-MH) batteries initially caused a sensation. But then the shortcomings came to light.
Features and application of Ni-cd batteries
Compared to metal hydride batteries, Ni-cd has two main disadvantages. This is less storage capacity and memory effect. The memory effect is called “remembering” the battery's lower discharge limit. That is, if such a battery is not completely discharged, the duration of the next cycle will be less by this same amount from full discharge to the limit that the battery “remembered”. To “reset” the memory, you need to fully charge and discharge such a battery two or three times.
It would seem that with such properties, this type of battery should go into oblivion. But this is not happening. Due to two other properties of this type of batteries - high current output and the ability to work well at negative temperatures.
Approximately 90% Ni-cd today are rechargeable assemblies for power tools, children's toys, electric shavers, self-contained vacuum cleaners, medical equipment, and more. The use in the household segment (instead of conventional primary batteries) is practically reduced to zero.
Some countries have legal restrictions on the use of Ni-cd cells due to the toxicity of cadmium. In new devices, their place is taken by lithium-ion batteries with a high current output.
Charging ni cd batteries
One element has a nominal voltage of 1.2V. During operation, this value can vary from 1.35V (fully charged) to 1V (full discharge). These elements have one interesting feature, which is tied to the shutdown mode in the charger (if it is automatic). After the capacitance is set, the voltage at the terminals is slightly reduced by 50-70 mV. Such a jump is denoted by ΔV (delta V). The charger reacts to such a decrease and cuts off the charge current.
In practice, only chargers of the intermediate and advanced level are able to operate on ΔV. And often you have to manually figure out how to charge ni cd batteries.
Any charge voltage will produce at the rate of 1.5-1.6v per element. But the charge current can be different. It can always be viewed on the charger itself (usually from the back side).
The battery capacity must be divided by the charge current and multiplied by a loss factor of 1.4. For example, 1000mAh / 200mA = 5 hours * 1.4 = 7 hours. What current to charge? The nominal charge current is 0.1C, where C is the battery capacity. For 1000mAh, the nominal current is 100mA. The charging time in this case will be 14 hours. Not very comfortable. An accelerated mode of 0.2-0.5C is almost always used. This shortens the battery life somewhat, but improves usability.
Important! Nickel-cadmium batteries have an average life of 500 charge-discharge cycles. The manufacturer declares, as a rule, up to 1000. Such indicators can be achieved only under ideal conditions and clearly maintaining the nominal operating conditions.
Basic rules for charging nickel cadmium batteries
- be sure to discharge the batteries before charging;
- connect the charger (or install batteries in it for household use) and wait for it to turn off when fully charged;
- if the charger does not provide automatic shutdown, calculate the required charging time and after its expiration make a shutdown;
- keep ni cd batteries in a discharged state.
Features and Applications of NI MH Batteries
The field of application of metal hydride batteries is directly related to their properties. The maximum capacity with the minimum volume allowed them to take place in those electronics, where disposable batteries have to be changed very often. These are cameras, wireless mice and keyboards, radio remote controls, children's toys.
Basically, two sizes of such elements are used - AA and AAA. These cells can be used anywhere where disposable batteries are used. But often this does not make economic sense (in the event that a disposable battery has been in the device for years)
The nominal voltage ni mh of the battery is 1.2v. With a slight deviation under load, this voltage is maintained throughout the entire battery life. The voltage of a disposable battery in operation gradually drops from 1.5 to 1 volt. That is the 1.2 average. This allows the battery to perfectly replace a disposable battery 99% of the time. Cases when exactly 1.5v is needed for the operation of the device are isolated and are often "treated" by changing the mode in the "battery / accumulator" menu of the device.
Attention! The maximum capacity (physical limit) for an AA battery is 2700mAh, for AAA 1000mAh. In case the label has a greater value and "mysterious" name of the manufacturer, you are guaranteed deception.
The memory effect when charging NiMH batteries is less noticeable than Ni-cd cells. For the first few years of mass sales, manufacturers placed the inscription “no memory effect”. Subsequently, this inscription was removed. The “charge after discharge” recommendation is also relevant for metal hydride batteries.
Nickel Metal Hydride Battery Charge
The charging voltage ni mh is the same as for nickel cadmium batteries. The charger will supply 1.5-1.6v per cell. The charging current ni mh of batteries can vary from 0.1 to 1C. But any manufacturer of household batteries must indicate their recommendation of this parameter to them. The manufacturer's recommendation is 0.1C. For example, for 2500mAh, the nominal charge current of ni mh batteries is 250mA. Charging time with rated current 14 hours. Using the same formula. Capacity / charge current, multiply the result by 1.4. With this mode, you can count on the number of cycles declared by the manufacturer. In accelerated mode, the service life is reduced.
Metal hydride batteries do not tolerate overheating, deep discharge, strong overcharge. Overheating can occur with a large charge current, increased internal resistance. Discontinue charging in case of strong heating. A deep discharge occurs when the element is not used for a long time. If inactive for a year or more, the battery will most likely need to be replaced. Overcharging occurs when the charger is used without a shutdown function or when the charging time is incorrectly calculated.
Chargers and charging methods
There are a huge number of chargers on sale. They implement different shutdown schemes or shutdown is not implemented at all. You can easily divide them into subspecies according to their appearance.
- The simplest. Plugged in - the charge went off, turned off - the charge is over. Control over the charging time lies with the user. Such devices have the right to exist in order to save money. You just need to choose one that will charge each element separately. If the charge channels are paired, a skew occurs. This mode will shorten the battery life. It's easy to distinguish. The number of LED indicators should match the number of charge channels.
- With AUTO lettering. Such an inscription indicates that a timer shutdown is implemented here. Usually 6 to 12 hours. Not a bad option. There will definitely not be an overcharge. But most likely there will be no full charge. In this case, you can choose the batteries specifically for this charger. But the correct operation of the charger will be the first 100-200 cycles.
- ΔV control. If the manufacturer has implemented this function, he will definitely write this on the package. If there is no inscription, the charger refers to point 2. With the presence of ΔV control, the charger is already fully automatic. Do not forget about separate charging of each channel (popular 10-12 years ago, chargers with an index of 508 have a ΔV control, but they perceive the batteries installed in it as one battery).
- With liquid crystal display. As a rule, its presence indicates that everything listed above has been implemented plus temperature control. Chargers with an entry-level display do not imply programming the mode and charge current, but with their function - to properly charge ni mh batteries, they do an excellent job.
- Charging - combine. Larger than in point 4. Assumes user programming of modes and charging current. If nothing is programmed in the “default” mode, the batteries are charged with the minimum current and the charge is turned off according to the ΔV control.
The more functional the charger, the more expensive it is. But even in an expensive version, the cost is about 50 alkaline batteries. Payback comes quickly enough. A charger of this class is usually universal. And it allows you to charge, in addition to nickel batteries, also lithium-ion batteries. And also has the function of measuring the capacity, internal resistance of batteries, a mode for resetting the memory effect of nickel batteries.
NI-MH batteries with low self-discharge
This is a fairly new technology. The abbreviation LSD is sometimes used. What is translated from English “low self-discharge” - low self-discharge.
Such batteries appeared on the market a little over 10 years ago and have proven themselves very well. Compared to conventional batteries, they have a lower internal resistance and, as a consequence, higher discharge currents. Their capacity is slightly lower than that of conventional NI-MH batteries. But due to the fact that an ordinary battery has a self-discharge of about 10% in the first day, they show themselves no less efficiently.
It is quite easy to distinguish such a battery from a regular one. On the packaging and on the element itself there will be an inscription “ready to use” ie “Ready to use”. Such elements are sold already charged. This is the best choice for amateur photography, when the task is not to make several thousand frames in one day.
NI MH Charging Rules
The answer to the question - how to charge ni mh batteries depends, first of all, on what kind of charger the user has. In order to charge correctly, it is enough to adhere to simple rules.
- It is advisable to discharge the batteries before charging. This is not a strict regulation unlike Ni-cd batteries, but it is desirable.
- The ambient temperature must be at least 5 o C. The upper temperature limit is 50 o C. This temperature can occur in summer when exposed to direct sunlight.
- Explore the functions of the charger. If it does not automatically shut off, calculate the charging time.
- Install the batteries in the charger and connect it to the mains. After a while, check the degree of heating of the batteries. In case of strong heating, stop charging.
- Disconnect the charger either after the estimated time has elapsed, or after the corresponding indication is turned on (depending on the type of charger).
- Store Ni-MH cells 10-20% charged. The voltage should not drop below 0.9v.
When properly charged, nickel-metal hydride batteries will last long enough. From 500 to 1000 charge-discharge cycles. The main reason for premature failure is prolonged non-use and, as a result, deep discharge. Often, the desire of users to abandon Ni-MH or Ni-cd technology and switch all their equipment to lithium-ion batteries is completely unjustified. These batteries are firmly established in both the household segment and industry.
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 “shaken” for maximum capacity. To do this, it is advisable to have a charger capable of discharging the batteries: set the charging to the minimum current and charge the battery, and then discharge it immediately by pressing the corresponding button on the charger. If such a device is not at hand, you can simply "load" the battery at full capacity and wait.
It may take 2-5 such cycles, depending on the duration and temperature of storage in warehouses and stores. Very often storage conditions are far from ideal, so repeated training will be very useful.
For the most effective and efficient operation of the battery for as long as possible, it must be further discharged, if possible, completely (it is recommended to put the device on charge only after it has turned off due to a discharge of the battery) and charge the battery in order to avoid the "memory effect" and shorten the life of the battery. To restore the battery to its full (as much as possible) capacity, it is also necessary to carry out the workout described above. In this case, the battery is discharged to the minimum permissible voltage per cell and the crystalline formations are destroyed in this case. It is necessary to make it a rule to train the 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 plugged in for at least 12 hours.
The memory effect can also be eliminated by discharging with a high current (2-3 times higher than the nominal).
"We wanted the best, but it turned out as always"
The first and simplest rule of correct charging of any battery is to use the charger (hereinafter referred to as charger) that was sold in the kit (for example, a mobile phone), or where the charging conditions meet the requirements of the battery manufacturer (for example, for finger-type Ni-MH batteries) ...
In any case, it is better to purchase batteries and chargers recommended by the manufacturer. Each company has its own production technology and battery operation features. Before using batteries and chargers, carefully read all attached instructions and other information materials.
As we wrote above, the simplest chargers are usually included in the delivery set. Such chargers, as a rule, give users a minimum of concern: phone manufacturers are trying to harmonize 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 have different capacities.
But there is one drawback here. Nickel batteries subject to the memory effect must be completely discharged from time to time, but the "device" is not capable of this: when a certain voltage threshold is reached, it turns off. The voltage at which the automatic shutdown occurs exceeds the value to which the battery must be discharged in order to destroy the crystals that reduce the battery capacity. In such cases, it is still better to use a memory with a discharge function.
There is an opinion that Ni-MH batteries can be charged only after their full (100%) discharge. But in fact, a complete discharge of the battery is undesirable, otherwise the battery will fail prematurely. The recommended depth of discharge is 85-90% - the so-called surface discharge.
In addition, it should be borne in mind that Ni-MH batteries require special charging modes, in contrast to Ni-Cd, which are the least demanding on the charging mode.
Although modern NiMH batteries can handle overcharging, the resulting overheating will reduce battery life. Therefore, there are three factors to consider when charging: time, amount of charge, and battery temperature. Today there are a large number of chargers that provide control over the charging mode.
Distinguish between slow, fast and impulse chargers. It should be noted right away that this division is rather arbitrary and depends on the manufacturer of the batteries. The approach to the charging problem is roughly the following: the company develops different types of batteries for different applications and sets recommendations and requirements for each type of the most favorable charging methods. As a result, batteries of the same appearance (size) may require different charging methods.
"Slow" and "fast" chargers differ in the speed of battery charging. The former charge the battery with a current equal to about 1/10 of the nominal, the charging time is 10 - 12 hours, while, as a rule, the state of the battery is not monitored, which is not very good (completely and partially discharged batteries must be charged in different modes).
"Fast" charge the battery with a current in the range from 1/3 to 1 of its nominal value. Charging time is 1-3 hours. Very often this is a dual-mode device that responds to changes in the voltage at the battery terminals during the charging process. First, the charge is accumulated in the "high-speed" mode, when the voltage reaches a certain level, the high-speed charge is stopped and the device is transferred to the slow "trickle" charging mode. These devices are ideal for Ni-Cd and Ni-MH batteries. Nowadays, the most common chargers using pulse charging technology. As a rule, they can be used for all types of batteries. This charger is especially well suited for extending the service life of Ni-Cd batteries, as this destroys the crystalline formations of the active substance (reduces the "memory effect") that occur during operation. However, for batteries with a significant "memory effect", the use of only a pulsed charging method is not enough - a deep discharge (recovery) is required according to a special algorithm in order to destroy large crystalline formations. Conventional chargers, even with a discharge function, are not capable of this. This can be done in the service department using special equipment.
For those who spend a lot of time behind the wheel, an in-car charger option is definitely a must. The simplest is made in the form of a cord that connects a cell phone to a car cigarette lighter socket (all "old" options are designed only for charging Ni-Cd and Ni-MH batteries). However, do not abuse this charging method: such operating conditions negatively affect the battery life.
If you have already chosen the charger that suits you, read the following recommendations for charging Ni-Cd and Ni-Mh batteries:
Charge only fully discharged batteries;
Do not place a fully charged battery on additional recharge, as this will significantly shorten its useful life;
Do not leave Ni-Cd and Ni-MH batteries in the charger after the end of the charge for a long time, 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 increased capacity with an intensive (fast) charge. The maximum temperature for heating batteries is + 55 ° C. In the design of fast chargers (from 30 minutes to 2 hours), temperature control of each battery is provided. When the battery case heats up to + 55 ° C, the device switches from the main charge mode to the additional charge 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 the destruction of the battery), which opens if the vapor pressure of the electrolyte inside the case exceeds the permissible limits.
Storage
If you have bought a battery and are not going to use it immediately, then you better read the rules for storing Ni-MH batteries.
First of all, the battery must be removed from the device and care must be taken to protect it from moisture and high temperatures. A strong decrease in the voltage on the battery due to self-discharge must not be allowed, that is, during long-term storage, the battery must be periodically charged.
Do not store the battery at high temperatures, this accelerates the degradation of active materials inside the battery. For example, continuous operation and storage at 45 ° C will reduce the number of cycles of a Ni-MH battery by about 60%.
At a low temperature, storage conditions are the best, but we note that it is for storage, since the energy output at subzero temperatures drops in any batteries, and it is not possible to charge 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, battery life is also significantly affected by the degree of charge. Some say that it is necessary to store it in a charged state, while others insist on a complete discharge. The best option is to charge the battery by 40% before storage.
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History of invention
Research into NiMH battery technology began in the 70s of the XX century and was undertaken as an attempt to overcome the shortcomings. However, the metal hydride compounds used at that time were unstable and the required characteristics were not achieved. As a result, the development process for NiMH batteries has stalled. New metal hydride compounds, sufficiently stable for use in batteries, were developed in 1980. Since the late 1980s, NiMH batteries have been continuously improved, mainly in terms of energy density. Their developers noted that there is the potential for NiMH technology to achieve even higher energy densities.
Options
- Theoretical energy consumption (Wh / kg): 300 Wh / kg.
- Specific energy consumption: about - 60-72 Wh / kg.
- Specific energy density (W · h / dm ³): about - 150 W · h / dm³.
- EMF: 1.25.
- Operating temperature: −60 ... + 55 ° C. (- 40 ... +55)
- Service life: about 300-500 charge / discharge cycles.
Description
Nickel-metal hydride batteries of the "Crohn" form factor, usually with an initial voltage of 8.4 volts, gradually reduce the voltage to 7.2 volts, and then, when the battery energy is depleted, the voltage decreases rapidly. This type of battery is designed to replace nickel cadmium batteries. Nickel-metal hydride batteries have about 20% more capacity for the same dimensions, but a shorter service life - from 200 to 300 charge / discharge cycles. Self-discharge is about 1.5-2 times higher than that of nickel-cadmium batteries.
NiMH batteries are practically free from the "memory effect". This means that you can charge an incompletely discharged battery if it has not been stored for more than a few days in this state. If the battery has been partially discharged and then not used for a long time (more than 30 days), then it must be discharged before charging.
Environmentally friendly.
The most favorable operating mode: low current charge, 0.1 of the nominal capacity, charging time - 15-16 hours (typical manufacturer's recommendation).
Storage
Batteries should be stored fully charged in the refrigerator, but not below 0 ° C. During storage, it is advisable to regularly (once every 1-2 months) check the voltage. It should not fall below 1.37. If the voltage drops, it is necessary to recharge the batteries. The only rechargeable battery that can be stored discharged is Ni-Cd rechargeable batteries.
Low self-discharge NiMH batteries (LSD NiMH)
The low self-discharge nickel-metal hydride battery, LSD NiMH, was first introduced in November 2005 by Sanyo under the brand name Eneloop. Later, many global manufacturers presented their LSD NiMH batteries.
This type of battery has a reduced self-discharge, which means it has a longer shelf life than conventional NiMH batteries. Batteries are marketed as "ready-to-use" or "pre-charged" and are marketed as replacements for alkaline batteries.
Compared to conventional NiMH batteries, LSD NiMH batteries are most useful when more than three weeks can elapse between charging and using the battery. Conventional NiMH batteries lose up to 10% of their charge capacity during the first 24 hours after charging, then the self-discharge current stabilizes at up to 0.5% of its capacity per day. For LSD NiMH this parameter is typically in the range of 0.04% to 0.1% capacity per day. The manufacturers claim that by improving the electrolyte and electrode, they managed to achieve the following advantages of LSD NiMH relative to the classic technology:
Among the shortcomings, it should be noted the relatively slightly smaller capacity. Currently (2012) the maximum achieved passport capacity of LSD is 2700 mAh.
Nevertheless, when testing Sanyo Eneloop XX batteries with a passport capacity of 2500mAh (min 2400mAh), it turned out that all of the batteries in a batch of 16 pieces (made in Japan, sold in South Korea) have an even larger capacity - from 2550 mAh to 2680 mAh ... Tested with LaCrosse BC-9009 charger.
An incomplete list of long-term storage batteries (with low self-discharge):
- Prolife by Fujicell
- Ready2Use Accu by Varta
- AccuEvolution by AccuPower
- Hybrid, Platinum, and OPP Pre-Charged by Rayovac
- eneloop by Sanyo
- eniTime by Yuasa
- Infinium by Panasonic
- ReCyko by Gold Peak
- Instant by Vapex
- Hybrio by Uniross
- Cycle Energy by Sony
- MaxE and MaxE Plus from Ansmann
- EnergyOn by NexCell
- ActiveCharge / StayCharged / Pre-Charged / Accu by Duracell
- Pre-Charged by Kodak
- nx-ready by ENIX energies
- Imedion from
- Pleomax E-Lock from Samsung
- Centura by Tenergy
- Ecomax by CDR King
- R2G by Lenmar
- LSD ready to use by Turnigy
Other Benefits of Low Self Discharge NiMH (LSD NiMH) Batteries
Low self-discharge nickel metal hydride batteries typically have significantly lower internal resistance than conventional NiMH batteries. This is very beneficial in high current consumption applications:
- More stable voltage
- Reduced heat generation especially in fast charge / discharge modes
- Higher efficiency
- High impulse current capacity (Example: camera flash charges faster)
- Possibility of continuous operation in devices with low power consumption (Example: remote controls, clocks.)
Charging methods
Charging is carried out with an electric current with a voltage across the cell up to 1.4 - 1.6 V. The voltage across a fully charged cell without load is 1.4 V. The voltage under load varies from 1.4 to 0.9 V. a discharged battery is 1.0 - 1.1 V (further discharge may damage the cell). To charge the battery, a constant or pulsed current with short-term negative pulses is used (to restore the "memory" effect, the "FLEX Negative Pulse Charging" or "Reflex Charging" method).
Monitoring the end of the charge by changing the voltage
One of the methods for determining the end of the charge is the -ΔV method. The image shows a graph of the cell voltage when charging. The charger charges the battery with constant current. After the battery is fully charged, the voltage across it begins to drop. The effect is observed only at sufficiently high charging currents (0.5C..1C). The charger should detect this fall and turn off the charging.
There is also the so-called "inflexion" - a method for determining the end of fast charging. The essence of the method is that it is not the maximum voltage on the battery that is analyzed, but the maximum of the voltage derivative with respect to time. That is, fast charging will stop at the moment when the voltage growth rate is maximum. This allows the fast charging phase to be completed earlier, when the battery temperature has not yet had time to rise significantly. However, the method requires measuring the voltage with greater accuracy and some mathematical calculations (calculating the derivative and digital filtering of the obtained value).
Control of the end of the charge by changing the temperature
When a cell is charged with direct current, most of the electrical energy is converted into chemical energy. When the battery is fully charged, the supplied electrical energy will be converted into heat. With a sufficiently large charging current, you can determine the end of the charge by a sharp increase in the cell temperature by installing a battery temperature sensor. The maximum permissible battery temperature is 60 ° C.
Areas of use
Replacement of a standard galvanic cell, electric vehicles, defibrillators, rocket and space technology, autonomous power supply systems, radio equipment, lighting equipment.
Battery capacity selection
When using NiMH batteries, you shouldn't always chase after a large capacity. The more capacious the battery, the higher (all other things being equal) its self-discharge current. As an example, consider batteries with a capacity of 2500 mAh and 1900 mAh. Batteries that are fully charged and not used for, for example, a month, will lose some of their electrical capacity due to self-discharge. A more capacious battery will lose charge much faster than a less capacious one. Thus, after, for example, a month, the batteries will have approximately equal charge, and after even longer time, the initially more capacious battery will contain a smaller charge.
From a practical point of view, high-capacity batteries (1500-3000 mAh for AA-batteries) make sense to use in devices with high energy consumption for a short time and without prior storage. For example:
- In radio controlled models;
- In the camera - to increase the number of pictures taken in a relatively short period of time;
- In other devices, in which the charge will be depleted in a relatively short time.
Low-capacity batteries (300-1000 mAh for AA-batteries) are more suitable for the following cases:
- When the use of the charge does not start immediately after charging, but after a considerable time;
- For periodic use in devices (hand-held lights, GPS-navigators, toys, walkie-talkies);
- For long-term use in a device with moderate power consumption.
Manufacturers
Nickel-metal hydride batteries are manufactured by various companies, including:
- Camelion
- Lenmar
- Our strength
- NIAI SOURCE
- Space
see also
Literature
- Khrustalev D.A. Accumulators. M: Emerald, 2003.
Notes (edit)
Links
- GOST 15596-82 Chemical current sources. Terms and Definitions
- GOST R IEC 61436-2004 Sealed nickel-metal hydride batteries
- GOST R IEC 62133-2004 Accumulators and storage batteries containing alkaline and other non-acidic electrolytes. Safety requirements for portable sealed accumulators and batteries from them for portable use
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