Metal hydride battery. Nickel-cadmium batteries

Nickel metal hydride batteries are a chemical reaction based current source. Marked with Ni-MH. Structurally, they are analogous to previously developed nickel-cadmium batteries (Ni-Cd), and in terms of the chemical reactions taking place are similar to nickel-hydrogen batteries. They are classified as alkaline power supplies.

Historical excursion

The need for rechargeable power supplies has been around for a long time. For different types of technology, compact models with increased charge storage capacity were very much needed. Thanks to the space program, a method has been developed for storing hydrogen in storage batteries. These were the first nickel hydrogen specimens.

Considering the design, the main elements are highlighted:

electrode (metal hydride hydrogen);
cathode (nickel oxide);
electrolyte (potassium hydroxide).

Previously used electrode materials were unstable. But constant experiments and studies led to the fact that the optimal composition was obtained. At the moment, lanthanum and nickel hydrite (La-Ni-CO) is used for the manufacture of electrodes. But various manufacturers also use other alloys, where nickel or part of it is replaced by aluminum, cobalt, manganese, which stabilize and activate the alloy.

Undergoing chemical reactions

During charging and discharging, chemical reactions occur inside the batteries associated with the absorption of hydrogen. The reactions can be written as follows.

While charging: Ni (OH) 2 + M → NiOOH + MH.
During discharge: NiOOH + MH → Ni (OH) 2 + M.

The following reactions take place at the cathode with the release of free electrons:

During charging: Ni (OH) 2 + OH → NiOOH + H2O + e.
During discharge: NiOOH + H2O + e → Ni (OH) 2 + OH.

At the anode:

During charging: M + H2O + e → MH + OH.
During discharge: MH + OH → M +. H2O + e.

Battery design

The main production of nickel metal hydride batteries is produced in two forms: prismatic and cylindrical.

Cylindrical Ni-MH cells

The design includes:

cylindrical body;
case cover;
valve;
valve cap;
anode;
anode collector;
cathode;
dielectric ring;
separator;
insulating material.

The anode and cathode are separated by a separator. This design is rolled up and placed in the battery case. Sealing is done with a cover and a gasket. A safety valve is provided on the cover. It is designed so that when the pressure inside the accumulator rises to 4 MPa, when triggered, it releases excess volatile compounds formed during chemical reactions.

Many were encountered with wet or capsized power supplies. This is the result of valve operation when overcharging. The characteristics change and their further operation is impossible. In its absence, the batteries simply swell and completely lose their performance.

Prismatic Ni-MH cells

The design includes the following elements:

The prismatic design assumes alternating placement of anodes and cathodes with their separation by a separator. Collected in this way in a block, they are placed in the case. The body is made of plastic or metal. The cover seals the structure. For safety and control over the state of the battery, a pressure sensor and a valve are placed on the cover.

An alkali is used as an electrolyte - a mixture of potassium hydroxide (KOH) and lithium hydroxide (LiOH).

For Ni-MH cells, polypropylene or non-woven polyamide acts as an insulator. The thickness of the material is 120–250 µm.

For the production of anodes, manufacturers use cermets. But recently, felt and foam polymers have been used to reduce costs.

Various technologies are used in the production of cathodes:

Characteristics

Voltage. When free, the internal battery circuit is open. And it is rather difficult to measure it. Difficulties are caused by the equilibrium of potentials on the electrodes. But after a full charge, after a day, the cell voltage is 1.3-1.35V.

The discharge voltage at a current not exceeding 0.2A and an ambient temperature of 25 ° C is 1.2-1.25V. The minimum value is 1V.

Energy capacity, W ∙ h / kg:

theoretical – 300;
specific – 60–72.

Self-discharge depends on the storage temperature. Storage at room temperature causes a capacity loss of up to 30% within the first month. The rate then slows down to 7% in 30 days.

Other parameters:

Electric driving force (EMF) - 1.25V.
Energy density - 150 W ∙ h / dm3.
Operating temperature - from -60 to + 55 ° С.
Duration of operation - up to 500 cycles.

Proper charging and control

Chargers are used to store energy. The main task of inexpensive models is to supply a stabilized voltage. To recharge nickel metal hydride batteries, a voltage of about 1.4-1.6V is required. In this case, the current strength should be 0.1 of the battery capacity.

For example, if the declared capacity is 1200 mAh, then the charging current should accordingly be selected close to or equal to 120 mA (0.12A).

Fast and accelerated charging is applied. The fast charging process takes 1 hour. The accelerated process takes up to 5 hours. Such an intensive process is controlled by changes in voltage and temperature.

Normal charging takes up to 16 hours. To reduce the charging time, modern chargers are usually manufactured in three stages. The first stage is a quick charge with a current equal to the nominal capacity of the battery or higher. The second stage is with a current of 0.1 capacity. The third stage - with a current of 0.05–0.02 of the capacity.

The charging process must be monitored. Overcharging is detrimental to the condition of the batteries. High gassing will cause the safety valve to operate and electrolyte will escape.

The control is carried out according to the following methods:

Advantages and disadvantages of Ni-MH cells

The latest generation batteries do not suffer from such a disease as the "memory effect". But after long-term storage (more than 10 days), it must still be completely discharged before charging. The likelihood of a memory effect arises from inaction.

Increased energy storage capacity

Environmental friendliness is ensured by modern materials. The transition to them greatly facilitated the disposal of used elements.

As for the shortcomings, there are also a lot of them:

high heat dissipation;
the temperature range of operation is small (from -10 to + 40 ° C), although manufacturers declare other indicators;
small interval of operating current;
high self-discharge;
non-observance of the polarity destroys the battery;
store for a short time.

Selection by capacity and operation

Before you buy Ni-MH batteries, you should decide on their capacity. High performance is not a solution to energy shortages. The higher the cell capacity, the more pronounced self-discharge.

Cylindrical nickel metal hydride cells are available in large numbers in sizes that are marked AA or AAA. Popularly nicknamed as finger - aaa and little fingers - aa. You can buy them in all electrical and electronics stores.

As practice shows, batteries with a capacity of 1200-3000 mAh, having the size aaa, are used in players, cameras and other electronic devices with a large consumption of electricity.

Batteries with a capacity of 300–1000 mAh, usual size aa are used on devices with little or no energy consumption (walkie talkie, flashlight, navigator).

Previously, the widespread metal hydride batteries were used in all portable devices. Single elements were installed in a box designed by the manufacturer for ease of installation. They were usually marked EN. They could be bought only from the official representatives of the manufacturer.

From operating experience

NiMH cells are widely advertised as high-energy cells, cold-resistant and memoryless. Having bought a digital camera Canon PowerShot A 610, I naturally supplied it with a capacious memory for 500 high quality images, and to increase the duration of shooting I bought 4 NiMH cells with a capacity of 2500 mAh from Duracell.

Let's compare the characteristics of the elements produced by the industry:

Options		Lithium ion Li-ion	Nickel Cadmium NiCd	Nickel- metal hydride NiMH	Lead acid Pb
Duration of service, charge / discharge cycles		1-1.5 years	500-1000		3 00-5000
Energy capacity, W * h / kg
Discharge current, mA * battery capacity
Voltage of one element, V
Self-discharge rate		2-5% per month	10% for the first day, 10% for each subsequent month	2 times higher NiCd	40% in year
Range of permissible temperatures, degrees Celsius	charging
Range of permissible temperatures, degrees Celsius	detente		-20... +65
Allowable voltage range, V		2,5-4,3 (coke), 3,0-4,3 (graphite)			5,25-6,85 (for batteries 6 B), 10,5-13,7 (for batteries 12 V)

Table 1.

From the table, we see NiMH cells have a high energy capacity, which makes them the preferred choice.

To charge them, an intelligent charger DESAY Full-Power Harger was purchased, which provides charging of NiMH cells with their training. The cells were charged with high quality, but ... However, on the sixth charge, it ordered a long life. Electronics burned out.

After replacing the charger and several charge-discharge cycles, the batteries began to sit down in the second or third ten pictures.

It turned out that despite the assurances, NiMH cells also have memory.

And most modern portable devices that use them have built-in protection that turns off the power when a certain minimum voltage is reached. This prevents the battery from being fully discharged. This is where the memory of elements begins to play its role. Incompletely discharged cells receive an incomplete charge and their capacity drops with each recharge.

Quality chargers allow charging without loss of capacity. But I could not find something on the sale of this for cells with a capacity of 2500mAh. It remains to periodically train them.

NiMH Cell Training

Everything written below does not apply to battery cells with strong self-discharge. ... They can only be thrown away, experience shows that they cannot be trained.

NiMH cell training consists of several (1-3) discharge - charge cycles.

Discharging is performed until the voltage on the battery cell drops to 1V. It is advisable to discharge the cells individually. The reason is that the ability to take charge can vary. And it gets stronger when you charge without training. Therefore, there is a premature operation of the voltage protection of your device (player, camera, ...) and the subsequent charging of an uncharged cell. The result is an increasing loss of capacity.

Discharging must be performed in a special device (Fig. 3), which allows it to be performed individually for each element. If there is no voltage control, then the discharge was carried out until the brightness of the lamp noticeably decreased.

And if you measure the burning time of the light bulb, you can determine the capacity of the battery, it is calculated by the formula:

Capacity \u003d Discharge current x Discharge time \u003d I x t (A * hour)

A battery with a capacity of 2500 mA hour is capable of delivering a current of 0.75 A to the load for 3.3 hours, if the time obtained as a result of discharge is less, respectively, and less residual capacity. And with a decrease in the capacity you need, you need to continue training the battery.

Now, to discharge the battery cells, I use a device made according to the scheme shown in Fig. 3.

It is made from an old charger and looks like this:

Only now there are 4 bulbs, as in Fig. 3. It is necessary to say separately about light bulbs. If the lamp has a discharge current equal to the nominal for this battery or slightly less, it can be used as a load and indicator, otherwise the lamp is only an indicator. Then the resistor must be of such a value that the total resistance of El 1-4 and the parallel resistor R 1-4 is about 1.6 ohms. Replacing a light bulb with an LED is unacceptable.

An example of a bulb that can be used as a load is a 2.4V krypton bulb for a torch.

A special case.

Attention! Manufacturers do not guarantee the normal operation of batteries with charging currents exceeding the rapid charging current I charge should be less than the battery capacity. So for batteries with a capacity of 2500mA * hour, it should be below 2.5A.

It happens that NiMH cells after discharge have a voltage of less than 1.1 V. In this case, it is necessary to apply the technique described in the above article in the MIR PC magazine. An element or series of elements is connected to a power source through a 21 W automotive light bulb.

Once again I draw your attention! Self-discharge of such elements must be checked! In most cases, it is elements with reduced voltage that have increased self-discharge. These elements are easier to throw away.

Charging is preferable individual for each element.

For two cells with a voltage of 1.2 V, the charging voltage should not exceed 5-6 V. With forced charging, the light is also an indicator. When the brightness of the bulb decreases, you can check the voltage on the NiMH cell. It will be greater than 1.1 V. Typically, this initial boost charge takes 1 to 10 minutes.

If a NiMH cell does not increase the voltage during forced charging for several minutes, it heats up - this is a reason to remove it from the charge and discard it.

I recommend using chargers only with the ability to train (regenerate) the cells when recharging. If there are no such, then after 5-6 working cycles in the equipment, without waiting for a complete loss of capacity, train them and reject elements with a strong self-discharge.

And they won't let you down.

In one of the forums commented on this article "written stupidly, but nothing else". So this is not" stupid ", but simple and available for execution in the kitchen for everyone who needs help. That is, as simple as possible. Advanced can put a controller, connect a computer, ......, but that's another history.

So that it does not seem stupid

There are "smart" chargers for NiMH cells.

Such a charger works with each battery separately.

He can:

individually work with each battery in different modes,

charge batteries in fast and slow mode,

individual LCD display for each battery compartment,

independently charge each of the batteries,

charge one to four batteries of different capacities and sizes (AA or AAA),

protect the battery from overheating,

protect each battery from overcharging,

determination of the end of charging by voltage drop,

identify faulty batteries,

pre-discharge the battery to the residual voltage,

restore old batteries (charge-discharge training),

check the capacity of the batteries,

display on the LCD: - charge current, voltage, reflect the current capacity.

Most importantly, I emphasize, this type of device allows you to work individually with each battery.

According to user reviews, such a charger allows you to restore most of the neglected batteries, and serviceable ones to operate the entire guaranteed service life.

Unfortunately, I did not use such a charger, since it is simply impossible to buy it in the provinces, but in the forums you can find many reviews.

The main thing is not to charge at high currents, despite the declared mode with currents of 0.7 - 1A, this is still a small-sized device and can dissipate power of 2-5 watts.

Conclusion

Any recovery of NiMh batteries is strictly individual (with each individual element) work. With constant monitoring and rejection of elements that do not accept charging.

And it's best to rebuild them with smart chargers that allow you to individually reject and cycle charge-discharge with each cell. And since such devices do not automatically work with batteries of any capacity, they are intended for cells of a strictly defined capacity or must have controlled charging and discharging currents!

History of invention

Research into NiMH battery technology began in the 70s of the 20th 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 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 "Krone" form factor, usually with an initial voltage of 8.4 volts, gradually reduce the voltage to 7.2 volts, and then, when the battery power 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 several days in this state. If the battery was partially discharged, and then not used for a long time (more than 30 days), then before charging it must be discharged.

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

Store batteries fully charged in the refrigerator, but not below 0 degrees. During storage, it is advisable to check the voltage regularly (every 1-2 months). 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 Eneloop brand. 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 beneficial when more than three weeks can elapse between charging and using the battery. Conventional NiMH batteries lose up to 10% of their charge capacity within 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 is typically in the range of 0.04% to 0.1% capacity per day. The manufacturers claim that by improving the electrolyte and electrode, the following advantages of LSD NiMH were achieved 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 from 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, watches.)

Charging methods

Charging is carried out with an electric current at 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 discharging may damage the cell). To charge the battery, direct or pulse 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 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 temperature change

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. Maximum permissible battery temperature 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 don't always have to chase after a large capacity. The more capacious the battery, the higher (other things being equal) its self-discharge current. As an example, let's 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 instance:

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 lamps, 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

Literature

Khrustalev D.A. Accumulators. M: Emerald, 2003.

Notes

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


Galvanic cell	Daniel Galvanic Cell \| Alkaline element \| \| Dry element \| Concentration element \| Zinc Air Cell \| Normal Weston Element
Electric batteries	Lead Acid \| Silver-zinc \| Nickel-Cadmium \| Nickel metal hydride \| Nickel-zinc battery \| Lithium Ion \| Lithium Polymer \| Lithium Iron Sulfide \| Lithium Iron Phosphate \| Lithium titanate \| Vanadium \| Iron-nickel
Fuel cells	Direct methanol \| Solid oxide \| Alkaline
Models

Nimh batteries are power supplies that are classified as alkaline batteries. They are similar to nickel hydrogen storage batteries. But the level of their energy capacity is higher.

The internal composition of ni mh batteries is similar to that of nickel cadmium power supplies. To prepare a positive conclusion, such a chemical element, nickel, is used, a negative one - an alloy that includes absorbing type hydrogen metals.

There are several typical designs of nickel metal hydride batteries:

Cylinder. To separate the current-carrying leads, a separator is used, which is given the shape of the cylinder. An emergency valve is concentrated on the cover, which opens slightly when the pressure rises significantly.
Prism. In such a nickel metal hydride battery, the electrodes are arranged alternately. A separator is used to separate them. To accommodate the main elements, a case prepared from plastic or special alloy is used. To control the pressure, a valve or a sensor is introduced into the cover.

Among the advantages of such a power source are:

Specific energy parameters of the power source increase during operation.
No cadmium is used in the preparation of conductive elements. Therefore, there are no problems with battery disposal.
Lack 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, there are:

Compliance with the established range of operating currents. Exceeding these indicators leads to a rapid discharge.
Operation of this type of power supply in severe frosts is not allowed.
Thermal fuses are introduced into the battery, with the help of which the overheating of the unit is determined, the temperature rise to a critical indicator.
A tendency to self-discharge.

Nickel Metal Hydride Battery Charging

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

The efficiency of the charging process is the part of the energy received by the power supply that is stored. The value of this indicator may vary. But at the same time, it is impossible to obtain 100% efficiency.

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

Drip type charging

It is necessary to use this type of charging for batteries with caution, as it leads to a decrease in the operating period. Since the disconnection of this type of charger is carried out manually, the process needs constant monitoring and regulation. In this case, the minimum current indicator is set (0.1 of the total capacity).

Since with such a charge of ni mh batteries, the maximum voltage is not established, they are guided only by the time indicator. To estimate the time interval, the capacitance parameters that the discharged power source has are used.

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

Fast recharge

When determining what current can be used to charge ni mh batteries in fast mode, the recommendations of the manufacturers are taken into account. The magnitude of the current 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 efficiency of fast charging 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, then the pressure inside the battery will begin to increase, the temperature indicator will increase.

In order to charge ni mh battery, perform the following actions:

Pre-charge

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

Switching to fast mode

The current build-up process takes 3-5 minutes. The temperature is monitored throughout the entire time period. If this parameter reaches a critical value, then the charger turns off.

Fast charging of NiMH batteries sets the current to 1 of the total capacity. In this case, it is very important to quickly disconnect the charger so as not to harm the battery.

A multimeter or voltmeter is used to monitor the voltage. This helps to eliminate false alarms that have a detrimental effect on the device's performance.

Some chargers for ni mh batteries work not with a constant, but with a pulse current. The current is supplied at a set frequency. The supply of a pulsed current contributes to the uniform distribution of the electrolytic composition and active substances.

Additional and maintenance charging

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

Accelerated charging

Some nickel cadmium battery chargers are equipped with a boost charge mode. For this, the charging current is limited by setting the parameters at the level of 9-10 of the capacity. It is necessary to reduce the charge current as soon as the battery is charged to 70 percent.

If the storage battery is charged in an accelerated mode for more than half an hour, then the structure of the conductive leads is gradually destroyed. Experts recommend using such a charge if you have some experience.

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

Temperature control of ni mh batteries. It is necessary to stop charging nimh batteries as soon as the temperature level rises rapidly.
Time limits are set for nimh power supplies to control the process.
Discharge and charge ni mh batteries at a voltage of 0.98. If this parameter is significantly reduced, then the chargers are turned off.

Recovery of nickel metal hydride power supplies

The process of recovering ni mh batteries is to eliminate the consequences of the "memory effect" associated with the loss of capacity. The likelihood of this effect is increased if the unit is not fully charged frequently. The device fixes the lower limit, after which the capacity decreases.

Before restoring the power source, the following items are prepared:

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

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

A fairly simple method is used to calculate the lost capacity. 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 probability of a deep discharge is reduced.

If the state of charge of the nickel metal hydride batteries has not been established, then the lamp must be connected carefully. The voltage level is monitored with a multimeter. 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 whole block. During the charging period, the existing charge is equalized.

Restoring a power source that has been in operation 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 leads are gradually changing. Before using such devices, the electrolytic composition is restored.

Watch a video about recovering such a battery.

Rules for Using Nickel-Metal Hydride Batteries

The service life of ni mh batteries largely depends on whether overheating or significant recharging of the power source is not allowed. Additionally, masters are advised to consider the following rules:

Regardless of how long power supplies are stored, they must be charged. The percentage of charge must be at least 50 of the total capacity. Only in this case there will be no problems during storage and maintenance.
Rechargeable batteries of this type are sensitive to overcharging and excessive heat. These indicators have a detrimental effect on the duration of use, the amount of current output. These power supplies require special chargers.
NiMH training cycles are optional. With the help of a proven charger, the lost capacity is restored. The number of recovery cycles largely depends on the state of the unit.
Between recovery cycles, they must take breaks, and also learn how to charge the battery in use. This time period is required in order for the unit to cool down, the temperature level dropped to the required value.
The recharging procedure or training cycle is carried out only in an acceptable temperature range: + 5- + 50 degrees. If this figure is exceeded, then the likelihood of a 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 allowed to connect an external source to restore power.
Cyclic recovery is carried out on condition that there is some experience. After all, not all chargers can be used to discharge the battery.
The storage procedure includes a number of simple rules. It is not allowed to store the power supply outdoors or in rooms where the temperature level drops to 0 degrees. This provokes solidification of the electrolyte composition.

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

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

Video about Nimh batteries

In the second half of the twentieth century, one of the best rechargeable chemical current sources were rechargeable batteries manufactured using nickel-cadmium technology. They are still widely used in various fields due to their reliability and simplicity.

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What is Nickel Cadmium Battery

Nickel-cadmium batteries are galvanic, rechargeable power supplies that were invented in 1899 in Sweden by Waldmar Jungner. Until 1932, their practical use was very limited due to the high cost of the metals used in comparison with lead-acid batteries.

Improvement in the technology of their production led to a significant improvement in their operational characteristics and made it possible in 1947 to create a sealed maintenance-free battery with excellent parameters.

Principle of operation and design of Ni-Cd battery

These batteries generate electrical energy due to the reversible process of interaction of cadmium (Cd) with nickel oxide-hydroxide (NiOOH) and water, as a result of which nickel hydroxide Ni (OH) 2 and cadmium hydroxide Cd (OH) 2 are formed, which causes the appearance of an electromotive force.

Ni-Cd batteries are produced in sealed cases, which contain electrodes separated by a neutral separator, containing nickel and cadmium in a solution of a jelly-like alkaline electrolyte (usually potassium hydroxide, KOH).

The positive electrode is a steel mesh or foil coated with nickel oxide-hydroxide paste mixed with a conductive material

The negative electrode is a steel mesh (foil) with pressed-in porous cadmium.

One nickel-cadmium cell is capable of delivering a voltage of about 1.2 volts, therefore, to increase the voltage and power of the batteries, they use many parallel-connected electrodes, separated by separators, in their design.

Technical characteristics and what are Ni-Cd batteries

Ni-Cd batteries have the following specifications:

the discharge voltage of one element is about 0.9-1 volts;
the rated voltage of the element is 1.2 v, to obtain voltages of 12v and 24v, several elements are connected in series;
full charge voltage - 1.5-1.8 volts;
working temperature: from -50 to +40 degrees;
the number of charge-discharge cycles: from 100 to 1000 (in the most modern batteries - up to 2000), depending on the technology used;
self-discharge level: from 8 to 30% in the first month after a full charge;
specific energy consumption - up to 65 W * hour / kilogram;
service life - about 10 years.

Ni-Cd batteries are produced in various housings of standard sizes and in non-standard versions, including disk, sealed ones.

Where are nickel-cadmium batteries used?

These batteries are used in devices that consume a large current, and also experience high loads during operation in the following cases:

on trolleybuses and trams;
on electric cars;
on sea and river transport;
in helicopters and airplanes;
in power tools (screwdrivers, drills, electric screwdrivers and others);
electric shavers;
in military technology;
portable radio stations;
in radio-controlled toys;
in lanterns for diving.

At present, due to the tightening of environmental requirements, most of the batteries of popular standard sizes (and others) are produced using nickel-metal hydride and lithium-ion technologies. At the same time, there are still many Ni Cd batteries of various standard sizes in operation, released several years ago.

Ni-Cd cells have a long service life, which sometimes exceeds 10 years, and therefore you can still find this type of battery in many electronic devices, in addition to those listed above.

Pros and cons of Ni-Cd battery

This type of battery has the following positive characteristics:

long service life and the number of charge-discharge cycles;
long service life and storage;
fast charging capability;
the ability to withstand heavy loads and low temperatures;
maintaining performance in the most adverse operating conditions;
low cost;
the ability to store these batteries in a discharged state for up to 5 years;
average resistance to overcharge.

At the same time, nickel-cadmium power supplies have a number of disadvantages:

the presence of a memory effect, manifested in the loss of capacity when charging the battery, without waiting for a complete discharge;
the need for preventive maintenance (several charge-discharge cycles) to gain full capacity;
full recovery of the battery after long-term storage requires three to four full charge-discharge cycles;
high self-discharge (about 10% in the first month of storage), leading to an almost complete discharge of the battery for a year of storage;
low energy density in comparison with other batteries;
high toxicity of cadmium, due to which they are prohibited in a number of countries, including the EU, the need to dispose of such batteries on special equipment;
more weight compared to modern batteries.

The difference between Ni-Cd and Li-Ion or Ni-Mh sources

Batteries with active components, including nickel and cadmium, have a number of differences from more modern lithium-ion and nickel-metal hydride power sources:

Ni-Cd cells, in contrast to the variants, have a memory effect, have a lower specific capacity with the same dimensions;
NiCd sources are more unpretentious, remain operational at very low temperatures, and are many times more resistant to overcharge and strong discharge;
Li-Ion and Ni-Mh batteries are more expensive, they are afraid of overcharge and strong discharge, but they have less self-discharge;
the service life and storage of Li-Ion batteries (2-3 years) is several times shorter than Ni Cd products (8-10 years);
nickel-cadmium sources quickly lose capacity when used in a buffer mode (for example, in a UPS). Although they can then be fully recovered by deep discharge and charging, it is best not to use Ni Cd products in trickle charge devices;
the same charging mode for Ni-Cd and Ni-Mh batteries allows you to use the same chargers, but you should take into account the fact that nickel-cadmium batteries have a more pronounced memory effect.

Based on the available differences, it is impossible to make an unambiguous conclusion about which battery is better, since all elements have both strengths and weaknesses.

Operating rules

During operation, a number of changes occur in Ni Cd power supplies, which lead to a gradual deterioration in characteristics and, ultimately, to a loss of performance:

the useful area and mass of the electrodes decreases;
the composition and volume of the electrolyte changes;
the separator and organic impurities decompose;
water and oxygen are lost;
current leaks appear associated with the growth of cadmium dendrites on the plates.

In order to minimize the damage to the battery that occurs during its operation and storage, it is necessary to avoid adverse effects on the battery, which are associated with the following factors:

the charge of an incompletely charged battery leads to a reversible loss of its capacity due to a decrease in the total area of \u200b\u200bthe active substance as a result of crystal formation;
regular strong recharge, which leads to overheating, increased gas formation, loss of water in the electrolyte and destroys the electrodes (especially the anode) and the separator;
undercharging, leading to premature depletion of the battery;
long-term operation at very low temperatures leads to a change in the composition and volume of the electrolyte, the internal resistance of the battery increases and its performance deteriorates, in particular, the capacity decreases.

With a strong increase in pressure inside the battery as a result of a fast charge with a high current and strong degradation of the cadmium cathode, excess hydrogen can be released in the battery, which leads to a sharp increase in pressure, which can deform the case, violate the assembly density, increase internal resistance and reduce the operating voltage.

In batteries equipped with an emergency pressure relief valve, the danger of deformation can be prevented, but irreversible changes in the chemical composition of the battery cannot be avoided.

Ni Cd batteries should be charged with a current of 10% (if it is necessary to quickly charge in special batteries - with a current of up to 100% in 1 hour) of their capacity (for example, 100 mA with a capacity of 1000 mAh) for 14-16 hours. The best mode of their discharge is with a current equal to 20% of the battery capacity.

How to repair a Ni Cd battery

Nickel-cadmium power supplies in case of loss of capacity can be almost completely restored by full discharge (up to 1 volt per cell) and subsequent charging in a standard mode. This training of batteries can be repeated several times to fully restore their capacity.

If it is impossible to restore the battery by discharge and charge, you can try to restore them by exposure to short current pulses (tens of times larger than the capacity of the element being restored) for several seconds. This action eliminates the internal short circuit in the battery cells, which occurs due to the growth of dendrites by burning them out with a strong current. There are special industrial activators that carry out such an effect.

Full restoration of the original capacity of such batteries is impossible due to irreversible changes in the composition and properties of the electrolyte, as well as degradation of the plates, but it makes it possible to extend the service life.

The method of recovery at home is to carry out the following actions:

with a wire with a cross section of at least 1.5 square millimeters, connect the minus of the element to be restored to the cathode of a powerful battery, for example, a car battery or from a UPS;
the second wire is securely attached to the anode (plus) of one of the batteries;
for 3-4 seconds, the free end of the second wire quickly touches the free positive terminal (with a frequency of 2-3 touches per second). In this case, it is necessary to prevent welding of wires at the junction;
a voltmeter checks the voltage at the restored source, in its absence, another recovery cycle is performed ;;
when an electromotive force appears on the battery, it is put on charge;

In addition, you can try to destroy the dendrites in the battery by freezing them for 2-3 hours, followed by their sharp tapping. When frozen, dendrites become brittle and collapse from shock, which could theoretically help get rid of them.

There are also more extreme recovery methods associated with adding distilled water to old elements by drilling out their bodies. But the full provision of the tightness of such elements in the future is very problematic. Therefore, it is not worth saving and putting health at risk of poisoning with cadmium compounds due to the gain of several work cycles.

Storage and disposal

It is best to store nickel-cadmium batteries in a discharged state at a low temperature in a dry place. The lower the storage temperature of such batteries, the less self-discharge they have. High-quality models can be stored for up to 5 years without significant damage to technical characteristics. To put them into operation, it is enough to charge them.

The harmful substances contained in one AA battery can pollute about 20 square meters of the territory. For the safe disposal of Ni Cd batteries, they must be handed over to recycling points, from where they are sent to factories, where they must be destroyed in special sealed ovens equipped with filters that trap toxic substances.