How to charge nickel metal hydride batteries? This issue, as well as many others closely related to it, will be considered in this article. The topic is relevant, as there are currently many battery-powered electrical devices.
Different types of batteries
Electric batteries exist with different charge volumes. Their sizes range from those that are no bigger than a button, to the giants used in industrial enterprises. It would seem that between some batteries, significantly different in appearance and size, there is nothing in common.
However, it is not. All of them work on a similar principle and are made from the same materials.
A bit of history
The first batteries appeared in the 19th century. They were made of nickel and cadmium. Therefore, such batteries are given the appropriate name. Initially, their work was quite satisfying to users. But over time, the need arose for more durable batteries. In addition, specialists involved in the development of electrical appliances began to think about speeding up the charging process. Nickel and metal hydride have been recognized as materials that can provide batteries with these characteristics.
But the process of creating a new type of battery dragged on for several decades. For the first time, they started talking about new generation batteries in the fifties of the twentieth century, and trial samples appeared only in the late seventies.
Features
The device nickel-metal hydride battery allows you to accumulate hydrogen, whose volumes are several times the size of the battery. Moreover, it is always formed in a certain part of the product. Its reserves accumulate closer to the contacts of nickel-metal hydride batteries.
These, as well as a number of other characteristics allow charging such devices up to several thousand times. However, nickel metal hydride batteries also have their drawbacks, which will be discussed in the next section.
Quick heat
Nickel-metal hydride batteries, due to the features of their design and the characteristics of the materials from which they are made, have a high degree of heatability. Therefore, the process of charging them requires a special, more “delicate” approach than their cadmium predecessors. Experts recommend taking the choice of chargers seriously.
You need to pay attention to this.
The charging of nickel-metal hydride batteries, like any other process, can be estimated as a coefficient of performance. How is it calculated in this case? When charging nickel metal hydride batteries, the electrical energy expended in this process causes heat to be generated. In addition, it contributes to certain chemical reactions. The efficiency of charging nickel-metal hydride batteries is the amount of energy spent on chemical processes. It is worth noting that never this ratio is 100%, even if we are talking about the most modern batteries and the most advanced memory.
It is also worth mentioning that this indicator for cadmium batteries is significantly higher than their more modern counterparts.
The charging speed depends on the magnitude of the current. Separate units were invented for her - a fraction of the total volume. They are indicated by the Latin letter C. There are three options for charging nickel-metal hydride batteries:
- Drip.
- Fast.
- With increased speed.
In fact, we can only talk about two species, since the first and second differ little from each other.
Drop charging can be considered that charge, the speed of which is 0.1 C. With a quick option, this figure is higher.
To use the latter type, more complex devices are required that can recognize the completion of the process and automatically shut down. This prevents overheating of the batteries and their damage. Drip charging due to the use of low voltage does not lead to an excessive increase in the temperature of the product. This means that it cannot cause deformation of nickel-metal hydride batteries (Ni-MH).
Each type of charging has its pros and cons. Some of them will be discussed below.
Quick charge
With this option, the performance of the batteries is maintained for a longer period. In addition, as the name implies, the speed of this process is quite fast. And therefore, less time is spent on charging than with the drip version. However, such a scenario requires the use of a more sophisticated device with built-in sensors that determine the battery level. Often, such devices suitable for fast charging are equipped with a display that shows the time required to complete charging, the voltage used, as well as some other information.
This means that the cost of such equipment is higher than that required for drip charging.
Slow option
When the process is slow, the AAA nickel-metal hydride battery does not require a device equipped with charge termination sensors.
Therefore, it usually costs less. But with it, the batteries will charge further. This method has another serious drawback. The longer the battery is exposed to electric current, the faster it will fail. So, saving on a charger, you can lose because of the need to often buy new batteries.
If we talk about cadmium batteries, then this is the option that is most preferable for them. The efficiency of this type of charging most often does not exceed the mark of 70%. Due to the negative impact on battery performance, it is not recommended for use by most manufacturers of AA nickel-metal hydride batteries, as well as other types of batteries.
However, recently in the specialized literature on electronics articles about the harmlessness of slow charging for batteries of all types produced by new technologies have increasingly begun to appear.
Charging technology
How to charge nickel metal hydride batteries?
Most manufacturers of such products write in their instructions the following indicators at which this process should take place. The current must be selected not exceeding 1C. If this rule is not observed, this can lead to the fact that the emergency valve, which restrains excessive pressure, will work and the battery will fail.
When charging batteries, you should also monitor compliance with a certain temperature regime. Typically, the instructions indicate the interval from 0 to 40 degrees Celsius. If the temperature does not go beyond this, then charging will most likely proceed safely. However, such a warning is more likely to use industrial batteries. It is unlikely that charging a battery for an ordinary household appliance is often carried out at temperatures above 40 and below 0 degrees Celsius.
About voltage and other parameters
The voltage applied to the batteries when charging them should not go beyond 0.8-8 volts. The efficiency of the quick version of this process is approximately 90%, which is considered a high value. But towards the end of the efficiency decreases sharply due to the fact that more and more energy begins to be spent on heat. Therefore, it is important that the device is turned off in a timely manner, without significant delay. Otherwise, the emergency valve, which serves to lower the pressure, is highly likely to operate.
Charging stage
In order to better understand how to charge nickel-metal hydride batteries, you should first consider in detail how this process occurs, carried out using a special electrical device.
So, first the device determines whether the battery is present in it or not. He then identifies the battery level. After this, pre-charging takes place, which flows into a quick and additional charge.
Next, the essence of each of these steps will be described in detail.
Battery presence
To determine whether the battery is inserted in the corresponding connectors of the device, the device supplies a voltage of 0.1 C to the contacts. To start charging, the voltage must not exceed the mark of 1.8 volts. If it is larger, then the device perceives this as the absence of a battery or its failure. During charging, the device several times checks for the presence of batteries in it. Why is this done? Sometimes users, without waiting for the end of the process, take out the batteries. In this case, in order not to waste energy, the device stops its supply. The shutdown is done for another reason. If the battery is faulty, then further charging can lead to undesirable consequences, for example, to a fire. That is why its premature shutdown occurs.
Charge level detection
This action is performed by the device also to prevent its possible damage. It is known that at a low level you cannot turn on the fast charging mode. Therefore, if the device determines that this indicator is high enough for the battery, then it will first start the preparatory mode. This is usually not required. Most often, the battery does not discharge to the limit at which the preliminary stage is turned on. But it may be needed if the battery has not been used for a long time or is worn out and does not hold the charge to the necessary extent.
Preliminary stage
As already mentioned, it is only required if the nickel-metal hydride battery is very discharged. This process takes no more than half an hour. If during this time the battery does not accumulate the desired level of energy, then it is perceived by the device as damaged. If this happens, charging stops.
Main stage
The transition to this stage is not carried out immediately, but gradually. It usually lasts no more than five minutes. Here, as throughout the entire charging process of the NiMH battery, temperature is measured. If it exceeds a critical level, the device turns off. But the most important thing from what is happening at this stage is a gradual increase in the charging current.
At the main stage, charge level is constantly monitored. This is necessary for timely shutdown of the device and termination of the process. How much the battery is currently charged is determined by several parameters.
Difference from nickel-cadmium samples
The discharge level in Ni-Cd batteries is usually determined from the voltage graph. It is known that it grows at the beginning and middle of the process, and closer to its end it begins to weaken. When the voltage reaches the set minimum, the device stops its work. This happens when charging nickel-cadmium batteries. But in the case of nickel metal hydride samples, this option is not suitable. More precisely, when measuring the charge, the decrease in voltage is also taken into account here, but the battery temperature is also added to this parameter. In order to prevent overheating of the battery, switching off does not occur when a specific temperature is reached, but when its growth begins to exceed 1 degree per minute.
But such a termination of charging is also not an ideal option.
Recently, memory models have appeared in which not ordinary current is used, but supplied by pulses. Experts say that such devices have a number of advantages, including a uniform charge distribution throughout the battery. Active substances that accumulate as a result of this process do not form too large crystals.
How to charge nickel metal hydride batteries? To do this, it is best to use a device equipped with the control methods described above. In addition, the charging off timer, which is sometimes found in such devices, will also be useful. The necessary time can be easily calculated, knowing the battery capacity, current value and efficiency of the device. To the received time, a stock is usually added, amounting to 5-10 percent of the entire period. Deactivation will occur if, prior to this, none of the other monitoring methods interrupt the device.
Extra charge
This stage begins after the end of the main process. It is necessary so that all nickel-metal hydride batteries in the device receive the same degree of charge. This makes the operation of devices using batteries more stable.
Emergency charge
What if you remembered at the very last moment that batteries would be needed to operate a device? You can use accelerated charging.
How to charge nickel metal hydride batteries this way? Experts say that until the charge level reaches 70 percent, the efficiency of the process is almost 100%. This means that energy is spent mainly on the accumulation of active substances in the battery, and not on raising the temperature. Therefore, at this stage, you can increase the current. However, it is not recommended to exceed the 10C mark. The main thing with this type of charge is to determine when those very 70 percent will end. Therefore, you need to know exactly what charge was already present in the battery before the accelerated process begins. This option, of course, is suitable only for people who are well versed in electronics.
How to store nickel metal hydride batteries? This question is also asked by many users of battery-powered electrical appliances. It is known that with a long break in use, batteries begin to degrade - their ability to hold a charge decreases. Experts give the following tips on this subject.
First, only batteries that are more than half discharged can be left without use. Secondly, during storage, the room temperature is considered optimal. It’s best not to wait until the battery is completely discharged, otherwise it will have to be restored.
Second Battery Life
How to restore nickel metal hydride batteries?
Surely many already know about the approximate principle of such an operation. It is necessary to cycle several times and charge almost completely (at least 0.9 volts). But this rule has some nuances. It is best to carry out such a "training" for each battery separately. Since, due to the characteristics of the production of these products, the characteristics of individual batteries may differ from each other. Therefore, charging and discharging will also take place at different speeds. This tip is especially true for nickel metal hydride screwdriver batteries.
As a rule, such electrical appliances use not one battery, but a set of several pieces. These batteries are best restored individually. It is worth noting that there are memory models that can discharge batteries. But such samples are more expensive than their simpler counterparts. Whether to save on batteries or chargers is up to users.
Conclusion
This article was devoted to the question "how to properly charge a nickel-metal hydride battery." It discusses some of the subtleties of this process. The main differences between NiMH batteries and others are also given.