How to charge NiMH batteries? This issue, as well as many others closely related to it, will be discussed in this article. The topic is relevant, as there are currently many electrical devices powered by batteries.
Different types of batteries
Electric batteries exist with different amounts of charge. Their sizes range from those that are no larger than a button to the giants used in industrial plants. It would seem that there is nothing in common between some batteries that differ significantly in appearance and dimensions.
However, this is not the case. They all 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 from nickel and cadmium. Therefore, such batteries have received the appropriate name. Initially, their work quite satisfied users. But over time there wasthe need for more durable batteries. In addition, specialists involved in the development of electrical appliances began to think about how to speed up the charging process. Nickel and metal hydride have been identified as materials capable of providing batteries with such characteristics.
But the process of creating a new type of battery dragged on for several decades. For the first time, new generation batteries were discussed in the fifties of the twentieth century, and their trial samples appeared only in the late seventies.
Features
The device of the nickel-metal hydride battery allows you to accumulate hydrogen, whose volumes are several times larger than the size of the battery. In addition, 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 you to charge such devices up to several thousand times. However, nickel-metal hydride batteries have their drawbacks, which will be discussed in the next section.
Quick heating
Nickel-metal hydride batteries, due to their design features and the characteristics of the materials from which they are made, have a high degree of heating. Therefore, the process of charging them requires a special, more "delicate" approach than their cadmium predecessors. Experts recommend taking the choice of chargers seriously.
This is neededpay attention
Charging nickel-metal hydride batteries, like any other process, can be evaluated in terms of efficiency. How is it calculated in this case? When charging nickel-metal hydride batteries, the electrical energy expended in this process causes heat to be released. In addition, it contributes to the flow of certain chemical reactions. The charging efficiency of nickel-metal hydride batteries is the amount of energy spent on chemical processes. It is worth noting that this ratio is never equal to 100%, even when it comes to the most modern batteries and the most advanced memory.
It is also worth mentioning that this figure for cadmium batteries is much higher than that of their more modern counterparts.
The charging speed depends on the amount of current. Separate units were invented for it - a share of the total volume. They are designated by the Latin letter C. There are three options for charging nickel-metal hydride batteries:
- Drip.
- Quick.
- With increased speed.
In fact, we can only talk about two types, since the first and second differ little from each other.
Drip charging can be considered that charging, the speed of which is 0.1 C. In the fast version, this figure is higher.
To use the latter type, more sophisticated devices are required that are able to recognize the completion of the process and automatically turn off. This prevents overheating of the batteries and their damage. Drip charging due tothe use of low voltage does not lead to excessive temperature rise of the product. Therefore, it cannot cause deformation of Nickel-Metal Hydride (Ni-MH) batteries.
Each type of charging has its pros and cons. Some of them will be discussed below.
Fast charging
With this option, the battery life is maintained for a longer period. Also, as the name suggests, the speed of this process is quite fast. And therefore, less time is spent on charging than with the drip version. However, this scenario requires the use of a more complex device with built-in sensors that determine the level of battery charge. It is not uncommon for these fast-charging devices to have a display that shows the time it takes to complete the charge, the voltage used, and some other information.
This means that the cost of such equipment is higher than that required for drip charging.
Slow option
In the slow process, the AAA NiMH battery does not require a device equipped with end-of-charge sensors.
So it's usually cheaper. But with its help, the batteries will be charged further. This method has another serious drawback. The longer the battery is exposed to electric current, the faster it fails. So, saving on a charger, you can lose because of the need to often buy new ones.batteries.
If we talk about cadmium batteries, then this option is the most preferable for them. The efficiency of this type of charging most often does not exceed 70%. Due to its negative effect 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 using new technologies have increasingly begun to appear.
Charging technology
How to charge NiMH batteries?
Most manufacturers of such products write in the instructions for them the following indicators at which this process should take place. The current must be chosen not exceeding 1C. If this rule is not observed, it may cause the overpressure relief valve to operate and damage the battery.
When charging batteries, you should also monitor compliance with a certain temperature regime. Typically, the instructions indicate an interval from 0 to 40 degrees Celsius. If the temperature does not go beyond these limits, then charging is likely to proceed safely. However, such a warning applies rather to the use of industrial batteries. It is unlikely that a battery for an ordinary household appliance is often charged at temperatures above 40 and below 0 degrees. Celsius.
About voltage and other parameters
The voltage supplied to the batteries when charging them should not go beyond 0.8-8 volts. The efficiency of the fast version of this process is about 90%, which is considered a high value. But closer to the end, the efficiency decreases sharply due to the fact that more and more energy begins to be spent on heat generation. Therefore, it is important that the shutdown of the device occurs in a timely manner, without significant delay. Otherwise, there is a high probability of operation of the emergency valve that serves to reduce pressure.
Charging stages
In order to better understand how to charge NiMH batteries, you should first consider in detail how this process takes place using a special electrical device.
So, first, the device determines whether the battery is present in it or not. It then identifies the battery level. After that, pre-charging occurs, which flows into fast and additional.
Next, the essence of each of these stages will be disclosed in detail.
Battery presence
To determine if the battery is inserted into the appropriate slots of the device, the device applies a voltage of 0.1 C to the contacts. To start charging, the voltage should not exceed 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 checks several times for the presence of batteries. What is this foris being 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. Disabling is done for another reason. If the battery is defective, further charging may lead to undesirable consequences, such as a fire. That is why it is prematurely shutting down.
Determining the level of charge
This action is performed by the device also to prevent its possible damage. It is known that when the level is low, you cannot turn on the fast charging mode. Therefore, if the device has determined that this indicator of the battery is high enough, then it will first start the preparatory mode. Usually this is not required. Most often, the battery does not discharge to the limit at which the preliminary stage is activated. But it may be necessary if the battery has not been used for a long time or is worn out and does not hold a sufficient charge.
Preliminary stage
As already mentioned, it is required only if the Ni-MH battery is heavily discharged. This process takes no more than half an hour. If during this time the battery does not accumulate the required 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 well as throughout the entire process of charging a NiMH battery, the temperature is measured. If sheexceeds a critical level, the device turns off. But the most important thing that happens at this stage is the gradual increase in the charging current.
At the main stage, the charge level is constantly monitored. This is necessary to timely turn off the device and terminate the process. How much the battery is currently charged is determined by several parameters.
Different from nickel-cadmium samples
The level of discharge in Ni-Cd batteries is usually determined by the voltage graph. It is known that it grows at the beginning and middle of the process, and towards the end of it begins to weaken. When the voltage reaches the set minimum, the device stops working. 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, a decrease in voltage is also taken into account here, but the temperature of the battery is also added to this parameter. To prevent the battery from overheating, the shutdown does not occur when a specific temperature is reached, but when it rises above 1 degree per minute.
But stopping charging like this isn't ideal either.
Recently, memory models have appeared that use not ordinary current, but supplied by pulses. Experts say that such devices have a number of advantages, including even distribution of charge throughout the battery. The active substances that accumulate as a result of this process do not form too largecrystals.
How to charge NiMH 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 required time can be easily calculated by knowing the battery capacity, the amount of current and the efficiency of the device. A margin of 5-10 percent of the entire period is usually added to the time received. The shutdown will occur if none of the other control methods has previously interrupted the operation of the device.
Extra charge
This stage starts after the end of the main process. It is necessary to ensure that all nickel-metal hydride batteries in the device receive the same degree of charge. This makes battery-powered appliances more stable.
Emergency Charging
What if you remembered at the very last moment that you need batteries to operate a device? You can use fast charging.
How to charge nickel-metal hydride batteries in 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 10C. The main thing with this type of charging is to determine when those same 70 percent will end. Therefore, it is necessaryknow exactly how much charge was already present in the battery before the start of the accelerated process. This option, of course, is only suitable for people who are well versed in electronics.
How to store NiMH batteries? This question is also asked by many users of electrical appliances powered by batteries. It is known that with a long break in use, batteries begin to degrade - the ability to hold a charge decreases. Experts give the following advice on this matter.
Firstly, only batteries that are more than half discharged can be left unused. Secondly, during storage, room temperature is considered optimal. It is best not to wait until the battery is completely discharged, otherwise its performance will have to be restored.
The second life of batteries
How to refurbish NiMH batteries?
Surely many people already know about the approximate principle of such an operation. It is necessary to make a cycle of charging and almost complete discharge several times (not lower than 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 nature 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. Especially this tip applies to nickel-metal hydride screwdriver batteries.
As a rule, in suchelectrical appliances use not one battery, but a set of several pieces. These batteries are best restored separately. It is worth noting that there are memory models that are capable of discharging 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.
