Discharge device for AA battery. Homemade charger for aa batteries

Most modern gadgets are mobile devices that have compact dimensions and can work offline. To do this, they are equipped with built-in power systems, the energy source of which is a battery. The modern market offers wide choose such elements.

But small AA batteries are most widely used. However, they have a limited resource and require regular recharging. For this purpose, special devices are used that are connected to a stationary power supply. One of these devices is a charger AA batteries. It is presented on the market with various models, let’s try to choose one of the best.

What is the device

This is an electronic device with compact dimensions. It serves to charge the battery with energy from an external source. This is usually AC power.

Charger circuit for Li Ion batteries It is quite simple and therefore the device can be assembled independently. It consists of the following elements:

• Voltage converter;
• Rectifier;
• Stabilizer;
• Devices for monitoring the charging process.

A transformer is usually used as a converter, but it can be replaced by a switching power supply. To monitor the charging operation, indicators such as an LED ammeter are used.

Where are charging for AA batteries used?

The main area of ​​use of such devices is mobile gadgets. They usually run on different types of batteries. These devices are used to charge them.

But since batteries can be of different types, the characteristics of the charger for 18650 Li Ion batteries are selected in accordance with their operating voltage and rated capacity.

Design features of the device

A charger is a small gadget designed to work with specific energy sources. You can also find on sale universal devices designed for retraining both one and several batteries.

But since finger-type cells are the most popular, the most devices for charging them are produced. They are designed to work with batteries of various sizes:

Some charger models come with replacement boards designed for different types of batteries. The latest developments in this industry involve equipping the device with an adapter, which allows it to be used in any country. But some still prefer to collect Charger for AA batteries with your own hands.

Let's watch the video, types of devices, operating principles and selection aspects:

Connection to the storage network is carried out using a cord. But there are samples that are connected directly. Their use is not always convenient.

Operating principle of the device

The main purpose of such a device is to retrain the current source after the resource of their capacity has been exhausted. This process in modern memory is carried out using three modes:

• fast charge;
• discharge;
• recharging.

The purpose of the first point is clear - it allows you to bring the battery into working condition. At the same time, the other two raise questions among non-professionals. However, without them, the battery may not charge.

It is these modes that are necessary to eliminate such effects as:

• self-discharge;
• memory effect.

The first occurs in case of prolonged non-use of the battery. In this case, contamination of the electrolyte or instability of the electrodes often occurs. The memory effect is associated with electrode manufacturing technology. And so that the current source does not fail prematurely, you should not recharge it if there is residual capacity. Therefore, the charger function includes the discharge mode.

Memory selection criteria

The purchase of such a device has its own specifics. One of the most important factors is the order in which the batteries are installed. In order not to make a mistake with the polarity and take into account all the existing features, you must carefully study the instructions and consider the drawings with options for the arrangement of elements. This will help you choose the model you need.

For example, using charging for 4 cells, you can only make a mistake with the polarity. But at the same time, when purchasing a device for 2 batteries, you will have to take into account many features of their installation.

Watch the video, criteria for choosing a charging device:

Experts advise purchasing a charger from the same manufacturer as the batteries.

When choosing a gadget, you should also pay attention to the way it is connected to the outlet. The most convenient are those that use a cord. Those connected without it often do not provide a reliable installation.

An important parameter is the charging time. By purchasing a universal charger for Li-Ion batteries Please note that the documentation provides calculated values. Wherein real time usually somewhat more and this is due to the specific operation of the device.

In addition to the parameters listed above, there is a whole list others that are no less important when choosing:

• Number of installed batteries;
• Standard size;
• Features of their location;
• Availability of protection against overheating and overvoltage;
• Automatic shutdown when fully charged.

However, you should also take into account the fact that devices with more functions are more expensive. And in some cases you can get by with the simplest, but at the same time cheapest sample.

The best charger for AA batteries

La Crosse BC-700 and NiMN model.

A large assortment of memory devices forces you to carefully approach the choice. Which company's products should you prefer? Choose a model from a European manufacturer?

As a rule, they are of high quality, but such products are also expensive. Chargers made in China are most often items that cannot be repaired and are not reliable.

Although among these products you can find high-quality and inexpensive models. There are good chargers of domestic design. In many respects they are not inferior to foreign products, but at the same time their price is much lower.

Which model to choose depends on the specific requirements of the buyer. And to make this easier, we will look at the characteristics of devices from various manufacturers.

Let's watch a video review of the Robition Smart S100 model:

Let's start with a model branded Robition Smart S100. These are products of one of the leading domestic companies. It is a charger with two channels, equipped with a discharge button. IN the lineup This manufacturer includes devices that differ in their functionality.

For example, the Ecocharger gadget, although not capable of discharging batteries, is capable of charging even a disposable alkaline battery. Moreover, this procedure can be performed with one element up to 5 times. This function is activated by a special switch located on the side panel of the case.

In addition, the device is a 4-channel device. This means that it is able to monitor the charge level of each battery individually. Readiness is indicated LED indicator. The cost of such a device does not exceed $20.

NiMN brand chargers are more expensive. They have wider functionality and are able to discharge the battery to restore its capacity. The devices, just like the previous ones, are capable of monitoring the charge level of each individual element. The use of this device allows the battery to be restored quickly due to the high charging current. Prices for devices of this brand range from 50 to 70 dollars.

Charging model La Crosse BC-700

For more than 4 years it has served me faithfully homemade charger for charging “aa” and “aaa” batteries (Ni-Mh, Ni-Ca) with a discharge function battery to a fixed voltage value (1 Volt). The battery discharge unit was created for the possibility of carrying out CTC(Control-training cycle), to put it simply: to restore battery capacity battered by incorrect Chinese chargers with a sequential charging formula of 2 or 4 batteries. As you know, this charging method shortens the life of batteries if they are not restored in time.

Charger Specifications:

• Number of independent charging channels: 4
• Number of independent discharge channels: 4
• Charge current: 250 (mA)
• Discharge current 140 (mA)
• Discharge 1 cut-off voltage (V)
• Indication: LED

The charger was not assembled for an exhibition, but what is called from improvised means, that is, the surrounding goods were disposed of, which would be a pity to throw away and there was no particular reason to store.

What can you use to make your own charger for “AA” and “AAA” batteries:

• CD-Rom case
• Power transformer from the radio (rewind)
• Field effect transistors with motherboards and HDD cards
• Other components were either bought or bitten out :)

As already noted, charging consists of several nodes that can live completely autonomously from each other. That is, you can work with 8 batteries at the same time: charge from 1 to 4 + discharge from 1 to 4. The photo shows that the battery cassettes are installed under the “AA” form factor in the common people’s “pen-type batteries”; if you need to work with “mini-pen-type batteries” “AAA”, it is enough to place a small caliber nut under the negative terminal. If desired, you can duplicate it with holders for size “aaa”. The presence of a battery in the holder is indicated by an LED (the flow of current is monitored).

Charge block

Charging is carried out with a stabilized current, each channel has its own current stabilizer. In order for the charge current to remain constant when connecting both 1 and 2, 3, 4 batteries, a parametric voltage stabilizer is installed in front of the current stabilizers. Naturally, the efficiency of this stabilizer is not high and you will need to install all the transistors on the heat sink. Plan the ventilation of the case and the size of the radiator in advance, taking into account that in a closed case the temperature on the radiator will be higher than in a disassembled state. You can upgrade the circuit by introducing the ability to select the charge current. To do this, the circuit must be supplemented with one switch and one resistor for each channel, which will increase the base current of the transistor and, accordingly, increase the charge current passing through the transistor into the battery. In my case, the charge block is mounted using a hinged mounting.

Battery discharge unit

The discharge unit is more complex and requires precision in the selection of components. It is based on a comparator type lm393, lm339 or lp239, the function of which is to supply a “logical one” or “zero” signal to the gate of a field-effect transistor. When the field-effect transistor opens, it connects a load in the form of a resistor to the battery, the value of which determines the discharge current. When the battery voltage drops to the set shutdown threshold of 1 (Volts). The comparator slams shut and sets a logical zero at its output. The transistor comes out of saturation and disconnects the load from the battery. The comparator has hysteresis, which causes the load to be reconnected not at a voltage of 1.01 (V) but at 1.1-1.15 (V). You can simulate the action of the comparator by downloading. By selecting the resistor values, you can adjust the device to the voltage you need. For example: by raising the shutdown threshold to 3 Volts, you can make a discharge for li-on and Li-Po batteries.
You can it was designed to use the lm393 comparator in a DIP package. The comparators must be powered from a stabilized 5-volt source; its role is played by a TL-431 amplified by a transistor.

It all started with the fact that my camera point-and-shoot device flatly refused to work with batteries freshly removed from the charger - four AA-size NiMH batteries. Take them as usual and throw them away. But for some reason, this time curiosity prevailed over common sense (or maybe it was the toad that spoke), and I wanted to understand whether it was possible to squeeze at least something else out of these batteries. The camera is very hungry for energy, but there are also more modest consumers - wireless mice or keyboards, for example.

Actually, there are two parameters that are interesting to the consumer - the battery capacity and its internal resistance. There are also few possible manipulations - discharge and charge. By measuring the current and time during the discharge process, you can estimate the battery capacity. According to the difference in battery voltage to Idling and under load, internal resistance can be estimated. By repeating the discharge-charge cycle (i.e., performing the “training”) several times, you can understand whether this action makes sense at all.

Accordingly, the following plan was formed - we make a controlled spark gap and charger with the ability to continuously measure process parameters, perform simple arithmetic operations on the measured values, and repeat the process the required number of times. We compare, draw conclusions, and finally throw away the batteries.

Measuring stand

The stand was made from what was found within a radius of three meters. If someone wants to repeat it, it is not at all necessary to follow the diagram exactly. The choice of element parameters can be quite wide, I will comment on this a little later.

The discharge unit is a controlled current stabilizer based on op-amp IC1B (LM324N) and field-effect transistor Q1. Almost any transistor, as long as there are enough permissible voltages, currents and power dissipation. And they are all small here. Resistor feedback and at the same time part of the load (together with Q1 and R20) for the battery - R1. Its maximum value should be such as to provide the required maximum current discharge. If we assume that the battery can be discharged down to 1 V, then to ensure a discharge current of, for example, 500 mA, resistor R1 should not be larger than 2 Ohms. The stabilizer is controlled by a three-bit resistive DAC (R12-R17). Here the calculation is as follows - the voltage at the direct input of the op-amp is equal to the voltage at R1 (which is proportional to the discharge current). We change the voltage at the direct input - the discharge current changes. To scale the DAC output to the desired range, there is a trimming resistor R3. It is better if it is multi-turn. The values ​​of R12-R17 can be any (in the region of tens of kilo-ohms), the main thing is that the ratio of their values ​​is 1/2. No special accuracy is required from the DAC, since the discharge current (voltage on R1) is measured directly by the instrumentation amplifier IC1D during the process. Its gain is K=R11/R10=R9/R8. The output is fed to the microcontroller ADC (A1). By changing the values ​​of R8-R11, the gain can be adjusted to the desired value. The voltage on the battery is measured by the second amplifier IC1C, K=R5/R4=R7/R6. Why control the discharge current? The point here is basically this. If you discharge with a constant high current, then due to the large internal resistance of worn-out batteries, the permissible voltage 1 V (and there is no other reference point for stopping the discharge) will be reached before the battery actually discharges. If you discharge with a constant low current, the process will take too long. Therefore, the discharge is carried out in stages. Eight steps seemed enough to me. If the hunt is more/less, then you can change the bit depth of the DAC. In addition, by turning the load on and off, you can estimate the internal resistance of the battery. I think that the controller operation algorithm during discharge does not require further explanation. At the end of the process, Q1 is locked, the battery is completely disconnected from the load, and the controller turns on the charge unit.

Charge block. Also a current stabilizer, only uncontrolled, but switchable. The current is set by the reference voltage source on IC2 (2.5 V, accuracy 1% according to the datasheet) and resistor R21. In my case, the charge current was classic - 1/10 of the nominal battery capacity. Feedback resistor - R20. You can use any other reference voltage source - depending on your taste and availability of parts. Transistor Q2 operates in a more rigid mode than Q1. Due to the noticeable difference between Vcc and battery voltage, significant power is dissipated across it. This is the price to pay for the simplicity of the circuit. But the radiator saves the situation. Transistor Q3 serves to force Q2 to turn off, i.e., to turn off the charge unit. Controlled by signal 12 of the microcontroller. Another reference voltage source (IC3) is needed for the controller’s ADC to operate. The measurement accuracy of our stand depends on its parameters. LED1 - to indicate the process status. In my case, it does not light up during the discharge process, lights up when charging and flashes when the cycle is completed.
The supply voltage is selected to ensure that the transistors open and operate in the required ranges. In this case, both transistors have a quite high gate unlocking voltage - about 2-4 V. In addition, Q2 is “backed up” by the battery voltage and R20, so the gate unlocking voltage starts from approximately 3.5-5.5 V. In turn The LM323 cannot raise the output voltage above Vcc minus 1.5 V. Therefore, Vcc must be quite large and in my case it is 9 V.

The charge control algorithm was based on the classic version of monitoring the moment the battery voltage begins to drop. However, in reality everything turned out to be not entirely true, but more on that later.
All measured values ​​during the “research” process were written to a file, then calculations were made and graphs were drawn.

I think that with measuring stand everything is clear, so let's move on to the results.

Measurement results

Graphs on the axes: time, hours (X) and power, W (Y) for the best and worst batteries. It can be seen that the stored energy (the area under the graphs) is significantly different. In numerical terms, the measured battery capacities were 1196, 739, 1237 and 1007 mAh. Not a lot, considering that rated capacity(which is indicated on the case) - 2700 mAh. And the spread is quite large. What about internal resistance? It was 0.39, 0.43, 0.32 and 0.64 Ohm, respectively. Terrible. It is clear why the soap dish refused to work - the batteries are simply not able to deliver a large current. Well, let's start training.

Cycle one. Again the output power of the best and worst battery.

Progress is visible to the naked eye! The numbers confirm this: 1715, 1444, 1762 and 1634 mAh. The internal resistance also improved, but very unevenly - 0.23, 0.40, 0.1, 0.43 Ohm. It would seem there is a chance. But alas, further discharge/charge cycles did not yield anything. The capacitance values, as well as the internal resistance, varied from cycle to cycle within about 10%. Which lies somewhere close to the limits of measurement accuracy. Those. Long training, at least for my batteries, did nothing. But it became clear that the batteries retained more than half of their capacity and would still work at low current. At least some savings on the farm.

Now I want to dwell a little on the charging process. Perhaps my observations will be useful to someone who is planning to design a smart charger.
Here is a typical charge graph (on the left is the battery voltage scale in volts).

After the start of charging, a voltage dip is observed. In different cycles it may be greater or lesser in depth, of slightly different duration, and sometimes absent. Then, for about 10 hours, there is a uniform increase and then an almost horizontal plateau. The theory states that with a low charge current there is no voltage drop at the end of the charge. I was patient and still waited for this fall. It’s small (it’s almost invisible to the eye on the chart), you have to wait a very long time for it, but it’s always there. After ten hours of charging and before the decline, the voltage on the battery, although it increases, is extremely insignificant. This has almost no effect on the final charge; no unpleasant phenomena such as heating of the battery are observed. Thus, when designing low-current chargers, there is no point in equipping them with intelligence. A timer for 10-12 hours is enough, and no special accuracy is required.

However, this idyll was disrupted by one of the elements. After about 5-6 hours of charging, very noticeable voltage fluctuations occurred.

At first I attributed this to a design flaw in my stand. The photo shows that everything was assembled using a hinged installation, and the controller was connected with rather long wires. However, repeated experiments have shown that such nonsense consistently occurs with the same battery and never occurs with others. To my shame, I did not find the reason for this behavior. Nevertheless (and this is clearly visible on the graph) the average voltage value is growing as it should.

Epilogue

That's all. Thank you for your attention.

I recently assembled another useless device :) It is designed to serve AA or AAA batteries - it is a discharge device with voltage control. It has two discharge modes, depending on the battery capacity. Also used as reject AA batteries, here is a convenient visualization of the voltage, since the control is carried out under load.

It is known that if you charge not completely discharged nickel-cadmium batteries, a “memory” effect appears - a decrease in the maximum capacity. To reduce the influence of this effect, it is recommended to discharge the battery to a voltage of 1 V before charging. Many expensive automatic chargers first discharge and only then charge the battery. But simple chargers do not have this function. This design and discharges two standard AA or AAA batteries.

Resistors R1 and R2, connected in series with diodes VD1 and VD2, are used as load elements for the batteries. Resistors limit the current, and diodes limit the discharge voltage, so in this device it is impossible to discharge the battery to zero.

The degree of battery discharge can be visually determined by the brightness of the HL1 LED, and you can additionally set pointer indicator voltage. The initial brightness of the glow is selected using resistor R3. Resistors - any type, power dissipation of resistors R1, R2 - 0.5 W to 1 W, R3 - 0.125 W to 0.25 W. The diodes must be silicon rectifiers with a permissible forward current of 1 A. The LED should be used in red and first checked that it shines at a voltage of 1.8..1.9 V.

Types of batteries and voltaic cells

Chargers for Ni-Cd and Ni-MH batteries

Testing methodology

capacity at various discharge modes;
the value of internal resistance;
self-discharge value (for batteries only);
presence of memory effect (only for batteries).

discharge with low direct current: 250 mA for AA format elements, 100 mA for AAA format;
discharge with high direct current: 750 mA for AA format elements, 300 mA for AAA format;

discharge with low direct current: 500 mA for AA format elements, 200 mA for AAA format;
discharge with high direct current: 2500 mA for AA format elements, 1000 mA for AAA format;
discharge with pulsed current: pulse duration 2.25 s, pause duration 6.0 s, current amplitude 2500 mA for AA format elements and 1000 mA for AAA format.

measurement of residual capacity at low current (only for "Ready To Use" models);
charger;
high current discharge without measuring capacity (training);
charger;
high current discharge with capacity measurement;
charger;
pulsed current discharge with capacitance measurement;
charger;
low current discharge with capacity measurement;
charger;
exposure for 7 days;
low current discharge with capacity measurement - then the result is compared with that obtained in the previous step and the percentage of capacity loss due to self-discharge for 1 week is calculated;

Closer to practice: examples of energy consumption

Only part of this set

Camera
Oscillogram division price – 200 mA

Photoflash
Oscillogram division price – 100 mA