For more than 4 years, faithfully serves me homemade charger for charging batteries "aa" and "aaa" (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 conducting CTC(Control-training cycle), to put it simply: to restore battery capacity battered by the wrong Chinese chargers with the formula for sequential charge of 2 or 4 batteries. As you know, this method of charging shortens the life of batteries if they are not restored in time.







Charger Specifications:

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

The charger was not going to the exhibition, but what is called from improvised means, that is, the surrounding good was disposed of, which is a pity to throw out and there is no particular reason to store it.

From what you can make your own charging for "AA" and "AAA" batteries:

  • Case from CD-Rom
  • Power transformer from the radio (rewound)
  • FETs with motherboards and HDD cards
  • Other components were either bought or bitten :)

As already noted, charging consists of several nodes that can live completely autonomously from each other. That is, you can simultaneously work with 8 batteries: 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 “finger-type batteries”, if you need to work with “AAA” “mini-finger-type batteries”, it is enough to put a small caliber nut under the negative terminal. If desired, you can duplicate the holders for the size "aaa". The presence of a battery in the holder is indicated by an LED (current flow 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 be unchanged 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 up to par and you will need to install all the transistors on the heat sink. Plan your case ventilation and heatsink dimensions in advance, taking into account that the temperature on the heatsink will be higher in a closed case 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 to the battery. In my case, the charge block is assembled by surface mounting.

battery discharge block


The discharge unit is more complex and requires precision in the selection of components. It is based on a comparator such as lm393, lm339 or lp239, the function of which is to supply a “logical one” or “zero” signal to the gate field effect transistor. When the field-effect transistor opens, it connects a load to the battery in the form of a resistor, the value of which determines the discharge current. When the voltage on the battery drops to the set cut-off threshold 1 (Volt). The comparator slams shut and sets its output to logic zero. The transistor comes out of saturation and disconnects the load from the battery. The comparator has a hysteresis, which causes reconnection load 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 the . By selecting the values ​​​​of the resistors, you can rebuild 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 may have designed it 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 the TL-431 reinforced with a transistor.

This charger can be used for both nickel-cadmium and nickel-metal hydride batteries. If you have li-ion battery, then you rather need .

Description of the charger for nickel-cadmium and nickel-metal hydride batteries

The circuit provides slow but efficient charging as the charge is carried out with a standard current - one tenth of the battery capacity combined with a charge time of 10 to 14 hours, without the risk of overcharging. If you are sure that the battery is only half discharged, then you can fully charge it in about 6-7 hours.

AA size batteries have a capacity of 1500 to 1800 mAh (milliamp hour), so the charging current should be between 150 and 180 mA. If you want to charge several NiCad batteries at once, simply connect them in series for the same charging current that will flow through the entire battery pack, charging them all at the same time.

The question now is how to get us D.C. 180 mA. The most elegant and accurate solution would be to use a current source. This role can be played by a current source included in the circuit. The LM317 microcircuit is quite well-known and the adjustment is carried out by selecting the resistance of the resistor, which is connected to the OUT and ADJ pins.

In our case (for 0.18 A), the resistance will be 6.94 ohms (1.25 / 0.18) = 6.94 ohms. This rating can be dialed from several series-parallel connected resistors, but it is easier to take a close standard value of 6.8 ohms.

To get a current of 180 mA, some voltage is needed. The maximum voltage when charging a NiCd battery is 1.5V, and the current source required is about 3V. If only one battery is charged, the supply voltage will be 4.5V.

If you are charging several NiCd batteries at once, you need to multiply 1.5 V by the number of batteries plus 3 V. For four batteries, this will be a 9 V supply voltage. If the voltage is too low, the charge current will be weak.


A simple compact charger for NiMH and NiCd batteries with additional useful features such as automatic shutdown and temperature control.


USB port found in almost all modern computers and laptops. The current supplied by USB 2.0 can be more than 500 milliamps, at a voltage of 5 volts, that is, at least 2.5 watts, and third-generation USB is even more. The use of such a power source is very convenient, as many chargers for smartphones / tablets also come with usb connector, and the computer is often at hand. Today we will make exercises for finger (AA) and little fingers (AAA) NiMH/NiCd batteries from the USB port. Industrial chargers for USB batteries can be counted on the fingers and usually they charge with a small current, which significantly increases the recharging time. In addition, having assembled a simple circuit, we get an excellent charger with a light indication and a temperature sensor, the cost of which is very small $ 1-2.


Our charger charges two NiCd/NiMH batteries at once with a current of more than 470 mA, which makes charging very fast. Rechargeable batteries can heat up, which will undoubtedly negatively affect them, reduce capacity, peak current output, and normal operation time. To prevent this from happening in the circuit, an automatic power cut is implemented as soon as the battery temperature is 33 or more degrees Celsius. For this useful feature An NTC thermistor with a resistance of 10 kΩ is responsible; when heated, its resistance decreases. Together with a fixed resistor R4, it forms a voltage divider. The thermistor must be in close contact with the batteries in order to perceive temperature changes well.


The main part of the circuit is a dual comparator-microcircuit LM393.

Analogues that can replace LM393: 1040CA1, 1401CA3, AN1393, AN6916.


When charging, the transistor heats up, it must be placed on a radiator. Instead of TIP32, it is possible to take almost any PNP structure with similar power, I used KT838A. The complete domestic analogue is the KT816 transistor, it has a different pinout and case.

The USB cable can be cut from an old mouse/keyboard or purchased. Or maybe solder the USB plug directly onto the board.

If the LED is on when power is applied, but the circuit does not charge anything, then you need to increase the resistance of the current-limiting resistor R6. To check the normal operation of the circuit, between the ground and the third pin of the microcircuit (Vref) should be about 2.37 Volts, and on the second pin (Vtmp) of the LM393 1.6-1.85 Volts.

It is desirable to charge two identical batteries so that their capacity is approximately equal. And then it turns out that one is already fully charged, and the second is only half.

The charging current can be set independently by changing the resistance of the resistor R1. Calculation formula: R1 = 1.6 * desired current.

For example, I want my batteries to be charged with a current of 200 mA, we substitute:

R1=1.6*200=320 ohm



This means that by installing a variable / trimmer resistor, we can add such an unusual function for chargers as an independent selection of the charging current. If, for example, the battery needs to be charged with a current of no more than 0.1C, then by unscrewing the resistor, we can easily set the value we need. This is very important for such miniature industrial batteries, in which the capacity is extremely small and due to their size.


Charging will stop when the batteries get hot. This can increase the charge time, so I recommend installing cooling in the form of a small fan.


If you have NiCd batteries, then they must be discharged to 1 Volt before charging, that is, so that 99% of the capacity is used. Otherwise, a negative memory effect will be felt.

When the banks are fully charged, the charging current will drop to about 10 mA. This current will prevent the natural self-discharge of NiMH/Camdium batteries. The first type has a 100% discharge per year, and the second type has about 10%.


The printed circuit board for the charger exists in several versions, in one of them the USB socket is conveniently located right on the board, that is, it is possible to use a male-male USB cable.




You can download boards in .lay format here

Features of charging Ni─MH batteries, charger requirements and main parameters

Nickel-metal hydride batteries are gradually spreading in the market, and their production technology is being improved. Many manufacturers are gradually improving their characteristics. In particular, the number of charge-discharge cycles increases and the self-discharge of Ni─MH batteries decreases. This type of battery was produced to replace Ni─Cd batteries and little by little they are pushing them out of the market. But there remain some uses where nickel-metal hydride batteries cannot replace cadmium batteries. Especially where high discharge currents are required. Both types of batteries require proper charging to extend their service life. We have already talked about charging nickel-cadmium batteries, and now it's the turn to charge Ni-MH batteries.

In the process of charging, a battery undergoes a series of chemical reactions, to which part of the supplied energy goes. The rest of the energy is converted into heat. The efficiency of the charging process is that part of the supplied energy that remains in the “reserve” of the battery. The efficiency value may vary depending on the charging conditions, but is never 100 percent. It is worth noting that the efficiency when charging Ni─Cd batteries is higher than in the case of nickel metal hydride. The process of charging Ni─MH batteries occurs with a large heat release, which imposes its own limitations and features. For more information, read the article at the link provided.


Charging speed is most dependent on the amount of current supplied. What currents to charge Ni─MH batteries is determined by the selected type of charge. In this case, the current is measured in fractions of the capacity (C) of Ni─MH batteries. For example, with a capacity of 1500 mAh current 0.5C will be 750 mA. Depending on the charge rate of nickel-metal hydride batteries, there are three types of charging:
  • Drip (charge current 0.1C);
  • Fast (0.3C);
  • Accelerated (0.5─1С).

By and large, there are only two types of charging: drip and accelerated. Fast and accelerated are practically the same thing. They differ only in the method of stopping the charge process.

In general, any charging of Ni─MH batteries with a current greater than 0.1C is fast and requires monitoring of some process termination criteria. Drip charging does not require this and can continue indefinitely.

Types of charging nickel-metal hydride batteries

Now, let's look at the features of different types of charging in more detail.

Drip charging of Ni─MH batteries

It is worth mentioning here that this type of charging does not increase the life of Ni─MH batteries. Since drip charging does not turn off even after full charge, the current is chosen very small. This is done so that the batteries do not overheat during prolonged charging. In the case of Ni─MH batteries, the current value can even be reduced to 0.05C. For nickel-cadmium, 0.1C is suitable.


With drip charging, there is no characteristic maximum voltage and only time can act as a limitation of this type of charging. To estimate the required time, you will need to know the capacity and initial charge of the battery. To calculate the charging time more accurately, you need to discharge the battery. This will eliminate the influence of the initial charge. The efficiency of drip charging Ni─MH batteries is at the level of 70 percent, which is lower than other types. Many nickel-metal hydride battery manufacturers do not recommend trickle charging. Although recently there is more and more information that modern models of Ni─MH batteries do not degrade during the drip charge process.

Fast charging nickel-metal hydride batteries

Manufacturers of Ni─MH batteries in their recommendations give characteristics for charging with a current value in the range of 0.75─1C. Keep these values ​​in mind when choosing how much current to charge Ni─MH batteries. Charging currents above these values ​​are not recommended as this may cause the safety valve to open to relieve pressure. Fast charging of nickel-metal hydride batteries is recommended at a temperature of 0-40 degrees Celsius and a voltage of 0.8-.8 volts.

Process efficiency fast charging much more than drip. It is about 90 percent. However, by the end of the process, the efficiency drops sharply, and the energy is converted into heat. Inside the battery, the temperature and pressure rise sharply. have an emergency valve that can open when pressure increases. In this case, the properties of the battery will be irretrievably lost. Yes, and myself heat has a detrimental effect on the structure of the battery electrodes. Therefore, clear criteria are needed by which the charging process will stop.

The requirements for the charger (charger) for Ni─MH batteries are presented below. For now, we note that such chargers charge according to a certain algorithm. The general steps of this algorithm are as follows:

  • determining the presence of a battery;
  • battery qualification;
  • pre-charging;
  • transition to fast charging;
  • fast charging;
  • recharging;
  • support charging.

At this stage, a current of 0.1C is applied and a voltage test is performed at the poles. To start the charging process, the voltage should be no more than 1.8 volts. Otherwise, the process will not start.

It is worth noting that the check for the presence of the battery is carried out at other stages. This is necessary in case the battery is removed from the charger.


If the memory logic determines that the voltage value is greater than 1.8 volts, then this is perceived as the absence of a battery or its damage.

Battery Qualification

Here, an approximate estimate of the battery charge is determined. If the voltage is less than 0.8 volts, then the fast charge of the battery cannot be started. In this case, the charger will turn on the pre-charge mode. Ni─MH batteries rarely discharge below 1 volt during normal use. Therefore, pre-charging is only activated in case of deep discharges and after long storage of the batteries.

Pre-charge

As mentioned above, pre-charging is enabled when Ni─MH batteries are deeply discharged. The current at this stage is set at 0.1÷0.3C. This stage is limited in time and is somewhere around 30 minutes. If during this time the battery does not restore the voltage of 0.8 volts, then the charge is interrupted. In this case, the battery is most likely damaged.

Transition to fast charging

At this stage, there is a gradual increase in the charging current. The increase in current occurs smoothly within 2-5 minutes. In this case, as in other stages, the temperature is controlled and the charge is turned off at critical values.

The charge current at this stage is in the range of 0.5÷1C. The most important thing at the stage of fast charging is the timely shutdown of the current. To do this, when charging Ni─MH batteries, control is used according to several different criteria.

For those who are not in the know, when charging, the voltage delta control method is used. In the process of charging, it constantly grows, and at the end of the process it begins to fall. Typically, the end of the charge is determined by a voltage drop of 30 mV. But this method of control with nickel-metal hydride batteries does not work very well. In this case, the voltage drop is not as pronounced as in the case of Ni─Cd. Therefore, to trigger a trip, you need to increase the sensitivity. And with increased sensitivity, the likelihood of false alarms due to battery noise increases. In addition, when charging several batteries, the operation occurs at different times and the whole process is smeared.

But still, stopping charging due to a voltage drop is the main one. When charging with a current of 1C, the voltage drop to turn off is 2.5÷12 mV. Sometimes manufacturers set detection not by a drop, but by the absence of a voltage change at the end of a charge.

At the same time, during the first 5-10 minutes of charging, the voltage delta control is turned off. This is due to the fact that when fast charging is started, the battery voltage can vary greatly as a result of the fluctuation process. Therefore, at the initial stage, control is turned off to eliminate false positives.

Due to the not too high reliability of charging off by voltage delta, control is also used according to other criteria.


At the end of the Ni─MH battery charging process, its temperature starts to rise. According to this parameter, the charge is turned off. To exclude the OS temperature value, monitoring is carried out not by absolute value, but by delta. Usually, a temperature increase of more than 1 degree per minute is taken as a criterion for terminating a charge. But this method may not work at charge currents less than 0.5C, when the temperature rises rather slowly. And in this case, it is possible to recharge the Ni-MH battery.

There is also a method for controlling the charging process by analyzing the derivative of the voltage. In this case, it is not the voltage delta that is monitored, but the rate of its maximum growth. The method allows you to stop fast charging a little earlier than the completion of the charge. But such control is associated with a number of difficulties, in particular, a more accurate voltage measurement.

Some chargers for Ni─MH batteries do not use direct current for charging, but pulsed current. It is delivered for 1 second at intervals of 20-30 milliseconds. As the advantages of such a charge, experts call a more uniform distribution of active substances throughout the volume of the battery and a decrease in the formation of large crystals. In addition, more accurate voltage measurement is reported in the intervals between current applications. As an extension of this method, Reflex Charging has been proposed. In this case, when a pulsed current is applied, the charge (1 second) and discharge (5 seconds) alternate. The discharge current is 1-2.5 times lower than the charge. As advantages, one can single out a lower temperature during charging and the elimination of large crystalline formations.

When charging nickel-metal hydride batteries, it is very important to control the end of the charging process by various parameters. There must be ways to abort the charge. For this, the absolute value of the temperature can be used. Often this value is 45-50 degrees Celsius. In this case, the charge must be interrupted and resumed after cooling. The ability to accept a charge in Ni─MH batteries at this temperature is reduced.

It is important to set a charge time limit. It can be estimated by the capacity of the battery, the magnitude of the charging current and the efficiency of the process. The limit is set at the estimated time plus 5-10 percent. In this case, if none of the previous control methods work, the charge will turn off at the set time.

Recharge stage

At this stage, the charging current is set to 0.1─0.3C. Duration about 30 minutes. Longer recharging is not recommended as it shortens battery life. The recharging stage helps to equalize the charge of the cells in the battery. It is best if, after a quick charge, the batteries cool down to room temperature, and then recharging starts. Then the battery will restore its full capacity.

Chargers for Ni─Cd batteries often put the batteries into drip charging mode after the charge process is complete. For Ni-MH batteries, this will only be useful if a very small current is applied (about 0.005C). This will be enough to compensate for the self-discharge of the battery.

Ideally, charging should have the function of switching on the maintenance charge when the battery voltage drops. Backup charging only makes sense if a sufficiently long time elapses between charging the batteries and using them.

Ultra-fast charging of Ni-MH batteries

And it is worth mentioning the ultra-fast battery charge. It is known that when charged to 70 percent of its capacity, a nickel-metal hydride battery has a charging efficiency close to 100 percent. Therefore, at this stage it makes sense to increase the current for its accelerated passage. Currents in such cases are limited to 10C. The main problem here is determining those very 70 percent of the charge at which the current should be reduced to a normal fast charge. This is highly dependent on the degree of discharge from which the battery charging began. High current can easily lead to overheating of the battery and destruction of the structure of its electrodes. Therefore, the use of ultra-fast charge is recommended only if you have the appropriate skills and experience.

General requirements for chargers for nickel-metal hydride batteries

It is not advisable to disassemble any individual models for charging Ni─MH batteries within the framework of this article. Suffice it to say that these can be narrowly focused chargers for charging nickel-metal hydride batteries. They have a wired charging algorithm (or several) and constantly work on it. And there are universal devices that allow you to fine-tune the charging parameters. For example, . Such devices can be used to charge various batteries. Including, and for, if there is a power adapter of the appropriate power.

It is necessary to say a few words about what characteristics and functionality a charger for Ni─MH batteries should have. The device must be able to adjust the charging current or its automatic installation depending on the type of batteries. Why is it important?

Now there are many models of nickel-metal hydride batteries, and many batteries of the same form factor may differ in capacity. Accordingly, the charging current must be different. If you charge with a current above the norm, there will be heating. If it is below the norm, then the charging process will take longer than expected. In most cases, the currents on the chargers are made in the form of "presets" for typical batteries. In general, when charging, manufacturers of Ni-MH batteries do not recommend setting a current of more than 1.3-1.5 amperes for type AA, regardless of capacity. If for some reason you need to increase this value, then you need to take care of forced cooling of the batteries.

Another problem is related to the charger power being cut off during the charging process. In this case, when the power is turned on, it will start again from the battery detection stage. The moment when fast charging ends is not determined by time, but by a number of other criteria. Therefore, if it passed, then it will be skipped when turned on. But the stage of recharging will take place again, if it has already been. As a result, the battery receives unwanted overcharging and excessive heating. Among other requirements for Ni-MH battery chargers is a low discharge when the charger is turned off. The discharge current in a de-energized charger should not exceed 1 mA.


It is worth noting the presence of another important function in the charger. It must recognize primary current sources. Simply put, manganese-zinc and alkaline batteries.

When installing and charging such batteries in the charger, they may well explode, since they do not have an emergency valve to relieve pressure. The charger is required to be able to recognize such primary current sources and not start charging.

Although it is worth noting here that the definition of batteries and primary current sources has a number of difficulties. Therefore, memory manufacturers do not always equip their models with similar functions.

I bought a bunch of holders for AA batteries (or just batteries) on Ali ... A thing is sometimes needed on the farm, especially if you assemble or repair any electronic devices or gadgets. Actually, there would be nothing more to write about them (well, just evaluate the resistance of the contacts, measure the length of the wires and evaluate the plastic by eye and tooth - what will be in the review), but I came across one article on the Internet and the idea was born to check whether it is possible to restore the capacity exhausted NiCd and NiMh batteries that have accumulated on the farm, and throwing them simply into a landfill does not raise a hand, because such elements need to be recycled ... What came of it, and did it work at all ... You can find out by reading the review ...
Attention- a lot of photos, traffic!!!

Here, in fact, the article itself, which I mentioned in the table of contents of the review ...


I started looking for more information about the restoration of lost NiCd and NiMh batteries and the search led me to an entertaining article in English, which you can read by clicking on the link: Those who do not know English can take advantage of the automatic translation into Russian Google system. From the article, I took out the main thing that NiCd and NiMh elements have memory (for NiCd this is very pronounced, for NiMh it is less pronounced, but still the effect takes place), and in order to prolong their life, they must be discharged to a certain voltage before charging.


Probably many people know about this, that the manufacturer recommends discharging the batteries to a residual voltage of 0.9-1V, and only then put them on charge. But often this is ignored and over time the elements lose their capacity, crystals of cadmium and nickel salts form in them. And in order to break them, at least partially, you need to discharge the batteries with a small current to a residual voltage of 0.4-0.5V ...

By the way, a little about how the battery works: The basis of any battery is positive and negative electrodes. Let's take a look at the NiCd battery. The positive electrode (cathode) contains nickel hydroxide NiOOH with graphite powder (5-8%), and the negative electrode (anode) contains metallic cadmium Cd in powder form.


Batteries of this type are often called rolled batteries, since the electrodes are rolled into a cylinder (roll) together with a separating layer, placed in a metal case and filled with electrolyte. The separator (separator), moistened with electrolyte, isolates the plates from each other. It is made of non-woven material, which must be resistant to alkali. The most common electrolyte is potassium hydroxide KOH with the addition of lithium hydroxide LiOH, which promotes the formation of lithium nickelates and increases the capacity by 20%.

Nickel-metal hydride batteries in their design are analogous to nickel-cadmium batteries, and in electrochemical processes - nickel-hydrogen batteries. The specific energy of a Ni-MH battery is significantly higher than the specific energy of Ni-Cd and Ni-H2 batteries
The NiMh (Nickel Metal Hydride) battery is designed in much the same way as NiCd:


The positive and negative electrodes, separated by a separator, are folded into a roll, which is inserted into the housing and closed with a sealing cap with a gasket. The cover has a safety valve that operates at a pressure of 2-4 MPa in the event of a failure in the operation of the battery.

Armed with knowledge, I decided to try to assemble something similar as in the article “Automatic discharger”, and in practice it will help to check whether it will help or not, to restore, at least partially, batteries that have lost their capacity ... I assembled such a test device according to the scheme given in the article. In the article, a 1V 75mA light bulb was used as an indication, I don’t know where the author found one. It was also suggested in the article to use an LED, but this idea will not work, since all LEDs do not shine at 1-1.5V ... Therefore, an ammeter was used as an indicator ...

The initial discharge current of a freshly charged battery is 250mA, and gradually decreases. With a residual voltage of 1V, the discharge current drops to 30-40mA, just about the same current is needed to try to break the "slag" crystals in the battery ...
I conducted a small test of the AAA Ni-Mh battery “killed” by the radiotelephone, in total 4 charge-discharge cycles were carried out. Testing was carried out in this way: The battery was discharged to the manufacturer's recommended voltage of 1V and was fully charged using the Soshine Automatic Charger (thanks to the Chinese)

Charger counts the amount of charge “pumped” into the battery, of course this is the wrong way to estimate the capacity, because it is necessary to measure the capacity of the battery during discharge, not charge (in the future we will measure the capacity correctly), but indirectly it can be judged whether the capacity of the “killed” one changes or not battery...

Lyrical digression

By the way, on Muska, many authors “sin” with this, measuring the capacity of batteries with the help of everyone’s favorite, “white doctor” ... Having measured the charge “blowing” into the battery, they talk about the battery capacity with an important air, not taking into account that not everything is “inflated” you can "blow" back, as well as numerous energy losses for self-discharge, battery heating, etc. Any review of a device with a USB port is considered incomplete if it does not include a photo of a “white doctor”. The Chinese probably got rich on sales of these super-devices for testing ...))))


A fully charged battery took 480 mAh of “charge” and was put into discharge in a manufactured discharge device… Discharge cut-off occurred at a residual battery voltage of 0.5V… This value depends on the parameters of the transistors used in the discharge device… The Charge-Discharge cycle was repeated 4 times ... The results of preliminary testing are given below:

1 charge - 680mAh

2- charge - 726mAh

3- charge - 737mAh

4- charge - 814mAh

Well, we see a positive trend ... At least, more and more “charge” enters the battery, but unfortunately this is only an indirect estimate of the capacity, and in order to assess it accurately, you need to discharge the battery by measuring the capacity ...
What are we going to do next?
For a correct assessment of the battery capacity, a new VM200 Charger-Discharge Device was ordered from the Chinese ... It is capable of discharging the battery and measuring the capacity, it will be much more accurate ...

Since you can immediately test 4 batteries, it was decided to remake the discharger, and make it also 4-channel. The VM200 charger-discharge device is of course capable of discharging the battery on its own, but it does this to a residual voltage of 0.9V, which is not enough, I need to discharge each element to 0.4V, so I found a diagram of another discharge device on the Internet

I translated this scheme into modern elements and multiplied it to 4 channels ...
It turned out such a discharge device:




Since in all 4 channels, I set the same cutoff voltage of the comparators, I managed with one zener diode and one construction resistor for all four channels ...
For those who want to repeat, I give a link to the printed circuit board, all the elements are signed on it

This is where we got to our holders for batteries or batteries ... I needed 4 pieces, the rest will go “in reserve” ... As usual, the link already goes to “nowhere”, so I put a similar product from another seller in the title. I'm attaching a screenshot of the order under the spoiler, otherwise they won't believe that I order spare parts from the Chinese ...))))

Screenshot of the order


While the Chinese, in full steam, on rickshaws, in the sweat of their brows, are bringing my 2 parcels to me, I will allow myself a short lyrical digression ... There will definitely be a couple of “muska” readers who will say that I am doing garbage, especially making printed circuit boards, and in general you don’t have to bathe, but just throw away used batteries ... Perhaps this is right, but everyone has their own way, someone drinks vodka, someone goes to the bathhouse, but I like to create something, even if it’s it seems pointless to someone ... The main thing is that I like it, but I wish you to just have a good rest, reading my review, maybe learn something new and discuss it in the comments, just don’t bring disputes to “holivar” ...)) )
While I was waiting for the parcel, I made an indication module, instead of a voltmeter for the first version of the board, which is on two transistors ...

having fun under the spoiler

This is all done on the LM3914 chip, almost according to the typical scheme from the datasheet. 5V power from some kind of charger cell phone... There is a jumper on the board that can switch the microcircuit from the "Point" mode to the "Column" mode and vice versa ...

back side


When one red LED is on, the battery voltage is 0.2V, when the entire bar is on, it means 1.2V on the battery. Each extinguished LED indicates that the voltage on the battery has dropped by another 0.1V ... It is convenient to use this board in the form of an indicator voltmeter with a fairly high accuracy ...

Finally, both parcels arrived, I will not describe unpacking, weighing, measuring dimensions, because it is clear that AA battery holders are slightly larger than the batteries themselves ... Here is a general view of the holder.


The plastic is elastic, holds the battery well, moreover, it is quite difficult to pull the battery out with your fingers, you have to pry it with some thin object, a screwdriver, for example.
Check the resistance of the spring contact. 2 milliohm...


The length of the wires (red and black) is about 15 cm.

Now let's set the cutoff voltage of the comparators, this can be done on any of the four channels. And let's check the current with which our batteries will be discharged ... We supply 5V to the discharge device from some kind of power source from a cell phone. We see that all the LEDs are on. Green indicates that power is connected, and red 4 LEDs tell us that all comparators are in the closed state and no discharge occurs.

Description of the setup process and photos under the spoiler

We connect a laboratory power supply to the first channel and give 1.2V - this is the voltage of a fully charged battery ... We see that the discharge with a current of 70mA has begun (on the right is an accurate ammeter with 4 digits after the decimal point)


Please note that the LED of the first channel has gone out, signaling that the discharge in this channel has begun ...


With a battery voltage of 0.5V, the discharge current is 40mA, in principle, just about this current is what we need to successfully break the formed crystals ...


At a voltage of 0.4V, the comparator closes and the discharge is over. Note that the current on the ammeter has become zero


Using a crimper (not cheap, professional, bought on Ali), we crimp the wires into special lugs for connectors


It turns out such a crimped tip ... It's nice to work with a professional tool, although it is not cheap, but the convenience and result are worth it.

Well ... everything is ready, we select candidates for the restoration of capacity. Numbers 1 and 2 are NiMh batteries from the Panasonic electric shaver, the initial capacity is not known. After 3 years in an electric razor, fully charged batteries were no longer enough for one shave. Numbers 3 and 4 NiCd batteries, the initial capacity of 600mA, worked their way in the electrocardiograph ...
Since the batteries have been lying without use for a long time, you first need to “cheer them up”, this can be done on the BM200 Charger by selecting the Gharge-Refresh mode - the charger will carry out 3 discharge cycles to 0.9V, and then fully charge and so on 3 times. In this case, the capacity increases slightly. Thus, we will eliminate the error, a slight increase in capacity, which will be added after several cycles of "training" for a long time lying without work batteries. The training was carried out, it took approximately 36 hours in time

Now you can start the recovery process...


We insert all the batteries into the charger, select the “Charging-Test” mode ... and wait ... After full charge current 200mA, the charger will discharge the batteries up to 0.9V with a current of 100mA and calculate the given capacity. We will operate with it as the initial capacity before recovery.


In the morning, the charger gave out the calculated capacity of the batteries, we will use it as initial values, Nickel-Cadmium batteries have lost half of their initial capacity, Nickel-metal hydride batteries, it is not known how many capacities they had initially, I suspect, somewhere around 1200mAh, but it doesn’t matter, the main thing for us is the dynamics and restoration of capacity.


We put all the batteries in the discharge device, we see that all the red LEDs have gone out, in all four channels the batteries have begun to discharge. When a residual voltage of 0.4V is reached on each battery, the comparators will close and the red LEDs will light up, signaling the end of discharging. This may take a long time...


I came home from work, all 4 red LEDs are lit on the discharge device. Just in case, I measured the residual voltage on all batteries with a voltmeter. Approximately 0.4V on each ...

Well, we begin to repeat the discharge-charge cycle. Long and tedious, day and night. All testing took 4 days. On the display of the VM200 memory, positive dynamics are visible, more and more charge “enters” the batteries ... It can be seen that the method works ...)))))


But dots over i will arrange the final test of battery capacity during discharge.
5 charge-discharge cycles have passed ... We put the batteries to determine the capacity, this is the “Gharge-Test” mode ... Well, here is the final result - the verdict ...


As we can see, what capacity it was, it has remained so ... The miracle did not happen, although everything said that the batteries were being restored, because. the “injected” capacity is growing ... But alas ...
At this point, the Muskovites, who have a humanitarian education, sadly closed the review and gave me a fat minus ... The Muskovites, who have an engineering education, giggled and thought that no one had yet deceived the laws of physics, chemistry, old age and an old woman with a scythe ... And they knew about it in advance … But… There is one small BUT…
As you remember, I wrote earlier about restoring AAA batteries from a radio phone, at the beginning of the article ... The batteries worked for 2 years and stopped holding a charge. If you remove the phone from charging, after 10-15 minutes the low battery icon flashed on the screen, and demanded to put the phone on charge. If his request was ignored, then the phone simply turned off. This was about a year ago. After 4 charge-discharge cycles, I again put the batteries in the phone, and they have been working in it for a year already, even if you have to put the phone on charge a little more often than with new batteries, BUT !!! The phone normally works for a year with refurbished batteries !!! Why and how, I don't know... But the fact remains...
Now let's return the charged batteries to the Panasonic razor ... Before the batteries were restored, it lasted for about 4-5 minutes after a full charge ... Then the razor inevitably “died” ... Well, let's check, I put the batteries back in place ... I shaved ... then I kept it for another 25 minutes the razor turned on ... It buzzes, as if it has new batteries ... I didn’t torment the engine further ... turned it off ... I feel that these batteries will still be enough for me for a while ...
I will not draw conclusions, everyone can draw them on their own ... Thanks to everyone who read my review to the end ...
At the end of the review, according to tradition, the animal ... The animal liked the plastic and the resistance of the spring contact, but really did not like the length of the wires ... It needs to be longer ... and the rustler should be at the end of the wires ...