Charging circuit for nickel-magnesium batteries. Homemade charger for aa batteries. Battery discharge unit

Traditional (“safe”) charging of nickel-cadmium batteries with a current value ten times less than the battery capacity does not satisfy all users, since in this case it takes more than ten hours to guarantee its full charging.

Meanwhile, batteries can be safely charged at high currents, thereby reducing charging time. At the same time, however, constant monitoring of the condition of the battery being charged is necessary to avoid its failure.

The moment when a nickel-cadmium battery is fully charged can be reliably determined by measuring its voltage versus charging time. In general form it is shown in Fig. 1.

A fully charged battery corresponds to the moment when the voltage across it reaches its maximum. Because the absolute value of the maximum may vary between instances, this parameter cannot be used to uniquely determine the end of charging.

"Intelligent" chargers periodically measure the voltage on the battery being charged, determine the moment when the change in voltage changes sign (the voltage begins to decrease), and stop charging.

More precisely, they usually translate Charger V safe mode low current charging. It should be noted that the decrease in voltage relative to the maximum after its passage is small - about 10 mV per element, and to register it you need measuring equipment with the appropriate resolution

The second parameter that is usually monitored when fast charging, - time. It is calculated based on the fast charging current, and even if during this time the voltage on the battery has not reached the maximum, charging is stopped.

This allows to some extent reduce the risk of failure of the charger if a defective battery is installed in it, which may not change the sign of the voltage change during the charging process.

There is another parameter that, along with the change in the sign of the voltage change on the battery, objectively reflects the completion of the charging process - the temperature of the battery case.

However, this parameter is one of the most difficult to control, since it requires establishing reliable thermal contact of the temperature sensor with the body of the battery being charged.

Moreover, in sealed batteries, which are mainly used in modern wearable equipment, this is basically impossible. Therefore, in practice, charging batteries with temperature control is not used.

But at the same time we also have to give up the limits - very fast modes charging.

Chip MAX713

To implement the described charging algorithms, specialized microcircuits are produced that perform all of the above monitoring and control functions. These include for example chip MAX713. It allows you to charge both a single cell and a battery consisting of several batteries.

The control time for fast charging can be in the range from 22 to 264 minutes (eight discrete values), and the current can be in the range from 4C to 0.33C (C is the battery capacity). All these parameters are set programmatically. The MAX713 chip also provides a function for monitoring the temperature of the battery being charged.

When calculating the fast charging mode of nickel-cadmium batteries, first select the charging current I, focusing on the required charging time. It should be noted that in the absence of reliable control of the temperature of the battery being charged, it is not recommended to select it above 2C.

At the end of the fast charging mode, the current is reduced to values ​​that are safe for a long period ("recharging"). In the MAX713 chip, for example, this value is selected to be about 30 mA and does not depend on the fast charging current.

Schematic diagram of the charger

The diagram of an “intelligent” charger for nickel-cadmium batteries, made on the MAX713 chip, is shown in Fig. 2. A 12 V power supply is connected to connector X1.

It must provide a load current that is at least 50 mA greater than the maximum charging current. With a supply voltage of 12V, you can charge batteries containing up to nine batteries.

In the author's version, a conventional network adapter was used to power the device, providing a load current of up to 300 mA at a voltage of 12 V. The HL1 LED indicates the operation of the device as a whole, and the HL2 LED indicates the fast charging mode.

Fig 2. Schematic diagram smart charger.

If it does not light up, it means that charging is complete. The battery is connected to connector X2. The charging current is regulated by transistor VT1. If, after turning on the device with the battery connected, the HL2 LED does not light up, then the battery is charged.

The microcircuit is programmed by connecting pins 3 (PGM0), 4 (PGM1). 9 (PGM2) and 10 (PGM3) to microcircuit pins 15 (+), 12 (WATT-) 16 (REF). They may also not be connected to anything (OPEN). Through the PGM0 and PGM1 pins, the number of batteries in the battery is programmed (Table 1). and through the PGM2 and PGM3 pins there is a fast charging end timer (Table 2).

Before selecting the final version of the device, the number of cells N in the battery to be charged and the charging current are specified.

Based on the first parameter, the connection of pins 3 and 4 of the microcircuit is determined (in accordance with Table 1), and according to the second parameter, the approximate charging time T (in hours) according to the formula T = C / 0.8I. Here C is substituted in mAh, and I in mA. In table 2 find the nearest larger value of the programmable charging time interval and determine the corresponding connection of pins 9 and 10 of the microcircuit.

At the next stage, the power P (in watts) that will be dissipated by the transistor T1 is calculated using the formula P = (Umax - Umin) * 1. Here Umax is the maximum voltage at the output of the power source, V; Umin, - minimum voltage on the battery, V: I - charging current A.

Umin is calculated based on the number of elements and the minimum voltage on one battery is usually assumed to be 1V. Based on this calculation, a transistor is selected and it is determined whether a heat sink is needed for it.

The resistance of resistor R2 (in kilo-ohms) is calculated using the formula R2=U/5 1, where U is the minimum voltage of the power source in volts. The resistance of resistor R5 (in ohms) is calculated using the formula R5=0 25/I, where I is current charging in amperes.

The ratings shown in the diagram correspond to a minimum power source voltage of 12V and a charging current of 0.25 A. With a supply voltage of 12V, you can charge batteries from no more than seven batteries.

Steven Avritch. A Smart Charger For Nickel-Cadmium Batteries - QST 1994 September p.40-42. R2001, 1.

It is no secret that at any moment you can find yourself in such conditions when there is a need to recharge “dead” batteries. For example, Ni-MH batteries are widely used in everyday life and in production - how to charge them correctly? Of course, you can use the simplest charger included with any item. household appliances. However, their strength is very low, so such a charge will “hold” for a very short time. The use of more complex chargers helps ensure that the battery not only operates at full capacity, but also uses all its possible resources. In addition, batteries are different. Their names directly depend on the composition from which they are made.

Common types of nickel batteries, their similarities and differences

There are many, which contain various chemical compounds. For household consumption, it is optimal to use nickel-metal hydride, cadmium and nickel-zinc elements. Of course, any battery needs some care, so it is always important to follow the operating and charging rules.

Ni-MH

Nickel-metal hydride batteries are secondary chemical current sources with much larger capacity than their predecessors, but their service life is shorter. One of the popular areas of application for nickel cells is model building (except for aviation, due to the fact that the battery is quite heavy in weight).

The first development of these cells began in the 70s of the twentieth century with the goal of improving CD batteries. 10 years later, in the late 80s, it was possible to ensure that the chemical compounds used to create Ni-MH batteries became more stable. In addition, they are much less susceptible to the “memory effect” than Ni-Cd: they do not immediately “remember” the charge current remaining inside if the element was not completely discharged before use. Therefore, they do not need a full discharge so often.

Ni-Cd

Despite the fact that Ni-MH have a number of obvious advantages over Ni-Cd, it is worth noting that the latter do not lose their popularity. Mainly because they don’t heat up as much when charging due to greater energy conservation inside the element. As is known, there is Various types chemical processes occurring between substances.

If you charge Ni-MH, the reactions will be exothermic, and if you charge cadmium batteries, they will be endothermic, which provides a higher efficiency. Thus, Cd can be charged at a higher current without fear of overheating.

Ni-Zn

Recently, much attention has been paid to discussions on the Internet about batteries that contain zinc. They are not as well known to consumers as the previous ones, but are ideal for use as batteries for digital cameras.

Their main feature is high voltage and resistance, due to which even at the end of the charge-discharge cycle there is no sharp drop in voltage, like with a Ni charge. If the camera contains metal hydride batteries, it will turn off even if the battery is not completely discharged, but Ni-Zn does not have this even at the end of the discharge.

Due to the specifics of these batteries, they may require an individual charger, or they can be charged on any universal “smart” charger, for example, ImaxB6. Ni-Zn batteries are also excellent for use in electric children's toys and blood pressure monitors.

Fast charging of NiMH batteries and other power sources

It is better to charge the battery using more complex models of the corresponding devices. Their current algorithms have a more complex sequence. Of course, doing this is a little more complicated than simply inserting the battery into the basic charger included in the package. But the quality of charging when using a “smart” device will be much higher. So how to charge Ni-MH batteries?

First, the current is turned on and the voltage at the battery terminals is checked (current parameters are 0.1 battery capacity, or C). If the voltage exceeds 1.8 V, this means that the battery is either missing or damaged. In this case, the process cannot be started. You need to either replace the damaged element with a intact one, or insert a new one into the device.

After checking the voltage, the initial discharge of the battery is assessed. If U is less than 0.8 V, then you cannot immediately proceed to fast charging, but if U = 0.8 V or more, then you can. This is the so-called “pre-charge phase”, used to prepare cells that are very discharged. The current value here is 0.1-0.3 C, and the duration is half an hour, no less. It should immediately be noted that At all stages it is important to constantly monitor the temperature . Especially when it comes to what current and how to properly charge a Ni-MH battery. Such batteries heat up much faster, especially towards the end of the process. Their temperature should not exceed 50°C.

Fast charging is only carried out if the previous checks have been carried out correctly. How to charge the battery correctly? So, the initial voltage is 0.8 V or a little more. Current flow begins. It is carried out smoothly and carefully for 2-4 minutes until the desired level is reached. Optimal current level for Ni-MH and Ni-Cd batteries - 0.5-1.0 C, but sometimes it is recommended not to exceed more than 0.75.

It is important to determine in time the end of the fast phase in order to avoid damaging the battery. The most reliable, in this case, is the dv method, which is used differently when charging nickel-cadmium and Ni-MH batteries. For Ni-Cd, the voltage becomes increasingly higher and falls towards the end of charging, so the signal for its end is the moment when U drops to a level of 30 mV.

Since in Ni-MH the drop in U of the charged elements is much less pronounced, in this case the dv=0 method is used. A period of time of 10 minutes is detected, during which the battery U remains stable - that is, with a zero voltage fluctuation threshold set.

Finally, there is a short recharging phase. Current - within 0.1-0.3 C, duration - up to half an hour. This is necessary to ensure that the battery is fully charged, as well as to equalize the charge potential in it.

An important point (this also applies to charging Ni-Cd batteries): if it is carried out immediately after fast charging, be sure to cool the battery for several minutes: the heated element is unable to accept the charge properly.

In addition to fast charging, there is also drip charging, which is produced by low currents. Some people believe that it “extends the life” of batteries, but this is not so. In essence, trickle charging is no different from the effect of a standard charger without “serious” adjustment of the current indicators. Any battery, if it is not used, sooner or later loses its accumulated energy, and it will still need a full charging process, regardless of its duration and “labor intensity”. This charging process is also attractive for many because the current indicators here do not need to be recorded due to their smallness. However, only a serious approach to the use of “smart” chargers can “extend the life” of batteries. As well as their proper storage, taking into account the characteristics of a particular type of battery.

Temperature factor and storage conditions

Modern chargers are equipped special system"assessment" of conditions environment, including temperature factors. Such a “charger” can determine for itself whether to charge under certain conditions or not. It has already been mentioned that the efficiency level inside the battery is highest at the beginning of the process, when hydride batteries do not heat up so much. At the end of the charging process or closer to it, the efficiency drops sharply, and all the energy, turning into heat due to exothermic chemical reactions, is released outside. It is important to stop charging the Ni-MH battery in time. And, if possible, get the latest charger that will accurately control this process.

Currently, all chargers, including CD batteries, can be charged with current up to 1C with the establishment of standards air cooling. The optimal temperature of the room in which charging is carried out is 20°C. It is not recommended to start the process at temperatures less than +5 and more than 50°C.

The unique thing about Ni-Cd is that it is the only type of cell that will not suffer if stored completely discharged, unlike Ni-MH. For better current delivery, it is recommended to charge nickel-cadmium batteries immediately before use. Also, after long-term storage, they require a “boost”: the Ni-Cd battery should be fully charged and discharged within 24 hours for optimal operation.

Nickel-metal hydride cells, unlike their predecessors, can easily fail when deeply discharged. Therefore, they should only be stored charged. In this case, the voltage should be checked regularly every two months. Its minimum level should always remain 1 V, and if it drops, recharging is necessary.

A new Ni-MH battery must be fully charged and discharged three times before use, then immediately placed on the “base” for 8-12 hours. Later, there will be no need to keep it on charge for a long time - remove it immediately after indicating a special indicator on the charger.

Although all these batteries have long been replaced by more capacious ones based on lithium, they are still actively used today. This is both more familiar and much cheaper. Besides, lithium batteries They work much worse at low temperatures.

For normal operation of any battery, you must always remember "The Three P's Rule":

1. Don't overheat!
2. Do not recharge!
3. Do not overdischarge!

You can use the following formula to calculate the charging time for a NiMH or multi-cell battery:

Charging time (h) = Battery capacity (mAh) / Charger current (mA)

Example:
We have a battery with a capacity of 2000mAh. The charging current in our charger is 500mA. We divide the battery capacity by the charging current and get 2000/500=4. This means that at a current of 500 milliamps, our battery with a capacity of 2000 milliamp hours will charge to full capacity in 4 hours!

And now in more detail about the rules that you need to try to follow for the normal operation of a nickel-metal hydride (Ni-MH) battery:

1. Store Ni-MH batteries with a small amount of charge (30 - 50% of its rated capacity).
2. Nickel-metal hydride batteries are more sensitive to heat than nickel-cadmium (Ni-Cd) batteries, so do not overcharge them. Overloading can negatively affect the battery's current output (the battery's ability to hold and release its accumulated charge). If you have a smart charger with " Delta Peak"(interrupting the battery charge when the voltage peak is reached), then you can charge the batteries with virtually no risk of overcharging and destruction of them.
3. Ni-MH (nickel metal hydride) batteries can (but not necessarily!) be “trained” after purchase. 4-6 charge/discharge cycles for batteries in a high-quality charger allows you to reach the limit of capacity that was lost during the transportation and storage of batteries in questionable conditions after leaving the manufacturing plant. The number of such cycles can be completely different for batteries from different manufacturers. High-quality batteries reach their capacity limit after only 1-2 cycles, while batteries of questionable quality with artificially high capacity cannot reach their capacity limit even after 50-100 charge/discharge cycles.
4. After discharging or charging, try to let the battery cool to room temperature (~20 o C). Charging batteries at temperatures below 5 o C or above 50 o C can significantly affect battery life.
5. If you want to discharge a Ni-MH battery, do not discharge it to less than 0.9V for each cell. When the voltage of nickel batteries drops below 0.9V per cell, most chargers with "minimal intelligence" cannot activate the charge mode. If your charger cannot recognize a deeply discharged cell (discharged less than 0.9V), then you should resort to using a “dumb” charger or connect the battery for a short time to a power source with a current of 100-150mA until the battery voltage reaches 0.9V.
6. If you constantly use the same battery assembly in an electronic device in recharging mode, then sometimes it is worth discharging each battery from the assembly to a voltage of 0.9V and recharging it full charge in an external charger. This complete cycling procedure should be performed once every 5-10 battery recharging cycles.

Charging table for typical Ni-MH batteries

The data in the table is valid for completely discharged batteries

The process of charging Ni-Mh batteries in aircraft modeling is slightly different from the generally accepted one. Typically, the modeler charges the batteries before heading out to the field by charging the battery overnight. But it happens that when quickly packing for flights, the batteries on board or equipment turn out to be completely or partially discharged and there is simply no time to charge them with a regular “night” charger.

The advantages of modern NiMh batteries are the ability to charge them with high current, up to 1C, without consequences for its health. The only thing you need to pay attention to when charging is the temperature and final charge voltage. You can look at the simplest charger, it is not automated and the control of the full charge is controlled by hand to increase the temperature. You can also buy a charger for all types of batteries.

To protect the battery from overcharging, voltage control can be entrusted to an automatic machine, which will turn off the battery when a certain voltage is reached and will maintain the battery in a charged state. About such automatic charger for Ni-Mh and Ni-Cd and will be discussed in this article.

Diagram of a ni-mh battery charger

Developed by me and assembled on a breadboard charger for NiMh and Ni-Cd, the circuit is simple, all elements are available.

The threshold element in the circuit is the zener diode D1; it opens when the stabilization voltage is reached, thereby opening the key on the transistors and turning on the relay, which turns off the battery. The voltage divider on R1-R2 sets the upper threshold, upon reaching which the battery is turned off; for 5 hydride cells it is 7.2v (switch s1 is closed). When the battery is connected to R5, the voltage drops to the battery voltage, and since it is less than 7.2V, D1 is closed and the relay is de-energized, while its contacts are closed and charging occurs. When 7.2V is reached, the zener diode opens, the relay is activated and disconnects the battery.

The battery voltage keeps the zener diode open and the relay on, the relay contacts remain open - this happens for some time until the battery voltage drops below 7.1V, at which time the zener diode closes and the relay again connects the battery to charge. This process is constantly repeated. The LED signals the end of charging.

Purpose of other elements charger for Ni-Mh following:

• C1 - reduces the frequency of relay switching in the absence of a connected battery (a sign of the charger is the relay clicking without a connected battery).
• D2 - protects transistors from breakdown by reverse voltage arising in the relay coil.
• R5 with a power of at least 2w - sets the charging current and is selected to obtain the desired current (12v incandescent lamps can be used instead).
• S1 - switches modes for charging 5 can and 8 can batteries.
• S2 is an optional element; it serves to force the charger into charge mode.
• The relay I have is of an unknown brand, from the control unit of a store refrigerator.
• D1 - can be replaced with any other 2...4v zener diode.

This is what happened to me. I installed two LEDs for beauty.

Setting up the Ni-Mh charger

Trim resistors to the middle position, connect the charger to a 12...18v power source, the relay starts to click periodically, S1 is closed, connect ni-mh battery with a voltmeter connected to it. Using resistor R1, we ensure that the LED does not glow and control the voltage on the battery. When we reach 7.2V, we begin to turn R1 until the LED lights up and the relay clicks (it is advisable to perform this operation several times for more accurate positioning of the resistor). That's it, the setup for the 5-cell battery is complete.

We open S1 and do the same with the 8-can battery, only now we rotate R2 and the response threshold is 11.5...11.6v. R1 cannot be turned at this time! When charging 8 can batteries from a 12V source, the LED will not light up, there are two options: Either hang the LED on a separate pair of relay contacts, or increase the charger supply voltage to 15...18V.

Similarly, you can configure this charger to work with Ni-Cd batteries.

In the process of charging with a current of about 500 mA, heating of Ni-Mh batteries with a capacity of 1700 mA was not noticed, as happens when charging with a low current overnight, while the battery is fully charged, giving up almost all of its capacity upon further discharge.

You can set the final voltage quite accurately and with some simple modifications you can adapt two such chargers for two cans

B Most people who use batteries in their portable equipment know firsthand that this is a very fastidious power source, especially when it comes to nickel-metal hydride batteries (hereinafter referred to as NiMH)

These batteries have a limited lifespan both in time and in the number of discharge-charge cycles. The charger with all the mechanisms involved in this process also plays an important role.

B Most users of NiMH batteries are not aware of the intricacies of working with these batteries and are often disappointed in their use, not realizing that short term and low capacity is the result of improper battery operation

The chargers that are included in the basic kit (see photo below) are, so to speak, “night lights,” i.e. they have the simplest scheme without stabilization, without shutdown function, discharge function, temperature control, delta shutdown, etc.

Actually, until recently, I only used such chargers, which created nothing but trouble for me when using batteries. Service life was minimal

So I decided to search online for chargers at auctions. Basically there were “night lights”, as well as modern intelligent NiMH chargers, microprocessor Chinese devices with all the necessary functions, but their price of 1500-3000 rubles did not suit me and by chance I came across a very old German charger Conrad VC4+1 for NiCd and NiMH + 1 crown 9v

IN There is no information on this charger on the Internet, only rare links to pages from German auctions.

Without thinking for a long time, I decided to buy this lot and after 2 weeks I had this charger in my hands. The price of the lot was 370 rubles and 250 rubles delivery, a total of 620 rubles for an ancient German charger with unknown qualities

Conrad VC4+1 Specifications and Features

After a short observation with a multimeter, as well as searching on the Internet, studying the inscriptions on back cover devices I can say the following:

– charging current adjustable from 15 mA to 4000 mA
– two charging modes: “fast 85 minutes with a current of 1C” and “drip current of 0.1C”
– automatic discharge before charging up to 0.9V
– temperature sensor on the positive contact of the device
– automatic shutdown with subsequent charge support
– charging with pulsed current and pulses
– socket for charging batteries of the “crown” type
– type of batteries NiCd and NiMH, sizes from AAA to D size
– preliminary drip charging of a completely dead battery
– four independent channels

This is what the original charger looks like, which I bought at an auction, I really wanted to hold it in my hands and use such an interesting device

I haven’t figured out the delta shutdown and the operation of the temperature sensor yet. Below I want to provide photos of the charger boards

As you can see, a hand with a soldering iron had already looked in here; apparently, the charger was under repair. Basically, as I understand it, the power points of the device were simply soldered

German technologies were already available to everyone a dozen years ago and people used fairly smart chargers. As you can see and the diagrams, this is far from a night light

I am very pleased with the purchase and consider myself very lucky. This is a very rare charger in Russia, very old, but has functionality that is quite enough to keep your batteries in perfect condition.

G I consider the main advantages to be the ability to regulate the charging current from 15 mA to 4000 mA, as well as automatic shutdown after 16 hours or 85 minutes (I did not notice a shutdown by voltage or delta) and support for full charge with pulses with a frequency of 1 in 20 seconds.

If anyone suddenly wants to buy such a charger for themselves, try searching on German online auctions. In Germany, this charge was quite common and well known.

Recently, smart chargers for NiMH batteries from LaCrosse, models bc-900, BC 1000 and technoline bc-700, have appeared on the market, as well as Chinese counterfeits and parodies. Such chargers differ both in appearance and in their operating principle and, of course, functionality. The price of smart chargers still remains high for the average user - 1500-3000 rubles, depending on the model and manufacturer


These devices promise to carry out all the necessary measures to ensure that NiMH serves its owner for a long time and faithfully, here is, for example, a list of features of the most expensive and functional models

TEST– full charge of the battery, followed by a full discharge to determine the actual capacity (indication on the screen), then full charge of the batteries
CHARGE– independent charge of each channel with a selected current (200/500/700/1000 mA)
DISCHARGE– battery discharge (adjustable) to reduce memory effect
TRAINING– up to 20 charge/discharge cycles up to full recovery battery capacity

Works with all NiCd and NiMH “AA” and “AAA” batteries
LCD screen shows information for each battery separately
Can charge “AA” and “AAA” size batteries simultaneously
Detects bad batteries
Battery overheat protection
Possibility to select the charging current power for each channel
Automatically switches to trickle charging when charging is complete to ensure maximum battery capacity
Charging automatically starts with a current of 200mA (optimal for extending battery life)

TO As you can see, the functionality really differs significantly from conventional “night lights,” but the next question arises: is such a smart charger worth $100?

Personally, since I already bought a Conrad VC4+1 and loved this charger for its antique charm and originality, now I will refuse to buy a LaCrosse, which in principle I do not regret. Because Many people don’t like the charging of the LaCrosse - for example, the rough regulation of the charge current.

During the operation of rechargeable batteries, it is recommended to periodically monitor their electrical capacity, measured in ampere-hours (Ah). To determine this parameter, it is necessary to discharge a fully charged battery with a stable current and record the time after which its voltage decreases to set value. To assess the condition of the battery more fully, it is necessary to know its capacity at different values ​​of discharge current.

H To measure the capacity of my batteries, I use a voltmeter that is connected in parallel with a resistance that is the load on the battery. I choose the resistance according to the average current of the consumer in which the battery is planned to be used - this is very important point for calculating capacity, since under different conditions of power consumption - the capabilities of batteries vary greatly. Thus, I take a fully charged battery, load it with the current I need and observe when the voltage on the battery under load drops to 1 - 0.9 volts, then I make a calculation by multiplying the discharge current by time. For example, the battery was discharged with a current of 500 mA for 2 hours, which means the battery capacity is 1000 mAh

If I would like to comment on your comments, I would like to hear feedback from owners of smart chargers, share your experience of using them, what disadvantages do they have?