Charger for nimh nicd batteries diagram. Homemade charger for aa batteries. Discharge process of nickel-cadmium batteries

How to charge Ni-Cd batteries, chargers, parameters

Today, Ni─Cd batteries are used in most portable tools and various electronic devices (cameras, players, etc.). However, recently there has been a tendency to replace them with lithium-ion batteries. In order for the battery of your equipment to serve for a long time, nickel-cadmium batteries must be used correctly, charged in a timely manner, and discharge-charge cycles must be carried out from time to time. Then the Ni─Cd battery will serve you for a long time. Today we will talk about how to charge nickel-cadmium batteries according to all the rules.

Types of chargers for nickel-cadmium batteries

Today on the market there are two main groups of devices designed to charge nickel-cadmium batteries:

• Automatic chargers;
• Reversible pulse memory.

Automatic charger for Ni-Cd batteries. These are simple and affordable devices. They are less complex and come in a design that allows you to charge two or 4 batteries at a time. To start charging nickel-cadmium batteries, insert the batteries into the charger. Use the charger switch to set the number of batteries to charge and connect the device to the network.

As a rule, an automatic charger for nickel-cadmium batteries has the following color indication. The red color of the indicator indicates that the batteries are being charged. To discharge the batteries, the device has a “discharge” switch. During the discharge process, the indicator will turn yellow. After the discharge has passed, the charger for Ni─Cd batteries will start charging itself. The green color of the indicator indicates that the discharge-charge cycle is complete.

In this case, we are talking about charging nickel-cadmium batteries separately. If these are batteries for a screwdriver or other power tool, then they come with a standard charger that allows you to charge the entire battery at once from a household electrical outlet.

Reversible pulse memory. These devices are more complex and more expensive than models of the first type. Manufacturers usually position them as professional. Such a charger for Ni─Cd batteries cyclically discharges and charges at different time intervals.

The battery is installed, the mode is set and work starts. The indicator will signal that charging is complete. With the help of such chargers, you can not only charge nickel-cadmium batteries, but also maintain them in working condition. An example is the widely used universal charger.

Nickel-cadmium batteries are less demanding on the characteristics of the charger than. But you can’t save on it, since cheap devices shorten the life of the batteries. Now, let's figure out how to charge a nickel-cadmium battery.

The process of discharging and charging Ni─Cd batteries

Discharge process of nickel-cadmium batteries

For this type of battery (as well as for others), the discharge characteristics depend on the characteristics of the battery, which determine its internal resistance. Among these features, one can note the structure and thickness of the electrodes. The discharge characteristics are affected by:

• thickness of the separator and its structure;
• assembly density;
• volume of electrolyte;
• some design characteristics.

When operating under conditions of prolonged discharge, disk batteries with pressed electrodes of large thickness are used. For them, the discharge curve shows a constant slow decrease in voltage to a value of 1.1 volts. The discharge capacity in the case of further discharge to 1 volt is equal to 5 to 10 percent of the nominal value. A feature of this type of battery is a significant drop in discharge capacity and voltage when the current increases to 0.2*C. The explanation for this is quite simple: the impossibility of discharging the active mass evenly throughout the entire electrode.

If you reduce the thickness of the electrodes and increase their number to four, then the discharge current for a disk battery can be increased to 0.6*C.

Rechargeable batteries with cermet electrodes have low internal resistance and high energy characteristics. Their discharge characteristics show a noticeably lower voltage drop. For this type of battery, the voltage value remains above 1.2 volts until the output is 0.9 of the rated capacity. With further discharge and a voltage drop from 1.1 to 1 volt, about 3 percent of the rated capacity is released. It is allowed to discharge this type of battery with discharge currents of up to 3-5*C.

Cylindrical Ni-Cd batteries can be discharged at higher currents. They use roll electrodes, which allows them to be discharged with a maximum current of 7-10*C.

In the images below you can see the effect of discharge current and temperature on the value of the discharge capacity.

The highest capacity value is achieved at a temperature of 20 degrees Celsius. The capacity practically does not decrease if the temperature is increased. But when the OS temperature is below zero, the value of the discharge capacity drops in proportion to the increase in the discharge current. The decrease in capacity at low temperatures is explained by a decrease in discharge voltage due to an increase in resistance.

The increase in resistance is explained by the limited volume of electrolyte in a sealed battery. The composition and concentration of the electrolyte greatly affects the characteristics. The temperature of formation of the solid phase directly depends on them. This can be crystalline hydrates, ice, salts, etc. When the electrolyte is frozen, there is no discharge at all. The performance of Ni─Cd is in most cases limited to a temperature of minus 20 degrees Celsius. In some cases, when adjusting the composition of the electrolyte and its concentration, manufacturers produce models of Ni─Cd batteries that are operational at minus 40.

Charging process of nickel-cadmium batteries

In the process of charging nickel-cadmium batteries, an important point is to limit excess charge. This is an important point, since when nickel-cadmium batteries are charged, the pressure inside them increases. During charging, oxygen is released and the current utilization rate gradually decreases. In the graph below you can see the dependence of the discharge capacity on the charging speed. Data given is for cylindrical batteries.

For a battery to be fully charged, it needs to reach 160 percent of its rated capacity. Charging of nickel-cadmium batteries should be carried out in the temperature range 0-40 C. The recommended interval is 10-30 C. As the temperature at the negative electrode decreases, oxygen absorption decreases and pressure increases. As a result, if there is a strong overcharge, the emergency valve may open due to an increase in pressure. As the temperature increases, the potential increases and oxygen is released very early on the positive electrode, which shortens the charging process in normal mode.

If the temperature is kept stable, the charging process is greatly influenced by the current. Its increase causes an increase in the rate of oxygen release. But the rate of its absorption does not change, since it depends on the design features of the battery. Gas absorption is influenced by the layout, structure, thickness of the electrodes, separator material, and electrolyte volume.

In particular, the greater the density of the electrode arrangement and the smaller their thickness, the faster the charging occurs. Therefore, cylindrical batteries charge at a high speed. On the charge curves you can see that for such models of Ni─Cd batteries at a current of 0.1─1C, the charging efficiency remains almost unchanged. A decrease in charge current causes a significant decrease in the capacity that the battery will give up when discharged.

The standard charging mode is considered to be as follows. A nickel-cadmium battery with a voltage of 1 volt is charged in approximately 14-16 hours with a current of 0.1C. Details of the charging process are specified by battery manufacturers. They may differ due to design features or increased active mass loading (this is done to increase capacity). For Ni-Cd batteries, constant current charging can be used throughout the entire time. A scheme can be used to stepwise or smoothly reduce the charging current during the process. This allows long-term charging without the risk of damaging the battery. In such modes, the charging current at the first stage can significantly exceed the value of 0.1*C.

There is often a need to increase the charging speed. Manufacturers are solving this problem by producing batteries that can efficiently charge at high currents. In this case, various control systems are used to protect the nickel-cadmium battery from excessive overcharging. These monitoring systems may contain both the batteries themselves and a charger for nickel-cadmium batteries.

For cylindrical Ni-Cd batteries, it is recommended to charge with a constant current of 0.2 C for 6-7 hours. A current mode of 0.3 C for 3-4 hours is also used. In the latter case, control over the charging time is mandatory. If an accelerated charge is carried out, then the recharge should be up to 120-140 percent of the capacity and no more. In this case, the Ni─Cd battery gains a discharge capacity no less than the nominal one. To operate in accelerated modes, manufacturers even offer batteries that can be charged in one hour. This mode uses various means of temperature and voltage control to ensure that nickel-cadmium batteries do not degrade as a result of sudden increases in pressure.

This time we will talk about designing a simple USB charger for Ni-Cd and Ni-Mh batteries.

The circuit of a fairly good charger is simple and can be implemented with a budget of only 20 rubles. This is already cheaper than any Chinese charger. The heart of our charger is the well-known LM317 linear stabilizer chip.

The input of the circuit is supplied with a voltage of 5 V from any USB port.

The microcircuit stabilizes the voltage to 1.5 V. This is the voltage of a fully charged Ni-Mh battery.

And the device works very simply. The battery will be charged with a voltage of 1.5-1.6 Volts from the microcircuit. Resistor R1, acting as a current sensor, simultaneously limits the charging current. By selecting it, the current can be reduced or increased.

When a battery is connected to the output of the circuit, a voltage drop is formed across resistor R1. It is enough to trigger a transistor, the collector circuit of which has an LED connected to it. The latter lights up and will go out as the battery charges until it turns off completely. This will happen at the end of the charging process.

Thus, the diode lights up when the battery is charging and goes out when the latter is fully charged. At the same time, as the battery charges, the current will decrease, and at the end its value will be 0.

It follows from this that overcharging and failure of the battery is impossible.

The LM317 chip operates in linear mode, so a small heat sink will not hurt. Although at a current of 300 mA the heating of the microcircuit is within normal limits. It is advisable to select an LED with a minimum operating voltage. Color is absolutely not important. Instead of BC337, it is allowed to use any low-power reverse conduction transistor, even on KT315. The desired power of resistor R1 is 0.5-1 Watt. All remaining resistors are 0.25 and even 0.125 Watts. Since the voltage range is very narrow, even resistor errors can affect the operation of the circuit. Therefore, it is strongly recommended to replace resistor R2 with a multi-turn resistor of 100 Ohms.

With its help, you can very accurately adjust the desired output voltage.

First you need to find all the necessary components, as well as a slot for batteries.

The device can charge batteries of almost any standard if you adapt the appropriate slot. When assembling, you do not need to use a printed circuit board. Installation is done using a hinged method. The components are glued under the battery slot and filled with hot glue, since the circuit is very reliable in operation.

The assembled device looks something like this:

But it can look much better.

You just need to choose an LED with the lowest possible glow voltage, otherwise it may not light up at all. This scheme can charge several batteries, but it is recommended to use it only to charge one.

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

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 fully charging it 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

S. Rychikhin

I suggest the option of a simple charger. To assemble it, you can use parts from old domestic equipment.

The device is an adjustable, stabilized current source that allows you to maintain a given value of the charging current throughout the entire battery charging process. The device diagram is shown in Fig. 1.

The mains voltage lowers transformer T1, rectifies the diode bridge VD1 and smoothes capacitor C1. The rectified and smoothed voltage is supplied to a current stabilizer assembled on transistors VT1, VT2, zener diode VD2 and resistors R2-R6.

The principle of operation of the current stabilizer is very simple: a conventional voltage stabilizer is assembled on transistor VT1, the base of which is supplied with a reference voltage from the zener diode VD2, and resistors R4-R6 are included in the emitter circuit, which set the battery charging current. Since the voltage at the base of transistor VT1, and therefore at these resistors, is stabilized, the current flowing through them and the emitter-collector section of transistor VT1 is stable. Consequently, the base current of transistor VT2, which regulates the charging current of the batteries, is also stable. Resistors R5 and R6 carry out coarse and fine adjustments of the charging current, respectively. The charging current is controlled according to the readings of the PA1 milliammeter. Diode VD3 prevents the connected batteries from discharging when the device is turned off. The HL1 LED indicates that the charger is connected to the network.

In the device, instead of those indicated in the diagram, you can use any transistors of the KT315 (VT1), KT814, KT816 (VT2) series. It is advisable to install transistor VT2 on a small heat sink with an area of ​​8... 10 cm2. The permissible forward current of diodes VD1 and VD3 must be no less than the maximum battery charging current. Zener diode VD2 - any voltage 10...12 V. Fixed resistors - MLT-0.5, variable - any. Capacitor C1 - any oxide capacitor, with a capacitance not less than that indicated in the diagram and a rated voltage not less than the amplitude value of the voltage on the secondary winding of transformer T1.

Transformer - frame scan output transformer of TVK-70L2 tube TV. Its magnetic circuit must be reassembled end-to-end by removing the paper insulating gasket in the gap between the ends of the magnetic circuit plates. The primary winding remains, but the secondary must be rewound. The primary winding contains 3000 turns of PEV-1 wire with a diameter of 0.12 mm, the secondary (rewind) winding contains 330 turns of PEV-2 wire with a diameter of 0.23 mm. The cross-section of the magnetic circuit is 18x23 mm. The voltage on the secondary winding of the modified transformer should be within 22...25 V. DC milliammeter - any with a total deviation current of 50 mA.

All parts of the charger, with the exception of transformer T1, LED HL1, variable resistors R5 and R6, milliammeter PA1 and control transistor VT2, are assembled on a printed circuit board, the drawing of which is shown in Fig. 2.

The appearance of the assembled device is shown in Fig. 3.

The charging algorithm is very simple: discharged batteries are connected to a charger and charged for 16 hours. The charging current is selected based on the nominal capacity of the battery. To do this, the battery capacity (in Ah) is multiplied by 100 and the charging current is obtained in milliamps. For example, for a TsNK-0.45 battery the charging current is 45 mA, and for a 7D-0.125 battery it is 12.5 mA.

An error-free assembled device does not need adjustment.
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