Battery charger from laptop power supply. A battery charger from a power supply is a useful and inexpensive device in half an hour

We are interested in the second type of chargers, because most vehicles are used for short distances, i.e. the car was started, driven a certain distance, and then turned off. Such operation leads to the car battery running out of charge quite quickly, which is especially typical in winter. Therefore, such stationary units are in demand, with the help of which you can very quickly charge the battery, returning it to working condition. The charging itself is carried out using a current of about 5 Amps, and the voltage at the terminals ranges from 14 to 14.3 V. The charging power, which is calculated by multiplying the voltage and current values, can be provided from the computer power supply, because its average power is about 300 -350 W.

Converting a computer power supply into a charger

The goal of the project is to build a universal regulated power supply that can be used to charge nickel or lead batteries, and not only car batteries. The charger will allow you to charge batteries with voltages from 4 to 30 V.

The first thing you will need to implement this project is a body. Suitable, for example, from a Chinese inverter 12-220 V. It is monolithic and made of aluminum.

You can take any other suitable size, for example, from a computer power supply.

The second is a network step-down switching power supply.

The output voltage of the unit used in this project is 19 V with a current of about 5 A.

This is a cheap universal laptop adapter. It is built on a PWM controller from the UC38 family, has stabilization and short circuit protection.

The third is a digital or analog voltammeter. The volt-ampere meter shown here was taken from a Chinese voltage stabilizer (30V, 5A).

Fourth is a few electronic components such as terminals and power cord.

The device is shown schematically in the following picture:

Now take a look at the power supply diagram. The TL431 chip is located near the optocoupler. It is this microcircuit that sets the output voltage. There are only 2 resistors in the harness, and by selecting them you can obtain the desired output voltage.

In this diagram it is designated as R13. In the existing block, its resistance is 20 kOhm. You need to connect a 10 kOhm variable in series to this resistor, approximately as in the picture:

By rotating the variable resistor, it is necessary to achieve an output voltage of around 30 V. Then you need to turn off the “variable” and measure its resistance, at which the output voltage was 30 V, and replace R13 with a resistor with a selected resistance. The result was approximately 27 kOhm. This completes the adapter conversion.

To limit the current, the PWM control method will be used, since the output current from the adapter from the laptop is very small.

In general, this circuit is a PWM voltage regulator without a separate current limiting unit. This square wave generator is based on the NE555 timer, which operates at a specific frequency. Diodes serve to constantly change the charging and discharging time of the frequency-setting capacitor. Thanks to this phenomenon, it is possible to change the duty cycle of the output pulses. Since the power transistor operates in switch mode (it is either open or closed), a fairly high efficiency can be observed. A variable resistor regulates the duty cycle of the pulses.

The required charging current can be set by changing the voltage, that is, by rotating a multi-turn variable resistor.

Literally any transistor will do. An n-channel field-effect transistor with a voltage of 60 V and a current of 20 A is used here.

Due to the key operating mode, its heating will not be great, unlike linear circuits, but heat removal will not interfere. This project uses an aluminum casing as a heat sink.

The PWM regulator circuit is really simple, economical and reliable, but also needs a little modification. The fact is that, according to the documentation, the NE555 microcircuit has a maximum permissible supply voltage of 16 V. And at the output of the converted adapter, the voltage is almost 2 times higher, and when the circuit is connected, the timer will definitely burn out.

There are several solutions to this situation. Take a look at 3 of them:

1. Use a linear regulator, say 5 to 12 V from the 78xx family or

build a simple stabilizer according to the following scheme:

The simplest solution would be to introduce a linear stabilizer into the circuit, for example, 7805. But it should be remembered that the maximum supply voltage, depending on the manufacturer, varies from 24 to 35 V. This project uses a KA7805 stabilizer with a maximum input voltage of 35 V according to the datasheet. If you cannot get such a chip, you can build a stabilizer from just three parts.

After assembly, you need to check the PWM regulator.

On the adapter board there are 2 active components that are subject to heating - the power transistor of the high-voltage circuit of the converter and a dual diode at the output of the circuit. They were soldered and attached to an aluminum housing. In this case, they need to be isolated from the main body.

The front panel is made of a piece of plastic.

The adapter circuit has short circuit protection, but does not have reverse polarity protection. But this can be fixed.

Since the adapter output voltage exceeded 30 V during testing, the digital voltammeter burned out. Do not exceed the voltage by even 1 V. You will have to do without it. The charge current will be shown using a multimeter.

The charger turned out to be good - it also charges batteries from a screwdriver without any problems.

Attached files:

How to make a simple Power Bank with your own hands: diagram of a homemade power bank

A rechargeable battery is a device that wears out and is discharged during operation. To charge the battery, a special device is used, which you can buy or make yourself. We will tell you below how to build a charger for a car battery from a computer and laptop power supply.

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How to charge a battery from a computer power supply?

The cost of high-quality chargers is high. Therefore, many car owners decide to convert the ATX power supply from a stationary PC into a charger. This procedure is not particularly complicated, but before you begin the task and convert the power supply to a charger that can charge a car battery, you should understand the requirements for the charger. In particular, the maximum voltage level supplied to the battery should be no more than 14.4 volts to prevent rapid battery wear.

User Vetal in his video showed how you can convert a power supply into a charger.

Getting ready to complete the task

To build a homemade charger from a computer power supply for 200W, 300W or 350W (PWM 3528), you will need the following materials and tools:

• crocodile clips for connecting to the battery;
• a resistor element of 2.7 kOhm, as well as 1 kOhm and 0.5 W;
• soldering iron with tin and rosin;
• two screwdrivers (Phillips and flat head);
• resistor elements of 200 Ohm and 2 W, as well as 68 Ohm and 0.5 W;
• regular 12V machine relay;
• two 25V capacitor elements;
• three 1N4007 diodes for 1 ampere;
• LED element (any color, but green is better);
• silicone sealant;
• voltammeter;
• two flexible copper wires (1 meter each).

You will also need the power supply itself, which must have the following characteristics:

• output voltage - 12 volts;
• rated voltage parameter - 110/220 V;
• power value - 230 W;
• maximum current parameter - no higher than 8 amperes.

Step-by-step instruction

The procedure for charging a machine battery is carried out under voltage, the value of which is from 13.9 to 14.4 volts. All stationary units operate with a voltage of 220 V, so the primary task is to reduce the operating parameter to 14.4 V. The charging device is based on a TL494 (7500) microcircuit; if it is not available, an analogue can be used. The microcircuit is needed to generate signals and is used as a driver of a transistor element designed to protect the device from increased current. On the additional power supply board there is another circuit - TL431 or another, similar, designed to adjust the output voltage parameter. There is also a resistor element for adjustment, with which you can adjust the output voltage in a narrow range.

Learn more about how to convert a computer power supply into a charger for a car battery from the video published by the Soldering Iron TV channel.

To convert a power supply from a computer into a car charger with your own hands, read the diagram and follow the instructions:

1. First, you need to remove all unnecessary components and elements from the ATX computer power supply, after which the cables are unsoldered from it. Use a soldering iron to avoid damaging the contacts. It is necessary to remove the 220/110 volt switch with the cables connected to it. By removing the switch, you can prevent the possibility of the PSU from burning out if you accidentally switch it to 110V.
2. Then unnecessary cables are unsoldered from the device and removed. Remove the blue wire connected to the capacitor element and use a soldering iron. In some power supplies, two wires are connected to the capacitor; both should be removed. Also on the board you will see a bunch of yellow cables with a 12 volt output, there should be four of them, leave them all. There should also be four black wires here, they should also be left, since this is ground or ground. We need to leave one more green wire, all the rest are removed.
3. Pay attention to the diagram. Using the yellow wiring, you can find two capacitor elements in a 12 volt circuit. Their operating voltage parameter is 16 V, so immediately remove them by desoldering and install two capacitors at 25 V. The capacitor elements swell and become inoperative. Even if they are intact and seem to be working, we recommend replacing them.
4. Now we need to complete the task so that the power supply is automatically activated every time it is plugged into a household network. The bottom line is that when the power supply is installed in a computer, it is activated if certain contacts at the output are closed. The surge protection needs to be removed. This element is designed to automatically disconnect the computer's power supply from the household network in case of overvoltage. It must be removed, because for optimal operation of the PC, 12 volts are required, and for the charger to function, 14.4 V is needed. The protection installed in the unit will perceive 14.4 volts as a voltage surge, as a result of which the charger will turn off and will not be able to charge the battery car.
5. Two pulses pass to the optocoupler on the board - actions from protection against voltage surges, shutdown, as well as activation and deactivation. There are a total of three optocouplers in the circuit. Thanks to these elements, communication is carried out between the input and output components of the block. These parts are called high voltage and low voltage. To prevent the protection from tripping during voltage surges, you should close the contacts of the optocoupler; this can be done using a jumper made of solder. This action will ensure uninterrupted operation of the power supply when it is connected to a household network.
6. Now we need to ensure that the outgoing voltage is 14.4 volts. To complete the task, you will need a TL431 board installed on an additional circuit. Thanks to this component, the voltage is adjusted on all channels coming from the device. To increase the operating parameter, you will need a tuning resistor element located on the same circuit. With it, you can increase the voltage to 13 volts, but this is not enough for optimal operation of the charger. Therefore, the resistor connected in series with the trimming component must be replaced. It should be removed and replaced with a similar part, the resistance of which should be below 2.7 kOhm. This will increase the range of adjustment of the output parameter and obtain the required 14.4 volts.
7. Remove the transistor element installed next to the TL431 board. This part may negatively affect the functionality of the circuit. The transistor will prevent the device from maintaining the desired output voltage. In the photo below you will see the element, it is marked in red.
8. In order for the device for charging the battery to have a stable output voltage, it is necessary to increase the operating parameter of the load along the channel where the voltage of 12 volts passed. There is an additional 5 volt channel, but it is not necessary to use it. To provide the load, you will need a resistor component, the operating resistance value of which will be 200 Ohms, and the power will be 2 W. A 68 Ohm part is installed on the additional channel, the power value of which is 0.5 W. Once the resistor elements are soldered, you can adjust the output voltage to 14.4 volts without requiring a load.
9. The output current should then be limited. This parameter is individual for any power supply. Our current value should be no more than 8 amperes. To achieve this, it will be necessary to increase the rating of the resistor component installed in the primary winding circuit, adjacent to the transformer device. The latter is used as a sensor designed to determine the overload value. To increase the nominal value, the resistor must be replaced; instead, a component with a resistance of 0.47 Ohms is mounted, and the power value will be 1 W. The resistor is carefully soldered off and a new one is soldered in its place. After completing this task, the part will be used as a sensor, so the output current will be no more than 10 amperes, even if a short circuit occurs.
10. To ensure protection of the machine battery from incorrect polarity when connecting a homemade charging device, an additional circuit is installed in the device. We are talking about a board that you have to make yourself, since it is not included in the block itself. To develop it, you will need a prepared 12-volt relay, which should have four terminals. You will also need diode components with a current strength of 1 ampere. Alternatively, parts 1N4007 can be used. The circuit must be supplemented with an LED, which will indicate the status of the charging process. If the light is on, then the car battery is connected to the charger correctly. In addition to these components, you will need a resistor element whose operating resistance will be 1 kOhm and power 0.5 W. The operating principle of the circuit is as follows. The battery is connected via cables to the output of a homemade charger. The relay is activated thanks to the energy remaining from the battery. After the element is triggered, the charging process from the charger begins, as evidenced by the activation of the diode light bulb.
11. When the coil is deactivated, a voltage surge occurs as a result of the electromotive force of self-induction. To prevent its negative impact on the operation of the charging device, two diode components must be added to the board in parallel. The relay is fixed to the power supply radiator device using sealant. Thanks to this material, it is possible to ensure elasticity, as well as immunity of parts to thermal loads. We are talking about compression and expansion, heating and cooling. When the glue has dried, the remaining components must be connected to the relay contacts. If there is no sealant, ordinary bolts are suitable for fixation.
12. At the last stage, wires with “crocodiles” are connected to the block. It is better to use cables of different colors, for example, black and red or red and blue. This will prevent polarity confusion. The length of the wire will be at least one meter, and their cross-section should be 2.5 mm2. Clamps are connected to the ends of the cables, designed for fixing to the battery terminals. To fix the wires on the body of a homemade charging device, two holes of the appropriate diameter are drilled in the radiator device. Two nylon ties are threaded through the resulting holes, with the help of which the cables will be fixed. An ammeter can be installed in the charger; it will allow you to control the current level. The device is connected in parallel to the power supply circuit.
13. All that remains is to test the performance of the self-assembled memory.

1. The jumper on the diagram is marked in red 2. Transistor element on the board that needs to be removed 3. Resistor element in the primary circuit to be replaced 4. Scheme for assembling a board designed to protect the power supply in case of polarity violation

Charger from laptop power supply

You can build a charging device from a laptop power supply.

You cannot connect the power supply directly to the battery terminals.

The output voltage varies around 19 volts, and the current value is about 6 amperes. These parameters are enough to charge the battery, but the voltage is too high. There are two ways to solve the problem.

Without reworking the power supply

You will need to connect the so-called ballast in the form of a powerful optical lamp in series with the car’s battery. The light source will be used as a current limiter. A simple and affordable option. One contact of the lamp is connected to the positive output of the laptop power supply, and its second contact is connected to the positive of the battery. The negative from the power supply is connected directly to the negative terminal of the battery via a wire. After this, the power supply can be connected to a household network. The method is very simple, but there is a possibility of failure of the lighting source. This will cause both the battery and the unit to fail.

With modification of the power supply

You will need to lower the power supply voltage parameter so that the output voltage is about 14-14.5 V.

Let's look at the process of manufacturing and assembling a charging device using the example of a power supply from a Great Wall laptop:

1. First you need to disassemble the power supply housing. When disassembling, do not damage it, as it will be used for further use. The board, which is located inside, can be connected to a voltmeter to find out exactly what its operating voltage is. In our case it is 19.2 volts. A board built on TEA1751+TEA1761 chips is used.
2. The task of reducing the voltage is being performed. To do this, you will need to find a resistor element located at the output. We need a part that connects the sixth pin of the TEA1761 circuit to the positive terminal of the power supply. This resistor element should be desoldered using a soldering iron and its resistance should be measured. The operating parameter is 18 kOhm.
3. Instead of the dismantled element, a 22 kOhm trimmer resistor component is installed, but before soldering it should be set to 18 kOhm. Carefully solder the part so as not to damage other elements of the circuit.
4. Gradually lowering the resistance value, it is necessary to ensure that the output voltage parameter is 14-14.5 volts.
5. When you get the optimal voltage for charging the car battery, the soldered resistor can be unsoldered. Its resistance parameter is measured, in our case it is 12.37 kOhm. A constant resistor is selected based on this value or one close to it. We use two resistors of 10 kOhm and 2.6 kOhm. The ends of both parts are installed in a thermal chamber, after which they are soldered into the board.
6. We recommend testing the resulting circuit before assembling the device. The output voltage will be 14.25 volts, which is enough to charge the battery.
7. Let's start assembling the device. Connect the wires with clamps. Before soldering them, make sure that the polarity is maintained at the output. Depending on the laptop unit, the negative contact can be made in the form of a central wire, and the positive contact can be made in the form of a braid.
8. As a result, you get a device that can properly charge the battery. The amount of current during charging varies around 2-3 amperes. If this parameter drops to 0.2-0.5 amperes, then the charging procedure can be considered complete. For more convenient use, the charger is equipped with an ammeter, fixing it on the case. You can use an LED lamp that will tell the car owner that the charging process is complete.

The kt819a channel provided a video in which a charger made from a laptop PSU is examined in detail.

How to properly charge a battery with a homemade charger?

In order to prevent rapid battery failure, it is necessary to take into account certain nuances regarding proper recharging.

1. First, disconnect the battery terminals from the clamps. Remove the bolts that secure the battery retaining bar.
2. Remove the device from its mounting location and take it home or to the garage.
3. Clean the housing from dirt. Pay attention to the terminals themselves. If they have oxidation, they should be cleaned. Use a toothbrush or a construction brush; fine-grit sandpaper will do. The main thing is not to clean off the work plaque.
4. If the battery is serviceable, open all its cans and check the electrolyte level in them. The working solution must cover all sections. If this is not the case, then charging the battery may cause the boiling liquid to evaporate quickly, which will affect the functionality of the battery and its overall health. If necessary, add distilled water to the jars. Visually inspect the battery case for defects; sometimes fluid leakage is associated with cracks. If the damage is serious, the battery must be replaced.
5. Connect the clamps of the homemade charger to the battery terminals, observing the polarity. After this, the device can be connected to a household network. There is no need to unscrew the caps on the cans.
6. When the charging procedure is completed, check the electrolyte level and if everything is fine, tighten the cans. Install the battery in the car and make sure it is in working order.

Conclusion

The main advantage of the device is that the car battery will not be able to recharge during the charging process. If you forget to disconnect the battery from the charger, this will not affect its service life and will not lead to rapid wear. If you don't equip your charger with an LED indicator, you won't be able to tell whether the battery is charged or not.. Alternatively, you can approximately calculate the recharging time using the readings given by an ammeter connected to the charger. You can calculate it using the formula: the current value is multiplied by the charging time in hours. In practice, it takes about a day to complete the recharging task, provided that the battery capacity is 55 A/h. If you want to clearly see the charge level, then you can add dial or digital indicators to the device.