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A computer power supply unit (hereinafter referred to as PSU / PSU) costs about $ 30, and laboratory source food can cost you $ 100 or more! By modifying a cheap and often free ATX power supply that can be found in any unnecessary computer, you can make a good laboratory power supply yourself with good power, short circuit protection and a stabilized 5V output. On most PSUs, the other outputs are not stabilized.

Steps

Take an ATX PSU or disconnect it from a non-working computer.

Disconnect the cable from the power supply and turn off the switch on the rear panel (if there is one). Also, make sure you are not grounded and that the remaining current will not pass through you.

Remove the screws that secure the PSU to the computer and pull it out.

Cut off the connectors (leave a few centimeters of wire on the connectors so you can use them later for something else).

Discharge the power supply by leaving it unplugged for a few days. Some people connect a resistor (10 ohm) between the black and red wire (power cord on the outside), however this ensures that only the low voltage is dropped - which is not dangerous anyway! However, high voltage capacitors may remain charged and, if kept current, can be potentially dangerous or even fatal.

Collect the necessary parts: screw terminals (terminals), a light emitting diode (LED) with a 330 ohm current limiting resistor, a switch (optional), a 10 ohm resistor of 10 watts or greater (see the Tips section), and insulating heat shrink tubing.

Open the PSU by removing the screws connecting the top and bottom of the case.

Separate the wires by color. If you have wires not listed here (brown, etc.), see the Tips section. Color code for wires: red = + 5V, Black = ground (0V), white = -5V, yellow = + 12V, blue = -12V, Orange = + 3.3V, Purple = + 5V stock (not used), Gray = PG (output) and green = ON (must be short-circuited with (0V) to turn on the power supply).

Drill holes in free space BP case. First mark the centers of the holes with a nail using a hammer, drill the holes with a drill or dremel, then enlarge the holes with a reamer until they are sized for the connecting terminals. Also, drill holes for the switch and LED (optional).

Insert the terminals into the corresponding holes and fasten with nuts at the back.

Make all the necessary connections.

• Connect one of the red wires to the load resistor, all other red wires to the red terminal;
• Connect one of the black wires to the other terminal of the load resistor, the second black wire to the LED cathode (short leg), the third black wire to the DC-ON switch, all other black wires to the black terminal;
• Connect the white wire to the -5V terminal, yellow to the + 12V terminal, blue to the -12V terminal, gray to the resistor (330 Ohm), and solder the second lead of the resistor to the anode of the LED (its longer leg);
• Please note that some PSUs may have either gray or brown wire as "Power Good" / "Power OK". (Most PSUs have a smaller orange wire that is used to detect +3.3 V, and this wire is usually tied in a connector to another orange wire. Make sure that this wire is connected to the other orange wires or your PSU will not work). This wire must be connected to either the orange wires (+3.3 V) or red (+5 V) for the system to function. When in doubt, try low voltage first (+3.3 V). If the power supply is not ATX or AT, it can have its own color scheme. If your scheme differs from the one shown here in the photo, follow the indications, not the color characteristic.
• Connect the green wire to the other output of the switch.
• Make sure insulating heat shrinkage is applied to all exposed ends.
• Secure the wires with ties or electrical tape, preferably by color.

1. Check that the connections are secure by gently pulling on the wires. Locate bare wires and insulate them to prevent short circuits. Use super glue to fix the LED in the hole. Replace the cover.

2. Connect the cable to the back of the PSU and plug it into a power outlet. Turn on the main switch on the PSU, if installed. Check if the indicator is on. You can check the operation of the power supply unit by connecting a 12 V light bulb to different outputs; can also be checked with a voltmeter. Make sure there is no short circuit in any wire. Put the power supply case externally in order.

   • You can use the 12V output of the power supply to charge your car battery! Be careful: if the battery is very discharged, the short circuit protection of the power supply will work. In this case, for overload protection, a 10 Ohm, 10/20 W pull-up resistor can be connected in series with the 12 V output. As soon as the voltage on the battery becomes close to 12 V (can be checked with a tester), you can remove the resistor and continue charging the battery. This device will help you if the battery is old, or it has "run out" due to attempts to start the car in winter, or you accidentally left the headlights or radio tape recorder turned on for a long time, or for some other reason.
   • You can also convert the unit into a power supply for other purposes - but that's another article.
   • If you do not need all nine wires soldered to the terminal (as is the case with grounded wires) you can cut them off on the PCB. 1-3 wires will be enough. This means that you must also cut off any wires that you do not intend to use.
   • If you have a 3.3V signal wire connected to the 3.3V pin, then you will not be able to use the 3.3V voltage as a step down voltage, for example, from 12 V to 8.7 V. The voltmeter will read 8.7 V, but when the load is connected to 8.7 V, the power supply protection may trip and shut down the entire circuit.
   • In some power supplies for correct work you need to connect the gray and green wires.
   • You can add another 3.3V output (for example to power 3V devices) by connecting the orange wire to the terminal (make sure the brown wire stays connected to the orange one). Note that they share power with the 5V output, so the connected load must not exceed the total power output of these two outputs.
   • Options: A separate (additional) switch is not necessary, just connect the green wire to the black wire. The power supply will be turned on by the rear switch, if equipped. The LED is also optional, you can simply cut and insulate the gray wire.
   • If you do not want or know how to solder / attach many wires to the connection terminals (for example, ground wires), you can cut them off the board. It is enough to leave 1-3 wires. Also cut off any wires that you do not plan to use.
   • You can install car cigarette lighter into the hole from the power cord. This way you can connect the car equipment to the power source.
   • If you are not sure if the power supply is working properly, check it first on your computer before rebuilding it. Has the computer turned on? Does the PSU fan start? You can connect the voltmeter leads to the auxiliary connector (floppy drive). The voltmeter should show a value close to 5V (between the red and black wires). The power supply may not start due to no load on the output, or the start output (green wire) may not be shorted to ground.
   • The + 5V line provides + 5V power in standby mode (for the power button on the motherboard, Wake-on-LAN, etc.). It typically delivers up to 500-1000mA current even when the main outputs are disabled. Can be used to power an LED that indicates the presence of mains voltage.
   • From this source you can get voltages of 5 V (+5, zero), 7 V (+12, +5), 10 V (+5, -5), 12 V (+12, zero), 17 V (+5, -12) and 24V (+12, -12) should be sufficient for most applications. Many ATXs with a 24-pin header for the motherboard do not have a -5V output. If you need a -5V output, look for an ATX box with a 20-pin connector, 20 + 4-pin connector, or AT.
   • After modifying the block, clean and tidy it up.
   • The PSU fan can be quite loud as it is designed to cool a sufficiently loaded PSU and computer components. Of course, you can turn off the fan altogether, but that's a bad idea. If you want everything to be normal, then cut the red wire going to the fan (12V) and connect it to the red wire coming from the PS (5V). The fan will now run significantly slower and quieter while still providing some cooling. If you need a high current strength, then it is better not to do this (do not reduce the fan speed). If you nevertheless decide to do this, then it is under your responsibility; the only thing you can wish for in this case is watch how quickly the block heats up. You can also replace the stock (factory) fan with a quieter model (soldering may be needed).
   • To have more space inside the unit, you can mount the fan on the outside of the case.
   • You can drill the hole a little more.
   • Some newer PSUs have "voltage sensing" wires that must be connected to the correct voltage wires for proper operation. The main harness (with 20 wires) should have four red wires and three orange wires. If there are only two or fewer orange wires, you need to connect the brown wire to them. If you only have three red wires, you need to connect another wire (sometimes pink) to them.
   • If you are not afraid to solder, you can replace the 10 W pull-up resistor with a fan. Check polarity - connect red and black wires respectively.
   • The -5V output has been removed from the ATX specification and is no longer present on any ATX unit.
   • If the power supply is not working, the LED is off, see if the fan is spinning. If the fan in the power supply is working, then most likely the LED is connected incorrectly (the positive and negative leads of the LED are reversed). Open the power supply case and swap the purple and gray wires (make sure the LED is not shunted).
   • An ATX power supply is a switching power supply (for more information, see https://ru.wikipedia.org/wiki/Pulse_voltage_regulator), it needs some load to work properly. To do this, we use a load resistor, on which it will generate heat. For good cooling, the resistor must be fixed to the metal wall of the unit case (you can also use a separate radiator, making sure it does not short-circuit anything). If a load is connected to the power supply whenever it is turned on, then you can do without a resistor. It is also possible to use a 12V illuminated switch as a load, which will act as necessary to turn on the power of the load.
   • For use with appliances with a high starting load (such as a 12V condenser fridge) connect a suitable 12V battery to prevent the power supply from automatically shutting down.

   Warnings

   • Do not touch wires / tracks leading to capacitors. Capacitors are cylindrical parts covered with a thin film, with bare metal at the top and marked with "+" or "K". Solid capacitors are shorter, slightly thicker and without a film jacket. They hold charge in the same way as batteries, but unlike batteries, they can drain very quickly. Even if you have discharged the unit, try not to touch the board with your hands, except in places where it is necessary. Ground (discharge to ground) everything you touch.
   • Make sure the capacitors are discharged. Connect the power cable, turn on the unit (short the green wire to ground), then disconnect the power cable and wait until the fan stops rotating.
   • If you suspect that the power supply is defective, do not use it! If it is defective, then the protection circuit may not work. Typically, the protection circuitry gradually discharges the high voltage capacitors. But if (for example) the unit is rated for 110 V, and was connected to 240 V, then the protection circuit is likely to fail. In this case, the power supply will most likely not shut down in the event of an overload or malfunction.
   • When drilling through the metal case, make sure that no metal chips get inside the power supply. This can lead to a short, which in turn can lead to fire, overheating or high voltage pulses at the output, which can damage your new power supply, which you have spent so much effort on.
   • High voltage is dangerous and can even be fatal (anything above 30 milliamperes / volt can be fatal in a matter of seconds if you touch bare wires with your hands), at least you will get a painful shock. Before working on the power supply, make sure the power cable is disconnected and the capacitors are discharged as described above. Use a multimeter when in doubt.
   • Do not remove the board until needed. Live tracks and soldering may remain under high voltage if you have not left the power supply unit for a while to discharge. If you still need to remove the board, use a voltmeter to check the voltage at large capacitors... When you put the board back in place, make sure there is a plastic spacer underneath it.
   • A computer power supply is great for testing or for powering simple electronics (such as chargers, soldering irons, etc.), but never beats a good laboratory power supply. If you are going to use the power supply for more than just testing, buy a good laboratory unit nutrition. They are not in vain that they are so expensive, there are reasons for that.
   • The resulting power supply provides high power output. Possible wiring errors can cause arcing or arcing at the low voltage outputs or burn the circuit you are working with. Therefore, laboratory power supplies have adjustable current limiters.
   • The original article states that you need to be sure to ground yourself. This is wrong and dangerous. Make sure you are NOT grounded when working on the power source so that current does not flow through you.
   • Such alteration will definitely void your warranty for the unit, if any.
   • Only people who know the work of BP well can deal with its creation.

Charger from a computer PSU

If you have an old computer power supply, you can find an easy use for it, especially if you are interested in DIY car battery charger.

Appearance this device The alteration is easy to carry out, and allows you to charge batteries with a capacity of 55 ... 65 A * h

that is, almost any battery.

Fragment schematic diagram alteration of the standard power supply unit is shown in the photo:

As DA1, almost all power supplies (PSUs) of personal computers (PCs) are used SHI controller TL494 or its analogue KA7500.

Automobile storage batteries (AKB) have an electric capacity of 55 ... 65 A.h. Being lead acid batteries, they require a current of 5.5 ... 6.5 A - 10% of their capacity for their charge, and such a current through the "+ 12V" circuit can provide any PSU with a power of more than 150 W.

You must first remove all unnecessary wires of the "-12 V", "-5 V", "+5 V", "+12 V" circuits.

Resistor R1 with a resistance of 4.7 kOhm, supplying a voltage of +5 V to pin 1, must be evaporated. Instead, a 27 kΩ trimmer resistor will be used, the top terminal of which will be supplied with voltage from the + 12V rail.

Conclusion 16 disconnect from the common wire, and cut the connection of the 14th and 15th pins.

The beginning of the conversion of the PSU into an automatic charger is shown in the photo:

On the back wall of the power supply unit, which will now become the front, on the board made of insulating material, we fix the potentiometer-regulator of the charging current R10. We also pass and fix the power cord and the cord for connecting to the terminals battery.

For reliable and convenient connection and adjustment, a resistor block was made:

Instead of the C5-16MV current-measuring resistor with a power of 5 W and a resistance of 0.1 Ohm, recommended in the original source, I installed two imported 5WR2J - 5 W; 0.2 ohm by connecting them in parallel. As a result, their total power became 10 W, and the resistance was the required 0.1 Ohm.

On the same board, there is a trimmer resistor R1 for tuning the assembled charger.

To exclude undesirable connections of the device case with the general charging circuit, it is necessary to remove part of the printed track.

Installation of the resistor block board and electrical connections according to the schematic diagram are shown in the photo:

The photo does not show the places of the rations to the terminals 1, 16, 14, 15 of the microcircuit. These conclusions must first be irradiated, and then thin stranded wires with reliable insulation must be soldered.

Before final assembly of the instrument variable resistor R1, at the middle position of the potentiometer R10, set the open circuit voltage in the range of 13.8 ... 14.2 V. This voltage will correspond to a full charge of the battery.

The complete set of the automatic charger is shown in the photo:

The leads for connecting to the battery terminals end with crocodile clips with tensioned insulating tubes of different colors. The positive terminal corresponds to the red color, and the negative terminal to the black one.

Warning : in no case should you confuse the connection of the wires! This will damage the device!

The charging process of the 6ST-55 battery is illustrated by the photo:

The DVM reads 12.45V, which is the initial charge cycle. First, the potentiometer is set to the "5.5" mark, which corresponds to the initial charge current of 5.5 A. As the charge progresses, the voltage across the battery increases, gradually reaching the maximum set by the variable resistor R1, and the charging current decreases, dropping to almost 0 at the end charging.

When fully charged the device goes into voltage stabilization mode, compensating for the self-discharge current of the battery. In this mode, without fear of overcharging or other undesirable phenomena, the device can remain indefinitely.

When repeating a device I came to the conclusion that the use of a voltmeter and an ammeter is completely unnecessary if the charger is used only for charging car batteries, where a full charge corresponds to a voltage of 14.2 V, and to set the initial charging current, the graduated scale of the potentiometer R10 from 5.5 is quite enough up to 6.5 A.

The result is a lightweight, reliable device with an automatic charging cycle that does not require human intervention during operation.

In the modern world, the development and obsolescence of personal computer components occurs very quickly. At the same time, one of the main components of a PC - the ATX form factor - is practically has not changed its design for the last 15 years.

Consequently, the power supply and ultra-modern gaming computer, and the old office PC work on the same principle, have common troubleshooting techniques.

The material presented in this article can be applied to any power supply unit for personal computers with a minimum of nuance.

A typical ATX power supply circuit is shown in the figure. Structurally, it is a classic pulse unit on the TL494 PWM controller, triggered by the PS-ON (Power Switch On) signal from the motherboard. The rest of the time, until the PS-ON pin is pulled to ground, only the Standby Supply with a voltage of +5 V at the output is active.

Let's take a closer look at the structure of the ATX power supply. Its first element is
:

Its task is to convert alternating current from the mains to direct current to power the PWM controller and the standby power supply. Structurally, it consists of the following elements:

• Fuse F1 protects the wiring and the power supply itself from overload in the event of a power supply failure, leading to a sharp increase in current consumption and, as a result, to a critical increase in temperature that can lead to a fire.
• A protective thermistor is installed in the "neutral" circuit, which reduces the current surge when the power supply unit is connected to the network.
• Next, a noise filter is installed, consisting of several chokes ( L1, L2), capacitors ( C1, C2, C3, C4) and a counter-winding choke Tr1... The need for such a filter is due to the significant level of interference that the impulse unit transmits to the power supply network - this interference is not only captured by television and radio receivers, but in some cases can also lead to incorrect operation of sensitive equipment.
• A diode bridge is installed behind the filter, which converts alternating current into pulsating direct current. The ripple is smoothed out by a capacitive-inductive filter.

Standby power supply- this is a low-power independent pulse converter based on the T11 transistor, which generates pulses, through an isolation transformer and a half-wave rectifier on the D24 diode, supplying a low-power integrated voltage regulator on the 7805 microcircuit. high voltage drop across the 7805 stabilizer, which under heavy load leads to overheating. For this reason, damage to the circuits powered from the standby source can lead to its failure and the subsequent impossibility of turning on the computer.

The basis of the pulse converter is PWM controller... This abbreviation has already been mentioned several times, but has not been deciphered. PWM is pulse width modulation, that is, the change in the duration of voltage pulses at their constant amplitude and frequency. The task of a PWM unit based on a specialized microcircuit TL494 or its functional analogs is to convert constant voltage into pulses of the appropriate frequency, which are smoothed by output filters after the isolation transformer. The voltage stabilization at the output of the pulse converter is carried out by adjusting the duration of the pulses generated by the PWM controller.

An important advantage of such a voltage conversion scheme is also the ability to work with frequencies significantly higher than 50 Hz of the mains. The higher the current frequency, the smaller the dimensions of the transformer core and the number of winding turns are required. That is why switching power supplies are much more compact and lighter than classic circuits with an input step-down transformer.

A circuit based on the T9 transistor and the following stages is responsible for turning on the ATX power supply. At the moment the power supply is switched on to the network, a voltage of 5V is supplied to the base of the transistor through the current-limiting resistor R58 from the output of the standby power supply, at the moment the PS-ON wire is shorted to ground, the circuit starts the TL494 PWM controller. In this case, the failure of the standby power supply will lead to the uncertainty of the operation of the power supply startup circuit and the probable failure of switching on, which has already been mentioned.

For recharging the battery the best way- ready-made charger (charger). But you can do it yourself. There are many different ways to assemble a homemade charger: from the most simple schemes using a transformer, up to pulse circuits with the possibility of adjustment. The average complexity of execution is the memory of computer unit nutrition. The article describes how to make a charger from a computer power supply for a car battery with your own hands.

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Manufacturing instruction

Converting a computer PSU into a charger is not difficult, but you need to know the basic requirements for a charger designed to charge car batteries. For a car battery, the charger must have the following characteristics: the maximum voltage supplied to the battery must have a value of 14.4 V, the maximum current depends on the charger itself. It is these conditions that are created in the electrical system of the car when recharging the battery from the generator (video by Rinat Pak).

Tools and materials

Considering the requirements described above, for making a charger with your own hands, you first need to find a suitable power supply. A used ATX is suitable in working condition, the power of which ranges from 200 to 250 W.

We take a computer as a basis, which has the following characteristics:

• output voltage 12V;
• rated voltage 110/220 V;
• power 230 W;
• maximum current value is not more than 8 A.

From tools and materials you will need:

• soldering iron and solder;
• screwdriver;
• a 2.7 kΩ resistor;
• resistor 200 Ohm and 2 W;
• resistor for 68 ohms and 0.5 watts;
• resistor 0.47 Ohm and 1 W;
• resistor 1 kOhm and 0.5 W;
• two 25 V capacitors;
• 12V automotive relay;
• three 1N4007 diodes for 1 A;
• silicone sealant;
• green LED;
• voltammeter;
• Crocodiles;
• flexible copper wires 1 meter long.

Having prepared all the necessary tools and spare parts, you can start making a charger for a battery from a computer power supply.

Algorithm of actions

The battery must be charged under voltage in the range of 13.9-14.4 V. All computers operate with a voltage of 12V. Therefore, the main task of the alteration is to raise the voltage coming from the PSU to 14.4 V.
The main modification will be carried out with the PWM operating mode. For this, the TL494 microcircuit is used. You can use a power supply unit with absolute analogs of this circuit. This circuit is used to generate pulses, and also as a driver for a power transistor, which performs the function of protecting against high currents. To regulate the voltage at the output of the computer power supply, the TL431 microcircuit is designed, which is installed on additional fee.

There is also a tuning resistor, which makes it possible to adjust the output voltage in a narrow range.

The work on alteration of the power supply consists of the following stages:

1. For alterations in the block, you first need to remove all unnecessary parts from it and unsolder the wires. In this case, the 220/110 V switch and the wires going to it are superfluous. The wires should be unsoldered from the power supply unit. The unit requires a voltage of 220 V. By removing the switch, we exclude the possibility of the unit burning out if the switch is accidentally switched to the 110 V position.
2. Next, we solder, bite off unnecessary wires or use any other method to remove them. First, we find the blue 12V wire coming from the capacitor, we solder it. There can be two wires, both must be removed. We only need a bundle of yellow wires with a 12V output, we leave 4 pieces. We also need a mass - these are black wires, we also leave 4 of them. In addition, you need to leave one green wire. The rest of the wires are completely removed or soldered.
3. On the board, along the yellow wire, we find two capacitors in a circuit with a voltage of 12V, they usually have a voltage of 16V, they must be replaced with capacitors of 25V. Over time, capacitors deteriorate, so even if the old parts are still in working order, it is better to replace them.
4. In the next step, we need to ensure that the unit works every time it is connected to the network. The fact is that the power supply unit in the computer works only if the corresponding wires in the output bundle are closed. In addition, overvoltage protection must be excluded. This protection is set in order to disconnect the power supply from the mains if the output voltage supplied to it exceeds a predetermined limit. It is necessary to exclude protection, since a voltage of 12 V is permissible for a computer, and we need to get 14.4 V at the output. For built-in protection, this will be considered an overvoltage and it will turn off the unit.
5. The overvoltage trip action signal as well as the enable and disable signals are passed through the same optocoupler. There are only three optocouplers on the board. With their help, communication is carried out between the low-voltage (output) and high-voltage (input) parts of the power supply unit. To prevent the protection from tripping in case of overvoltage, you need to close the contacts of the corresponding optocoupler with a solder jumper. Thanks to this, the unit will be in the on state all the time if it is connected to the mains and will not depend on what voltage is at the output.
6. Then, in order to obtain a stable output voltage at idle, it is necessary to increase the load on the PSU output along the channel where the voltage was 12 V, and it will become 14.4 V, and along the 5 V channel, but we do not use it. A 200 Ohm 2 W resistor will be used as the load for the first 12 V channel, and the 5 V channel will be supplemented with a 68 Ohm 0.5 W resistor for the load. Once these resistors are installed, the no-load output voltage at no-load can be adjusted to 14.4 V.
7. Next, you need to limit the output current. It is individual for each power supply unit. In our case, its value should not exceed 8 A. To achieve this, you need to increase the value of the resistor in the primary winding circuit at power transformer, which is used as an overload sensor. To increase the rating, the installed resistor must be replaced with a more powerful one with a resistance of 0.47 Ohm and a power of 1 W. After this replacement, the resistor will function as an overload sensor, so the output current will not exceed 10 A even if the output wires are shorted to simulate a short circuit.
8. At the last stage, you need to add a protection circuit for the power supply from connecting the charger to the battery of wrong polarity. This is the circuit that will really be created by hand and is absent from the computer's power supply. To assemble the circuit, you need a 12V car relay with 4 terminals and 2 diodes rated for 1A current, for example, 1N4007 diodes. In addition, a green LED must be connected. Thanks to the diode, it will be possible to determine the state of charge. If it lights up, it means that the battery is connected correctly and is charging. In addition to these details, you also need to take a 1 kOhm resistor with a power of 0.5 W. The figure shows the protection circuit.
9. The principle of operation of the circuit is as follows. The rechargeable battery with the correct polarity is connected to the charger output, that is, to the power supply. The relay is activated by the energy remaining in the battery. After the relay is activated, the battery starts charging from the assembled charger through the closed contact of the power supply relay. Charging is confirmed by a lit LED.
10. To prevent overvoltage that occurs when the coil is disconnected due to the self-induction electromotive force, a 1N4007 diode is connected in parallel to the relay. It is better to glue the relay to the radiator of the power supply with silicone sealant. Silicone retains elasticity after drying, it is resistant to thermal stress, such as: compression and expansion, heating and cooling. When the sealant dries up, the rest of the elements are attached to the relay contacts. Bolts can be used as fasteners instead of sealant.
11. It is better to select wires for the charger in different colors, for example, red and black. They must have a cross section of 2.5 sq. mm, be flexible, copper. The length must be at least one meter. At the ends of the wires must be equipped with crocodiles, special clips, with which the charger is connected to the battery terminals. To fix the wires in the body of the assembled device, you need to drill the corresponding holes in the radiator. Through them you need to thread two nylon ties, which will hold the wires.

Ready charger

To control the strength of the charging current, an ammeter can also be mounted in the charger case. It must be connected in parallel to the power supply circuit. As a result, we have a charger that we can use to charge the car's battery and not only.

Conclusion

The advantage of this charger is that the battery will not be recharged when using the device and will not deteriorate, no matter how long it is connected to the charger.

The disadvantage of this charger is the absence of any indicators by which one could judge the state of charge of the battery.

It is difficult to determine if the battery is charged or not. You can calculate the approximate charging time by using the readings on the ammeter and applying the formula: current in amperes multiplied by the time in hours. It was experimentally found that a full charge of a conventional 55 A / h battery takes 24 hours, that is, a day.

This charger has an overload and short circuit function. But if it is not protected against wrong polarity, you cannot connect the charger to the battery with the wrong polarity, the device will fail.

Hello, now I will talk about rework ATX codegen 300w 200xa power supply into a laboratory power supply with voltage regulation from 0 to 24 Volts, and current limiting from 0.1 A to 5 Amperes. I will lay out the scheme that I got, maybe someone can improve or add something. The box itself looks like this, although the sticker may be blue or a different color.

Moreover, the boards of the 200xa and 300x models are almost the same. Under the board itself there is an inscription CG-13C, maybe CG-13A. Perhaps there are other models similar to this one, but with different inscriptions.

Soldering unnecessary parts

Initially, the diagram looked like this:

It is necessary to remove all unnecessary, atx connector wires, unsolder and rewind unnecessary windings on the group stabilization choke. Under the choke on the board, where it says +12 volts, we leave that winding, we wind the rest. Unsolder the braid from the board (main power transformer), in no case bite it off. Remove the radiator along with the Schottky diodes, and after we remove all unnecessary things, it will look like this:

The final layout after the rework will look like this:

In general, we solder all the wires, details.

Making a shunt

We make a shunt from which we will relieve stress. The meaning of the shunt is that the voltage drop across it tells the PWM how it is loaded by current - the power supply output. For example, the resistance of the shunt we got 0.05 (Ohm), if you measure the voltage on the shunt at the time of passage of 10 A, then the voltage on it will be:

U = I * R = 10 * 0.05 = 0.5 (Volt)

I will not write about the manganin shunt, since I did not buy it and I do not have it, I used two tracks on the board itself, we close the tracks on the board as in the photo to get the shunt. It is clear that it is better to use manganin, but even so it works more than normal.

We put the choke L2 (if any) after the shunt

In general, they need to be counted, but if anything, a program for calculating chokes was slipping somewhere on the forum.

We supply a common minus to the PWM

It is possible not to serve if it is already ringing on the 7th leg of the PWM. It's just that on some boards on pin 7 there was no general minus after the parts were soldered (I don’t know why, I could be mistaken that there wasn’t :)

We solder a wire to the 16th PWM pin

We solder to the 16th PWM pin - a wire, and this wire is fed to the 1 and 5 legs of the LM358

Between 1 leg of the PWM and the plus output, we solder a resistor

This resistor will limit the voltage supplied by the PSU. This resistor and R60 forms a voltage divider that will divide the output voltage and supply it to 1 leg.

The inputs of the op-amp (PWM) on the 1st and 2nd legs are used for the task of the output voltage.

The task on the output voltage of the PSU comes to the 2nd leg, since 5 volts (vref) can come to the second leg as much as possible, then the reverse voltage should come to the 1st leg also no more than 5 volts. For this we need a voltage divider of 2 resistors, R60 and the one that we install from the output of the PSU to 1 leg.

How it works: let's say a variable resistor is put on the second leg of the PWM 2.5 Volts, then the PWM will give out such pulses (increase the output voltage from the PSU output) until 2.5 (volts) comes to 1 leg of the op-amp. Suppose if this resistor is not present, the power supply will reach the maximum voltage, because there is no feedback from the PSU output. The resistor value is 18.5 kOhm.

We install capacitors and a load resistor on the output of the power supply unit

The pull-up resistor can be supplied from 470 to 600 Ohm 2 Watt. Capacitors of 500 microfarads for a voltage of 35 volts. I did not have capacitors with the required voltage, I put 2 in series of 16 volts 1000 microfarads. We solder capacitors between 15-3 and 2-3 PWM legs.

Soldering the diode assembly

We put the diode assembly on the one that was 16C20C or 12C20C, this diode assembly is designed for 16 amperes (12 amperes, respectively), and 200 volts of reverse peak voltage. Diode assembly 20C40 will not work for us - do not think about installing it - it will burn out (checked :)).

If you have any other diode assemblies, see that the reverse peak voltage is at least 100 V and for the current, which is higher. Conventional diodes will not work - they will burn out, these are ultra-fast diodes, just for a switching power supply.

We put a jumper for the PWM power supply

Since we removed the piece of the circuit that was responsible for supplying power to the PSON PWM, we need to power the PWM from the 18 V power supply on duty. Actually, we install a jumper instead of the Q6 transistor.

We solder the output of the power supply +

Then we cut the common minus that goes to the body. We do it so that the general minus does not touch the case, otherwise, short-circuiting the plus, with the PSU case, everything will burn out.

We solder the wires, the common minus and +5 Volts, the output of the power supply attendant

We will use this voltage to power the volt-ammeter.

We solder the wires, common minus and +18 volts to the fan

We will use this wire through a 58 Ohm resistor to power the fan. Moreover, the fan must be turned so that it blew on the radiator.

We solder the wire from the braid of the transformer to a common minus

Solder 2 wires from the shunt for the LM358 op-amp

We solder the wires, as well as resistors to them. These wires will go to the LM357 op-amp through 47 ohm resistors.

We solder the wire to the 4th leg of the PWM

With a positive +5 Volt voltage at this PWM input, there is a limitation of the control limit at the C1 and C2 outputs, in this case, with an increase at the DT input, there is an increase in the duty cycle at C1 and C2 (you need to look at how the transistors are connected at the output). In a word - stopping the output of the power supply unit. This 4th PWM input (we supply +5 V there) will be used to stop the PSU output in the event of a short circuit (above 4.5 A) at the output.

Putting together the current amplification and short circuit protection circuit

Attention: this is not a complete version - for details, including photos of the rework process, see the forum.

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