How to make a car charger from a computer power supply. DIY charger from a computer power supply

When converting computer switching power supplies (hereinafter referred to as UPS) with a TL494 control chip into power supplies for powering transceivers, radio equipment and chargers for car batteries, a number of UPSs accumulated that were faulty and could not be repaired, were unstable, or had a control chip of a different type .

They also got around to the remaining power supplies, and after some experimentation they developed the technology for converting them into chargers (hereinafter referred to as chargers) for car batteries.
Also, after the release, emails began to arrive with various questions, like what and how, where to start.

Where to begin?

Before you begin the rework, you should carefully read the book, it provides a detailed description of the operation of the UPS with the TL494 control chip. It would also be a good idea to visit the sites and, where the issues of redesigning computer UPSs are discussed in detail. For those radio amateurs who could not find the specified book, we will try to explain “on the fingers” how to “tame” a UPS.
And so about everything in order.

And so let’s consider the case when the battery is not yet connected. The AC mains voltage is supplied through the thermistor TR1, mains fuse FU1, and noise suppression filter to the rectifier on the diode assembly VDS1. The rectified voltage is smoothed by a filter on capacitors C6, C7, and the output of the rectifier produces a voltage of + 310 V. This voltage is supplied to a voltage converter using powerful key transistors VT3, VT4 with a pulse power transformer Tr2.

Let’s immediately make a reservation that for our charger there are no resistors R26, R27, intended for slightly opening transistors VT3, VT4. The base-emitter junctions of transistors VT3, VT4 are shunted by circuits R21R22 and R24R25, respectively, as a result of which the transistors are closed, the converter does not work, and there is no output voltage.

When the battery is connected to the output terminals Cl1 and Cl2, the VD12 LED lights up, voltage is supplied through the VD6R16 chain to pin No. 12 to power the MC1 microcircuit and through the VD5R12 chain to the middle winding of the matching transformer Tr1 of the driver on transistors VT1, VT2. Control pulses from pins 8 and 11 of the MC1 chip are sent to the driver VT1, VT2, and through the matching transformer Tr1 to the base circuits of the power key transistors VT3, VT4, opening them one by one.

The alternating voltage from the secondary winding of the power transformer Tr2 of the + 12 V voltage generation channel is supplied to a full-wave rectifier based on an assembly of two VD11 Schottky diodes. The rectified voltage is smoothed out by the LC filter L1C16 and goes to the output terminals Cl1 and Cl2. The output of the rectifier also powers the standard fan M1, intended for cooling UPS parts, connected through a damping resistor R33 to reduce the rotation speed of the blades and fan noise.

The battery is connected through terminal Cl2 to the negative output of the UPS rectifier through resistor R17. When the charging current flows from the rectifier to the battery, a voltage drop is formed across resistor R17, which is supplied to pin No. 16 of one of the comparators of the MC1 chip. When the charging current exceeds the set level (by moving the charge current setting resistor R4), the MC1 microcircuit increases the pause between output pulses, reducing the current to the load and thereby stabilizing the battery charging current.

The output voltage stabilization circuit R14R15 is connected to pin No. 1 of the second comparator of the MC1 microcircuit, and is designed to limit its value (at + 14.2 - + 16 V) in the event of the battery being disconnected. When the output voltage increases above the set level, the MC1 microcircuit will increase the pause between output pulses, thereby stabilizing the output voltage.
Microammeter PA1, using switch SA1, is connected to different points of the UPS rectifier, and is used to measure the charging current and voltage on the battery.

As a PWM control regulator MC1, a microcircuit of the TL494 type or its analogues is used: IR3M02 (SHARP, Japan), µA494 (FAIRCHILD, USA), KA7500 (SAMSUNG, Korea), MV3759 (FUJITSU, Japan, KR1114EU4 (Russia).

Let's start the renovation!

We unsolder all the wires from the output connectors, leave five yellow wires (+12 V voltage generation channel) and five black wires (GND, case, ground), twist four wires of each color together and solder them, these ends will subsequently be soldered to output terminals of the memory.

Remove the 115/230V switch and sockets for connecting cords.
In place of the upper socket, we install a PA1 microammeter for 150 - 200 µA from cassette recorders, for example M68501, M476/1. The original scale has been removed and a homemade scale made using the FrontDesigner_3.0 program has been installed instead; scale files can be downloaded from the magazine’s website. We cover the place of the lower socket with tin measuring 45×25 mm and drill holes for the resistor R4 and the switch for the type of measurement SA1. On the rear panel of the case we install terminals Cl 1 and Cl 2.

Also, you need to pay attention to the size of the power transformer (on the board - the larger one), in our diagram (Fig. 5) this is Tr 2. The maximum power of the power supply depends on it. Its height should be at least 3 cm. There are power supplies with a transformer less than 2 cm high. The power of these is 75 W, even if it is written 200 W.

In the case of remaking an AT type UPS, remove resistors R26, R27 that slightly open the transistors of the key voltage converter VT3, VT4. In case of alteration of an ATX type UPS, we remove the parts of the duty converter from the board.

We solder all the parts except: noise suppression filter circuits, high-voltage rectifier VDS1, C6, C7, R18, R19, inverter on transistors VT3, VT4, their base circuits, diodes VD9, VD10, power transformer circuits Tr2, C8, C11, R28, driver on transistors VT3 or VT4, matching transformer Tr1, parts C12, R29, VD11, L1, output rectifier, according to the diagram (Fig. 5).

We should end up with a board that looks something like this (Fig. 6). Even if a microcircuit like DR-B2002, DR-B2003, DR-B2005, WT7514 or SG6105D is used as a control PWM regulator, it is easier to remove them and make them from scratch on TL494. We manufacture the A1 control unit in the form of a separate board (Fig. 7).

The standard diode assembly in the +12 V rectifier is designed for too low a current (6 - 12 A) - it is not advisable to use it, although it is quite acceptable for a charger. In its place, you can install a diode assembly from a 5-volt rectifier (it is designed for a higher current, but has a reverse voltage of only 40 V). Since in some cases the reverse voltage on the diodes in the +12 V rectifier reaches a value of 60 V! , it is better to install an assembly on Schottky diodes with a current of 2×30 A and a reverse voltage of at least 100 V, for example, 63CPQ100, 60CPQ150.

We replace the rectifier capacitors of the 12-volt circuit with an operating voltage of 25 V (16-volt ones often swelled).

The inductance of inductor L1 should be in the range of 60 - 80 µH, we must unsolder it and measure the inductance, we often came across specimens at 35 - 38 µH, with them the UPS operates unstable, buzzes when the load current increases more than 2 A. If the inductance is too high, more 100 μH, reverse voltage breakdown of the Schottky diode assembly may occur if it was taken from a 5-volt rectifier. To improve cooling of the +12 V rectifier winding and the ring core, remove unused windings for the -5 V, -12 V and +3.3 V rectifiers. You may have to wind several turns of wire to the remaining winding until the required inductance is obtained (Fig. 8).

If the key transistors VT3, VT4 were faulty, and the original ones cannot be purchased, then you can install more common transistors like MJE13009. Transistors VT3, VT4 are screwed to the radiator, usually through an insulating gasket. It is necessary to remove the transistors and, to increase thermal contact, coat the gasket on both sides with thermal conductive paste. Diodes VD1 - VD6 designed for a forward current of at least 0.1 A and a reverse voltage of at least 50 V, for example KD522, KD521, KD510.

We replace all electrolytic capacitors on the +12 V bus with a voltage of 25 V. During installation, it is also necessary to take into account that resistors R17 and R32 heat up during operation of the unit; they must be located closer to the fan and away from the wires.
The VD12 LED can be glued to the PA1 microammeter from above to illuminate its scale.

Setup

When setting up the memory, it is advisable to use an oscilloscope; it will allow you to see the pulses at the control points and will help us significantly save time. We check the installation for errors. We connect the rechargeable battery (hereinafter referred to as the battery) to the output terminals. First of all, we check the presence of generation at pin No. 5 of the MS sawtooth voltage generator (Fig. 9).

We check the presence of the indicated voltages according to the diagram (Fig. 5) at pins No. 2, No. 13 and No. 14 of the MC1 microcircuit. We set the resistor R14 slider to the position of maximum resistance, and check for the presence of pulses at the output of the MC1 microcircuit, at pins No. 8 and No. 11 (Fig. 10).

We also check the signal shape between pins No. 8 and No. 11 of MS1 (Fig. 11), on the oscillogram we see a pause between pulses; the lack of pulse symmetry may indicate a malfunction of the basic driver circuits on transistors VT1, VT2.

We check the shape of the pulses on the collectors of transistors VT1, VT2 (Fig. 12),

And also the shape of the pulses between the collectors of these transistors (Fig. 13).

The lack of pulse symmetry may indicate a malfunction of the transistors themselves VT1, VT2, diodes VD1, VD2, the base-emitter junction of transistors VT3, VT4 or their base circuits. Sometimes a breakdown of the base-emitter junction of transistor VT3 or VT4 leads to the failure of resistors R22, R25, the diode bridge VDS1, and only then to the blowing of fuse FU1.

According to the diagram, the left terminal of resistor R14 is connected to a reference voltage source of 16 V (why 16 V - to compensate for losses in the wires and in the internal resistance of a heavily sulfated battery, although 14.2 V is also possible). By reducing the resistance of resistor R14 until the pulses disappear at pins No. 8 and No. 11 of the MS, more precisely at this moment the pause becomes equal to the half-cycle of pulse repetition.

First start-up, testing

A correctly assembled, error-free device starts up immediately, but for safety reasons, instead of a mains fuse, we turn on a 220 V 100 W incandescent lamp; it will serve as a ballast resistor and in an emergency will save the UPS circuit parts from damage.

Set the resistor R4 to the minimum resistance position and turn on Charger(charger) into the network, and the incandescent lamp should flash briefly and go out. When the charger operates at a minimum load current, the radiators of transistors VT3, VT4 and the diode assembly VD11 practically do not heat up. As the resistance of resistor R4 increases, the charging current begins to increase; at a certain level, the incandescent lamp will flash. Well, that's all, you can remove the llama and put fuse FU1 in place.

If you still decide to install a diode assembly from a 5-volt rectifier (we repeat that it can withstand current, but the reverse voltage is only 40 V), turn on the UPS to the network for one minute, and use resistor R4 to set the current to load 2 - 3 A, turn off the UPS. The radiator with the diode assembly should be warm, but under no circumstances hot. If it is hot, it means that this diode assembly in this UPS will not work for a long time and will definitely fail.

We check the charger at the maximum current into the load; for this it is convenient to use a device connected in parallel with the battery, which will prevent the battery from being damaged by long-term charges during the setup of the charger. To increase the maximum charging current, you can slightly increase the resistance of resistor R4, but you should not exceed the maximum power for which the UPS is designed.

By selecting the resistances of resistors R34 and R35, we set the measurement limits for the voltmeter and ammeter, respectively.

Photos

Installation of the assembled device is shown in (Fig. 14).

Now you can close the lid. Appearance The memory is shown in (Fig. 15).

We would like to present a charger with a charging current of up to 40 A. The device was created using an ATX power supply from a computer, with a slight modification of the circuit. This current and voltage are perfect for charging car batteries or as a starter rectifier.

Charging circuit diagram 12V 40A

Circuit diagram for a charger from a 40 amp ATX computer power supply

The charger is equipped with a module for monitoring and adjusting current and measuring voltage. LED digital indicator (you can buy ready-made from Aliexpress). One switchable mode (green LED) is voltage measurement, the second (red LED) is current measurement. Although if you assemble the structure, install two at once.

• The current adjustment range is 1.9 to 42 A, the charging voltage is set to 15 V.

This device consists of two converters: the main and auxiliary, which have 15 V for powering the controller and fans, as well as 5 V for power measuring instrument. The converter is stand-by like in an ATX power supply.

Transformer winding data

Power converter based on TL494 (KA7500) controller. Transformer on a ferrite core ERL35, the primary winding of 45 turns is wound with two 0.6 mm wires in three layers, and the secondary winding is 12 turns of copper tape 0.25 x 8 mm in two layers. One half of the secondary winding is located between the first and second layers of the primary winding, and the second half is between the second and third.

Power transistors are used IRF740. Each of the transistors has a separate control transformer made on an EE16 ferrite core; these transformers have a ratio of 1:1 and are wound with 0.25 mm wire, 40 turns each winding.
The output rectifier is made using MBR4060 diodes and two chokes. The chokes are wound with 0.5 mm wire, 10 turns each.

The current control system used a 1 milliohm 2 W measuring resistor, which also serves as a shunt for the device. The voltage across the measuring resistor is negative relative to ground, so I used a simple converter built from a measurement amplifier, which gives an output voltage signal of 0-5 V with 1V/10A. High-current tracks are reinforced with 2.5 mm2 copper wire and filled with solder. Output cables with a cross section of 6 mm2 with crocodiles at the ends.

Converted charger housing

Naturally, the case was not redesigned and remained from the original ATX power supply, only for better cooling a second fan was installed next to it. The board (as you can see from the photo) was soldered from scratch, but you can use a ready-made one as a basis.

Homemade ready-made charger from a PC power supply

Of course, for a car starter, 40 A is not enough. Approximately 200 A is needed to, for example, start a diesel engine. But if the battery is already weak, then these 40 Amps will support it well. you can follow the link.

You can make your own charger from a regular computer power supply.

What properties will it have: the voltage for the battery will be 14 V, but the charging current will depend on the device. This charging method is provided by the car's generator in standard operating mode.

The difference between this article and other similar ones is that the assembly of the product is quite simple. You don't need to make homemade boards and fancy transistors.

Actually what we need:
1) a regular power supply from a computer is approximately 230 W, that is, a 12 V channel consumes 8 A.
2) a 12V automotive relay (with four contacts) and two diodes for a current of 1A
3) several resistors of different powers (depending on the model of the power supply itself)

After opening this power supply, the author discovered that it was based on a UC3843 chip. This chip is used as a pulse generator and for overcurrent protection. The voltage regulator on the output channels is represented by the TL431 microcircuit:

A tuning resistor was also installed there, which serves to regulate the output voltage in a certain range.

To make a charger out of this power supply, we will need to remove unnecessary parts.

We unsolder the 220\110V switch and all its wires from the board.
We don’t need it, because our power supply will always operate at 220 voltage.

Then we remove all the wires at the output, except for the bundle of black wires (there are 4 wires) - this is 0V or “common”, and the bundle of yellow wires (there are 2 wires in the bundle) - this is “+”.

Then we will make the unit work constantly when connected to the network. As a standard, it works only if the necessary wires in those bundles are closed. It is also necessary to remove the overvoltage protection, since it turns off the unit if the voltage rises above a certain value.

The whole reason is that we need 14.4V at the output of the device and not the standard 12.

It turned out that the turn-on and protection signals operate through one optocoupler, and there are only three of them.
In order for charging to work, you will always have to close the contacts of this optocoupler with a jumper:

After this action, the power supply will operate regardless of the network voltage.

The next step is to set the output voltage to 14.4V instead of 12. To do this, we had to replace the resistor that was connected in series with the trimmer with a 2.7 kOhm resistor:

Now we have to dismantle the transistor, which is next to TL431. (why it is unknown, but it blocks the operation of the microcircuit) This transistor was located in this place:

To stabilize, we add a load to the output of the power supply in the form of a 200 Ohm 2W (14.4V) resistor and for the 5V channel a 68 Ohm resistor:

After installing these resistors, you can begin to regulate the output voltage without a load at 14.4V. To limit the output current to 8A (the permissible value for our unit), you need to increase the power of the resistor in the power transformer circuit, which is used as an overload sensor.

We install a 47 Ohm 1 W resistor instead of the standard one.

Still, it wouldn’t hurt to add protection against reverse polarity connections. We take a simple 12V car relay and two 1N4007 diodes. Also, in order to see the operating mode of the device, it would be nice to make 1 more diode and a 1kOhm 0.5W resistor.

The scheme will be like this:

Operating system: when the battery is connected with the correct polarity, the relay is turned on due to the charge remaining in the battery. After the relay is triggered, the battery is charged from the power supply through the closed contact of the relay; this is what the external diode will show us.

A diode, which is connected in parallel to the relay coil, serves to protect against overvoltage when it is turned off, resulting from self-induction EMF.

To glue the relay, it is better to use silicone sealant, as it will remain elastic even after drying.

Then the wires are soldered to the battery. It’s better to take flexible ones, with a cross-section of 2.5mm2, about a meter long. To connect to the battery, “crocodiles” are used at the ends of the wires. To secure them in the case, the author used a pair of nylon ties (he threaded them through the holes drilled in the radiator)

There are quite a few different chargers based on a power supply floating around the Internet. So I decided to tell you about the history of the development of my charging scheme. The scheme was created so that our catmobile would still continue to drive in the cold winter, and anyone could assemble it, more or less a radio cat. The main emphasis in the circuit design of chargers is ease of modification. In our age of “Chinization” of electronics and the electronics industry, it is often easier, cheaper and more accessible to take a ready-made AT/ATX power supply and remake it to suit any of your needs, rather than buy separately a power transformer, bridge diodes, thyristor and other parts. First, I’ll tell you about the simplest (well, it couldn’t be simpler!!!) and reliable charger based on an AT power supply, without a current indicator (although no one bothers to install an ammeter).
Well, we found a suitable AT block assembled on the TL494. We wash it, clean it, dry it and lubricate the fan.

A small digression.

About the quality of components for AT and ATX units. I want to talk about important element circuits - 310 volt filter capacitor in the primary circuit. Not only such a parameter as ripple of the output voltage with the mains frequency under heavy load depends on it, but also, which is very important, the heating of the output switches themselves. If the capacity is not enough, then they have to work up to 35% of their time at a greater pulse width than with normal capacity, since the average rectified voltage is no longer 310 volts, but 250 - 260 volts due to ripples. The controller has to handle such dips by increasing the width and open time of the transistor. Consequently, they have to operate at a higher current than with sufficient capacity. It follows from this: more current - more heating - less efficiency. (It is already small 60 - 75% depending on the block). Having carried out some measurements of older and very old AT power supplies and newer ATX, it turned out that the Chinese have completely lost their conscience. If capacitors were installed before, as it is written on it, so it was. Now the 50% tolerance is always a minus.

I went through hundreds of blocks: It says 470 MKF, you unsolder it and measure - 300 -330 MKF, even a new capacitor - the same story.
Well, okay, let them write what they want: Well, we need to replace in the AT unit, on the basis of which we will build the charging 200 MKF with these same 330 MKF, or even better, 470 MKF (real 470). It will be easier for transistors.

It's the same story with chokes.

AT throttle: ATX throttle:

They are not finished, and the ring is smaller... The consequence of reducing the inductance of the group stabilization choke will be an acoustic whistle at low currents (1-2 amperes). The inductance of this inductor is calculated based on the continuity of the current through it at minimum loads. When the unit is turned on, it immediately reaches a power of at least 150W (depending on the computer). Certain currents flow through the inductor, no less than a certain value. The inductor can be designed for this minimum current value, but then, when turned on without a load, the current through the inductor will become intermittent, which will lead to some troubles... The PWM control circuit is designed for the case of continuous current, therefore, with intermittent current, the regulation will be go astray, the inductor will sing, the voltages at the outputs will jump, causing additional recharging currents of the electrolytic capacitors... Of course, in this case, the RC feedback correction circuit will come to our aid, but it is impossible to dull the reaction speed to voltage changes indefinitely, In some the torque of the TL494 during a short circuit simply will not have time to reduce the pulse width and the transistors will fail. This process is quite fast. Therefore, you need to be careful with this. Okay, that was a lyrical digression. Let's continue the "tambourine dance" with the charger.

Circuit with a soft charging current characteristic.

Standard AT block board. Let's look at the diagram to see what needs to be desoldered (and there is a lot, a lot of extra stuff that needs to be desoldered), and what to be soldered in order to get the simplest charging for the battery. The circuit is taken as a standard one, a standard AT unit, and the ratings of already installed elements may differ significantly from yours. There is NO NEED to change them to those indicated in the diagram! We solder only the overvoltage protections that have become unnecessary, 5 volt channel, -12 volt channel. In general, according to the scheme, we leave the following.

As a result, to get a full, adjustable charging of 10 amperes and 15.8 V with a fan controlled by the load current, you need to add only eight parts!!! Namely: replace two electrolytes, add a shunt of a very approximate resistance of 0.01 ohm -0.08 ohm (for example, three centimeters of a shunt from a Chinese cartoon - it works great). Photo of the original shunt (the author's donor was taken from a Soviet Tseshka):

A 120 ohm resistor, 3.9k, and about 18k, a 10k variable resistor, a 10 nano capacitor and turn the winding on the inductor along the -5 volt channel for the fan. Just don’t forget that the fan should now be connected like this: red to the case, and black to -5:.-12V. We solder the shunt into the gap of the pigtail from the power transformer. When you set the resistor to 3.9k, select its resistance based on the charge current of 10 amperes on a real battery. You won't believe it - that's all! This is simply an unprecedented simplicity of converting practically scrap metal into a completely worthy thing! If the diodes on the +12V channel were originally FR302, then you need to replace them with more powerful ones, for example, remove them from a more modern ATX power supply. Moreover, he is not afraid of a short circuit - he is included in the current limitation. But reversing the polarity of the connection to the battery will lead to a big bang! About "KNOW-HOW", unique protection against overload and short circuit will be written in the article. Colored circles and lines indicate added additional elements.

Setting up: All switching on until complete setting is carried out by connecting it to the network only in series with a 60 watt incandescent light bulb. We check the installation.

Setting up the voltage channel.

We connect the multimeter with crocodiles in voltage measurement mode in the range of up to 200 volts. We plug it into the network. The output voltage should be within 16 volts plus/minus 4 volts. If it’s about 5 volts, it means you forgot to replace the resistor in the voltage control circuit (1 pin of TL494) with 18k. If it is about 23-25V, and the output switches gradually heat up without load, then it means that there is a break in the voltage control circuit (1 pin of TL494) or the resistance of 18k is too high, and the unit has reached the full pulse width and still cannot gain voltage to turn on the reverse communications. We set this resistor to a voltage of approximately 15.8 - 16.2 volts. If you set it to 14.4 V, then after about 1 hour the battery will stop charging at all (tested many times on different batteries).

Setting the current channel.

We temporarily replace the resistor connected in series with the current regulator with a 22k trimmer and set it to the position of minimum resistance. We connect the multimeter with crocodiles in current measurement mode in the range of 10 amperes. We connect the unit to the network through a light bulb. If the light flashes and continues to glow brightly, it means something is wrong, check the installation. If the ammeter shows a current in the range from 1 to 4 amperes, then everything is fine. We set the variable resistor to maximum resistance mode, and use the trimming resistor to adjust the current to 15 -16 amperes. Sometimes the light bulb does not allow you to set it this way, so set it to approximately this current. Now, having connected the discharged battery and the ammeter in series to the output, remove the light bulb and plug it into the network. Using a trimming resistor we adjust the current more precisely, but already 10 amperes. Then we unsolder the trimmer, measure and solder in a constant resistor of the same resistance. The cooling fan should rotate at a speed proportional to the current. If at maximum current or short the speed is too high (voltage above 20 volts), then it is necessary to unwind 10 turns from the winding minus 5 volts of the fan power channel. The voltage on the fan with selected turns should be from 6 volts to 17 volts. That's it, the setup is complete.