Charger with current stabilization. Adjustable voltage stabilizer for charger Charger circuit for cars with stable voltage
I recently had to build my own charger for a car battery with a current of 3 - 4 amperes. Of course, I didn’t want to split hairs, I didn’t have time, and first of all I remembered the charging current stabilizer circuit. Using this scheme it is very simple and reliable to make a charger.
Here is the circuit diagram for the charger:
An old microcircuit (K553UD2) was installed, although it was old, there was simply no time to try new ones, and besides, it was at hand. The shunt from the old tester fit perfectly in place of resistor R3. The resistor can, of course, be made from nichrome yourself, but the cross-section must be sufficient to withstand the current through it and not heat up to the limit. 
We install the shunt parallel to the ammeter, select it taking into account the dimensions of the measuring head. Actually, we install it on the head terminal itself.
This is how it looks printed circuit board charger current stabilizer:
Any transformer can be used from 85 W and above. The secondary winding should have a voltage of 15 volts, and the wire cross-section should start from 1.8 mm (copper diameter). A 26MV120A took the place of the rectifier bridge. It may be too big for this type of design, but it is very easy to install, just screw it on and put on the terminals. You can install any diode bridge. For him, the main task is to withstand the appropriate current.
The case can be made from anything; the case from an old radio tape recorder worked well for me. For good air flow top cover drilled holes. Instead of the front panel, a sheet of PCB was installed. The shunt, the one on the ammeter, must be adjusted based on the readings of the test ammeter.
We attach a transistor to the back wall of the radiator.
Well, we have assembled the current stabilizer, now we need to check it by short-circuiting (+) and (-) together. The regulator should provide smooth adjustment over the entire range of charging current. If necessary, you can use the selection of resistor R1.
It is important to remember that all the voltage goes to the control transistor and it gets very hot! Once checked, open the jumper!
Everything is ready and you can now use a charger that will consistently maintain current throughout the entire charging range. It is necessary to monitor the voltage reading on the battery using a voltmeter, since such a charger does not have an automatic shutdown after charging is complete.
CHARGING DEVICE FOR CAR BATTERIES
Charger circuits for car batteries are quite common and each has its own advantages and disadvantages. Most of the simplest charger circuits are built on the principle of a voltage regulator with an output node assembled using thyristors or powerful transistors. These circuits have significant drawbacks - the charging current is not constant and depends on the voltage achieved on the battery. A large number of circuits do not have protection against output short circuit, which leads to breakdown of the output power elements. The proposed scheme is devoid of these shortcomings, is quite reliable (developed in 1995 and manufactured in about 20 copies, which have never failed) and is designed to be repeated by “average” radio amateurs.
The device provides charging current up to 6A, current and voltage control using a dial indicator, short circuit protection and automatic shutdown after a specified time using a timer. The circuit consists of a driver sawtooth voltage(transistors VT1, VT2), comparator DA1 , signal amplifier from a current-sensing shunt on an operational amplifier DA2 and output power thyristors VD5, VD6 , which are installed on small radiators, for which the metal body of the device can be used. Setting up the circuit is carried out in several stages: 1. The amplitude of the “saw” on a variable resistor is measured with an oscilloscope R6 , which should be about 2V, otherwise select a resistor R4 e they are brought to this value. Next, the shunt is loaded R18 current 6A and selection of resistors R15, R17 achieve a voltage level at input 3 of the comparator equal to the amplitude of the sawtooth voltage (2V) - after which the charger begins to normally regulate the output current. 2. A battery to be charged is connected to the output of the device in series with an external reference ammeter, the current regulator is set to 3 ... 6 A, and the charger toggle switch is switched to the “current” position. Selecting a resistor R14 achieve correct current readings on the scale of the built-in device. 3. The battery is connected directly to the output of the charger and the voltage on it is monitored using an external reference voltmeter. Selecting a resistor R20 achieve correct readings from the built-in dial gauge on the voltage scale. This completes the setup. Any available head can be used as a measuring device, the linear scale of which must be prepared in advance. Shunt R18 can be made from a piece of nichrome wire with a diameter of about 2 mm and a length of about 15 cm. The accuracy of setting the resistance does not play a big role, because selection of resistors R15, R17 the required output signal value is set DA2 . If the thyristors are not started reliably enough, capacitor C6 can be removed and resistor R11 replaced with a two-watt one, rated 510 Ohm... 1 kOhm. The timer does not require separate settings; if desired, you can not make it - the rest of the circuit will not change. The main electronic elements are assembled on a printed circuit board.
This circuit has stood the test of time, does not contain scarce or less common elements, but over the past period a new accessible element base has appeared, allowing the construction of power supplies with higher characteristics. The circuits presented on the following pages of the section were developed relatively recently, use currently available elements and are suitable for repetition by intermediate-level radio amateurs:
Under certain conditions, the car battery discharges. This can happen either due to natural wear and tear of the part or due to improper use. For example, if you leave your car in a car park over the winter, it is likely that you will need a charger to revive the car.
Attention! You can assemble a charger for a car battery with your own hands, the main thing is to do everything exactly according to the diagram.
Battery discharging process
Before you begin restoring the device, it is necessary to consider in detail the reason that led to this situation. The scheme of operation is quite simple. The battery is charged from the generator.
To ensure that the release of gases during charging does not exceed permissible limits, a special relay is installed. It provides required level supply of electricity. Typically this indicator is set at 14.1 V. The error is allowed within 0.2 V.
However, in order for a car battery to be fully charged, you need a charger with an output power of 14.5 V; its circuit is quite simple. It is not surprising that almost every motorist can make the device.
If the temperature outside is above zero, a half-charged battery can start the car. Unfortunately, in the winter you may have serious problems in the same situation. The fact is that when it’s -20 outside, the battery capacity is halved. It is not surprising that in this situation, most motorists are thinking about a battery charger circuit that could be easily assembled.
Under the influence of negative temperatures, the viscosity of the lubricant increases. The strength of inrush currents also increases. As a result, it will be impossible to start the car without lighting a cigarette. Of course, it’s better not to let this happen.
Important! Before winter, the best battery prevention is to charge it using a charger that you assembled based on one of the circuits presented in the article.
Of course, a battery charger can be purchased at a store, but its cost is not small. Perhaps it is for this reason that more and more motorists are turning to old schemes that allow them to assemble a working device with their own hands in a few hours.
About car chargers
If you want and have some agility, you can even charge the battery using a single diode. True, you will also need a heater for this, but usually every garage has one.
The circuit diagram for such a primitive charger is quite simple. The battery is connected via a diode to electrical network. The heater power can be in the range of 1-2 kilowatts. Fifteen hours of such therapy is enough to bring the battery back to life.
Important! The efficiency of a charger whose electrical circuit consists of a heater and a diode is only 1 percent.
If, as an alternative, we consider chargers whose operating circuits contain transistors, then such devices differ in that generate enormous amounts of heat. They are also at risk of short circuiting. Particularly expensive when using them is the error in choosing the polarity when connecting to the battery contacts.
Often, when creating a charger, drivers use circuits that include thyristors. Unfortunately, they are not able to provide high stability of the current supplied to the battery.
Another significant drawback of charger circuits with thyristors is acoustic noise. We cannot ignore radio interference that can affect operation. mobile phones or other radio equipment.
Important! A ferrite ring can significantly reduce radio interference from a charger with thyristors. It needs to be put on the power cord.
What schemes are popular on the Internet?
There are many technical solutions, each of which has its own pros and cons. Most often on the Internet you can find a circuit diagram for a charger from a computer power supply.
There are several important nuances in such a decision. Many motorists choose this particular path of creating a charging device because the structural diagrams of power supplies for computers are identical to each other. Nevertheless electrical circuits they have different ones. Therefore, in order to work with devices of this class, specialized education is required. It will be quite difficult for self-taught and amateurs to cope with similar work.
It is better to focus your attention on the capacitor circuit. It has the following advantages:
- Firstly, it gives relatively high efficiency.
- Secondly, this design generates minimal heat.
- Thirdly, it guarantees a stable current source.
- The fourth indisputable advantage is quite good protection against accidental short circuiting.
Unfortunately, it was not possible to do without shortcomings. Sometimes during operation of this charger there is a loss of contact with the battery. As a result, the voltage increases several times. This creates a resonant circuit. This disables the entire circuit.
Current schemes
General structure
Despite the apparent complexity, this structure quite easy to create. In fact, it consists of several complete systems. If you don't feel confident enough to collect it. You can eliminate some elements while maintaining most of the performance.
For example, you can exclude from this figure all the elements that are responsible for automatic shutdown. This will greatly simplify the process of radio engineering work.
Important! In the overall structure, a special role is played by the electrical system, which is responsible for protecting against incorrect connection of poles.
A relay is used to protect the charger from incorrect pole connection. In this case, if connected incorrectly, the diode will not allow current to pass through, and the circuit will remain operational.
Provided that all contacts are connected correctly, current flows to the terminals and the device provides power to the car battery. This type of protection system can be used with thyristor and transistor equipment.
Ballast capacitors
When you make a capacitor-type charging system, special attention should be paid to the radio engineering structure responsible for stabilizing the current strength. It is best to organize its operation by connecting the primary winding T1 and capacitors C4-C9 in series.
Important! Increasing the capacitance of the capacitor allows you to achieve an increase in current power.
The figure above shows a fully completed electrical structure capable of charging a battery. The only thing needed is a diode bridge. Is it true, It is worth noting that the reliability of this system is extremely low. The slightest violation of contact leads to breakdown of the transformer.
The capacitor value directly depends on the battery charge, the relationship is as follows:
- 0.5 A - 1 µF;
- 1 A - 3.4 µF;
- 2 A - 8 µF;
- 4 A - 16 µF;
- 8 A - 32 µF.
It is best to connect capacitors in groups parallel to each other. A two-bar device can be used as a switch. Sometimes engineers use toggle switches in their circuits.
Results
There are many simple battery charger circuits. In order to make them yourself, you do not need any special radio engineering knowledge. All you need is perseverance and the desire to restore your car battery at no cost. It is most practical to use a capacitor circuit. It has high efficiency and has good short circuit resistance.
Charger for car batteries is an irreplaceable thing that every car enthusiast should have, no matter how good the battery is, since it can fail at the most inconvenient moment.
We have repeatedly reviewed the designs of numerous chargers on the pages of the site. The charger is, in theory, nothing more than a power supply with current and voltage stabilization. It works simply - we know that the voltage of a charged car battery is about 14-14.4 Volts, you need to set exactly this voltage on the charger, then set the desired charging current, in the case of acid starter batteries this is a tenth of the battery capacity, for example - a 60 A battery /h, we charge it with a current of 6 Amps.
As a result, as the battery charges, the current will drop and eventually reach zero - as soon as the battery is charged. This system is used in all chargers; the charging process does not need to be constantly monitored, since all output parameters of the charger are stable and do not depend on changes in mains voltage.
Based on this, it becomes clear that to build a charger you need to have three nodes.
1) Step-down transformer or switching power supply plus rectifier
2) Current stabilizer
3) Voltage stabilizer
With the help of the latter, the voltage threshold is set to which the battery will be charged, and today we will talk specifically about the voltage stabilizer.
The system is ugly as hell, only 2 active components, minimum costs, well, assembly will take no more than 10 minutes if you have all the components.
What we have. a field-effect transistor as a power element, an adjustable zener diode that sets the stabilization voltage, this voltage can be set manually using a variable (or better yet, a tuning, multi-turn) 3.3 kOhm resistor. A voltage of up to 50 Volts can be supplied to the input of the stabilizer, and at the output we already obtain a stable voltage of the required rating.
The minimum possible voltage is 3V (depending on field effect transistor) the fact is that in order for a field-effect transistor to open at its gate, you need to have a voltage above 3 volts (in some cases more) except for field-effect transistors, which are designed to work in circuits with a logical control level.
The stabilizer can switch currents up to 10 Amps depending on conditions, in particular on the type of field-effect transistor, the presence of a radiator and active cooling.
The TL431 adjustable zener diode is a popular item and can be found in any computer power supply; it is used to control the output voltage and is located next to the optocoupler.
I disassembled one of my chargers to show what the stabilizer looks like, there is no need to judge strictly the quality of installation, a friend’s charger has been working for 2 years without any complaints, I made it in a hurry and didn’t bother too much.
And I also want to note one point, if you decide to change the oil in your car, then I would like to recommend the excellent trading house “Maslyonka”, which deals specifically in this direction. Come in and choose industrial oil, there are no fakes here...
