Electronic circuits of Kravtsov Vitaly. Adjustable Voltage Stabilizer for Charger

A 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 pulse source 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 incredibly simple, only 2 active components, minimal costs, and assembly will take no more than 10 minutes if all components are available.

What do 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, trimmer, 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 3 Volts (depending on the field-effect transistor), the fact is that in order for the 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 that are designed to operate 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 strictly judge the quality of installation, the charger has been working for a friend for 2 years without any complaints, he made it on a quick fix 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 want to recommend an excellent trading house“Maslyanka”, which works precisely in this direction. Come in and choose industrial oil, there are no fakes here...

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 the required level of power supply. 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 the 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 the operation of 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. However, their electrical circuits are different. 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 such work.

It is better to focus your attention on the capacitor circuit. It has the following advantages:

1. Firstly, it gives relatively high efficiency.
2. Secondly, this design generates minimal heat.
3. Thirdly, it guarantees a stable current source.
4. 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 its apparent complexity, this structure is quite simple 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 general 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.

For those who don’t have time to “bother” with all the nuances of charging a car battery, monitoring the charging current, turning it off in time so as not to overcharge, etc., we can recommend simple diagram charging a car battery with automatic shutdown when the battery is fully charged. This circuit uses one low-power transistor to determine the voltage on the battery.

Scheme of a simple automatic car battery charger

List of required parts:

• R1 = 4.7 kOhm;
• P1 = 10K trimmer;
• T1 = BC547B, KT815, KT817;
• Relay = 12V, 400 Ohm, (can be automotive, for example: 90.3747);
• TR1 = secondary winding voltage 13.5-14.5 V, current 1/10 of the battery capacity (for example: battery 60A/h - current 6A);
• Diode bridge D1-D4 = for a current equal to the rated current of the transformer = at least 6A (for example D242, KD213, KD2997, KD2999...), installed on the radiator;
• Diodes D1 (in parallel with the relay), D5.6 = 1N4007, KD105, KD522...;
• C1 = 100uF/25V.
• R2, R3 - 3 kOhm
• HL1 - AL307G
• HL2 - AL307B

The circuit lacks a charging indicator, current control (ammeter) and limitation charging current. If desired, you can put an ammeter at the output at the break of any of the wires. LEDs (HL1 and HL2) with limiting resistances (R2 and R3 - 1 kOhm) or light bulbs in parallel with C1 “mains”, and to the free contact RL1 “end of charge”.

Changed scheme

A current equal to 1/10 of the battery capacity is selected by the number of turns of the secondary winding of the transformer. When winding the transformer secondary, it is necessary to make several taps to select the optimal charging current option.

The charge of a car (12-volt) battery is considered complete when the voltage at its terminals reaches 14.4 volts.

The shutdown threshold (14.4 volts) is set by trimming resistor P1 when the battery is connected and fully charged.

When charging a discharged battery, the voltage on it will be about 13V; during charging, the current will drop and the voltage will increase. When the voltage on the battery reaches 14.4 volts, transistor T1 turns off relay RL1, the charging circuit will be broken and the battery will be disconnected from the charging voltage from diodes D1-4.

When the voltage drops to 11.4 volts, charging resumes again; this hysteresis is provided by diodes D5-6 in the emitter of the transistor. The circuit's response threshold becomes 10 + 1.4 = 11.4 volts, which can be considered to automatically restart the charging process.

This homemade simple automatic car charger will help you control the charging process, not track the end of charging and not overcharge your battery!

Website materials used: homemade-circuits.com

Another version of the charger circuit for a 12-volt car battery with automatic shutdown at the end of charging

The scheme is a little more complicated than the previous one, but with clearer operation.

Table of voltages and percentage of battery discharge not connected to the charger

P O P U L A R N O E:

Descriptions of oscillographic TV attachments have already been published on the pages of the magazine (Radio, 1959, No. 1; 1965, No. 8, etc.). However, unlike them, the proposed set-top box does not require intervention in the TV circuit (it is connected to the TV antenna socket). Together with a sweep frequency generator, it can be used to set up IF amplifiers for radio receivers.

The battery is a fairly expensive car part. Therefore, she needs care and control! Below we will look at an indicator that is designed to monitor the voltage of a car battery. It controls the voltage of the vehicle’s on-board network and is powered by it.

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.

This is what the charger current stabilizer circuit board looks like:

The case can be made from anything; the case from an old radio tape recorder worked well for me. For good air passage, I drilled holes on the top cover. 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.