Compliance with the operating mode of rechargeable batteries, and in particular the charging mode, guarantees their trouble-free operation throughout their entire service life. Batteries are charged with a current, the value of which can be determined by the formula
where I is the average charging current, A., and Q is the nameplate electric capacity of the battery, Ah.
A classic charger for a car battery consists of a step-down transformer, a rectifier and a charging current regulator. Wire rheostats (see Fig. 1) and transistor current stabilizers are used as current regulators.
In both cases, these elements generate significant thermal power, which reduces the efficiency of the charger and increases the likelihood of its failure.
To regulate the charging current, you can use a store of capacitors connected in series with the primary (mains) winding of the transformer and acting as reactances that dampen excess network voltage. A simplified version of such a device is shown in Fig. 2.
In this circuit, thermal (active) power is released only on the diodes VD1-VD4 of the rectifier bridge and the transformer, so the heating of the device is insignificant.
The disadvantage in Fig. 2 is the need to provide a voltage on the secondary winding of the transformer one and a half times greater than the rated load voltage (~ 18÷20V).
The charger circuit, which provides charging of 12-volt batteries with a current of up to 15 A, and the charging current can be changed from 1 to 15 A in steps of 1 A, is shown in Fig. 3.
It is possible to automatically turn off the device when the battery is fully charged. It is not afraid of short-term short circuits in the load circuit and breaks in it.
Switches Q1 - Q4 can be used to connect various combinations of capacitors and thereby regulate the charging current.
The variable resistor R4 sets the response threshold of K2, which should operate when the voltage at the battery terminals is equal to the voltage of a fully charged battery.
In Fig. Figure 4 shows another charger in which the charging current is smoothly regulated from zero to the maximum value.
The change in current in the load is achieved by adjusting the opening angle of the thyristor VS1. The control unit is made on a unijunction transistor VT1. The value of this current is determined by the position of the variable resistor R5. The maximum battery charging current is 10A, set with an ammeter. The device is provided on the mains and load side with fuses F1 and F2.
A version of the charger printed circuit board (see Fig. 4), 60x75 mm in size, is shown in the following figure:
In the diagram in Fig. 4, the secondary winding of the transformer must be designed for a current three times greater than the charging current, and accordingly, the power of the transformer must also be three times greater than the power consumed by the battery.
This circumstance is a significant drawback of chargers with a current regulator thyristor (thyristor).
Note:
The rectifier bridge diodes VD1-VD4 and the thyristor VS1 must be installed on radiators.
It is possible to significantly reduce power losses in the SCR, and therefore increase the efficiency of the charger, by moving the control element from the circuit of the secondary winding of the transformer to the circuit of the primary winding. such a device is shown in Fig. 5.
In the diagram in Fig. 5 control unit is similar to that used in the previous version of the device. SCR VS1 is included in the diagonal of the rectifier bridge VD1 - VD4. Since the current of the primary winding of the transformer is approximately 10 times less than the charging current, relatively little thermal power is released on the diodes VD1-VD4 and the thyristor VS1 and they do not require installation on radiators. In addition, the use of an SCR in the primary winding circuit of the transformer made it possible to slightly improve the shape of the charging current curve and reduce the value of the current curve shape coefficient (which also leads to an increase in the efficiency of the charger). The disadvantage of this charger is the galvanic connection with the network of elements of the control unit, which must be taken into account when developing a design (for example, use a variable resistor with a plastic axis).
A version of the printed circuit board of the charger in Figure 5, measuring 60x75 mm, is shown in the figure below:
Note:
The rectifier bridge diodes VD5-VD8 must be installed on radiators.
In the charger in Figure 5 there is a diode bridge VD1-VD4 type KTs402 or KTs405 with the letters A, B, C. Zener diode VD3 type KS518, KS522, KS524, or made up of two identical zener diodes with a total stabilization voltage of 16÷24 volts (KS482, D808 , KS510, etc.). Transistor VT1 is unijunction, type KT117A, B, V, G. The diode bridge VD5-VD8 is made up of diodes, with a working current not less than 10 amperes(D242÷D247, etc.). The diodes are installed on radiators with an area of at least 200 sq.cm, and the radiators will become very hot; a fan can be installed in the charger case for ventilation.
Probably every motorist is familiar with the problem of a dead or completely failed battery. Of course, resuscitating a car is not so difficult, but what if there is absolutely no time and you need to go urgently? After all, not everyone has a charger. From this material you will learn how to make a charger for a car battery with your own hands, what types there are.
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Pulse chargers for batteries
Not so long ago, transformer-type chargers were found everywhere, but today finding such a charger will be quite problematic. Over time, transformers faded into the background, losing ground. Unlike a transformer, a pulse charger allows you to provide full power, but this advantage is not the main one.
Working with a transformer required some skill, but with pulse memory devices they are quite easy to operate. In addition, unlike transformers, their cost is more affordable. Also, the transformer is characterized by large dimensions, and the dimensions of the pulse devices are more compact.
The battery of a pulse device, unlike a transformer, is charged in two stages. The first is constant voltage, the second is constant current. Usually, modern memory devices are based on similar, but quite complex circuits. So, if this device fails, the motorist will most likely have to buy a new one.
As for lead-acid batteries, these batteries are, in principle, temperature sensitive. If it’s hot outside, then the charge level should be at least half, and if the temperature is sub-zero, then the battery should be charged at least 75%. Otherwise, the charger will simply stop functioning and will need to be recharged. 12-volt pulse chargers are excellent for such purposes, since they do not have a negative impact on the battery itself (video author: Artem Petukhov).
Automatic chargers for car batteries
If you are a novice motorist, then it would be better for you to use an automatic battery charger. These chargers are equipped with rich functionality and protective options, which allows you to warn the driver if the connection is incorrect. In addition, the automatic charger will prevent voltage from being applied if it is not connected correctly. Sometimes charging can independently calculate the charge level and battery capacity.
Automatic memory circuits are equipped with additional devices - timers, which allow you to perform several different tasks. We are talking about fully charging the battery, rapid charging, as well as full. When the task is completed, the charger will notify the motorist about this and will automatically turn off.
As you know, if the precautions for using batteries are not followed, sulfitation, that is, salts, can occur on the battery plates. Thanks to the charge-discharge cycle, you can not only remove salts, but also increase the service life of the battery as a whole. In general, the cost of modern 12-volt chargers is not particularly high, so every motorist can purchase such a device. But there are times when the device is needed right now, but there is no way to charge the battery. You can try to make a simple homemade 12 volt charger with and without an ammeter, we will talk about this later.
How to make a device yourself
How to make a simple homemade one? Several methods are given below (video author - Crazy Hands).
Charger for battery from PC power supply
A good 12 volt one can be built using a working power supply from a computer and an ammeter. This rectifier with ammeter is suitable for almost all batteries.
Almost every power supply is equipped with a PWM - a working controller on a chip. To properly charge the battery, you need about 10 current (from a full battery charge). So if you have a power supply greater than 150W, you can use it.
- The wires should be removed from the -5 volt, -12 volt, +5V and +12V connectors.
- After this, resistor R1 is unsoldered; instead, a 27 kOhm resistor should be installed. Also, output 16 must be disconnected from the main drive.
- Next, on the back side of the power supply you need to mount a current regulator of type R10, and also run two wires - the network wire and for connecting to the terminals. Before making a rectifier, it is advisable to prepare a block of resistors. To make it, you just need to connect two resistors in parallel to measure current, the power of which will be 5 W.
- To set the rectifier to 12 volts, you also need to install another resistor on the board - a trimmer. To avoid possible connections between the electrical circuit and the housing, remove a small portion of the trace.
- Next, in the diagram it is necessary to tin and solder the wiring on pins 14, 15, 16 and 1. Special clamps must be mounted on the pins so that the terminal can be hooked. In order not to confuse plus and minus, the wires should be marked; for this you can use insulating tubes.
If you will only use a 12-volt do-it-yourself charger to charge the battery, then you will not need an ammeter and voltmeter. Using an ammeter will allow you to know the exact state of charge of the battery. If the dial scale on the ammeter does not fit, then you can draw your own on the computer. The printed scale is installed in the ammeter.
The simplest memory using an adapter
You can also make a device where the main function of the current source will be performed by a 12 volt adapter. This device is quite simple; its manufacture does not require a special circuit. One important point should be taken into account - the voltage indicator in the source must correspond to the battery voltage. If these indicators differ, then you will not be able to charge the battery.
- Take the adapter; the end of its wire should be cut and exposed to 5 cm.
- Then the wires with different charges should be moved away from each other by about 35-40 cm.
- Now you should install clamps on the ends of the wires, as in the previous case, they should be marked in advance, otherwise you may get confused later. These clamps are connected to the battery one by one, only after that it will be possible to turn on the adapter.
In general, the method is simple, but the difficulty of the method is to choose the right source. If during charging you notice that the battery gets very hot, you need to interrupt this process for a few minutes.
Charger from a household light bulb and diode
This method is one of the simplest. To build such a device, prepare in advance:
- a regular lamp, high power is welcome, as it affects the charging speed (up to 200 W);
- a diode through which current flows in one direction, for example, such diodes are installed in laptop chargers;
- plug and cable.
The connection procedure is quite simple. A more detailed diagram is presented in the video at the end of the article.
Conclusion
Please note that in order to make a high-quality memory, it is not enough just to read this article. You must have certain knowledge and skills and familiarize yourself with the videos presented here in detail. An incorrectly assembled device can damage the battery. On sale in the automotive market you can find inexpensive and high-quality chargers that will last for many years.
Video “How to build a charger from a diode and a light bulb?”
Find out how to do this type of exercise correctly from the video below (video author: Dmitry Vorobyev).
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 a simple car battery charging scheme 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 charging current limitation. 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.
Every car owner needs a battery charger, but it costs a lot, and regular preventive trips to a car service center are not an option. Battery service at a service station takes time and money. In addition, with a discharged battery, you still need to drive to the service station. Anyone who knows how to use a soldering iron can assemble a working charger for a car battery with their own hands.
A little theory about batteries
Any battery is a storage device for electrical energy. When voltage is applied to it, energy is stored due to chemical changes inside the battery. When a consumer is connected, the opposite process occurs: a reverse chemical change creates voltage at the terminals of the device, and current flows through the load. Thus, in order to get voltage from the battery, you first need to “put it down,” that is, charge the battery.
Almost any car has its own generator, which, when the engine is running, provides power to the on-board equipment and charges the battery, replenishing the energy spent on starting the engine. But in some cases (frequent or difficult engine starts, short trips, etc.) the battery energy does not have time to be restored, and the battery is gradually discharged. There is only one way out of this situation - charging with an external charger.
How to find out the battery status
To decide whether charging is necessary, you need to determine the state of the battery. The simplest option - “turns/does not turn” - is at the same time unsuccessful. If the battery “doesn’t turn”, for example, in the garage in the morning, then you won’t go anywhere at all. The “does not turn” condition is critical, and the consequences for the battery can be dire.
The optimal and reliable method for checking the condition of a battery is to measure the voltage on it with a conventional tester. At an air temperature of about 20 degrees dependence of the degree of charge on voltage on the terminals of the battery disconnected from the load (!) is as follows:
- 12.6…12.7 V - fully charged;
- 12.3…12.4 V - 75%;
- 12.0…12.1 V - 50%;
- 11.8…11.9 V - 25%;
- 11.6…11.7 V - discharged;
- below 11.6 V - deep discharge.
It should be noted that the voltage of 10.6 volts is critical. If it drops below, the “car battery” (especially a maintenance-free one) will fail.
Correct charging
There are two methods of charging a car battery - constant voltage and constant current. Everyone has their own features and disadvantages:
Homemade battery chargers
Assembling a charger for a car battery with your own hands is realistic and not particularly difficult. To do this, you need to have basic knowledge of electrical engineering and be able to hold a soldering iron in your hands.
Simple 6 and 12 V device
This scheme is the most basic and budget-friendly. Using this charger, you can efficiently charge any lead-acid battery with an operating voltage of 12 or 6 V and an electrical capacity of 10 to 120 A/h.
The device consists of a step-down transformer T1 and a powerful rectifier assembled using diodes VD2-VD5. The charging current is set by switches S2-S5, with the help of which quenching capacitors C1-C4 are connected to the power circuit of the primary winding of the transformer. Thanks to the multiple “weight” of each switch, various combinations allow you to stepwise adjust the charging current in the range of 1–15 A in 1 A increments. This is enough to select the optimal charging current.
For example, if a current of 5 A is required, then you will need to turn on the toggle switches S4 and S2. Closed S5, S3 and S2 will give a total of 11 A. To monitor the voltage on the battery, use a voltmeter PU1, the charging current is monitored using an ammeter PA1.
The design can use any power transformer with a power of about 300 W, including homemade ones. It should produce a voltage of 22–24 V on the secondary winding at a current of up to 10–15 A. In place of VD2-VD5, any rectifier diodes that can withstand a forward current of at least 10 A and a reverse voltage of at least 40 V are suitable. D214 or D242 are suitable. They should be installed through insulating gaskets on a radiator with a dissipation area of at least 300 cm2.
Capacitors C2-C5 must be non-polar paper with an operating voltage of at least 300 V. Suitable, for example, are MBChG, KBG-MN, MBGO, MBGP, MBM, MBGCh. Similar cube-shaped capacitors were widely used as phase-shifting capacitors for electric motors in household appliances. A DC voltmeter of type M5−2 with a measurement limit of 30 V was used as PU1. PA1 is an ammeter of the same type with a measurement limit of 30 A.
The circuit is simple, if you assemble it from serviceable parts, then it does not need adjustment. This device is also suitable for charging six-volt batteries, but the “weight” of each of the switches S2-S5 will be different. Therefore, you will have to navigate the charging currents using an ammeter.
With continuously adjustable current
Using this scheme, it is more difficult to assemble a charger for a car battery with your own hands, but it can be repeated and also does not contain scarce parts. With its help, it is possible to charge 12-volt batteries with a capacity of up to 120 A/h, the charge current is smoothly regulated.
The battery is charged using a pulsed current; a thyristor is used as a regulating element. In addition to the knob for smoothly adjusting the current, this design also has a mode switch, when turned on, the charging current doubles.
The charging mode is controlled visually using the RA1 dial gauge. Resistor R1 is homemade, made of nichrome or copper wire with a diameter of at least 0.8 mm. It serves as a current limiter. Lamp EL1 is an indicator lamp. In its place, any small-sized indicator lamp with a voltage of 24–36 V will do.
A step-down transformer can be used ready-made with an output voltage on the secondary winding of 18–24 V at a current of up to 15 A. If you don’t have a suitable device at hand, you can make it yourself from any network transformer with a power of 250–300 W. To do this, wind all windings from the transformer except the mains winding, and wind one secondary winding with any insulated wire with a cross-section of 6 mm. sq. The number of turns in the winding is 42.
Thyristor VD2 can be any of the KU202 series with the letters V-N. It is installed on a radiator with a dispersion area of at least 200 sq. cm. The power installation of the device is done with wires of minimal length and with a cross-section of at least 4 mm. sq. In place of VD1, any rectifier diode with a reverse voltage of at least 20 V and withstanding a current of at least 200 mA will work.
Setting up the device comes down to calibrating the RA1 ammeter. This can be done by connecting several 12-volt lamps with a total power of up to 250 W instead of a battery, monitoring the current using a known-good reference ammeter.
From a computer power supply
To assemble this simple charger with your own hands, you will need a regular power supply from an old ATX computer and knowledge of radio engineering. But the characteristics of the device will be decent. With its help, batteries are charged with a current of up to 10 A, adjusting the current and charge voltage. The only condition is that the power supply is desirable on the TL494 controller.
For creating DIY car charging from a computer power supply you will have to assemble the circuit shown in the figure.
Step by step steps required to finalize the operation will look like this:
- Bite off all the power bus wires, with the exception of the yellow and black ones.
- Connect the yellow and separately black wires together - these will be the “+” and “-” chargers, respectively (see diagram).
- Cut all traces leading to pins 1, 14, 15 and 16 of the TL494 controller.
- Install variable resistors with a nominal value of 10 and 4.4 kOhm on the power supply casing - these are the controls for regulating the voltage and charging current, respectively.
- Using a suspended installation, assemble the circuit shown in the figure above.
If the installation is done correctly, then the modification is complete. All that remains is to equip the new charger with a voltmeter, an ammeter and wires with alligator clips for connecting to the battery.
In the design it is possible to use any variable and fixed resistors, except for the current resistor (the lower one in the circuit with a nominal value of 0.1 Ohm). Its power dissipation is at least 10 W. You can make such a resistor yourself from a nichrome or copper wire of the appropriate length, but you can actually find a ready-made one, for example, a 10 A shunt from a Chinese digital tester or a C5-16MV resistor. Another option is two 5WR2J resistors connected in parallel. Such resistors are found in switching power supplies for PCs or TVs.
What you need to know when charging a battery
When charging a car battery, it is important to follow a number of rules. This will help you Extend battery life and maintain your health:
The question of creating a simple battery charger with your own hands has been clarified. Everything is quite simple, all you have to do is stock up on the necessary tools and you can safely get to work.
Sometimes it happens that the battery in the car runs out and it is no longer possible to start it, since the starter does not have enough voltage and, accordingly, current to crank the engine shaft. In this case, you can “light it” from another car owner so that the engine starts and the battery starts charging from the generator, but this requires special wires and a person willing to help you. You can also charge the battery yourself using a specialized charger, but they are quite expensive and you don’t have to use them very often. Therefore, in this article we will take a detailed look at the homemade device, as well as instructions on how to make a charger for a car battery with your own hands.
Homemade device
Normal battery voltage when disconnected from the vehicle is between 12.5 V and 15 V. Therefore, the charger must output the same voltage. The charge current should be approximately 0.1 of the capacity, it can be less, but this will increase the charging time. For a standard battery with a capacity of 70-80 Ah, the current should be 5-10 amperes, depending on the specific battery. Our homemade battery charger must meet these parameters. To assemble a charger for a car battery, we need the following elements:
Transformer. Any old electrical appliance or one purchased on the market with an overall power of about 150 watts is suitable for us, more is possible, but not less, otherwise it will get very hot and may fail. It’s great if the voltage of its output windings is 12.5-15 V and the current is about 5-10 amperes. You can view these parameters in the documentation for your part. If the required secondary winding is not available, then it will be necessary to rewind the transformer to a different output voltage. For this:
Thus, we found or assembled the ideal transformer to make our own battery charger.
We will also need:
Having prepared all the materials, you can proceed to the process of assembling the car charger itself.
Assembly technology
To make a charger for a car battery with your own hands, you need to follow the step-by-step instructions:
- We create a homemade battery charging circuit. In our case it will look like this:
- We use transformer TS-180-2. It has several primary and secondary windings. To work with it, you need to connect two primary and two secondary windings in series to obtain the desired voltage and current at the output.
- Using a copper wire, we connect pins 9 and 9’ to each other.
- On a fiberglass plate we assemble a diode bridge from diodes and radiators (as shown in the photo).
- We connect pins 10 and 10’ to the diode bridge.
- We install a jumper between pins 1 and 1’.
- Using a soldering iron, attach a power cord with a plug to pins 2 and 2’.
- We connect a 0.5 A fuse to the primary circuit, and a 10-amp fuse to the secondary circuit, respectively.
- We connect an ammeter and a piece of nichrome wire into the gap between the diode bridge and the battery. One end of which is fixed, and the other must provide a moving contact, thus the resistance will change and the current supplied to the battery will be limited.
- We insulate all connections with heat shrink or electrical tape and place the device in the housing. This is necessary to avoid electric shock.
- We install a moving contact at the end of the wire so that its length and, accordingly, the resistance are maximum. And connect the battery. By decreasing or increasing the length of the wire, you need to set the desired current value for your battery (0.1 of its capacity).
- During the charging process, the current supplied to the battery will itself decrease and when it reaches 1 ampere, we can say that the battery is charged. It is also advisable to directly monitor the voltage on the battery, but to do this it must be disconnected from the charger, since when charging it will be slightly higher than the actual values.
The first start-up of the assembled circuit of any power source or charger is always carried out through an incandescent lamp if it lights up at full intensity - either there is an error somewhere, or the primary winding is short-circuited! An incandescent lamp is installed in the gap of the phase or neutral wire feeding the primary winding.
This circuit of a homemade battery charger has one big drawback - it does not know how to independently disconnect the battery from charging after reaching the required voltage. Therefore, you will have to constantly monitor the readings of the voltmeter and ammeter. There is a design that does not have this drawback, but its assembly will require additional parts and more effort.
A visual example of the finished product
Operating rules
The disadvantage of a homemade charger for a 12V battery is that after the battery is fully charged, the device does not automatically turn off. That is why you will have to periodically glance at the scoreboard in order to turn it off in time. Another important nuance is that checking the charger for spark is strictly prohibited.
Additional precautions to take include:
- when connecting the terminals, make sure not to confuse “+” and “-”, otherwise a simple homemade battery charger will fail;
- connection to the terminals should only be made in the off position;
- the multimeter must have a measurement scale greater than 10 A;
- When charging, you should unscrew the plugs on the battery to avoid its explosion due to boiling of the electrolyte.
Master class on creating a more complex model
That, in fact, is all I wanted to tell you about how to properly make a charger for a car battery with your own hands. We hope that the instructions were clear and useful for you, because... This option is one of the simplest types of homemade battery charging!
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