Currently, there is no point in making a simple charger for a car battery. Many stores sell ready-made options with reasonable prices. However, it’s more pleasant to do something with your own hands. In addition, you can use the means at hand, and the final cost will seem meager.
At the same time, it is worth noting that circuits in the absence of precise adjustment of the current and voltage at the output, which do not have a current cut-off at the end of the charge, are relevant only for lead-acid batteries. The use of home-made devices to AGM-batteries or gel batteries, as a rule, ends with their damage.
The simplest scheme
The simplest assembly scheme for a car battery charger includes transformers. And most interestingly, it is assembled from available components. But professional factory analogues are designed in the same way. And, despite the primitiveness of a home-made device, it is sufficiently functional.
In addition, this charge has a rather high efficiency, and during operation it is not capable of generating heat. In addition, the device has a stable current, and regardless of charge and feed fluctuations. In addition, there is short circuit protection.
Snap needed
To assemble a DIY battery charger for a car battery yourself, you need a TH61-22 transformer with a series connection of the windings. Its efficiency is not lower than 0.8, and the current strength does not exceed 6 A. The secondary winding of the transformer should produce a voltage of not more than 20 volts with a current strength of 8 amperes. If the finished part could not be found, then you can use any other transformer with which to rewind the secondary winding to obtain the necessary output current characteristics.
Other accessories will also be needed:
- Capacitors of the MBGCH series are capable of working with an alternating voltage of 350 V (not less).
- Diodes capable of withstanding a current load of 10 A.
- Device for changing voltage.
As for the last point, in this case, you can use an ammeter capable of working with direct current.
Or use an electromagnetic head like M24.
Step-by-step assembly process
You can make a homemade charger for your battery according to the following instructions:
- First, a circuit is selected that will be implemented - in this case, a capacitor.
- Now you should choose a case of suitable dimensions, where a board with all the necessary details will be conveniently located. You can even opt for a milliammeter case.
- The transformer is mounted on an aluminum plate, which, in turn, is fixed in the housing.
- A textolite plate is placed inside the case, on which capacitors, relays and other details are placed.
- Now the voltage regulator and terminals for the terminals should be fixed on the case.
- Outside, a massive aluminum radiator is placed to cool power diodes. In addition to it, you need a fuse and a plug to supply current.
- All parts must be connected according to the diagram.
- Wires with fixed “crocodiles” that come from the charger and are designed to be connected to the battery should be with a cross-section of at least 1 mm 2 .
Most home-made devices can not boast of high efficiency, up to 90%. But, on the other hand, they are simple, and from this no less reliable purchased counterparts. In addition, they cope with their task.
If you want, you can use a more complex scheme with a set of additional options. Such chargers are able to work in different modes, including automatic. They may also have protective systems against overheating and overcharging the battery.
The simplest charger transistors
At the same time, it is possible to do without a winding at all, supplementing the circuit with an electronic voltage stabilizer, placing it at the output. Such a scheme will be relevant in conditions of garage use, since it is possible to adjust the charge current in the event of voltage dips.
The regulator here is the composite transistor KT814-KT837, a variable resistor will regulate the output. During the assembly process, instead of the Zener diode 1N 754A, you can use the Soviet analog D814A.
A similar circuit with electronic adjustment is assembled using a surface mount method where there is no need to etch a printed circuit board. At the same time, it should be borne in mind that field-effect transistors should be placed on a radiator, which will significantly heat up.
For this reason, it is optimal to take a computer cooler, which usually cools the processor. Its fan is connected to the battery charger outputs. The power of the resistor R1 should be 5 W, not less. It can be wound from nichrome or fechral or connected in parallel with 10 resistors of 1 W (10 Ohms). The resistor can not be included at all in the circuit of the simplest charger, just do not forget that its presence allows you to protect the transistors when the wires are shorted.
Choosing a transformer, it is worth focusing on the output voltage - 12.6-16 V. You can choose a local part from which to connect two windings in parallel. In an extreme case, start looking for a finished device with the desired potential difference.
Home-made device on a thyristor
Those homemasters who are afraid to hold a soldering iron in their hands can be advised to assemble a battery charger with a smooth adjustment of the charge current. Moreover, such a circuit is devoid of the disadvantages that are inherent in the resistor analog.
In this case, the regulator is by no means a heat dissipator (usually a powerful rheostat is used in this capacity), but an electronic key on the thyristor. In this case, the entire load is perceived by this semiconductor element. And since the simple circuit of the thyristor charger is designed for a current of 10 A, this device can replenish the energy of the battery with a capacity of up to 90 A / h. And by adjusting the degree of opening of the transition by the resistor R5 on the transistor VT1, a smooth and very accurate control of the VS1 trinistor is provided.
Despite the simplicity of the circuit, it is reliable, easy to assemble and configure. At the same time, there is one important condition for ensuring the proper operation of a home-made device of this type. We are talking about the power of the transformer, which should be three times the supply current of the charge. In other words, with an upper limit of 10 A, the parameter should be at least 450-500 watts.
It is worth noting that the resulting design will be distinguished by its massiveness. However, as a stationary charger for a car battery, such a scheme is quite acceptable.
Simple impulse charger circuit
If there is no desire to search for a transformer or its alteration, then you can pay attention to another option. If an unnecessary charger for a laptop is lying around in the household, you should not throw it away clearly, since this is a good option for creating a switching power supply for the battery.
Since the output voltage should not exceed 14.1-14.3 V, then any ready-made unit for this is not suitable. Nevertheless, you can do it alteration.
As a rule, in such devices, stabilizing power supply is carried out by a circuit, which includes the following elements:
- chip TL431;
- control optocoupler.
As soon as the output voltage exceeds the permissible limits (this is set by the resistors), the microcircuit lights the optocoupler LED. Thus, the PWM controller receives a signal about the need to reduce the duty cycle of the pulses that are supplied to the transformer.
At first glance, everything seems complicated, and it’s not clear how to make a simple charger. At the same time, the manufacture of such a device is affordable for every home master with a personal car.
Reassembly of a switching power supply
To begin with, it is worth opening the case, after which you should find the very TL431 chip. Now you need to pay attention to its output contact, near which there are two resistors (in the diagrams they are usually marked R12 and R13), connected by a REF pin.
It is optimal to adjust the upper arm of the divider. By reducing the resistance, the voltage at the output of the charger is also reduced. If the parameter is increased, then the potential difference will also increase. If the power supply is designed for 12 V, then you need a resistor with a large resistance, and at 19 V - with a lower one.
Now, from the simple charger scheme for the car battery, you should drop out the selected resistor (R13) and place a trimming element that is pre-configured for the same resistance instead. After that, it is necessary to give a load to the charger output (for example, connect the bulb from the headlight). Turn on the engine and smoothly rotate the engine "trimmer" and at the same time control the voltage.
As soon as the required limits are reached (14.1-14.3 V), the power supply is disconnected from the network, and the engine "trimmer" is fixed in the adopted position. For this is good nail polish. Now it remains to assemble the housing in the reverse order. As a result, it does not take so much time than reading this entire instruction.
Waste desktop computer unit
In this case, the “manufacture" of a battery charger is complex. However, this option of assembling a charger with your own hands does not require deep knowledge in electronics. In addition, the basis already exists - an old unnecessary power supply from a stationary computer, which is still operational.
They usually provide output voltage +5 V and +12 V with a current of the order of 2 A. These parameters is sufficient for the assembly of a low-power device to be faithfully serve host vehicle for many years.
A full charge of the battery will require a certain amount of time, and considerable. Mostly it all depends on the battery capacity. However, the use of such a home-made device will avoid the effect of desulfation of the plates.
Assembly process
The actual assembly process of a simple charger circuit, which will be carried out at home (or in the garage), can look like this:
- Open the housing and remove all wires except the green one. Only pre-mark or remember the junction of black (GND) and yellow (+12 V).
- The green wire is soldered to the place where it was black. This is done so that the unit starts without a PC motherboard. Next, in place of soldering the black wire, put a tap for the negative battery cable. At the place where the yellow wire was, the positive contact of charging the battery is soldered.
- Find the TL 494 chip (or its equivalent). With all the variety of computer power supplies, these elements cannot be dispensed with.
- From the first leg of the microcircuit (usually the lower left), you should find a resistor connected to the +12 output (yellow wire).
- The resistor found is evaporated, after which its parameter is measured by the tester. Choose a variable resistor close to the nominal value and set the desired resistance. Now you can solder the element instead of the removed resistor with flexible wires.
- Run the power supply and adjust the variable transistor to obtain the desired output voltage - no more than 14.3. The main thing here is not to overdo it because the limit is 15 V and the device simply turns off.
- Dissolve the variable resistor from the simple charger circuit, save the setting and measure the resulting resistance. Now it remains to choose a resistor with the obtained value (one or several) and solder it into the circuit.
- Check the power supply for the required voltage. It then remains to collect the body in the reverse order. As an additional option, you can connect a voltmeter to the outputs ("+" and "-"), placing it on the case for clarity.
The resulting device is sufficiently reliable and fully capable of replacing factory analogues.
However, during the use of such a device, one should not forget that it is equipped with overload protection, but this does not save if the polarity is not observed. In other words, when connecting the charger to the battery, mix up the plus and minus signs (which happens, albeit infrequently), it will fail instantly!
Useful recommendation
If the simplest circuit of the battery charger is not equipped with automatic battery charge control, you should use the simplest network daily relay from Chinese manufacturers. As a result, you can not monitor the time the unit is disconnected from the mains.
The cost of this device is typically less than 200 rubles. Knowing the amount of time it takes to charge the battery, you can, having set the required shutdown time, calmly go about your business.
The need for a timely shutdown of electricity is due to the fact that if you completely forget about charging the battery, this threatens with serious consequences:
- boiling electrolyte;
- destruction of plates;
- battery failure.
But the new battery is much more expensive than the total investment in a makeshift charger!
Terms of use
The main drawback of almost any simple 12-volt battery charger for the battery is the inability to turn off the device after it is fully charged. However, we have already considered how to fix this nuance, but this is still not easier. There are other features that are not present during the use of factory analogues.
One of the important nuances is that the procedure for checking the memory “for spark” is strictly prohibited! In addition, it is necessary to carefully monitor during the connection of the charger to the battery, so as not to reverse the polarity in any case. Otherwise, it threatens a complete failure of the memory.
And, most importantly, the connection to the terminals should only be done in the off state.
Safety precautions
When making homemade charging, do not forget about the elementary safety rules:
- All devices, without exception, should be located on a refractory surface, including the battery.
- The initial use of charging should be carried out with full control of all parameters. It is necessary to provide control over the heating temperature of all elements of the charger and battery. Boiling electrolyte should be avoided, voltage and current must be controlled by a tester. All this will allow you to determine the duration of a full charge of the battery, which will help in the future.
It is not a problem to independently assemble a charger for a car battery in a simple scheme. The main thing is to observe safety precautions. After all, you have to deal with a dangerous voltage of 220 V!