Charger with current stabilization. Adjustable voltage stabilizer for charger Charger circuit for cars with stable voltage
In this article we’ll talk about another car charger. We will charge the batteries with a stable current. The charger circuit is shown in Figure 1.
The circuit uses a rewound transformer from a TS-180 tube TV as a network transformer, but TS-180-2 and TS-180-2V are also suitable. To rewind the transformer, we first carefully disassemble it, not forgetting to note which sides the core was glued together with; the position of the U-shaped parts of the core must not be confused. Then all secondary windings are wound up. If you use the charger only at home, you can leave the shielding winding. If the device is intended to be used in other conditions, the shielding winding is removed. The top insulation of the primary winding is also removed. After this, the coils are impregnated with bakelite varnish. Of course, impregnation in production takes place in a vacuum chamber, if there is no such possibility, then we impregnate it using the hot method - into hot varnish heated in a water bath, throw the coils and wait for an hour until they are saturated with varnish. Then we let the excess varnish drain and put the coils in a gas oven with a temperature of about 100... 120˚С. In extreme cases, the winding of the coils can be impregnated with paraffin. After this, we restore the insulation of the primary winding with the same paper, but also impregnated with varnish. Next, we wind it on the reels... now let's do the math. To reduce the no-load current, and it will obviously increase, since we do not have the necessary ferropaste for gluing twisted, cut cores, we will use all the turns of the coil windings. So. The number of turns of the primary winding (see table) is 375+58+375+58 = 866 turns. The number of turns per volt is equal to 866 turns divided by 220 volts, we get 3.936 ≈ 4 turns per volt.
We calculate the number of turns of the secondary winding. Let's set the voltage of the secondary winding to 14 volts, which will give us a voltage of 14 √2 = 19.74 ≈ 20 volts at the output of the rectifier with filter capacitors. In general, the lower this voltage, the less useless power in the form of heat will be released on the transistors of the circuit. And so, we multiply 14 volts by 4 turns per volt, we get 56 turns of the secondary winding. Now let's set the current of the secondary winding. Sometimes you need to quickly recharge the battery, which means you need to increase the charging current to the limit for some time. Knowing the overall power of the transformer - 180 W and the voltage of the secondary winding, we will find the maximum current 180/14 ≈ 12.86 A. The maximum collector current of the KT819 transistor is 15A. According to the reference book, the maximum power of this transistor in a metal case is 100W. This means that with a current of 12A and a power of 100W, the voltage drop across the transistor cannot exceed... 100/12 ≈ 8.3 volts, and this is provided that the temperature of the transistor crystal does not exceed 25˚C. This means a fan is needed, since the transistor will operate at the limit of its capabilities. We choose a current equal to 12A, provided that each arm of the rectifier will already have two 10A diodes. According to the formula:
We multiply 0.7 by 3.46, we get the wire diameter? 2.4 mm.
You can reduce the current to 10A and use a wire with a diameter of 2mm. To facilitate the thermal regime of the transformer, the secondary winding can not be covered with insulation, but simply covered with an additional layer of bakelite varnish.
KD213 diodes are installed on 100x100x3mm aluminum plate radiators. They can be installed directly on the metal body of the charger through mica spacers using thermal paste. Instead of 213-x, you can use D214A, D215A, D242A, but diodes KD2997 with any letter are best suited, the typical value of the forward voltage drop for which is 0.85V, which means that with a charge current of 12A, heat will be released on them in the form of 0.85 12 = 10W. The maximum rectified direct current of these diodes is 30A, and they are not expensive. The LM358N microcircuit can work with input signal voltages close to zero; I have not seen any domestic analogues. Transistors VT1 and VT2 can be used with any letters. A strip of tinned tin was used as a shunt. The dimensions of my strip cut from a tin can () are 180x10x0.2mm. With the values of resistors R1,2,5 indicated in the diagram, the current is regulated in the range from approximately 3 to 8A. The lower the value of resistor R2, the greater the stabilization current of the device. Read how to calculate the additional resistance for a voltmeter.
About the ammeter.
My strip, cut to the dimensions indicated above, quite by chance has a resistance of 0.0125 Ohm. This means that when a current of 10A passes through it, U=I R = 10 0.0125=0.125V = 125 mlV will drop across it. In my case, the used measuring head has a resistance of 1200 Ohms at a temperature of 25˚C. Lyrical digression.
Many radio amateurs, thoroughly adjusting the shunts for their ammeters, for some reason never pay attention to the temperature dependence of all the elements of the circuits they assemble. We can talk on this topic endlessly, I will give you just a small example. Here is the active resistance of my measuring head frame at different temperatures. And for what conditions should the shunt be calculated?
And so on. With a frame resistance of 1200 Ohms and a total deflection current of the device needle of 100 μA, we need to apply a voltage of 1200 0.0001 = 0.12 V = 120 mlV to the head, which is less than the voltage drop across the shunt resistance at a current of 10 A. Therefore, install an additional resistor in series with the measuring head, preferably a tuning one, so as not to have to worry about the selection.
The stabilizer is mounted on a printed circuit board (see photo 3). I limited the maximum charge current for myself to six amperes, therefore, with a stabilization current of 6A and a voltage drop across a powerful transistor of 5V, the released power is 30W, and blown by a fan from the computer, this radiator heats up to a temperature of 60 degrees. With a fan this is a lot, a more efficient radiator is needed. Approximately determine what is needed. My advice to all of you is to install radiators designed for operating PP devices without coolers, it’s better that the dimensions of the device increase, but when this cooler stops, nothing will burn out.
When analyzing the output voltage, its oscillogram was very noisy, which indicates instability of the circuit, i.e. the circuit was excited. It was necessary to supplement the circuit with capacitor C5, which ensured stable operation of the device. Yes, also, in order to reduce the load on the KT819, I reduced the voltage at the rectifier output to 18V (18/1.41 = 12.8V, i.e. the voltage of the secondary winding of my transformer is 12.8V). Download the PCB drawing. Goodbye. K.V.Yu.
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 sawtooth voltage driver (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 by selecting 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:
CHARGING DEVICE FOR CAR BATTERIES
The option is described below circuit, which, despite its great complexity, is easier to configure due to the use of an operational amplifier to normalize the voltage of the current-measuring shunt. In this circuit as a shunt R13 You can use almost any wirewound resistor with a resistance of 0.01 ... 0.1 Ohm and a power of 1 ... 5 W. The voltage required for normal regulation of current in the load is 0 ... 0.6 V at pin 1 of the microcircuit DA1 achieved by the ratio of resistor resistances R9 and R11 . Resistor values R11 and R12 must be the same and be within 0.5 ... 100 kOhm. Resistor resistance R9 calculated using the formula:R9(Ohm) = 0.1 *I exit max(A)* R11(Ohm) / I exit max (A) * R13(Ohm). Variable resistor R2 can be any suitable, with a resistance of 1 ... 100 kOhm. After selection R2 calculate the required resistor resistance value R4, which determined by the formula:R4(kOhm) = R2(kOhm) * (5 V - 0.1 * I exit max(A)) / 0.1 * I exit max(A). Variable resistor R14 can also be any suitable with a resistance of 1 ... 100 kOhm. Resistor value R15 determines the upper limit of output voltage regulation. The value of this resistor should be such that at the maximum output voltage on the resistor motor, in the lowest position in the circuit, the voltage is 5.00V. The figure shows the ratings for a maximum output current of 6A and a maximum voltage of 15 V, but the limit values of these parameters can be easily recalculated according to the above formulas.
Structurally, the main part of the circuit is made on a printed circuit board measuring 45 x 58 mm. Other elements: power transformer, diode bridge VD2, transistor VT1, diode VD5 , inductor Dr1, electrolytic capacitors C2, C7, variable resistors and fuses are placed using the volumetric mounting method in the charger housing. This approach made it possible to use elements of different sizes in the circuit and was caused by the need to replicate the design.
Requirements for the element base are described on the previous pages. A correctly assembled circuit begins to work immediately and practically does not require adjustment. The described design can be used not only as a charger, but also as a laboratory power supply with an adjustable output current limitation.
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, in theory, is 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 incredibly simple, only 2 active components, minimal costs, and assembly will take no more than 10 minutes if all components are available.
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 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 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...
