A 12 volt power supply will allow you to power almost any household appliance, including even a laptop. Please note that up to 19 volts is supplied to the laptop input. But it will work perfectly if you run the power from 12. True, the maximum current is 10 Amps. Only very rarely does consumption reach such a value; the average is kept at the level of 2-4 Amps. The only thing to consider is that when replacing a standard power source with a self-made one, you cannot use the built-in battery. But still, a 12 volt power supply is ideal even for such a device.
Power Supply Parameters
The most important parameters of any power supply are the output voltage and current. Their values depend on one thing - on the used wire in the secondary winding of the transformer. How to make a selection of it will be described a little below. For yourself, you must decide in advance for what purpose it is planned to use a 12 volt power supply. If you need to power low-power equipment - navigators, LEDs, and so on, then 2-3 amperes is enough at the output. And then this will be a lot.
But if you plan to carry out more serious actions with it - for example, charging the car’s battery , then you will need 6-8 amperes at the output. The charging current should be ten times less than the battery capacity - this requirement must be taken into account. If there is a need to connect devices whose supply voltage differs significantly from 12 Volts, then it is more reasonable to set the adjustment.
How to choose a transformer
The first element is a voltage converter. The transformer helps to convert an alternating voltage of 220 volts to the same in amplitude, only with a value much less. At least you need a lower value. For powerful power supplies, a transformer of the TC-270 type can be taken as a basis. It has high power, even there are 4 windings that issue 6.3 volts each. They were used to power the radio tubes. Without much work, you can make a 12 Volt 12 Ampere power supply from it, which can even charge a car’s battery.
But if you are not completely satisfied with its windings, then you can remove the secondary all, leave only the network. And wind the wire. The problem is how to calculate the required number of turns. To do this, you can use a simple calculation scheme - count how many turns the secondary winding contains, which produces 6.3 Volts. Now just divide 6.3 by the number of turns. And you get the amount of voltage that can be removed from one turn of the wire. It remains only to calculate how much it takes to wind the turns in order to get 12.5-13 Volts at the output. It will be even better if the output turns out to be 1-2 volts higher than the required voltage.
Rectifier manufacturing
What is a rectifier and what is it for? This is a semiconductor diode device, which is a converter. With its help, alternating current turns into direct current . To analyze the operation of the rectifier stage, it is more convenient to use an oscilloscope. If you see a sinusoid in front of the diodes, then after them there will be an almost flat line. But small pieces from the sinusoid will still remain. Get rid of them after.
The choice of diodes should be taken with the utmost seriousness. If a 12-volt power supply will be used as a battery charger, you will need to use elements with a reverse current of up to 10 amperes. If you intend to supply low-current consumers, then the bridge assembly will be quite enough. Here it is worth stopping. Preference should be given to the rectifier circuit, assembled as a bridge - of four diodes. If applied on one semiconductor (half-wave circuit), then the efficiency of the power supply is almost halved.
Filter block
Now that the output has a constant voltage, it is necessary that the power supply circuit for 12 Volts be slightly improved. For this purpose, you need to use filters. To power household appliances, it is enough to use an LC-chain. It is worth telling about it in more detail. An inductance, a choke, is connected to the positive output of the rectifier stage. Current must pass through it, this is the first stage of filtration. Next comes the second - an electrolytic capacitor with a large capacity (several thousand microfarads).
After the inductor, an electrolytic capacitor is connected to the plus. Its second output is connected to a common wire (minus). The essence of the electrolytic capacitor is that it allows you to get rid of the entire variable component of the current. Remember, the rectifier output left small pieces of a sinusoid? Here, it is from it that you need to get rid, otherwise the power supply 12 Volt 12 Amps will interfere with the device connected to it. For example, a radio or radio will make a strong hum.
Output voltage stabilization
To implement the stabilization of the output voltage, you can use only one semiconductor element. This can be either a zener diode with a working voltage of 12 Volts, or more modern and advanced assemblies such as LM317, LM7812. The latter are designed to stabilize the voltage at 12 volts. Therefore, even if the output of the rectifier stage is 15 Volts, only 12 will remain after stabilization. Everything else goes into heat. And this means that it is extremely important to install a stabilizer on the radiator.
Voltage Adjustment 0-12 Volt
For greater versatility of the device, you should use a simple circuit that can be built in a few minutes. This can be implemented using the previously mentioned assembly LM317. Only the difference from the switching circuit in the stabilization mode will be small. A 5 kΩ resistor is included in the wire break, which goes to minus. A resistance of about 220 ohms is connected between the output of the assembly and the variable resistor. And between the input and output of the stabilizer, reverse voltage protection is a semiconductor diode. Thus, the 12-volt power supply, assembled with its own hands, turns into a multifunctional device. Now it remains only to assemble it and graduate the scale. Or you can even put an electronic voltmeter at the output, by which you can watch the current voltage value.