How to make a 12-220v car inverter with their own hands
Inverter (converter) is used to connect to the on-board network of the car various devices operating from 220 volts, for example, a powerful amplifier or a laptop. Converters, which are sold in stores, can not always give the necessary power, so many drivers who understand electronics, make a car inverter 12 220v with their own hands. Devices that make their own hands are better suited to power specific devices, as well as being cheaper than serious units sold in stores.
How an inverter works
The basis of the car inverter – the generator with pulse-width modulation (PWM). This device is powered by a 12 volt battery and produces rectangular pulses (meander) with variable duty cycle (voltage presence/absence time ratio). When the duty cycle is equal to one, the inverter provides the maximum current. The lower the duty cycle, the lower the current. The output voltage always corresponds to 220 volts. The frequency of the oscillator ranges from 50 kHz to 5 megahertz, depending on the circuit and parts. The conversion of the high-frequency voltage into a low-frequency voltage (50 hertz) is done by smoothing out the meander in the oscillating circuit formed by the transformer and capacitor, as well as filtering out harmonics. After all, the PWM generator not only generates an alternating voltage of 220 volts with high frequency, but through varying the change in duty cycle, it modulates the output voltage with a sinusoidal signal with a frequency of 50 hertz.
When the inverter operates without a load, the PWM generator signal duty cycle is minimal and the output voltage is 220 volts. Connecting the load causes the current to increase and the output voltage to drop below 220v. The feedback system compares the output voltage with the set standard, and then sends a signal to the generator that increases the pulse duty cycle. This increases the output power and raises the voltage. When the load is switched off, the output voltage rises above 220 volts, whereupon the feedback system reduces the pulse duty cycle until the voltage returns to normal. The change in duty cycle and output current increases the load on the battery, so its voltage often drops below 12 volts. In this case, the feedback circuit increases the duty cycle even more, up to unity.
Often, the converter made with your own hands, in which there is no feedback, reacts to the connection to a discharged battery by reducing the output voltage. Therefore, they are not very suitable for powering an amplifier or a laptop, but will be quite able to ensure the functioning of devices with reactive load – hand-held power tools, lamps, boilers.
If the converter is needed to power an amplifier, receiver, TV or laptop computer, you can’t do without feedback. Some circuit complexity is compensated by the fact that the feedback compensates voltage drops, thus ensuring normal operation of the amplifier or other devices.
On the Internet there are a huge number of schemes of devices that convert the energy of the car battery (12 volts) in the AC voltage of 220 volts and suitable for making their own hands. Therefore, it is necessary to choose a circuit, focusing on access to the element base and experience in working with such devices. If there is a radio parts store near you, you can ask them what controllers and power transistors are most available and already under them pick up the most suitable circuit. You can also use the parts that are in any computer power supply. From there you can get:
- controller (PWM generator);
- ferrite ring for the transformer;
- power transistors;
- filtering chokes.
If you are not sure that you can make a complex device with feedback with your own hands, assemble a 12 → 220 volt inverter based on a multivibrator at 50 Hz. The transformer can be taken from an old transistor TV or an uninterruptible power supply (UPS). This inverter takes much more space than a high frequency device, but it is easier to set up and the parts are easier to find.
Connecting and using an inverter
Car inverter with 12 to 220 volt power over 120 watts consumes a current of more than 10 amps, so it is undesirable to connect it to the regular cigarette lighter or ignition switch. This is especially true for modern cars. After all, a higher current will lead to the fuse burnout, and the installation of a “bug” instead of it can end with the ignition of the wiring. Therefore, the inverter with power over 120 watts should be connected to the battery through a fuse and a switch with a relay. To do this you will have to lay your own hands a separate wire and install somewhere socket for 220 volts. It can be put either under the front panel on the passenger side, or in the trunk. It is very inconvenient to open the hood every time, connect the inverter to the battery and drag the wire into the car. It is easier to press the button which will turn on the relay and the 12 to 220 converter will start working.
Any 12 volt battery operated inverter, in addition to the voltage with a frequency of 50 Hz, produces a huge number of harmonics, most of which are multiples of the frequency of the PWM generator. These harmonics appear due to the meander effect on the oscillating circuit formed by the transformer and capacitor. If the harmonics level is high, they will affect the operation of the amplifier, CD player or receiver connected to the car onboard network (12 volt) filling their signal with noise, crackling, growling and other extraneous sounds. However, harmonics will not affect the operation of a laptop, lamp or hand-held power tool.
To reduce the influence of parasitic harmonics, 12 – 220 volt inverter is covered with a thin tin screen and connected to the minus terminal of the battery. You can also fight harmonics by increasing the frequency of the PWM generator, in addition by connecting your own hands additional chokes in the input and output voltage circuits. High inductance does not interfere with the passage of direct current. However, for alternating current, a different rule applies – the higher the frequency or inductance, the higher the reactance. Given that the frequency of the parasitic harmonics is much higher than the frequency of the generator, a properly chosen choke reduces their intensity by a factor of ten.