You can make a 12/220 volt voltage converter yourself from literally improvised materials. You can even take units from a simple uninterruptible power supply as a basis - it is, in fact, a double converter - first, the voltage drops to 12 V to ensure battery charging.
And then the voltage is increased to 220 V, the current is converted from direct to alternating current. Such devices can be used to power household appliances outside the house - drills, grinders, televisions, etc. It is not difficult to make such a device yourself, and its cost price will be lower than that of similar devices that are sold in stores.
Inverter operation principle
The second name of the converter is the inverter. In fact, it is a pulse-width modulated signal generator . Power is supplied from a 12-volt DC source (in this case, from a battery). At the output of the device, pulses appear in which the duty cycle varies. Depends on the ratio of the time during which there is or is no voltage. With a duty cycle equal to unity, the maximum current value is output. With a decrease in duty cycle, the current decreases.
The voltage at any time at the output is 220 V. Even the simplest 12V-220V converter can operate in a wide frequency range - 50 kHz ... 5 MHz. It all depends on the specific scheme and the elements used in it. The voltage frequency is very high, it will be fatal to power household appliances. To reduce it to the standard 50 Hz, it is necessary to use special design transformers. PWM modulator allows you to create an alternating voltage from a constant voltage with the required frequency.
Feedback system
If there is no load for the PWM modulator, the duty cycle of the pulses is at a minimum level, the voltage value is 220 V. As soon as the load is connected to the device, the current will increase sharply and the voltage will drop, it will be less than 220 V. If you decide to make a voltage converter from 12 to 220 volts with your own hands, then be sure to consider the presence of feedback. It allows you to compare the output voltage with a reference value.
If there is a difference in voltage, then a signal is applied to the generator, which allows to increase the duty cycle of the pulses. Using this system, it is possible to achieve maximum output power and a more stable voltage. As soon as the load is disconnected, the voltage again bounces above 220 V - a feedback system that fixes and reduces the value of the duty cycle of the pulses. And so on until the moment the tension is equalized.
Work with a dead battery
When changing the duty cycle and the value of the output current, the load on the power source increases. This leads to its discharge and lower voltage. And if a feedback system is used, it increases the duty cycle of signals as much as possible, sometimes to a maximum of one. DIY do-it-yourself voltage converters 12/220 volts without feedback react very strongly to dead batteries. During operation, the value of the output voltage is necessarily reduced.
If you plan to connect such equipment as grinders, electric bulbs, boilers or kettles, then their work will not be affected by a decrease in voltage. But in the event that the converter is needed to connect television equipment, laptops, computers, servers, amplifiers, feedback is simply necessary. It allows you to compensate for all power surges, which will ensure stable operation of the devices.
Scheme selection
To make a 12/220 V voltage converter yourself, you need to choose a specific circuit. And be sure to consider the power of the devices that you plan to connect to it. Estimate approximately what load will be powered by the inverter. Be sure to add another 25% in reserve to the received power, it will not be superfluous. Based on the data obtained, you can choose a specific scheme. And, of course, one of the important points is the elemental base.
Evaluate your financial capabilities if you plan to purchase all the components. And you need a lot of expensive items. Fortunately, they are almost all found in modern technology - in uninterruptible power supplies, PSU computers and laptops. By the way, a standard UPS can be used as a voltage converter, even alterations are not necessary. Connect a more powerful battery to it and that's it. But you have to charge the battery from an additional power source - the standard will not be able to generate the desired current value.
Converter circuit elements
The standard design of the inverter for converting DC voltage from 12 V to AC 220 consists of such elements that can be found in any modern technology:
- PWM modulator - a special design microcontroller.
- Ferrite rings for the manufacture of RF transformers.
- Power field effect transistors IGBT.
- Electrolytic capacitors.
- Constant resistance of various power.
- Inductors for filtering current.
In the event that you are not confident in your own strengths, you can assemble the converter yourself according to the multivibrator scheme. A transformer for such a device is suitable from a UPS or transistor TV power supply. Such a device has one drawback - impressive dimensions. But it turns out to be much easier to set up than complex designs that work with high-frequency current.
Inverter Operation
If you decided to make a 12/220 voltage converter with your own hands in a simple scheme, then its power can be low. But it is quite enough to power household equipment. But if the power is higher than 120 W, then the current consumption rises to 10 amperes as a minimum. Therefore, when used in a car, it cannot be plugged into the cigarette lighter socket - all wires will melt and fuses will fail.
Therefore, car inverters, whose power is over 120 W, must be connected to the battery using an additional fuse and relay. Be sure to lay the wire from the battery to the installation site of the car inverter. To turn on the converter, you can use a key switch or a button paired with an electromagnetic relay - it allows you to remove high current from the controls.
Harmonics of the parasitic type
When making 12/220 voltage converters with your own hands, the main thing is to suppress all stray harmonics as much as possible. In any design, even the most expensive, not only voltage with a frequency of 50 Hz is generated, but also harmonics. They appear during the operation of a PWM modulator, their frequencies are multiple.
To slightly reduce the effect of stray harmonics, the case is closed by a sheet of tin and it is connected to the negative terminal. You can still achieve a reduction in the level of harmonics by increasing the frequency directly of the PWM modulator and installing filtering chokes at the output.