DIY voltage converter 12 to 220 and 220 to 12 volts

Recommendation points

• Inverter housing
• Determining the load and purchasing components
• Fighting for a sinusoid – analyzing typical circuits
• Transformer: pick up or yourself
• Installation of radioelements

A car voltage inverter is sometimes incredibly useful, but most of the products in stores either sin in quality, or do not suit in terms of power, and are not cheap at the same time. But after all, the inverter circuit consists of the simplest parts, therefore we offer instructions for assembling a voltage converter with our own hands.

Inverter housing

The first thing to consider is the loss of electricity conversion, released in the form of heat on the keys of the circuit. On average, this value is 2–5% of the rated power of the device, but this indicator tends to grow due to improper selection or aging of components.

The removal of heat from semiconductor elements is of key importance: transistors are very sensitive to overheating and this is expressed in the rapid degradation of the latter and, probably, their complete failure. For this reason, the base for the case should be a heat sink – an aluminum radiator.

Of the radiator profiles, a common “hairbrush” with a width of 80–120 mm and a length of about 300–400 mm is well suited. shields of field-effect transistors are fastened to the flat part of the profile with screws – metal spots on their rear surface. But even with this, not everything is simple: there should be no electrical contact between the screens of all the transistors of the circuit, therefore the radiator and fasteners are insulated with mica films and cardboard washers, while a thermal interface is applied on both sides of the dielectric gasket with a metal-containing paste .

Determining the load and purchasing components

It is extremely important to understand why an inverter is not just a voltage transformer, and also why there is such a diverse list of such devices. First of all, remember that by connecting the transformer to a direct current source, you will not get anything at the output: the current in the battery does not change polarity, respectively, the phenomenon of electromagnetic induction in the transformer is absent as such.

The first part of the inverter circuit is an input multivibrator that simulates the oscillations of the network for making a transformation. It is usually assembled on two bipolar transistors that can swing power switches (for example, IRFZ44, IRF1010NPBF or more powerful – IRF1404ZPBF), for which the most important parameter is the maximum permissible current. It can reach several hundred amperes, but in general, you just need to multiply the current value by the battery voltage to get an approximate number of watts of output power without taking into account losses..

Simple converter based on multivibrator and power field switches IRFZ44

The frequency of operation of the multivibrator is not constant, it is a waste of time to calculate and stabilize it. Instead, the current at the output of the transformer is converted back to constant current by means of a diode bridge. Such an inverter can be suitable for powering purely active loads – incandescent lamps or electric heaters, stoves.

On the basis of the resulting base, you can collect other circuits that differ in the frequency and purity of the output signal. The selection of components for the high-voltage part of the circuit is easier to make: the currents here are not so high, in some cases the assembly of the output multivibrator and filter can be replaced with a pair of microcircuits with the appropriate strapping. Capacitors for the load network should be electrolytic, and for circuits with a low signal level – mica.

A variant of the converter with a frequency generator on K561TM2 microcircuits in the primary circuit

It is also worth noting that in order to increase the final power it is not at all necessary to purchase more powerful and heat-resistant components of the primary multivibrator. The problem can be solved by increasing the number of converter circuits connected in parallel, but each of them will require its own transformer.

Option with parallel connection of circuits

Fighting for a sinusoid – analyzing typical circuits

Voltage inverters are today used everywhere by both motorists who want to use household appliances away from home, and by residents of autonomous homes powered by solar energy. And in general, we can say that the width of the spectrum of current collectors that can be connected to it directly depends on the complexity of the converter device.

Unfortunately, a pure “sine” is present only in the main power grid, it is very, very difficult to achieve the conversion of direct current into it. But in most cases this is not required. To connect electric motors (from a drill to a coffee grinder), a pulsating current with a frequency of 50 to 100 hertz is sufficient without smoothing.

ESL, LED lamps and all kinds of current generators (power supplies, chargers) are more critical to the choice of frequency, since it is at 50 Hz that their scheme of operation is based. In such cases, microcircuits, called a pulse generator, should be included in the secondary vibrator. They can switch a small load directly, or act as a “conductor” for a series of power switches of the inverter output circuit.

But even such a cunning plan will not work if you plan to use the inverter to provide stable power supply to networks with a mass of dissimilar consumers, including asynchronous electrical machines. Here pure “sine” is very important and only digitally controlled frequency converters can do this..

Transformer: pick up or yourself

For the assembly of the inverter, we only need one circuit element that performs the transformation of low voltage to high voltage. You can use transformers from power supplies of personal computers and old UPSs, their windings are just designed for the transformation of 12 / 24-250 V and vice versa, it remains only to correctly determine the conclusions.

And yet it is better to wind the transformer with your own hands, since the ferrite rings make it possible to do it yourself and with any parameters. Ferrite has excellent electromagnetic conductivity, which means that transformation losses will be minimal even if the wire is hand wound and not tight. In addition, you can easily calculate the required number of turns and wire thickness using calculators available on the network..

Before winding, the core ring must be prepared – remove the sharp edges with a file and wrap tightly with an insulator – fiberglass impregnated with epoxy glue. This is followed by the winding of the primary winding from a thick copper wire of the calculated cross-section. After dialing the required number of turns, they must be evenly distributed over the surface of the ring at equal intervals. The winding terminals are connected according to the diagram and insulated with heat shrinkage.

The primary winding is covered with two layers of Mylar tape, then the high-voltage secondary winding and another layer of insulation are wound. An important point – you need to wind the “secondary” in the opposite direction, otherwise the transformer will not work. Finally, a semiconductor thermal fuse must be soldered to one of the taps, the current and operating temperature of which are determined by the parameters of the secondary winding wire (the fuse case must be tightly tied to the transformer). From above, the transformer is wrapped with two layers of vinyl insulation without an adhesive backing, the end is fixed with a tie or cyanoacrylate glue.

Installation of radioelements

It remains to assemble the device. Since there are not so many components in the circuit, they can be placed not on the printed circuit board, but by surface mounting with attachment to the heatsink, that is, to the device body. We solder to the pin legs with a mono-core copper wire of a sufficiently large cross-section, then the junction is strengthened with 5-7 turns of thin transformer wire and a small amount of POS-61 solder. After the connection has cooled, it is insulated with a thin heat shrink tube.

High power circuits with complex secondary circuits may require a printed circuit board with transistors in a row at the edge for free attachment to the heatsink. Glass fiber laminate with a foil thickness of at least 50 microns is suitable for making a seal, but if the coating is thinner, reinforce low voltage circuits with copper wire jumpers.

Making a printed circuit board at home is easy today – Sprint-Layout allows you to draw clipping stencils for circuits of any complexity, including for double-sided boards. The resulting image is printed by a laser printer on high-quality photo paper. Then the stencil is applied to the cleaned and defatted copper, ironed with an iron, the paper is washed out with water. The technology was named “laser-ironing” (LUT) and is described in the network in sufficient detail.

You can etch the remains of copper with ferric chloride, electrolyte or even table salt, there are plenty of ways. After etching, the stuck toner must be washed off, drilled the mounting holes with a 1 mm drill and walked along all the tracks with a soldering iron (submerged arc) to tin the copper of the contact pads and improve the conductivity of the channels.