Hello. Today I will talk about a fairly powerful converter (inverter) from 12 volts DC to 220 volts AC. The declared power of this converter is as much as 3000 W. I’ll try to show whether this is true or not in the review.
The review will also include disassembly, a detailed examination of all the internals, and testing.
I bought the subject for $55.38 + $19.57 shipping, total $74.95. Now it's a little more expensive.
For those interested, please...
The package is the most ascetic: an inverter, 2 short cables, instructions in English and Chinese. 
Block by block, the internal filling of the device can be represented as follows: 
Now I will describe it in words. At the inverter input there are 4 converters from 12 volts DC to 300 volts DC. All these 4 converters are connected in parallel. Each converter consists of 2 CMP1405 field-effect transistors, a step-up transformer and a full-wave rectifier using UF2004 diodes. The transistors are quite powerful (maximum drain current is 140 amperes), but the diodes are not so good. The diodes are only 2 ampere. But because in a diode bridge they work alternately, then in theory the maximum output current of each of the 4 converters is 4 amperes. Those. 16 amps with 4 converters. Those. the total output power is as much as 4800 W. It seems that there is also a reserve. 
The generator on the TL494 chip controls the operation of field-effect transistors of all converters 
The maximum drain current of these transistors is 25 amperes, and if we take into account that the transistors also operate alternately, then here too we have a very large power reserve. 
This is the so-called “modified sine wave”. Most of these converters and various uninterruptible power supplies output alternating current with exactly this signal shape. It is much easier and cheaper to obtain such alternating current than a “pure sine wave”, and most modern electrical appliances can be used as a load. The exception is various loads with an inductive component, for example, asynchronous electric motors, transformers, etc. Switching power supplies and commutator motors work perfectly even on direct current, so they can “digest” a “modified sine wave” well. 
A 12V/220V inverter is a necessary thing on a household. Sometimes it’s simply necessary: the network, for example, has disappeared, and the phone is dead and there’s meat in the refrigerator. Demand determines supply: for ready-made models of 1 kW or more, from which you can power any electrical appliances, you will have to pay somewhere from $150. Possibly over $300. However, making a voltage converter with your own hands in our time is accessible to anyone who knows how to solder: assembling it from a ready-made set of components will cost three to four times less + a little work and metal from scrap trash. If there is one for car batteries, you can generally spend 300-500 rubles. And if you also have basic amateur radio skills, then, after rummaging through the stash, it is quite possible to make a 12V DC/220V AC 50Hz inverter for 500-1200 W for nothing. Let's consider the possible options.
A 12-220 V voltage converter to power a load up to 1000 W or more can generally be made independently in the following ways (in order of increasing costs):
Assembly methods according to paragraphs. 1 and 2 are actually not that simple. The housings of ready-made factory inverters also serve as heat sinks for powerful transistor switches inside. If you take a “semi-finished product” or “loose”, then there will be no housing for them: given the current cost of electronics, manual labor and non-ferrous metals, the difference in prices is explained precisely by the absence of the second and, possibly, the third. That is, you will have to make a radiator for powerful keys yourself or look for a ready-made aluminum one. Its thickness at the location where the keys are installed should be at least 4 mm, and the area for each key should be at least 50 square meters. see for each kW of power output; with blowing from a 12 V computer fan-cooler 110-130 mA – from 30 sq. cm*kW*key.
For example, there are 2 keys in a set (module) (they can be seen, they stick out from the board, see on the left in the figure); modules with keys on the radiator (on the right in the figure) are more expensive and are designed for a certain, usually not very high power. There is no cooler, the power required is 1.5 kW. This means you need a radiator of 150 sq. see. In addition to this, there are also installation kits for keys: insulating heat-conducting gaskets and fittings for mounting screws - insulating cups and washers. If the module has thermal protection (there will be some other piece sticking out between the keys - a thermal sensor), then a little thermal paste to glue it to the radiator. Wires - of course, see below.
The 12V DC/220V AC 50Hz inverter, to which you can connect any devices within the permissible power limit, is made from a computer UPS quite simply: the standard wires to “your” battery are replaced with long ones with clamps for the car battery terminals. The wire cross-section is calculated based on the permissible current density of 20-25 A/sq. mm, see also below. But because of a non-standard battery, problems can arise - with it, and it is more expensive and more necessary than a converter.
UPS also uses lead-acid batteries. This is today the only widely available secondary chemical power source capable of regularly delivering large currents (extra currents) without being completely “killed” in 10-15 charge-discharge cycles. In aviation, silver-zinc batteries are used, which are even more powerful, but they are monstrously expensive, are not widely available, and their service life is negligible by everyday standards - approx. 150 cycles.
The discharge of acid batteries is clearly monitored by the voltage on the bank, and the UPS controller will not allow the “foreign” battery to be discharged beyond measure. But in standard UPS batteries the electrolyte is gel, while in car batteries it is liquid. The charging modes in both cases are significantly different: the same currents cannot be passed through the gel as through a liquid, and in a liquid electrolyte, if the charge current is too low, the mobility of the ions will be low and not all of them will return to their places in the electrodes. As a result, the UPS will chronically undercharge the car battery; it will soon become sulfated and become completely unusable. Therefore, a battery charger is required for the inverter on the UPS. You can make it yourself, but that's another topic.
The suitability of the converter for a particular purpose also depends on the battery. A boost voltage inverter does not take energy for consumers from the “dark matter” of the Universe, black holes, the holy spirit, or anywhere else just like that. Only from the battery. And from it he will take the power supplied to consumers, divided by the efficiency of the converter itself.
If you see “6800W” or more on the body of a branded inverter, believe your eyes. Modern electronics make it possible to fit even more powerful devices into the volume of a cigarette pack. But let’s say we need a load power of 1000 W, and we have a regular 12 V 60 A/h car battery at our disposal. The typical value of inverter efficiency is 0.8. This means it will take approx. 100 A. For such a current, wires with a cross-section of 5 square meters are also needed. mm (see above), but that’s not the main thing here.
Car enthusiasts know: if you run the starter for 20 minutes, buy a new battery. True, new machines have time limiters for its operation, so perhaps they don’t know. And certainly not everyone knows that the starter of a car, once spun up, takes a current of approx. 75 A (within 0.1-0.2 s at startup - up to 600 A). The simplest calculation - and it turns out that if the inverter does not have automatic equipment that limits the battery discharge, then ours will run out completely in 15 minutes. So choose or design your converter taking into account the capabilities of the existing battery.
Note: This implies a huge advantage of 12/220 V converters based on computer UPSs - their controller will not allow the battery to drain completely.
The service life of acid batteries does not noticeably decrease if they are discharged with a 2-hour current (12 A for 60 A/h, 24 A for 120 A/h and 42 A for 210 A/h). Taking into account the conversion efficiency, this gives a permissible long-term load power of approx. 120 W, 230 W and 400 W respectively. For 10 min. load (for example, to power a power tool), it can be increased by 2.5 times, but after this the ABC must rest for at least 20 minutes.
Overall, the result is not entirely bad. Of the ordinary household power tools, only the grinder can take 1000-1300 W. The rest, as a rule, cost up to 400 W, and screwdrivers up to 250 W. A refrigerator from a 12 V 60 A/h battery will work through an inverter for 1.5-5 hours; quite enough to take the necessary measures. Therefore, making a 1 kW converter for a 60 A/h battery makes sense.
In order to reduce the weight and size of the device, with rare exceptions (see below), voltage converters operate at increased frequencies from hundreds of Hz to units and tens of kHz. No consumer will accept a current of such frequency, and the loss of its energy in conventional wiring will be enormous. Therefore, inverters 12-200 are built for the following output voltage. types:
In order to increase efficiency, voltage conversion is carried out not only at higher frequencies, but also with heteropolar pulses. However, it is impossible to power very many consumer devices with a sequence of multi-polar rectangular pulses (the so-called meander): large surges at the meander fronts with even a slightly reactive load will lead to large energy losses and can cause a malfunction of the consumer. However, it is also impossible to design the converter for sinusodal current - the efficiency will not exceed approx. 0.6.
A quiet, but significant revolution in this industry occurred when microcircuits were developed specifically for voltage inverters, forming the so-called. a modified sinusoid (on the left in the figure), although it would be more correct to call it pseudo-, meta-, quasi-, etc. sinusoid. The current shape of the modified sinusoid is stepped, and the pulse fronts are prolonged (the meander fronts are often not visible at all on the screen of a cathode-ray oscilloscope). Thanks to this, consumers with transformers on iron or noticeable reactivity (asynchronous electric motors) “understand” the pseudosine wave “as real” and work as if nothing had happened; Hi-Fi audio with a network transformer on hardware can be powered with a modified sine wave. In addition, a modified sinusoid can be smoothed out in fairly simple ways to an “almost real” one, the differences from a pure one on an oscilloscope are barely noticeable by eye; Converters of the “Pure Sine” type are not much more expensive than conventional ones, on the right in Fig.
However, it is not advisable to run devices with capricious analog components and UPSs from a modified sine wave. The latter are extremely undesirable. The fact is that the middle platform of the modified sinusoid is not a pure zero voltage. The UPS starting unit from a modified sine wave does not operate clearly and the entire UPS may not exit the startup mode into operating mode. The user sees this at first as ugly glitches, and then smoke comes out of the device, as in the joke. Therefore, the devices in the UPS must be powered from Pure Sine type inverters.
So, for now it is clear that it is best to make an inverter for an output of 220 V 50 Hz, although we will also remember about the AC output. In the first case, to control the frequency you will need a frequency meter: the norm for fluctuations in the frequency of the power supply network is 48-53 Hz. AC electric motors are especially sensitive to its deviations: when the frequency of the supply voltage reaches the tolerance limits, they heat up and “go away” from the rated speed. The latter is very dangerous for refrigerators and air conditioners; they can irreparably fail due to depressurization. But we don’t need to buy, rent, or beg for a loan an accurate and multifunctional electronic frequency meter - we don’t need its accuracy. Either an electromechanical resonant frequency meter (pos. 1 in the figure) or a pointer of any system, pos. 2:
Both are inexpensive, sold on the Internet, and in large cities in electrical specialty stores. An old resonant frequency meter can be found at the iron market, and one or the other, after setting up the inverter, is very suitable for monitoring the network frequency in the house - the meter does not respond to connecting them to the network.
In most cases, 220 V 50 Hz power is required by consumers that are not particularly powerful, up to 250-350 W. Then the basis for a 12/220 V 50 Hz converter can be a UPS from an old computer - if, of course, one is lying around in the trash or someone is selling it cheap. The power delivered to the load will be approx. 0.7 from the rated UPS. For example, if “250W” is written on its body, then devices up to 150-170 W can be connected without fear. You need more - you must first test it on a load of incandescent lamps. It lasted 2 hours – it can deliver such power for a long time. How to make a 12V DC/220V AC 50Hz inverter from a computer power supply, see the video below.
Let's say there is no computer UPS or you need more power. Then the choice of key elements becomes important: they must switch high currents with minimal switching losses, be reliable and affordable. In this regard, bipolar transistors and thyristors are confidently becoming a thing of the past in this area of application.
The second revolution in the inverter business is associated with the advent of powerful field-effect transistors (“field transistors”), the so-called. vertical structure. However, they have revolutionized the entire technology of power supply for low-power devices: it is becoming increasingly difficult to find a transformer on iron in household appliances.
The best of the high-power field devices for voltage converters are insulated gate induced channel (MOSFET), e.g. IFR3205, left in the figure:
Due to the negligible switching power, the efficiency of an inverter with a DC output on such transistors can reach 0.95, and with an AC 50 Hz output 0.85-0.87. Analogues of MOSFET with a built-in channel, e.g. IFRZ44, give lower efficiency, but are much cheaper. A pair of one or the other allows you to bring the power in the load to approx. 600 W; both can be paralleled without problems (on the right in the figure), which makes it possible to build inverters with a power of up to 3 kW.
Note: The power loss of switching switches with a built-in channel when operating on a significantly reactive load (for example, an asynchronous electric motor) can reach 1.5 W per switch. Keys with an induced channel are free from this drawback.
The third element that made it possible to bring voltage converters to their current state is the specialized TL494 microcircuit and its analogues. All of them are a pulse-width modulation (PWM) controller that generates a modified sine wave signal at the outputs. The outputs are multi-polar, which allows you to control pairs of keys. The reference conversion frequency is set by a single RC circuit, the parameters of which can be changed within wide limits.
The circle of 220 V DC consumers is limited, but it is they who need an autonomous power supply not only in emergency situations. For example, when working with power tools on the road or in the far corner of your own site. Or it is always present, say, at the emergency lighting of the entrance to the house, hallway, corridor, local area from a solar battery that recharges the battery during the day. The third typical case is charging your phone on the go from the cigarette lighter. Here the output power is needed very little, so the inverter can be made with just 1 transistor according to the relaxation generator circuit, see next. video clip.
Already to power 2-3 LED light bulbs you need more power. When trying to “squeeze” it, the efficiency of blocking generators drops sharply, and you have to switch to circuits with separate timing elements or full internal inductive feedback; they are the most economical and contain the least number of components. In the first case, to switch one switch, the self-induction EMF of one of the transformer windings is used together with a timing circuit. In the second, the frequency-setting element is the step-up transformer itself due to its own time constant; its value is determined primarily by the phenomenon of self-induction. Therefore, both inverters are sometimes called self-induction converters. Their efficiency, as a rule, is no higher than 0.6-0.65, but, firstly, the circuit is simple and does not require adjustment. Secondly, the output voltage is more trapezoidal than square wave; “demanding” consumers “understand” it as a modified sine wave. Disadvantage: field switches in such converters are practically inapplicable, because often fail due to voltage surges on the primary winding during switching.
An example of a circuit with external timing elements is given in pos. 1 pic:
The author of the design was unable to squeeze more than 11 W out of it, but apparently, he confused ferrite with carbonyl iron. In any case, the armored (cup) magnetic circuit in his own photo (see figure on the right) is in no way ferrite. It looks more like an old carbonyl one, oxidized on the outside with time, see fig. on right. It is better to wind the transformer for this inverter on a ferrite ring with a ferrite cross-sectional area of 0.7-1.2 square meters. cm. The primary winding should then contain 7 turns of wire with a copper diameter of 0.6-0.8 mm, and the secondary winding should contain 57-58 turns of wire 0.3-0.32 mm. This is for straightening with doubling, see below. For “pure” 220 V - 230-235 turns of wire 0.2-0.25. In this case, when replacing KT814 with KT818, this inverter will deliver power up to 25-30 W, which is enough for 3-4 LED lamps. When replacing KT814 with KT626, the load power will be approx. 15 W, but the efficiency will increase. In both cases, the key radiator is from 50 square meters. cm.
At pos. Figure 2 shows a diagram of the “antediluvian” converter 12-220 with separate feedback windings. It's not that archaic. First, the output voltage under load is trapezoidal with rounded fractures and no spikes. It's even better than a modified sine wave. Secondly, this converter can be designed without any modifications in the circuit for a power of up to 300-350 W and a frequency of 50 Hz, then a rectifier is not needed, you just need to install VT1 and VT2 on radiators from 250 kW. see each. Thirdly, it protects the battery: when overloaded, the conversion frequency drops, the output power decreases, and if you load it even more, the generation stops. That is, to avoid over-discharging the battery, no automation is required.
The procedure for calculating this inverter is given in the scan in Fig.:
The key quantities in it are the conversion frequency and the working induction in the magnetic circuit. The conversion frequency is selected based on the material of the available core and the required power:
| Type Magnetic cores | Induction/conversion frequency | |||
|---|---|---|---|---|
| Up to 50 W | 50-100 W | 100-200 W | 200-350 W | |
| “Power” iron from power transformers with a thickness of 0.35-0.6 mm | 0.5 T/(50-1000)Hz | 0.55 T/(50-400)Hz | 0.6 T/(50-150)Hz | 0.7 T/(50-60)Hz |
| “Sound” iron from UMZCH output transformers with a thickness of 0.2-0.25 mm | 0.4 T/(1000-3000)Hz | 0.35 T/(1000-2000)Hz | - | - |
| “Signal” iron from signal transformers with a thickness of 0.06-0.15 mm (not permalloy!) | 0.3 T/(2000-8000)Hz | 0.25 T/(2000-5000)Hz | - | - |
| Ferrite | 0.15 T/(5-30) kHz | 0.15 T/(5-30) kHz | 0.15 T/(5-30) kHz | 0.15 T/(5-30) kHz |
This “omnivorousness” of ferrite is explained by the fact that its hysteresis loop is rectangular and the working induction is equal to the saturation induction. The decrease in the calculated values of induction in steel magnetic cores compared to typical values is caused by a sharp increase in switching losses of non-sinusoidal currents as it increases. Therefore, from the core of the power transformer of the old 270 W “coffin” TV in this 50 Hz converter it will be possible to remove no more than 100-120 W. But - without fish, there is cancer in fish.
Note: If you have a steel magnetic core with a deliberately oversized cross-section, do not squeeze the power out of it! Let the induction be better - the efficiency of the converter will increase, and the shape of the output voltage will improve.
It is better to rectify the output voltage of these inverters using a circuit with parallel voltage doubling (item 3 in the figure with diagrams): the components for it will cost less, and the power losses on a non-sinusoidal current will be less than in a bridge. Capacitors should be taken “power”, designed for high reactive power (designated PE or W). If you put “sound” ones without these letters, they may simply explode.
A simple 50 Hz inverter (item 4 in the figure above with diagrams) is an interesting design. For some types of standard power transformers, the intrinsic time constant is close to 10 ms, i.e. half a period of 50 Hz. By adjusting it with timing resistors, which will also act as limiters of the switch control current, you can immediately obtain a smoothed 50 Hz square wave at the output without complex formation circuits. Transformers TP, TPP, TN for 50-120 W are suitable, but not just any kind. You may have to change the resistor values and/or connect 1-22 nF capacitors in parallel with them. If the conversion frequency is still far from 50 Hz, it is useless to disassemble and rewind the transformer: the magnetic circuit glued with ferromagnetic glue will fluff up, and the parameters of the transformer will deteriorate sharply.
This inverter is a weekend dacha converter. It will not drain the car battery for the same reasons as the previous one. But it is enough to illuminate a house with a veranda with LED lamps and a TV or a vibration pump in a well. The conversion frequency of the adjusted inverter when the load current changes from 0 to maximum does not go beyond the technical norms for power supply networks.
The windings of the original transformer are routed like this. In typical power transformers, there is an even number of secondary windings for 12 or 6 V. Two of them are “set aside”, and the rest are soldered in parallel into groups of an equal number of windings in each. Next, the groups are connected in series so that you get 2 half-windings of 12 V each, this will be a low-voltage (primary) winding with a midpoint. Of the remaining low-voltage windings, one is connected in series with the 220 V mains winding; this will be the step-up winding. An additive is needed because... The voltage drop across switches made of bipolar composite transistors, together with its losses in the transformer, can reach 2.5-3 V, and the output voltage will be underestimated. Additional winding will bring it up to normal.
The efficiency of the described converters does not exceed 0.8, and the frequency varies noticeably depending on the load current. The maximum load power is less than 400 W, so it’s time to think about modern circuit solutions.
The circuit of a simple converter 12 V DC/220 V DC for 500-600 W is shown in the figure:
Its main purpose is to power hand-held power tools. Such a load is not demanding on the quality of the supplied voltage, so the keys are taken cheaper; IFRZ46, 48 are also suitable. The transformer is wound on ferrite with a cross-section of 2-2.5 square meters. cm; A power transformer core from a computer UPS is suitable. Primary winding - 2x5 turns of a bundle of 5-6 winding wires with a copper diameter of 0.7-0.8 mm (see below); secondary - 80 turns of the same wire. No adjustment is required, but there is no monitoring of battery discharge, so during operation you need to attach a multimeter to its terminals and do not forget to look at it (the same applies to all other homemade voltage inverters). If the voltage drops to 10.8 V (1.8 V per cell) - stop, turn off! It dropped to 1.75 V per cell (10.5 V for the entire battery) - this is already sulfation!
The quality characteristics of the inverter, in particular its efficiency, are quite strongly influenced by the stray field of its transformer. The fundamental solution to reduce it has long been known: the primary winding, which “pumps” the magnetic circuit with energy, is placed close to it; secondary ones above it in descending order of their power. But technology is such a thing that theoretical principles in specific designs sometimes have to be turned inside out. One of Murphy's laws states approx. so: if the piece of hardware still doesn’t want to work as it should, try doing the opposite in it. This fully applies to a high-frequency transformer on a ferrite ring magnetic core with windings made of relatively thick rigid wire. Wind the voltage converter transformer on a ferrite ring like this:
Note: on electrical circuit diagrams, the beginnings of the windings, if relevant, are indicated by a dot.
A modified sine wave from a PWM controller is not the only way to get 50 Hz at the inverter output, suitable for connecting any household electricity consumers, and it wouldn’t hurt to “smooth” that too. The simplest of them is the good old iron transformer; it “irons” well due to its electrical inertia. True, it is becoming increasingly difficult to find a magnetic core rated at more than 500 W. Such an isolation transformer is switched on to the low-voltage output of the inverter, and a load is connected to its step-up winding. By the way, most computer UPSs are built according to this scheme, so they are quite suitable for this purpose. If you wind the transformer yourself, then it is calculated similarly to the power one, but with a trace. features:
Examples of circuit solutions for 12-200 V 50 Hz converters with an isolation transformer are shown in the figure:
On the one on the left, the keys are controlled by the so-called master oscillator. a “soft” multivibrator, it already generates a meander in blocked fronts and smoothed fractures, so no additional smoothing measures are required. The instability of the frequency of a soft multivibrator is higher than that of a regular one, so to adjust it you need a potentiometer P. With keys on the KT827, you can remove power up to 200 W (radiators from 200 sq. cm without blowing). Keys on KP904 from old junk or IRFZ44 allow you to increase it to 350 W; single on IRF3205 up to 600 W, and paired on them up to 1000 W.
An inverter 12-220 V 50 Hz with a master oscillator on TL494 (on the right in the figure) maintains the frequency firmly in all conceivable operating conditions. To more effectively smooth out a pseudosinusoid, the so-called phenomenon is used. indifferent resonance, in which the phase relationships of currents and voltages in the oscillatory circuit become the same as with acute resonance, but their amplitudes do not increase noticeably. Technically, this can be solved simply: a smoothing capacitor is connected to the boost winding, the capacitance value of which is selected according to the best shape of the current (not voltage!) under load. To control the shape of the current, a 0.1-0.5 Ohm resistor is connected to the load circuit at a power of 0.03-0.1 of the rated value, to which an oscilloscope with a closed input is connected. The smoothing capacitance does not reduce the efficiency of the inverter, but you cannot use computer programs for simulating low-frequency oscilloscopes to configure it, because the input of the sound card they use is not designed for an amplitude of 220x1.4 = 310 V! The keys and powers are the same as before. case.
A more advanced 12-200 V 50 Hz converter circuit is shown in Fig.:
It uses complex compound keys. To improve the quality of the output voltage, it uses the fact that the emitter of planar epitaxial bipolar transistors is doped much more heavily than the base and collector. When TL494 applies a closing potential, for example, to the base of VT3, its collector current will stop, but due to the resorption of the emitter space charge, it will slow down the closing of T1 and voltage surges from the self-induction emf Tr will be absorbed by circuits L1 and R11C5; they will “tilt” the fronts more. The output power of the inverter is determined by the overall power Tr, but not more than 600 W, because It is impossible to use paired powerful switches in this circuit - the spread in the value of the gate charge of MOSFET transistors is quite significant and the switching of the switches will be unclear, which is why the shape of the output voltage may even worsen.
Choke L1 is 5-6 turns of wire with a diameter of 2.4 mm on copper, wound on a piece of ferrite rod with a diameter of 8-10 m and a length of 30-40 mm with a pitch of 3.5-4 mm. The throttle magnetic circuit must not be short-circuited! Setting up a circuit is quite a painstaking task and requires a lot of experience: you need to select L1, R11 and C5 according to the best shape of the output current under load, as in the previous one. case. But Hi-Fi, powered from this converter, remains “hi-fi” to the most demanding ears.
Already the winding wire for a powerful 50 Hz transformer will cost a pretty penny. Magnetic cores from “coffin” transformers up to 270 W overall are more or less available, but in an inverter you cannot squeeze more than 120-150 W out of this, and the efficiency will be 0.7 at best, because “coffin” magnetic cores are wound from a thick tape, the eddy current losses in which are large at non-sinusoidal voltage on the windings. Finding an SL magnetic core made of a thin strip capable of delivering more than 350 W at an induction of 0.7 Tesla is generally problematic, it will be expensive, and the entire converter will be huge and heavy-lifting. UPS transformers are not designed for frequent operation in long-term mode - they heat up and their magnetic circuits in inverters degrade quite quickly - the magnetic properties deteriorate greatly, the power of the converter drops. Is there a way out?
Yes, and this solution is often used in branded converters. This is an electrical bridge made of switches on high-voltage power field-effect transistors with a breakdown voltage of 400 V and a drain current of more than 5 A. Suitable from the primary circuits of computer UPSs, and from old trash - KP904, etc.
The bridge is powered by a constant 220 V DC from a simple 12-220 inverter with rectification. The arms of the bridge open in pairs, crosswise, alternately, and the current in the load included in the diagonal of the bridge changes direction; The control circuits of all keys are galvanically separated. In industrial designs, the keys are controlled by special devices. IC with optocoupler isolation, but in amateur conditions both can be replaced with an additional low-power inverter 12 V DC - 12 V 50 Hz, powered by a small transformer on hardware, see fig. The magnetic core for it can be taken from a Chinese market low-power power transformer. Due to its electrical inertia, the quality of the output voltage is even better than a modified sine wave.
I decided to dedicate a separate article to the manufacture of a DC AC step-up voltage converter for 220V. This, of course, is remotely related to the topic of LED spotlights and lamps, but such a mobile power source is widely used at home and in the car.
There are 3 optimal ways to make a 12 to 220 inverter with your own hands:
From the Chinese you can find good radio constructors and ready-made blocks for assembling DC to AC 220V converters. In terms of price, this method will be the most expensive, but it requires the least amount of time.
The second method is to upgrade an uninterruptible power supply (UPS), which without a battery is sold in large quantities on Avito and costs from 100 to 300 rubles.
The most difficult option is assembly from scratch; you can’t do it without amateur radio experience. We will have to make printed circuit boards, select components, a lot of work.
Let's consider the design of a conventional step-up voltage converter from 12 to 220. The operating principle for all modern inverters will be the same. The high-frequency PWM controller sets the operating mode, frequency and amplitude. The power part is made of powerful transistors, the heat from which is transferred to the device body.
A fuse is installed at the input to protect the car battery from short circuits. A thermal sensor is attached next to the transistors, which monitors their heating. If the 12v-220v inverter overheats, an active cooling system consisting of one or more fans is turned on. In budget models, the fan can work constantly, and not just under high load.
Power transistors at the output
The signal shape at the output of a car inverter is generated by a high-frequency generator. A sine wave can be of two types:
Not every electrical device can work with a modified sine wave, which has a rectangular shape. Some components change their operating mode, they can heat up and start to get dirty. You can get something similar if you dim an LED lamp whose brightness is not adjustable. The crackling and flashing starts.
Expensive DC AC step-up voltage converters 12V-220V have a pure sine wave output. They cost much more, but electrical appliances work great with it.
In order not to invent anything and not to buy ready-made modules, you can try a computer uninterruptible power supply, abbreviated as UPS. They are designed for 300-600W. I have an Ippon with 6 sockets, 2 monitors, 1 system unit, 1 TV, 3 surveillance cameras, a video surveillance management system are connected. I periodically switch it to operating mode by disconnecting the 220 from the network so that the battery is discharged, otherwise the service life will be greatly reduced.
Electrician colleagues connected a regular car acid battery to an uninterruptible power supply, it worked perfectly for 6 hours continuously, and they watched football in the country. The UPS usually has a built-in gel battery diagnostic system that detects its low capacity. How it will react to the automobile is unknown, although the main difference is gel instead of acid.
UPS filling
The only problem is that the UPS may not like surges in the car network when the engine is running. For a real radio amateur, this problem is solved. Can only be used with the engine turned off.
Mostly UPSs are designed for short-term operation when 220V in the outlet disappears. For long-term continuous operation, it is highly advisable to install active cooling. Ventilation is useful for a stationary option and for a car inverter.
Like all devices, it will behave unpredictably when starting the engine with a connected load. The car's starter draws a lot of volts, at best it will go into protection as if the battery fails. At worst, there will be surges in the 220V output, the sine wave will be distorted.
To assemble a stationary or automotive 12v 220v inverter with your own hands, you can use ready-made blocks that are sold on eBay or from the Chinese. This will save time on board manufacturing, soldering and final setup. It is enough to add a housing and wires with crocodiles to them.
You can also purchase a radio kit, which is equipped with all radio components; all that remains is to solder it.
Approximate price for autumn 2016:
To search on Aliexpress, enter the query in the search bar “inverter 220 diy”. The abbreviation "DIY" stands for "do-it-yourself assembly."
500W board, output 160, 220, 380 volts
A radio kit costs less than a ready-made board. The most complex elements may already be on the board. Once assembled, it requires virtually no setup, which requires an oscilloscope. The range of radio component parameters and ratings are well chosen. Sometimes they put spare parts in a bag, in case you tear off the leg due to inexperience.
A powerful inverter is mainly used to connect construction power tools during the construction of a summer house or hacienda. A low-power 500-watt voltage converter differs from a powerful 5,000-10,000-watt converter in the number of transformers and power transistors at the output. Therefore, the manufacturing complexity and price are almost the same; transistors are inexpensive. The power is optimally 3000 W, you can connect a drill, grinder and other tools.
I will show several inverter circuits from 12, 24, 36 to 220V. It is not recommended to install these in a passenger car; you can accidentally damage the electrics. The circuit design of DC AC converters 12 to 220 is simple, a master oscillator and a power section. The generator is made on the popular TL494 or analogues.
A large number of booster circuits from 12v to 220v for DIY production can be found at the link
http://cxema.my1.ru/publ/istochniki_pitanija/preobrazovateli_naprjazhenija/101-4
In total there are about 140 circuits, half of them are boost converters from 12, 24 to 220V. Powers from 50 to 5000 watts.
After assembly, you will need to adjust the entire circuit using an oscilloscope; it is advisable to have experience working with high-voltage circuits.
To assemble a powerful 2500 Watt inverter you will need 16 transistors and 4 suitable transformers. The cost of the product will be considerable, comparable to the cost of a similar radio designer. The advantage of such costs will be a pure sine output.
A car voltage inverter can sometimes be incredibly useful, but most of the products in stores are either poor in quality or not satisfactory in terms of power, and are not cheap. But the inverter circuit consists of the simplest parts, so we offer instructions for assembling a voltage converter with your own hands.
The first thing to consider is the electricity conversion losses released in the form of heat on the circuit switches. On average, this value is 2-5% of the rated power of the device, but this figure tends to increase due to improper selection or aging of components.
Heat removal 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.
For radiator profiles, a regular “comb” with a width of 80-120 mm and a length of about 300-400 mm is suitable. The field-effect transistor screens are attached to the flat part of the profile with screws - metal spots on their rear surface. But this is not all simple: there should be no electrical contact between the screens of all transistors in the circuit, so the radiator and fastenings are insulated with mica films and cardboard washers, while a thermal interface is applied to both sides of the dielectric spacer with metal-containing paste.
It is extremely important to understand why an inverter is not just a voltage transformer, and also why there is such a diverse range of such devices. First of all, remember that by connecting a transformer to a DC source, you will not get anything at the output: the current in the battery does not change polarity, accordingly, 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 network oscillations to perform the transformation. It is usually assembled on two bipolar transistors capable of driving 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 amps, but in general you just need to multiply the current by the battery voltage to get an approximate number of watts of power output without taking into account losses.
A simple converter based on a multivibrator and power field switches IRFZ44
The operating frequency of the multivibrator is not constant; calculating and stabilizing it is a waste of time. Instead, the current at the output of the transformer is converted back to DC using a diode bridge. Such an inverter can be suitable for powering purely active loads - incandescent lamps or electric heaters, stoves.
Based on the obtained base, you can assemble other circuits that differ in the frequency and purity of the output signal. It is easier to select components for the high-voltage part of the circuit: the currents here are not so high, in some cases the output multivibrator and filter assembly can be replaced with a pair of microcircuits with appropriate wiring. Electrolytic capacitors should be used for the load network, and mica capacitors for circuits with low signal levels.
Option of a converter with a frequency generator based on K561TM2 microcircuits in the primary circuit
It is also worth noting that 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
Voltage inverters are used everywhere today, both by 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 complexity of the converter device directly determines the width of the range of current collectors that can be connected to it.
Unfortunately, pure “sine” is present only in the main power supply network; it is very, very difficult to achieve conversion of direct current into it. But in most cases this is not required. To connect electric motors (from drills to coffee grinders), a pulsating current with a frequency of 50 to 100 hertz without smoothing is sufficient.
ESL, LED lamps and all kinds of current generators (power supplies, chargers) are more critical to the choice of frequency, since their operating circuit is based on 50 Hz. 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 in the inverter output circuit.
But even such a cunning plan will not work if you plan to use an inverter to provide stable power to networks with a mass of heterogeneous consumers, including asynchronous electrical machines. Here, pure “sine” is very important and only frequency converters with digital signal control can implement this.
To assemble the inverter, we only need one circuit element that transforms low voltage into high voltage. You can use transformers from power supplies of personal computers and old UPSs; their windings are designed to transform 12/24-250 V and back, all that remains is to correctly determine the conclusions.
Still, it’s better to wind the transformer with your own hands, since 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 wound manually and not tightly. In addition, you can easily calculate the required number of turns and wire thickness using calculators available on the Internet.
Before winding, the core ring needs to be prepared - remove the sharp edges with a file and wrap tightly with an insulator - fiberglass impregnated with epoxy glue. Next comes the winding of the primary winding from 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 shrink.
The primary winding is covered with two layers of Mylar insulating tape, then a high-voltage secondary winding and another layer of insulation are wound. An important point is that the secondary must be wound in the opposite direction, otherwise the transformer will not work. Finally, a semiconductor thermal fuse must be soldered into the gap to one of the taps, the current and response temperature of which are determined by the parameters of the secondary winding wire (the fuse body must be tightly wound to the transformer). The transformer is wrapped on top with two layers of vinyl insulation without an adhesive base, the end is secured with a tie or cyanoacrylate glue.
All that remains is to assemble the device. Since there are not so many components in the circuit, they can be placed not on a printed circuit board, but mounted mounted to a radiator, that is, to the device body. We solder the pin legs with a single-core copper wire of a sufficiently large cross-section, then the connection point 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 circuitry may require a printed circuit board with transistors lined up on the edge for loose attachment to the heatsink. Fiberglass with a foil thickness of at least 50 microns is suitable for making a signet; if the coating is thinner, reinforce the low-voltage circuits with jumpers made of copper wire.
Today it’s easy to make a printed circuit board at home - the Sprint-Layout program allows you to draw clipping stencils for circuits of any complexity, including double-sided boards. The resulting image is printed by a laser printer on high-quality photo paper. Then the stencil is applied to cleaned and degreased copper, ironed, and the paper is washed away with water. The technology is called “laser ironing” (LIT) and is described on the Internet in sufficient detail.
You can etch away copper residues with ferric chloride, electrolyte, or even table salt; there are plenty of ways. After etching, the baked-on toner needs to be washed off, drill mounting holes with a 1 mm drill and go over all the tracks with a soldering iron (submerged arc) to tin the copper of the contact pads and improve the conductivity of the channels.
The inverter consists of a master oscillator of 50 Hertz (up to 100 Hz), which is built on the basis of the most common multivibrator. Since the publication of the scheme, I have observed that many have successfully repeated the scheme, the reviews are quite good - the project was a success.
This circuit allows you to get almost mains 220 Volts with a frequency of 50 Hz at the output (depending on the frequency of the multivibrator. The output of our inverter is rectangular pulses, but please do not rush to conclusions - such an inverter is suitable for powering almost all household loads, with the exception of those loads that have built-in motor that is sensitive to the shape of the supplied signal.
TV, players, chargers for laptops, laptops, mobile devices, soldering irons, incandescent lamps, LED lamps, LDS, even a personal computer - all this can be powered without any problems from the proposed inverter.
A few words about the power of the inverter. If you use one pair of power switches of the IRFZ44 series with a power of about 150 watts, the output power is indicated below depending on the number of pairs of keys and their type
The inverter has a REMOTE function (remote control). The trick is that to start the inverter you need to apply a low-power plus from the battery to the line to which low-power multivibrator resistors are connected. A few words about the resistors themselves - take everything with a power of 0.25 watts - they will not overheat. The transistors in the multivibrator need to be quite powerful if you are going to pump several pairs of power switches. Of ours, KT815/17 or even better KT819 or imported analogues are suitable.
Capacitors are frequency-setting capacitors, their capacity is 4.7 μF; with this arrangement of multivibrator components, the inverter frequency will be around 60 Hz.
Well, that’s all, I’ll only add that power switches at high power will heat up like a stove, they need a very good heat sink, plus active cooling. Do not forget to isolate the pairs of one arm from the heat sink to avoid short-circuiting of the transistors.
The inverter does not have any protection or stabilization; perhaps the voltage will deviate from 220 Volts.
Download the PCB from the server
Sincerely - AKA KASYAN
