Schematic diagram of an induction heating device. DIY induction heaters: step by step instructions. There are certain conditions for the organization of work

Electric energy is quite expensive today, but heating equipment operating on this resource does not lose popularity.

This is because electric heating is the most convenient way to heat a home.

Of particular interest to users are devices operating on the principle of electromagnetic induction.

Mainly because such a device can be easily assembled by yourself. In this article, we will talk about the features of these units, study their strengths and weaknesses, and also learn how to make an induction heater with our own hands.

The operation of all electric heaters, both conventional and induction, is based on the same principle: when an electric current is passed through a certain conductor, the latter will begin to heat up.

The amount of heat released per unit of time depends on the current strength and the resistance value of a given conductor - the larger these indicators, the more the material will heat up.

The whole question is how to cause an electric current to flow? You can connect the conductor directly to a source of electrical energy, which we do by plugging a cord from an electric kettle, oil heater or, for example, a boiler into the outlet. But another way can be applied: as it turned out, the flow of electric current can be provoked by exposing the conductor to an alternating (precisely alternating!) Magnetic field. This phenomenon, discovered in 1831 by M. Faraday, was called electromagnetic induction.

There is one trick here: the magnetic field can be constant, but then the position of the conductor in it must be constantly changed. In this case, the number of lines of force passing through the conductor and their direction relative to it will change. The easiest way is to rotate the conductor in the field, which is done in modern power generators.

Principle of electromagnetic induction

But you can change the parameters of the field itself. With a permanent magnet, such a trick, of course, will not work, but with an electromagnet - completely. The work of an electromagnet, who forgot, is based on the opposite effect: an alternating current flowing through a conductor generates a magnetic field around it, the parameters of which (polarity and intensity) depend on the direction of the current and its magnitude. For a more tangible effect, the wire can be laid in the form of a coil.

Thus, by changing the parameters of the electric current in the electromagnet, we will change all the parameters of the magnetic field induced by it, up to the change in the location of the poles to the opposite.

And then this magnetic field, which is indeed variable, will induce an electric current in any conductive material located within it. And the material at the same time, of course, will heat up. This is the principle of operation of modern induction heaters.

Looking for the most economical electric water heater? Then take a look. Read about the advantages and disadvantages of the device in the article.

Have you decided to install an electric boiler as a backup heat generator? Read about which model is better to choose.

The induction furnace is a multifunctional device. It can be purchased at the store, but it is more interesting and cheaper to make it yourself. At this link you will find the assembly diagram of the device and learn about the features of the operation of the furnace.

Induction heat generator in the heating system

The induction water heaters used in heating circuits have both advantages common to all electric heaters and inherent only to them. Let's start with the first group:

1. In terms of ease of use, electric heaters are ahead of even gas equipment, as they do without ignition. In addition, they are much safer: the owner does not have to be afraid of fuel leakage or combustion products.
2. Electrical equipment does not need a chimney and maintenance in the form of removing carbon deposits and soot.
3. The efficiency of an electric heater does not depend on its power. It can be set to the very minimum, and at the same time the efficiency of the unit will remain at the level of 99%, while the efficiency of a gas or solid fuel boiler in such conditions will be significantly lower than the passport one.
4. In the presence of an electric heat generator, the heating system can operate in the lowest temperature mode, which is very important during the off-season. In the case of using a gas or solid fuel boiler, the “return” temperature drop below 50 degrees is not allowed, since in this case condensate forms on the heat exchanger (when using solid fuel, it contains acid).
5. And the last thing: when using electric heating, you can do without a liquid coolant, however, this does not apply to induction heaters.

Simple induction heater

Let's move on to the advantages of directly "inductors":

1. The contact area of ​​the coolant with the hot surface in induction heaters is thousands of times larger than in devices with tubular electric heaters. Therefore, the environment warms up much faster.
2. All elements of the "inductor" are mounted only from the outside, without any tie-ins. Accordingly, leaks are completely excluded.
3. Since heating is carried out in a non-contact way, an induction type heater can work with absolutely any coolant, including all types of antifreeze (a special one would be needed for a heating element electric boiler). At the same time, water can contain a relatively large amount of hardness salts - an alternating magnetic field prevents the formation of scale on the walls of the heat exchanger.

For every barrel of honey, as you know, there is a fly in the ointment. Here, too, it could not have done without it: not only is electricity in itself quite expensive, but also induction heaters are among the most expensive type of electric heating equipment.

Do-it-yourself induction heater - design diagram

Simplicity of design is one of the advantages of an induction heater. Inside the round shielded case there is a coil, in the language of physicists it is called an inductor. It connects to an AC power source. Inside the coil is a piece of steel pipe, ending with two nozzles. The latter allow you to connect the heater to the heating system.

Thus, after connecting, a coolant will follow through the pipe, while it will heat up under the influence of the alternating field generated by the coil. From contact with the pipe, respectively, the coolant will also heat up.

Diagram of an induction heater

In some models of induction heaters, the coil is connected directly to the mains, as a result of which the magnetic field created by it changes polarity at a frequency of 50 Hz. But there is a more efficient connection scheme. It differs from the one just described by the presence of a converter that increases the oscillation frequency of the current supplied to the coil from 50 Hz to several tens of kilohertz. Such a converter is called an inverter. It consists of three modules:

1. Rectifier, which is a conventional diode bridge.
2. Basically an inverter. The main characters are a couple of so-called. key transistors that can switch very quickly.
3. A control circuit that "conducts" the key transistors.

It is easy to see that the processes occurring inside the heater are very similar to the operation of a step-down transformer, only in this case the secondary winding is short-circuited and is located inside the primary.

Another difference is that in the case of a transformer, heating is a side effect that they try to prevent (for example, they collect a magnetic circuit from separate insulated plates).

How to make an induction heater yourself?

The simplest do-it-yourself induction heater is done like this:

1. At one end of a segment of a thick-walled polypropylene pipe, it is necessary to weld a sleeve, having previously fixed a nylon fine-mesh mesh on the end of the pipe.
2. Turning the pipe with the mesh down, it is necessary to fill it with chopped stainless wire with a diameter of 5–7 mm (the length of the cuts is about 5 cm).
3. The free end of the pipe must also be closed with a sleeve and mesh. Due to this, the steel backfill, which plays the role of the core, will be held inside.
4. From the outside, an adapter is welded into each coupling to the desired diameter (corresponds to the diameter of the heating circuit.).
5. 90 turns of copper wire should be wound on the pipe.
6. The resulting coil must be connected to an inverter from the cheapest welding machine, designed for welding current up to 20A and equipped with the function of its smooth adjustment.
7. It remains to connect the heater to the heating system, fill it with coolant and apply current to the coil.

For ease of maintenance, ball valves can be installed at the inlet and outlet of the heater - this will make it possible to dismantle the device without draining the heating circuit.

To avoid rupture of the system due to overheating of the coolant, on the one hand, a safety valve should be connected to the heater through a tee.

In the presence of a 3-phase network, the heater can be improved by installing three coils instead of one.

1. Induction heaters may only be used in systems with forced circulation. Heat is generated quite intensively, therefore, during natural circulation, especially taking into account the significant hydraulic resistance of the chopped wire core, overheating of the coolant is possible.
2. The safety valve must not be neglected. It must be mounted either on the heater, as described above, or elsewhere in the system. Obviously, if the circulation pump fails, overheating of the coolant cannot be avoided, and in the absence of a safety valve, this phenomenon will lead to a rupture of the system.
3. The heater should be connected through the RCD. It is also advisable to equip the heating system with a thermostat.

Often, craftsmen place a homemade induction heater in an insulated metal case. In this case, it must be grounded.

Due to the lack of full-fledged shielding in a home-made "inductor", it should be placed no closer than 80 cm from the ceiling or floor. The distance between the appliance and the wall must be at least 30 cm.

Remember that an alternating electromagnetic field exists not only inside the coil, but also outside, so it can heat up any nearby metal objects. For example, fasteners or buttons on the wearer's clothing.

Induction heating technology has found wide application in industry and began to penetrate into the domestic sphere. attract with their cost-effectiveness and simplicity of design. Read about the design of the device and see examples of homemade designs.

You will learn about the types of cast-iron heating stoves and options for their installation in the material.

Related video

Almost a year was spent on the results of this article, and a lot of money was spent, so please read to the end before drawing conclusions from the first lines - many things will become clear.
It all started with the fact that the topic of replacing the heating of the house was ripe. Gas is good, of course, but our boiler is quite old and we don’t want to change it - it has a continuously adjustable temperature maintenance, and modern ones are discrete, i.e. they do not have burning at half or 1/4 a quarter of the maximum, and the smoother the adjustment, the more economical any heater. Yes, the savings are not big, but I can spend even 200-300 rubles of savings at my own discretion, and without paying for gas.
Well, as expected, it all started with a search engine. I drive in the search query "Induction boiler" and began to study the pages found ... And I had to think seriously ...

First of all, I was embarrassed by the nonsense that was full of pages describing the induction boiler, the principle of induction heating and the squalor of control schemes. You can check it yourself by typing in the search engine INDUCTION BOILER WITH YOUR HANDS or INDUCTION BOILER DRAWINGS. On almost all pages there are links to a video where a man in the bathroom puts an induction stove behind the heat exchanger and happily broadcasts that everything is ready, vilely silent about the fact that the stoves have automatic shutdown and he restarts the stove every 2-3 hours.
On one of the pages promoting induction boilers, outright paranoia was expressed, I can’t resist and quote:
The heating element heats up because a current flows through its conductor with increased resistance, therefore, in any case, it heats up to the specified 600 - 750 * C and the coolant always boils on its surface. Because of this, the heating element quickly becomes overgrown with scale. From this, heat transfer decreases, and the heater eventually burns out.
In an induction boiler, you can use different coolants, even petroleum products, if they are not overheated above 70 * C.
WHAT??!!! 600-750 degrees?! Okay, we take an oil heater, throw out the thermostat and heat it to the maximum, after praying that it does not burst. Of course, it is better to see once than hear a hundred times. So LOOKING
So, the temperature of the spiral is 421 degrees at a radiator temperature of 168 degrees, and this is taking into account the fact that there is oil inside, and its thermal conductivity is 5 times worse than water. Where does the toga come from 600-750 degrees? So, just in case, the melting temperature of aluminum is 660 degrees, copper is 1100. However, I know from where - some nichrome alloys have a maximum operating temperature of 750 ° C, but there are great doubts whether it will be achieved.
Does the heating element get scaled up? Also, did you screw up the photo? Hmm...

Oho-hoyushki ho-ho ... For those who don’t know, this is a heating element from a washing machine and at one time I changed them quite often, because I worked in a repair shop. So, this is the terrible word SCALP:
Scale is hard calcium deposits that do not dissolve well and are formed as a result of steam generation or water heating. In addition to lime scale, when water is heated, carbon dioxide is also formed. But its quantity matters only on an industrial scale for working with hard water. So in boiler rooms, when descaling boilers, it is necessary to ventilate the premises, but also when boiling water, it is also necessary to ensure good ventilation in the room.
The formation of scale during the heating of water always occurs if the water is hard. Only here the scale can be different, because. water hardness may not necessarily be carbonate. It is clear that the reason for the formation of carbonate scale are calcium and magnesium salts. If the formation of scale occurs due to calcium silicate, then the scale is sulphate. Silicic compounds of substances such as iron, aluminum or calcium lead to the formation of silicate scale. So, the formation of scale after working with hard water does not mean that carbonate scale has fallen out. Although it should be clarified that carbonate scale is the most common.
Ha! From this it is not difficult to conclude that scale is supplied only with a new portion of water, and the water in the system is changed extremely rarely, and this same layer of scale forms only once and thickens a little with each new portion of water, and water is added to the system also not often. Therefore, the boiler heating element shown in the photo will reach the state approximately 20 years after the aluminum radiators rot, since the scale settles not only on the heating element body, but also on the bodies of the boiler itself, less, but still settles.
And by the way, it is quite possible to get rid of scale in heating - 100 grams of anti-scale in the system will completely eliminate this problem - it has been verified by operating the electric boiler for three heating seasons.
But back to advertising induction boilers:
In TEN-boilers, only water can be used as a heat carrier, and besides, it is best to use distilled water.
In maintenance, heating elements are less practical than induction boilers, because the transitional contact between the power supply conductor and the conductor of the heating element itself is constantly overheated, because of this it oxidizes and weakens. It is necessary to constantly ensure that the power supply conductor does not burn out, otherwise, when burning out, the threaded connection of the heating element may be damaged and such a working heating element has to be changed. this problem does not exist in induction boilers, because the connection of its heating element with the power supply is carried out through an alternating current electromagnetic field.
Well, yes, of course, of course. Does the inductor coil connect to the outlet wirelessly? COOL! Most often, burnout occurs at connection points under heavy loads and continuous round-the-clock operation, so overheated contacts somehow do not sound convincing ... Okay, what's next?
Induction boilers can be placed anywhere, not even in a separate place. They are fireproof and operate silently.
Aha!!! And the stingray heater inside the boiler is constantly knocking on the walls with its head and is it not possible to be in the room at all?
Induction boilers provide a much higher electrical safety for a person than heating elements - boilers, because the heating element itself can burn out in two ways: a) with depressurization of the housing; in this case, heated nichrome crumbles from water getting on it - there is no danger of a person getting energized; b) without case depressurization; in this case, heated nichrome can stick to the body of the heating element. The heating element continues to work, and through the water the metal body of the boiler is energized.
It is a completely logical argument if the boiler is installed in violation of safety rules - any power device must be grounded. And he can kill a fool with a battery, well, if with a slingshot and in the head.
So far, it has not been possible to make the induction coil of an induction boiler with powers of 3 kW or more at 50 Hz small and compact. Therefore, a heating element boiler has much smaller dimensions with the same power than an induction boiler.
Duck and never succeed - the frequency is low, only 50 Hz, but a certain inductance is needed, and even a wire, so that it does not heat up when these same 3 kW pass through it. So the induction boiler will always be big.
Well, the schematic diagrams of induction boilers are generally something. On one of the sites it was suggested to use the following scheme for an induction boiler:

Really, he smiled for quite a long time - with a power supply of 10 ... 30 volts, are they going to heat up the boiler? Yes, the power supply for this fart will generate more heat than this toy for middle school children.
Frankly, I also came across one rather curious version of the thyristor circuit, but operation at audio frequencies did not attract my attention.

One of the advertising slogans literally made me laugh:
Savings on electricity consumption
Consumption of 2.5 kW instead of 4–5 is an excellent result. But it was not enough for ambitious and thrifty home craftsmen. But where to get cheap electricity for the stove? It turns out that the answer has been known for a long time.
This device is called an inverter, and it converts direct current into alternating current. With it, you can reduce the current consumption for heating to almost zero.
To reduce energy consumption, we need the following:
Two accumulators not less than 190 Ah (preferably 250 Ah). 4 kW inverter.
Battery charger (24 V).
The main pipes must be made of non-magnetic material (plastic, aluminum, copper).
We connect the batteries in parallel and put them on constant “charging”. The process that occurs in the electrical circuit:
The batteries produce a direct current, which is fed to the inverter.
The inverter converts direct current to 220 V alternating current.
The current from the inverter is supplied to the induction furnace, which operates in normal mode (flow).
The charger constantly recharges the batteries.
Honestly, this is a quote from the Internet and I can’t even imagine who it is intended for.

In general, the advertisement of the induction boiler disappointed, but still the embarrassment remained - the manufacturers on interruption claimed that the induction boiler has a much greater performance compared to the heating element. This is the hook I fell for - the performance of the boiler is, in fact, quite a good saving in terms of light.
I didn’t have enough determination to make an induction boiler right away, so I decided to try to assemble an induction heating battery first. The first thing that asked for itself was an induction stove, but there was no agreement with the toad on the topic of its purchase, therefore, having found an induction cooker diagram on the Internet, a power unit was isolated from it, which was assembled.

The circuit turned out to be quite capricious, not after the death of several IGBT transistors, I decided that such experiments could be left without pants, since I took transistors from disassembly, so I was not very grief-stricken. Bought.
I immediately ordered IRFPS37N50 from the same seller, as if I sensed that something was not good. Yes, and delivery in this version was relatively inexpensive - two orders, and one payment for delivery.
In general, having played enough with a single-cycle, I came to the conclusion that the thing is good, but the slightest mistake in the adjustment kills the power transistors. Therefore, I decided to go the other way - to try to assemble a push-pull circuit of an induction heater, since powerful field workers were already on hand. After a little thought, I decided to use the IR2153 half-bridge driver, and so that it would not be killed by heavy gates, I powered it with 1.5 A emitter followers. The result was the following circuit:

The idea was quite simple - film capacitors do not hold large currents very well, so use several of them, and if there are several of them, you can choose the capacitance in such a way that the resulting LC circuit is driven into resonance and get maximum magnetic fields.
As a heat exchanger, it was decided to use a square pipe - the heat exchange area both outside and inside, and this is naturally only at hand.

There were suspicions that the electronics would get very hot, since on the single-stroke version it was necessary to use a radiator blower. Well, so that the air flow would not chase in vain, it was decided to use it as a convection flow - to direct it through the pipe into the square tube of the heat exchanger, thereby increasing the performance of the structure.

The location of the coils between the heat exchange registers completely shields them, which does not allow high-frequency electromagnetic radiation to escape the load, because this is not only harmful, but also reduces the efficiency of this device. Well, so that in case of damage to the insulation of the wire itself, the coils do not touch the heat exchanger, corrugated cardboard impregnated with epoxy glue was used. It was possible to use fiberglass, but such a large piece was not at hand.
You can also fix the coils on the sealant, in principle, the main thing is that they hold on quite tightly even when the heater falls. Although, of course, to drop such a thing, if only during transportation - a heavy toy turned out, but you can’t wear it on yourself, so there were no thoughts about weight at all. High-temperature cambrics were put on the ends of the coils - not heat shrink, with fiberglass, it is much more expensive than heat shrink and looks like a material. Of course, round coils have a higher quality factor, but I needed to arrange the coil in such a way that it would heat the ENTIRE area of ​​the heat exchanger. That is why two rectangular coils were made. Two, because it was possible to connect them either in series or in parallel, and this expanded the probability of falling into resonance - I had no idea what inductance would turn out in the final.
A drawing was made, printed on paper, glued with tape to a chipboard sheet, holes were drilled in the corners, into which carnations were inserted. The studs were pre-dressed with pieces of heat shrink tubing and coils were wound on this template. After winding, the coils were shed with epoxy glue and heated with a hair dryer for better impregnation of bundles of stranded wire, with which the coils were wound. A wire with a diameter of 0.35 mm was used, there were 28 cores in the bundle. Later I made more coils and washed them with sealant - it was painfully liquid they turned out, although they fought quite well.

Then all this was collected in one apparatus and adjusted. As it turned out, unlike the single-cycle version, power transistors with the same radiator did not need airflow, but the fan was still left - heat exchange with it is much better. However, the speed was reduced to the minimum audibility - so it will have more resources, it will drive less dust inside, and it will not irritate with a buzz.
After assembly, of course, it was necessary to compare what is actually more profitable - an oil pan or an induction one. A whole bunch of measurements were taken, but each time the inductor turned out to be a winner in relation to the oiler, which pretty much infuriated the viewers from YouTube. Yes, of course, some measurements were not entirely correct, but the last series practically did not cause criticism, although opinions that I did not go to school and I don’t know the conservation law still flickered. Yes, I actually did not encroach on this law - we are talking about performance and nothing more.
In general, the latest measurements were summarized in a table based on the results of which you yourself draw conclusions, which is more profitable.

HEATING A SMALL ROOM TO A TEMPERATURE OF 40°C
	Used kW	Average wind speed	Average outdoor temperature
oil heater
induction heater
MAINTAINING THE TEMPERATURE IN THE SAME ROOM DURING THE DAY THE POWER IS ALL ABOUT THE SAME
Induction
oily
convection
Two Shrovetide
MORE ABOUT THE WEATHER DATA FROM THE SYNOPTIC WEBSITE

More details about what and how was done is shown in the video. Shown in VERY detail, so it's over an hour and a half, so stock up on popcorn.

Immediately, questions like "Could you assemble a control board for me?" began to appear. Yes, he could, of course, but there are only two nuances:
It's expensive, because I have to make boards manually, FULLY manually, since I don't see a queue for this device and I don't need to order boards at the factory with a minimum lot of 10 pieces. And the manufacture of the board is both ironing and manual drilling, and tinning, i.e. quite a lot of time that I can’t just take and donate - you know, the life span is limited and spending it on something that I’m not interested in and without taking money for it is just stupid.
The probability of bringing this design to mind for an untrained solderer is not very high, since in addition to the board, an inductor is also required, and these are coils, the number of turns in which directly depends on the method of their connection, the thickness of the steel and the distance between the coil and steel.
In general, I decided to save myself from idle chatter on this topic and made a video with recommendations on the manufacture of inductors, and if someone has a desire to purchase a board, I just send him to watch this video with the question "Can you do the same?". The rows of buyers are melting like snow in the rain...

The result of the competition between the induction heater and the oil one, of course, impressed me and the idea of ​​assembling an induction boiler sat VERY tightly in my head. The first thing to decide was which inductor to assemble. Of course, unlike domestic induction boilers, I was not going to make it at 50 Hz. And for this, more serious capacitors were already needed - it was too much on the Internet for pictures of torn filmmakers. Therefore, capacitors for induction cookers were ordered - they will definitely withstand both current and voltage. To suppress power surges, capacitors were ordered and to create resonance, MKP series capacitors were purchased, which are used in induction cookers. For nutrition, I took at 5 microfarads and 3 microfarads, for the inductor at 0.27 microfarads. Where I already bought a sign that the product is not available, so choose MKP CAPACITORS yourself.
Another factor for the creation of the induction boiler was their mass production, though not ours, but more compact and high-frequency - Chinese induction boilers with a capacity of 6 kW and 10 kW. True, it was clear from the photos that the Chinese ran into a maximum power of 3 kW from one section of the heater, since they used single-cycle converters - this can be seen from the presence of two and three identical control boards with forced ventilation. Using a push-pull bridge inverter, I expected to get 4-5 kW from one section, and given that the power unit can serve 2 sections of the inductor, there were no problems with power at all.
Why is the power of the induction boiler limited? Everything is quite banal - a certain inductance is necessary to obtain resonance. If the resonance is at audio frequencies, then both the control and the inductor itself will become audible, and this will be VERY tiring, to put it mildly. If we go to higher frequencies, then we will be forced to reduce the number of turns, and the strength of the magnetic field necessary for the occurrence of Foucault currents, i.e. eddy currents, which heat the steel, will decrease. After all, the strength of the magnetic field is directly proportional to the number of turns and the current flowing through them. Winding a step-up transformer to get more voltage did not decrease for two reasons:
Dimensions and cost of ferrite
The problem of the insulation of the inductor, and the power part of the control
Yes, yes, insulation here is also of great importance - at resonance and a bridge inverter, it applies about 800 volts to the inductor coil. If you double the frequency, you will also have to reduce the number of turns by 2 times, and to obtain the same power, you will have to increase the applied voltage by 2 times, and this is already 1600 volts. No, I didn’t dare to start such a thing, and I don’t advise you either - this thing is becoming too dangerous.
The first version of the control scheme made it clear that in addition to increased accuracy, the scheme needs to be slightly changed, which was done. However, I managed to check something on the first option:

I wasn’t impressed at all ... However, after a little reflection, I came to the conclusion that I was in a hurry with the check - the magnetic field around the inductor coil was not closed, and this led to losses - the steel sheet that was next to the boiler warmed up noticeably during the experiment .
Well, since I still lost control of the induction boiler, it was decided to assemble an indestructible stand for testing inductors, and, in fact, a new, more thoughtful control for the induction boiler.
After sitting in the evening, as a result, such a scheme of the test stand turned out. In principle, from the non-traditional here, only the first stage of current limitation - the effective value is formed not by the duration of the pulses, as is usually customary in the TL494 controller, but by changing the conversion frequency. This solution is primarily due to the fact that there is no need to deal with self-induction pulses, which cause heating of power transistors, and since the load has a reactance that increases with the frequency used, there was no doubt about the performance of this circuit solution. In addition, an analog frequency meter was introduced into the circuit, which allows you to orient yourself in the frequencies used. Of course, the scale of the frequency meter was graduated according to the readings of a real frequency meter.

ENLARGE SCHEME

The boiler control also underwent some changes and the final circuit diagram took on the following form:

ENLARGE SCHEME

The circuits have a common principle of controlling the current flowing through the load - frequency control. In the stand, the frequency depends on the current flowing through the load, while for the boiler this dependence is formed by a thermostat. Moreover, the adjustment has two steps - the first decrease in consumption occurs when the coolant temperature reaches a certain value and is carried out in steps. The second stage of adjustment is smooth and changes the power supplied to the boiler inductor depending on the temperature of the heated room. Thus, the inertia of the heater is completely absent.
After an unsuccessful test of the first version of the induction boiler, the shielding of the coils with ferrite rods was tested - the performance increase was pronounced. This, of course, inspired, but not much - the project became too expensive - a lot of ferrite was required, but it is not cheap.
The solution to the problem came in two stages. At first it was decided to use a toroidal heat exchanger with a labyrinth inside, but after a little thought, a sketch of a toroidal induction boiler without a labyrinth and with a different arrangement of inlet and outlet pipes appeared.
The first inclusion showed that there were too few turns on the boiler and the coil had to be compacted and wound.
Before assembling the control board for the induction boiler, there was essentially a week left, but my hands itched - the boiler was already ready and the readiness of the test stand also haunted.
A heating model was assembled and tested with several options for electric boilers, but the final experience was thwarted - the diameter of the pipes turned out to be too small and the water in the boiler with a heating element just boiled:

The heating model was redesigned - a circulation pump was added, which will prevent water from boiling, and the volume of water in the model increased from one and a half buckets to six and a half, which made it possible to significantly increase the duration of the experiment. So, the hour of X, well, or the moment of truth has come:

To be honest, I'm upset. There was no magical performance boost. It is clear that with self-circulation, the likelihood of growth would most likely be - with a slow movement of water, bubbles form on the surface of the heating element, which are carried away into the expansion tank, taking away heat, but when using a circulation pump, this effect is nullified - the heating element is washed too intensively with water and gas formation decreases tenfold.
Of course, the induction boiler was also driven into resonance, but the dependence of the flowing current is linear - it starts to increase as the frequency increases and approaches resonance, and after passing it, the current also decreases linearly. No bursts of current flowing through the coil were detected.
Well, since the model was assembled full-fledged, I could not resist not trying to play around with the electrode boiler:

For these experiments, a new, modern electric meter was also bought, which, after the completion of the measurements, simply turned out to be unnecessary. Of course, my curious nose was stuck in it too:

In general, I did not begin to assemble the boiler control board to the end - there is no difference in the heat output of an induction boiler and a boiler on heating elements, therefore I will not need this board. No, I won’t disassemble it until the end - there are both TL494 and IR2110 available, and I haven’t soldered the power transistors to it yet. Let it fall for now. But I will take the ideas of induction heating into service - with a similar set of power devices, you can slowly or quickly heat a lot of steel things for various purposes. So the experience was gained and the stand was left for further experiments.
Of course, it’s a pity that the idea with an induction boiler turned out to be untenable, but there is a technology for manufacturing induction heaters, which are electronically more complicated than factory convection heaters, but using more accurate temperature maintenance, or using continuous control, as in a boiler, you can achieve decent savings.
I remind you once again - this is not about efficiency, but about productivity and I don’t have to wave textbooks in physics and thermodynamics in front of my nose - the experiments described in the textbooks were set in ideal conditions, and the dwelling will never be in such conditions, it always has heat exchange with the environment. I didn’t have enough mind to calculate mathematically what and how will happen, so I collected several models and checked everything EXPERIENCELY and saw everything with my own eyes. So calm down your sarcasm and if in doubt, you can repeat everything - all the circuit diagrams, all the designs used are described in sufficient detail.

Diagram of a 500-watt induction heater that you can make yourself! There are many similar schemes on the Internet, but interest in them disappears, since basically they either do not work or work but not as we would like. This induction heater circuit is fully operational, proven, and most importantly, not complicated, I think you will appreciate it!

Components and Coil:

The working coil contains 5 turns, a copper tube with a diameter of about 1 cm was used for winding, but less is possible. This diameter was not chosen by chance, water is supplied through the tube to cool the coil and transistors.

Transistors set IRFP150 as IRFP250 was not at hand. Film capacitors 0.27 uF 160 volts, but you can put 0.33 uF and higher if you can’t find the first ones. Please note that the circuit can be powered with voltages up to 60 volts, but in this case, it is recommended to set the capacitors to 250 volts. If the circuit is powered by voltages up to 30 volts, then 150 is enough!

Zener diodes can be set to any 12-15 volts from 1 watt, for example 1N5349 and the like. Diodes can be used UF4007 and the like. Resistors 470 Ohm from 2 watts.

A few pictures:

Instead of radiators, copper plates were used, which are soldered directly to the tube, since water cooling is used in this design. In my opinion, this is the most efficient cooling, because the transistors heat up well and no fans and super radiators will save them from overheating!

The cooling plates on the board are arranged in such a way that the coil tube passes through them. The plates and the tube need to be soldered together, for this I used a gas burner and a large soldering iron for soldering car radiators.

The capacitors are located on a two-sided textolite, the board is also soldered to the coil tube in a straight line, for better cooling.

The inductors are wound on ferrite rings, I personally took them out of a computer power supply, the wire was used in copper insulation.

The induction heater turned out to be quite powerful, it melts brass and aluminum very easily, it also melts iron parts, but a little slower. Since I used IRFP150 transistors, according to the parameters, the circuit can be powered with voltage up to 30 volts, so the power is limited only by this factor. So all the same I advise you to use IRFP250.

That's all! Below I will leave a video of the operation of the induction heater and a list of parts that can be bought on AliExpress at a very low price!

Buy parts on Aliexpress:

Buy Transistors IRFP250 Buy Diodes UF4007 Buy Capacitors 0.33uf-275v

When a person faces the need to heat a metal object, fire always comes to mind. Fire is an old fashioned, inefficient and slow way to heat metal. He spends the lion's share of energy on heat, and smoke always comes from the fire. It would be great if all these problems could be avoided.

Today I will show you how to assemble an induction heater with your own hands with a ZVS driver. This fixture heats most metals with a ZVS driver and electromagnetism. Such a heater is highly efficient, does not produce smoke, and heating such small metal products as, say, a paper clip is a matter of a few seconds. The video shows the heater in action, but the instructions are different.

Step 1: How it works

Many of you are now wondering - what is this ZVS driver? It is a highly efficient transformer capable of creating a powerful electromagnetic field that heats the metal, the basis of our heater.

To make it clear how our device works, I will talk about the key points. The first important point is the 24V power supply. The voltage should be 24V at a maximum current of 10A. I will have two lead acid batteries connected in series. They power the ZVS driver board. The transformer gives a steady current to the spiral, inside which is placed the object that needs to be heated. A constant change in the direction of the current creates an alternating magnetic field. It creates eddy currents inside the metal, mostly of high frequency. Due to these currents and the low resistance of the metal, heat is generated. According to Ohm's law, the current strength, transformed into heat, in a circuit with active resistance, will be P \u003d I ^ 2 * R.

The metal that makes up the object you want to heat is very important. Iron-based alloys have higher magnetic permeability and can use more magnetic field energy. Because of this, they heat up faster. Aluminum has a low magnetic permeability and heats up, respectively, longer. And objects with high resistance and low magnetic permeability, such as a finger, will not heat up at all. The resistance of the material is very important. The higher the resistance, the weaker the current will pass through the material, and the less heat will be generated. The lower the resistance, the stronger the current will be, and according to Ohm's law, there will be less voltage loss. It's a little tricky, but due to the relationship between resistance and power output, maximum power output is achieved when the resistance is 0.

The ZVS transformer is the most complicated part of the device, I will explain how it works. When the current is turned on, it goes through two induction chokes to both ends of the coil. Chokes are needed to make sure that the device does not give out too much current. Next, the current goes through 2 470 Ohm resistors to the gates of the MIS transistors.

Because perfect components don't exist, one transistor will turn on before the other. When this happens, it takes over all the incoming current from the second transistor. He will also short out second to ground. Because of this, not only will the current flow through the coil to the ground, but the gate of the second transistor will also be discharged through the fast diode, thereby blocking it. Due to the fact that a capacitor is connected in parallel with the coil, an oscillatory circuit is created. Due to the resonance that has arisen, the current will change its direction, the voltage will drop to 0V. At this moment, the gate of the first transistor is discharged through the diode to the gate of the second transistor, blocking it. This cycle is repeated thousands of times per second.

The 10K resistor is designed to reduce excess transistor gate charge by acting as a capacitor, and the zener diode must keep the gate voltage of the transistors at 12V or lower so they don't explode. This transformer high frequency voltage converter allows metal objects to heat up.
It's time to assemble the heater.

Step 2: Materials

Few materials are needed to assemble the heater, and most of them, fortunately, can be found for free. If you see a cathode ray tube lying around just like that, go and pick it up. It contains most of the parts needed for the heater. If you want better parts, buy them from an electrical parts store.

You will need:

Step 3: Tools

For this project you will need:

Step 4: FET Cooling

In this device, the transistors turn off at a voltage of 0 V, and they do not heat up very much. But if you want the heater to run longer than one minute, you need to remove heat from the transistors. I made both transistors one common heat sink. Make sure that the metal gates do not touch the absorber, otherwise the MOS transistors will short out and explode. I used a computer heatsink and it already had a bead of silicone sealant on it. To check the insulation, touch the middle leg of each MIS transistor (gate) with a multimeter, if the multimeter beeps, then the transistors are not isolated.

Step 5: Capacitor Bank

Capacitors get very hot due to the current constantly passing through them. Our heater needs a 0.47uF capacitor. Therefore, we need to combine all the capacitors into a block, thus we will get the required capacitance, and the heat dissipation area will increase. The voltage rating of the capacitors must be higher than 400V to account for inductive voltage peaks in the resonant circuit. I made two copper wire rings, to which I soldered 10 0.047 uF capacitors in parallel to each other. Thus, I got a capacitor bank with a total capacity of 0.47 microfarads with excellent air cooling. I will install it parallel to the working spiral.

Step 6: Working Spiral

This is the part of the device in which the magnetic field is created. The spiral is made of copper wire - it is very important that copper is used. At first I used a steel coil for heating, and the device did not work very well. Without a workload, it consumed 14 A! For comparison, after replacing the coil with copper, the device only consumed 3 A. I think that the steel coil had eddy currents due to the iron content, and it was also subjected to induction heating. I'm not sure that this is the reason, but this explanation seems to me the most logical.

For a spiral, take a large section of copper wire and make 9 turns on a piece of PVC pipe.

Step 7: Chain Assembly

I made a lot of trials and made a lot of mistakes while getting the chain right. Most of the difficulties were with the power supply and with the spiral. I took a 55A 12V switching power supply. I think this power supply gave too high initial current to the ZVS driver, which caused the MIS transistors to explode. Perhaps additional inductors would have fixed this, but I decided to simply replace the power supply with lead-acid batteries.
Then I suffered with the coil. As I said, the steel coil was not suitable. Due to the high current consumption of the steel coil, several more transistors exploded. In total, 6 transistors exploded in me. Well, they learn from mistakes.

I have remade the heater many times, but here I will tell you how I put together the most successful version of it.

Step 8: Putting the device together

To assemble the ZVS driver, you need to follow the attached diagram. First I took a zener diode and connected it to a 10K resistor. This pair of parts can be immediately soldered between the drain and source of the MIS transistor. Make sure the zener diode is facing the drain. Then solder the MIS transistors to the breadboard with the contact holes. On the underside of the breadboard, solder two fast diodes between the gate and drain of each transistor.

Make sure the white line is facing the shutter (Figure 2). Then connect the plus from your power supply to the drains of both transistors through 2220 ohm resistors. Ground both sources. Solder the working coil and capacitor bank parallel to each other, then solder each end to a different gate. Finally, apply current to the gates of the transistors through a 2.50 µH inductor. They may have a toroidal core with 10 turns of wire. Your circuit is now ready to use.

Step 9: Installation on the base

In order for all the parts of your induction heater to stick together, they need a base. For this, I took a wooden block 5 * 10 cm. The circuit board, the capacitor bank and the working coil were glued with hot glue. I think the unit looks cool.

Step 10: Functional Check

To turn on your heater, simply connect it to a power source. Then place the object that you need to heat in the middle of the working coil. It should start to warm up. My heater made a paperclip glow red in 10 seconds. Larger objects, like nails, heated up in about 30 seconds. During the heating process, the current consumption increased by approximately 2 A. This heater can be used for more than just entertainment.

After use, the device does not produce soot or smoke, it even affects isolated metal objects, such as getters in vacuum tubes. Also, the device is safe for humans - nothing will happen to the finger if it is placed in the center of the working spiral. However, you can burn yourself on an object that has been heated.

Thanks for reading!

© When using site materials (quotes, images), the source must be indicated.

The induction furnace was invented long ago, back in 1887, by S. Farranti. The first industrial plant was put into operation in 1890 by Benedicks Bultfabrik. For a long time, induction furnaces were exotic in the industry, but not because of the high cost of electricity, then it was no more expensive than now. There was still a lot of incomprehensibility in the processes taking place in induction furnaces, and the element base of electronics did not allow creating effective control circuits for them.

In the induction-furnace sphere, a revolution took place literally before our eyes today, thanks to the appearance, firstly, of microcontrollers, the computing power of which exceeds that of personal computers ten years ago. Secondly, thanks to ... mobile communications. Its development required the appearance on sale of inexpensive transistors capable of delivering several kW of power at high frequencies. They, in turn, were created on the basis of semiconductor heterostructures, for the research of which the Russian physicist Zhores Alferov received the Nobel Prize.

Ultimately, induction stoves not only completely changed in industry, but also widely entered into everyday life. Interest in the subject gave rise to a lot of homemade products, which, in principle, could be useful. But most authors of designs and ideas (there are many more descriptions in the sources than workable products) have a poor idea of ​​both the basics of the physics of induction heating and the potential danger of illiterate designs. This article aims to clarify some of the most confusing points. The material is built on the consideration of specific structures:

1. An industrial channel furnace for melting metal, and the possibility of creating it yourself.
2. Crucible furnaces of the induction type, the easiest to perform and the most popular among homemade people.
3. Induction hot water boilers, rapidly replacing boilers with heating elements.
4. Household cooking induction appliances that compete with gas stoves and surpass microwaves in a number of parameters.

Note: all the devices under consideration are based on the magnetic induction created by the inductor (inductor), and therefore are called induction. Only electrically conductive materials, metals, etc. can be melted/heated in them. There are also electric induction capacitive furnaces based on electric induction in the dielectric between the capacitor plates; they are used for “gentle” melting and electrical heat treatment of plastics. But they are much less common than inductor ones, their consideration requires a separate discussion, so let's leave it for now.

Operating principle

The principle of operation of the induction furnace is illustrated in fig. on right. In essence, it is an electrical transformer with a short-circuited secondary winding:

• The alternating voltage generator G creates an alternating current I1 in the inductor L (heating coil).
• Capacitor C together with L form an oscillatory circuit tuned to the operating frequency, this in most cases increases the technical parameters of the installation.
• If the generator G is self-oscillating, then C is often excluded from the circuit, using the inductor's own capacitance instead. For the high-frequency inductors described below, it is several tens of picofarads, which just corresponds to the operating frequency range.
• The inductor, in accordance with Maxwell's equations, creates an alternating magnetic field with strength H in the surrounding space. The magnetic field of the inductor can either be closed through a separate ferromagnetic core or exist in free space.
• The magnetic field, penetrating the workpiece (or melting charge) W placed in the inductor, creates a magnetic flux F in it.
• Ф, if W is electrically conductive, induces a secondary current I2 in it, then the same Maxwell equations.
• If Ф is sufficiently massive and solid, then I2 closes inside W, forming an eddy current, or Foucault current.
• Eddy currents, according to the Joule-Lenz law, gives off the energy received by it through the inductor and the magnetic field from the generator, heating the workpiece (charge).

From the point of view of physics, the electromagnetic interaction is quite strong and has a rather high long-range action. Therefore, despite the multi-stage energy conversion, the induction furnace is able to show an efficiency of up to 100% in air or vacuum.

Note: in a non-ideal dielectric medium with permittivity >1, the potentially achievable efficiency of induction furnaces drops, and in a medium with magnetic permeability >1, it is easier to achieve high efficiency.

channel furnace

The channel induction melting furnace is the first one used in the industry. It is structurally similar to a transformer, see fig. on right:

1. The primary winding, fed with industrial (50/60 Hz) or increased (400 Hz) frequency current, is made of a copper tube cooled from the inside by a liquid heat carrier;
2. Secondary short-circuited winding - melt;
3. An annular crucible made of a heat-resistant dielectric in which the melt is placed;
4. Type-setting of plates of transformer steel magnetic core.

Channel furnaces are used for remelting duralumin, non-ferrous special alloys, and producing high-quality cast iron. Industrial channel furnaces require melt seeding, otherwise the "secondary" will not short-circuit and there will be no heating. Or arc discharges will occur between the crumbs of the charge, and the entire melt will simply explode. Therefore, before starting the furnace, a little melt is poured into the crucible, and the remelted portion is not completely poured. Metallurgists say that the channel furnace has a residual capacity.

A duct furnace with a power of up to 2-3 kW can also be made from an industrial frequency welding transformer. In such a furnace, up to 300-400 g of zinc, bronze, brass or copper can be melted. It is possible to melt duralumin, only the casting must be allowed to grow old after cooling, from several hours to 2 weeks, depending on the composition of the alloy, in order to gain strength, toughness and elasticity.

Note: duralumin was generally invented by accident. The developers, angry that it was impossible to alloy aluminum, threw another “no” sample in the laboratory and went on a spree out of grief. Sobered up, returned - but none changed color. Checked - and he gained strength almost steel, remaining light as aluminum.

The “primary” of the transformer is left as standard, it is already designed to work in the short-circuit mode of the secondary with a welding arc. The “secondary” is removed (it can then be put back and the transformer can be used for its intended purpose), and an annular crucible is put on instead. But trying to convert a welding RF inverter into a channel furnace is dangerous! Its ferrite core will overheat and break into pieces due to the fact that the dielectric constant of the ferrite >> 1, see above.

The problem of residual capacity in a low-power furnace disappears: a wire of the same metal, bent into a ring and with twisted ends, is placed in the charge for seeding. Wire diameter – from 1 mm/kW furnace power.

But there is a problem with the annular crucible: the only suitable material for a small crucible is electroporcelain. At home, it is impossible to process it yourself, but where can I get a purchased suitable one? Other refractories are not suitable due to high dielectric losses in them or porosity and low mechanical strength. Therefore, although the channel furnace gives the highest quality melt, does not require electronics, and its efficiency already exceeds 90% at a power of 1 kW, they are not used by home-made people.

Under the usual crucible

The residual capacity irritated metallurgists - expensive alloys melted. Therefore, as soon as sufficiently powerful radio tubes appeared in the 20s of the last century, an idea was immediately born: throw a magnetic circuit onto (we will not repeat the professional idioms of harsh men), and put an ordinary crucible directly into the inductor, see fig.

You can’t do this at an industrial frequency, a low-frequency magnetic field without a magnetic circuit concentrating it will spread (this is the so-called stray field) and give up its energy anywhere, but not into the melt. The stray field can be compensated by increasing the frequency to a high one: if the diameter of the inductor is commensurate with the wavelength of the operating frequency, and the entire system is in electromagnetic resonance, then up to 75% or more of the energy of its electromagnetic field will be concentrated inside the “heartless” coil. Efficiency will be corresponding.

However, already in the laboratories it turned out that the authors of the idea overlooked the obvious circumstance: the melt in the inductor, although diamagnetic, but electrically conductive, due to its own magnetic field from eddy currents, changes the inductance of the heating coil. The initial frequency had to be set under the cold charge and changed as it melted. Moreover, within the larger limits, the larger the workpiece: if for 200 g of steel you can get by with a range of 2-30 MHz, then for a blank with a railway tank, the initial frequency will be about 30-40 Hz, and the working frequency will be up to several kHz.

It is difficult to make suitable automation on lamps, to “pull” the frequency behind a blank - a highly qualified operator is needed. In addition, at low frequencies, the stray field manifests itself in the strongest way. The melt, which in such a furnace is also the core of the coil, to some extent collects a magnetic field near it, but all the same, to obtain an acceptable efficiency, it was necessary to surround the entire furnace with a powerful ferromagnetic screen.

Nevertheless, due to their outstanding advantages and unique qualities (see below), crucible induction furnaces are widely used both in industry and by do-it-yourselfers. Therefore, we will dwell in more detail on how to properly do this with your own hands.

A bit of theory

When designing a home-made "induction", you must firmly remember: the minimum power consumption does not correspond to the maximum efficiency, and vice versa. The stove will take the minimum power from the network when operating at the main resonant frequency, Pos. 1 in fig. In this case, the blank/charge (and at lower, pre-resonant frequencies) works as one short-circuited coil, and only one convective cell is observed in the melt.

In the main resonance mode in a 2-3 kW furnace, up to 0.5 kg of steel can be melted, but the charge / billet will take up to an hour or more to heat up. Accordingly, the total consumption of electricity from the network will be large, and the overall efficiency will be low. At pre-resonant frequencies - even lower.

As a result, induction furnaces for metal melting most often operate at the 2nd, 3rd, and other higher harmonics (Pos. 2 in the figure). The power required for heating / melting increases; for the same pound of steel on the 2nd, 7-8 kW will be needed, on the 3rd 10-12 kW. But warming up occurs very quickly, in minutes or fractions of minutes. Therefore, the efficiency is high: the stove does not have time to “eat” a lot, as the melt can already be poured.

Furnaces on harmonics have the most important, even unique advantage: several convective cells appear in the melt, instantly and thoroughly mixing it. Therefore, it is possible to conduct melting in the so-called. fast charge, obtaining alloys that are fundamentally impossible to smelt in any other melting furnaces.

If, however, the frequency is “lifted up” 5-6 or more times higher than the main one, then the efficiency drops somewhat (slightly) but another remarkable property of harmonic induction appears: surface heating due to the skin effect, which displaces the EMF to the surface of the workpiece, Pos. 3 in fig. For melting, this mode is rarely used, but for heating blanks for surface carburizing and hardening, it is a nice thing. Modern technology without such a method of heat treatment would be simply impossible.

About levitation in the inductor

And now let's do the trick: wind the first 1-3 turns of the inductor, then bend the tube / bus by 180 degrees, and wind the rest of the winding in the opposite direction (Pos 4 in the figure). Connect it to the generator, insert the crucible into the inductor in the charge, give current. Let's wait for the melting, remove the crucible. The melt in the inductor will collect into a sphere, which will remain hanging there until we turn off the generator. Then it will fall down.

The effect of electromagnetic levitation of the melt is used to purify metals by zone melting, to obtain high-precision metal balls and microspheres, etc. But for a proper result, melting must be carried out in a high vacuum, so here the levitation in the inductor is mentioned only for information.

Why an inductor at home?

As you can see, even a low-power induction stove for residential wiring and consumption limits is rather powerful. Why is it worth doing it?

Firstly, for the purification and separation of precious, non-ferrous and rare metals. Take, for example, an old Soviet radio connector with gold-plated contacts; gold / silver for plating was not spared then. We put the contacts in a narrow tall crucible, put them in an inductor, melt at the main resonance (professional speaking, at the zero mode). Upon melting, we gradually reduce the frequency and power, allowing the blank to solidify for 15 minutes - half an hour.

After cooling, we break the crucible, and what do we see? Brass bollard with a clearly visible gold tip that only needs to be cut off. Without mercury, cyanides and other deadly reagents. This cannot be achieved by heating the melt from the outside in any way, convection in it will not work.

Well, gold is gold, and now black scrap metal is not lying on the road. But here the need for uniform, or precisely dosed over the surface / volume / temperature of heating of metal parts for high-quality hardening from a do-it-yourselfer or an IP individual will always be found. And here again the inductor stove will help out, and the electricity consumption will be feasible for the family budget: after all, the main share of the heating energy falls on the latent heat of metal fusion. And by changing the power, frequency and location of the part in the inductor, you can heat exactly the right place exactly as it should, see fig. above.

Finally, by making a specially shaped inductor (see figure on the left), it is possible to release the hardened part in the right place, without breaking the carburization with hardening at the end / ends. Then, where necessary, we bend, spit, and the rest remains solid, viscous, elastic. At the end, you can heat it up again, where it was released, and harden it again.

Let's start the stove: what you need to know

The electromagnetic field (EMF) affects the human body, at least warming it up in its entirety, like meat in a microwave. Therefore, when working with an induction furnace as a designer, foreman or operator, you need to clearly understand the essence of the following concepts:

PES is the energy flux density of the electromagnetic field. Determines the overall physiological effect of EMF on the body, regardless of the frequency of radiation, because. The EMF PES of the same intensity increases with the radiation frequency. According to the sanitary standards of different countries, the allowable PES value is from 1 to 30 mW per 1 sq. m. of the body surface with a constant (over 1 hour per day) exposure and three to five times more with a single short-term, up to 20 minutes.

Note: The United States stands apart, they have an allowable PES of 1000 mW (!) per sq. km. m. body. In fact, the Americans consider its external manifestations to be the beginning of the physiological impact, when a person already becomes ill, and the long-term consequences of exposure to EMF are completely ignored.

PES with distance from a point source of radiation falls on the square of the distance. Single-layer shielding with galvanized or fine-mesh galvanized mesh reduces PES by 30-50 times. Near the coil along its axis, the PES will be 2-3 times higher than on the side.

Let's explain with an example. There is an inductor for 2 kW and 30 MHz with an efficiency of 75%. Therefore, 0.5 kW or 500 W will go out of it. At a distance of 1 m from it (the area of ​​a sphere with a radius of 1 m is 12.57 sq. M.) per 1 sq. m. will have 500 / 12.57 \u003d 39.77 W, and about 15 W per person, this is a lot. The inductor must be placed vertically, before turning on the furnace, put a grounded shielding cap on it, monitor the process from afar, and immediately turn off the furnace after it is completed. At a frequency of 1 MHz, the PES will drop by a factor of 900, and a shielded inductor can be operated without special precautions.

SHF - ultra-high frequencies. In radio electronics, microwaves are considered with the so-called. Q-band, but according to the physiology of the microwave, it starts at about 120 MHz. The reason is the electrical induction heating of the cell plasma and resonance phenomena in organic molecules. Microwave has a specifically directed biological effect with long-term consequences. It is enough to get 10-30 mW for half an hour to undermine health and / or reproductive capacity. Individual susceptibility to microwaves is highly variable; working with him, you need to regularly undergo a special medical examination.

It is very difficult to stop microwave radiation, as the pros say, it “siphons” through the slightest crack in the screen or at the slightest violation of the quality of the ground. An effective fight against microwave radiation of equipment is possible only at the level of its design by highly qualified specialists.

Furnace components

Inductor

The most important part of an induction furnace is its heating coil, the inductor. For home-made stoves, an inductor made of a bare copper tube with a diameter of 10 mm or a bare copper bus with a cross section of at least 10 square meters will go to a power of up to 3 kW. mm. The inner diameter of the inductor is 80-150 mm, the number of turns is 8-10. The turns should not touch, the distance between them is 5-7 mm. Also, no part of the inductor should touch its screen; the minimum clearance is 50 mm. Therefore, in order to pass the coil leads to the generator, it is necessary to provide a window in the screen that does not interfere with its removal / installation.

The inductors of industrial furnaces are cooled with water or antifreeze, but at a power of up to 3 kW, the inductor described above does not require forced cooling when it is operated for up to 20-30 minutes. However, at the same time, he himself becomes very hot, and scale on copper sharply reduces the efficiency of the furnace, up to the loss of its efficiency. It is impossible to make a liquid-cooled inductor yourself, so it will have to be changed from time to time. Forced air cooling cannot be used: the plastic or metal case of the fan near the coil will “attract” EMFs to itself, overheat, and the efficiency of the furnace will drop.

Note: for comparison, an inductor for a melting furnace for 150 kg of steel is bent from a copper pipe with an outer diameter of 40 mm and an inner diameter of 30 mm. The number of turns is 7, the diameter of the coil inside is 400 mm, the height is also 400 mm. For its buildup in the zero mode, 15-20 kW are needed in the presence of a closed cooling circuit with distilled water.

Generator

The second main part of the furnace is the alternator. It is not worth trying to make an induction furnace without knowing the basics of radio electronics at least at the level of a medium-skilled radio amateur. Operate - too, because if the stove is not under computer control, you can set it to the mode only by feeling the circuit.

When choosing a generator circuit, solutions that give a hard current spectrum should be avoided in every possible way. As an anti-example, we present a fairly common circuit based on a thyristor switch, see fig. above. The calculation available to a specialist according to the oscillogram attached to it by the author shows that the PES at frequencies above 120 MHz from an inductor powered in this way exceeds 1 W / sq. m. at a distance of 2.5 m from the installation. Killer simplicity, you will not say anything.

As a nostalgic curiosity, we also give a diagram of an ancient lamp generator, see fig. on right. These were made by Soviet radio amateurs back in the 50s, fig. on right. Setting to the mode - by an air capacitor of variable capacity C, with a gap between the plates of at least 3 mm. Works only on zero mode. The tuning indicator is a neon light bulb L. A feature of the circuit is a very soft, “tube” radiation spectrum, so you can use this generator without any special precautions. But - alas! - you won’t find lamps for it now, and with a power in the inductor of about 500 W, the power consumption from the network is more than 2 kW.

Note: the frequency of 27.12 MHz indicated in the diagram is not optimal, it was chosen for reasons of electromagnetic compatibility. In the USSR, it was a free (“garbage”) frequency, for which permission was not required, as long as the device did not give interference to anyone. In general, C can rebuild the generator in a fairly wide range.

On the next fig. on the left - the simplest generator with self-excitation. L2 - inductor; L1 - feedback coil, 2 turns of enameled wire with a diameter of 1.2-1.5 mm; L3 - blank or charge. The inductor's own capacitance is used as the loop capacitance, so this circuit does not require tuning, it automatically enters the zero mode mode. The spectrum is soft, but if the phasing of L1 is incorrect, the transistor burns out instantly, because. it is in active mode with a DC short circuit in the collector circuit.

Also, the transistor can burn out simply from a change in the outside temperature or self-heating of the crystal - no measures are provided to stabilize its mode. In general, if you have old KT825 or the like lying around somewhere, then you can start experiments on induction heating from this schematic. The transistor must be installed on a radiator with an area of ​​at least 400 square meters. see with airflow from a computer or similar fan. Capacity adjustment in the inductor, up to 0.3 kW - by changing the supply voltage in the range of 6-24 V. Its source must provide a current of at least 25 A. The power dissipation of the resistors of the base voltage divider is at least 5 W.

Scheme next. rice. on the right - a multivibrator with an inductive load on powerful field-effect transistors (450 V Uk, at least 25 A Ik). Due to the use of capacitance in the circuit of the oscillatory circuit, it gives a rather soft spectrum, but out-of-mode, therefore it is suitable for heating parts up to 1 kg for quenching / tempering. The main drawback of the circuit is the high cost of components, powerful field devices and high-speed (cutoff frequency of at least 200 kHz) high-voltage diodes in their base circuits. Bipolar power transistors in this circuit do not work, overheat and burn out. The radiator here is the same as in the previous case, but airflow is no longer needed.

The following scheme already claims to be universal, with a power of up to 1 kW. This is a push-pull generator with independent excitation and a bridged inductor. Allows you to work on mode 2-3 or in surface heating mode; the frequency is regulated by a variable resistor R2, and the frequency ranges are switched by capacitors C1 and C2, from 10 kHz to 10 MHz. For the first range (10-30 kHz), the capacitance of capacitors C4-C7 should be increased to 6.8 uF.

The transformer between the cascades is on a ferrite ring with a cross-sectional area of ​​​​the magnetic circuit from 2 sq. see Windings - from enameled wire 0.8-1.2 mm. Transistor heatsink - 400 sq. see for four with airflow. The current in the inductor is almost sinusoidal, so the radiation spectrum is soft and no additional protective measures are required at all operating frequencies, provided that it works up to 30 minutes a day, after 2 days on the 3rd.

Video: homemade induction heater at work

Induction boilers

Induction boilers will undoubtedly replace boilers with heating elements wherever electricity is cheaper than other types of fuel. But their undeniable advantages have also given rise to a mass of homemade products, from which a specialist sometimes literally makes his hair stand on end.

Let's say this design: an inductor surrounds a propylene pipe with running water, and it is powered by a 15-25 A welding RF inverter. Option - a hollow donut (torus) is made of heat-resistant plastic, water is passed through the pipes through it, and wrapped around for heating bus, forming a coiled inductor.

The EMF will transfer its energy to the water well; it has a good electrical conductivity and an anomalously high (80) dielectric constant. Remember how the droplets of moisture remaining on the dishes are shot in the microwave.

But, firstly, for a full-fledged heating of an apartment or in winter, at least 20 kW of heat is needed, with careful insulation from the outside. 25 A at 220 V gives only 5.5 kW (and how much does this electricity cost according to our tariffs?) At 100% efficiency. Okay, let's say we're in Finland, where electricity is cheaper than gas. But the consumption limit for housing is still 10 kW, and you have to pay for the bust at an increased rate. And the apartment wiring will not withstand 20 kW, you need to pull a separate feeder from the substation. What would such a job cost? If the electricians are still far from overpowering the district and they will allow it.

Then, the heat exchanger itself. It must be either massive metal, then only induction heating of the metal will operate, or made of plastic with low dielectric losses (propylene, by the way, is not one of these, only expensive fluoroplastic is suitable), then the water will directly absorb the EMF energy. But in any case, it turns out that the inductor heats the entire volume of the heat exchanger, and only its inner surface gives off heat to water.

As a result, at the cost of a lot of work with a risk to health, we get a boiler with the efficiency of a cave fire.

An industrial induction heating boiler is arranged in a completely different way: simple, but not feasible at home, see fig. on right:

• A massive copper inductor is connected directly to the network.
• Its EMF is also heated by a massive metal labyrinth-heat exchanger made of ferromagnetic metal.
• The labyrinth simultaneously isolates the inductor from water.

Such a boiler costs several times more than a conventional one with a heating element, and is suitable for installation only on plastic pipes, but in return it gives a lot of benefits:

1. It never burns out - there is no hot electric coil in it.
2. The massive labyrinth reliably shields the inductor: PES in the immediate vicinity of the 30 kW induction boiler is zero.
3. Efficiency - more than 99.5%
4. It is absolutely safe: its own time constant of a coil with a large inductance is more than 0.5 s, which is 10-30 times longer than the tripping time of the RCD or machine. It is also accelerated by the "recoil" from the transient during the breakdown of the inductance on the case.
5. The breakdown itself due to the “oakness” of the structure is extremely unlikely.
6. Does not require separate grounding.
7. Indifferent to lightning strike; she can't burn a massive coil.
8. The large surface of the labyrinth ensures efficient heat exchange with a minimum temperature gradient, which almost eliminates the formation of scale.
9. Great durability and ease of use: an induction boiler, together with a hydromagnetic system (HMS) and a sump filter, has been operating without maintenance for at least 30 years.

About homemade boilers for hot water supply

Here in fig. a diagram of a low-power induction heater for hot water systems with a storage tank is shown. It is based on any power transformer of 0.5-1.5 kW with a primary winding of 220 V. Dual transformers from old tube color TVs - “coffins” on a two-rod magnetic core of the PL type are very well suited.

The secondary winding is removed from such, the primary is rewound onto one rod, increasing the number of its turns to operate in a mode close to a short circuit (short circuit) in the secondary. The secondary winding itself is water in a U-shaped elbow from a pipe covering another rod. Plastic pipe or metal - it doesn't matter at the industrial frequency, but the metal pipe must be isolated from the rest of the system with dielectric inserts, as shown in the figure, so that the secondary current closes only through water.

In any case, such a water heater is dangerous: a possible leak is adjacent to the winding under mains voltage. If we take such a risk, then in the magnetic circuit it is necessary to drill a hole for the grounding bolt, and first of all tightly, into the ground, ground the transformer and the tank with a steel bus of at least 1.5 square meters. see (not sq. mm!).

Next, the transformer (it should be located directly under the tank), with a double-insulated mains wire connected to it, a ground electrode and a water heating coil, is poured into one “doll” with silicone sealant, like an aquarium filter pump motor. Finally, it is highly desirable to connect the entire unit to the network through a high-speed electronic RCD.

Video: “induction” boiler based on household tiles

Inductor in the kitchen

Induction hobs for the kitchen have become familiar, see fig. According to the principle of operation, this is the same induction stove, only the bottom of any metal cooking vessel acts as a short-circuited secondary winding, see fig. on the right, and not only from a ferromagnetic material, as often people who don’t know write. It's just that aluminum utensils are falling into disuse; doctors have proven that free aluminum is a carcinogen, and copper and tin have long been out of use due to toxicity.

Household induction cookers are a product of the high-tech age, although the idea of ​​​​its origin was born at the same time as induction melting furnaces. Firstly, to isolate the inductor from the cooking, a strong, resistant, hygienic and EMF-free dielectric was needed. Suitable glass-ceramic composites are relatively recent in production, and the top plate of the cooker accounts for a significant portion of its cost.

Then, all cooking vessels are different, and their contents change their electrical parameters, and cooking modes are also different. Careful twisting of the handles to the desired fashion here and the specialist will not do, you need a high-performance microcontroller. Finally, the current in the inductor must be, according to sanitary requirements, a pure sinusoid, and its magnitude and frequency must vary in a complex way according to the degree of readiness of the dish. That is, the generator must be with digital output current generation, controlled by the same microcontroller.

It makes no sense to make a kitchen induction cooker yourself: it will take more money for electronic components alone at retail prices than for a ready-made good tile. And it is still difficult to manage these devices: whoever has one knows how many buttons or sensors are there with the inscriptions: "Ragout", "Roast", etc. The author of this article saw a tile with the words “Navy Borscht” and “Pretanière Soup” listed separately.

However, induction cookers have a lot of advantages over others:

• Almost zero, unlike microwaves, PES, even sit on this tile yourself.
• Possibility of programming for the preparation of the most complex dishes.
• Melting chocolate, melting fish and bird fat, making caramel without the slightest sign of burning.
• High economic efficiency as a result of rapid heating and almost complete concentration of heat in the cookware.

To the last point: look at fig. on the right, there are graphs for heating up cooking on an induction cooker and a gas burner. Those who are familiar with integration will immediately understand that the inductor is 15-20% more economical, and it can not be compared with a cast-iron “pancake”. The cost of money for energy when cooking most dishes for an induction cooker is comparable to a gas stove, and even less for stewing and cooking thick soups. The inductor is still inferior to gas only during baking, when uniform heating is required from all sides.

Video: failed induction cooker heater

Finally

So, it is better to buy ready-made induction electrical appliances for heating water and cooking, it will be cheaper and easier. But it won’t hurt to start a home-made induction crucible furnace in a home workshop: subtle methods of melting and heat treatment of metals will become available. You just need to remember about PES with microwave and strictly follow the rules of design, manufacture and operation.