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Contactless charging. Mophie battery cases add Qi support to iPhone. Examples of wireless chargers

The phenomenon of electromagnetic induction was observed even before Faraday, but the great Michael was the first to find an explanation for it and tried to transmit electric force over a distance by induction. Currently, the transmission of electricity over short distances at higher frequencies without wires is increasingly widespread; In this way, car batteries of ordinary cars and even traction batteries of electric vehicles are charged. As a result, do-it-yourself wireless charging is a request that is very popular among tinkerers. What fuels interest in the topic is that manufacturers of wireless chargers set their prices from the heart, and power receivers with wireless power supply are disproportionately expensive compared to their wired counterparts of the same type.

Wireless phone charging is very convenient: no need to fuss with wires and plugs, especially at night when your eyes are already sticking together. In addition, phones, smartphones and tablets are becoming thinner. In general, this is not bad, but the charge connector, which should pass a current of up to 2A, has become so flimsy that it can break due to awkward movement or fail, the contacts will slightly oxidize. And without wires - just put the device (gadget) on charge, and it charges.

In the induction boom, chargers for gadgets stand apart; the controversy surrounding them is extremely hot. Some consider wireless charging almost a product of hellish forces: they say, there is something built into it that zombifies the user into actively accepting certain religious, commercial or political trends, and at the same time ruins his health. Others, on the contrary, identify the electromagnetic field (EMF) of charging with the almost mystical power of Qi, which guarantees ascending reincarnation to the owner. The truth in this case lies not in the middle, but completely to the side, so the purpose of this article is to provide information about the following:

  • How, being, as they say, not in the know and not wanting to bother with all sorts of intricacies, when buying exactly choose wireless charging harmless and safe. The power of Qi is already a matter of pure faith. Its existence, like any other something else omnipresent, omniscient and omnipotent, cannot be proven or refuted by the arguments of reason.
  • The principle of operation and design of WPC standard chargers for gadgets.
  • How to properly charge the battery of a phone, smartphone, tablet.
  • Methods of transmitting electricity over a distance without wires.
  • Harmful factors and dangers associated with the use of wireless chargers.
  • Is it possible and how to convert an old mobile phone to the WPC standard?
  • How to make wireless charging with your own hands at home, suitable for any WPC standard gadgets and completely safe, costing no more than $10 for components.

How to choose harmless charging

Einstein once said: “If a scientist cannot explain to a five-year-old child what he does, then he is either mad or a charlatan.” The power of Qi is the power of Qi, but all our actual achievements are based on objective knowledge that does not depend on the subject. Let's say we brought an Amazonian savage to our home, there are others like that there. They took him to the TV and said: “If you plug this thing, a plug, here into the socket, and press here, then a picture will appear here, and sound will come from here.” If the savage does everything as told, the TV will turn on, the picture will appear, the sound will play, although the savage has no idea about electricity and electronics, and considers a thunderstorm to be an indigestion for his gods. So the kettle is full, as they say, maybe choose wireless charging for your gadget, which you can use without fear:

  1. Make sure that the device has a WPC standard compliance icon (see below);
  2. Please show the charging: in addition to the Power or I/O indicator, there should be a Charge indicator or indicated by the same icon as on the gadget;
  3. please turn it on. Power should light up, but Charge should not;
  4. We put the gadget on charge – Charge should light up, and the gadget’s display should show the charge;
  5. We lift the gadget no more than 3 cm above the charging platform - Charge should go out and the display should show that charging has stopped.

This type of wireless charging can be safely used at home if it is located no closer than 1.5-2 m from places of long-term stay of people(bed, desk, favorite sofa in front of the TV). You can’t keep wireless charging turned on in a child’s room. incl. and described below, which can be constantly turned on on the nightstand by an adult’s bed.

What is WPC

WPC is an abbreviation for Wireless Power Consortium, the name of the company that first brought wireless charging to the market. WPC technology is nothing new, much less supernatural; The components of WPC charging and its operating principle are shown in Fig. The familiar iron transformer also operates on the transmission of electricity by induction. The peculiarity of WPC is that the operating frequency is increased to tens of kHz or even MHz; this allows you to separate the primary and secondary windings at some distance and do without a ferromagnetic core, because The energy flux density (PED) of EMF increases with frequency; Also, with increasing frequency, the technical ability to concentrate EMF in a limited area increases. But at the same time, the biological effect of EMF increases with frequency, which is why small and weak wireless charging can be more dangerous than an industrial induction heating installation.

Note: WPC is still, in our opinion, an industry standard; it has not yet been formalized by international agreements. Therefore, the technical data of gadgets with WPC, especially from alternative manufacturers, may differ so that they are charged only from “their” charger. If you do wireless charging yourself, you need to give the design margin and the technological ability to modify the transmitter for a specific device, see below.

Devices designed for recharging using the WPC system are indicated by a special icon (item 1 in the figure). It means that the device has a receiving coil of 25 turns and an RF AC-to-DC converter. A number of gadgets are available with or without WPC. Then the induction receiver is either “thrown” and located under the battery cover (pos. 2), or modular, pos. 3. In any case, a connector (item 4) or clamping contacts are provided for the WPC receiver, where you should connect the homemade receiver when modifying the gadget for WPC. The polarity is determined by the multitester when wired charging is connected, because... Wireless charging contacts are paralleled with those of conventional charging.

Note: Under no circumstances should the WPC receiver be connected directly to the battery! In the best case, an expensive battery will soon fail, because... In the device it is charged in a special way, see below. And modern high-capacity lithium batteries can simply explode if charged directly to the terminals!

In some gadgets, the WPC receiver is hidden under a cover, the removal of which requires partial disassembly of the device, pos. 5. One way or another, if your model without WPC has a “twin” with wireless charging discovered by searching on the Internet, then yours will also have a cavity for the receiver: it would be too expensive to produce various parts of the case. This greatly simplifies the modification of the gadget for WPC, but you need to make sure that this model is produced in both versions.

About the charging mode

The battery in any gadget is charged under the control of a special controller, which first determines how discharged the battery is. If it is more than 75%, then an increased fast (boosted) charge current is immediately supplied, equal to approximately the 3-hour discharge current, if the charger provides it. No - the charging takes the current that it can provide when the output voltage drops to 5 V. Therefore, many devices from USB ports take a long time to charge, because standard USB power output 5 V 350 mA.

The forced charge is designed to eliminate the polarization of the battery electrodes, which causes the so-called. hysteresis. The capacity of the “hysteresis” battery continuously decreases, and its resource turns out to be much less than declared. A fast charge with a current of less than 3 hours does not completely eliminate the hysteresis, and the battery soon runs out. As a result, charging for a smartphone or tablet must provide a charge current of more than 1.5 A, because in “smart” gadgets, batteries are 1800-4500 mAh, i.e. their 3-hour discharge current will be 0.9-1.5 A.

After the battery has been charged for approx. up to 25% capacity, the charging current gradually decreases to the value of a small forming (recharging) current until the battery is “pumped” for approx. by 75%. Forming the battery with a small current avoids electrodegradation of the electrolyte, which also reduces the battery life. The forming current is approx. current of 12-hour battery discharge.

Finally, when the battery is fully charged, the controller passes a very tiny current through it for the minimum required time to prevent chemical degradation of the electrolyte, and only then gives a signal about the end of the charge. Therefore, keeping a gadget with a working and properly designed controller on charge for more time is not at all harmful, on the contrary. The author has an old Motorola W220 phone. For the sake of experience, it is charged all the time, except when you need to leave the house with it. Over more than 10 years of use, the battery has not noticeably lost its capacity: the 4 days of “hibernation” and 4 hours of continuous conversation specified in the phone’s passport have not decreased. And other users of the same model had to change the completely depleted battery.

Induction or radiation?

Induction

The transfer of electrical power over a distance occurs through an electromagnetic field (EMF), in which a certain energy is stored. For inductive energy transfer, in addition to the transmitter, you also need a receiver, not necessarily electronic. It could be, for example, an aluminum pan, in the metal of which the EMF transmitter induces Foucault eddy currents that heat the dishes. The currents induced in the receiver create their own EMF, which interacts with the EMF of the transmitter. As a result, a common EMF is formed between the transmitter and the receiver, which transfers power from the first to the latter. Hence the first characteristic feature of inductive energy transfer is the influence of the receiver on the operating mode of the transmitter, the so-called. source response to load.

Note: EMF with the induction method of energy transfer is especially highly concentrated near the source-receiver system in the presence of ferromagnetic materials there. An example is an electrical transformer based on iron or, at higher frequencies, on a ferrite core.

It is advisable to transmit power by induction at lower frequencies, because High frequency EMF (HF) does not penetrate deep into conductors, this is the so-called. surface effect or skin effect, and with increasing frequency, energy losses due to radiation increase. The EMF energy flux density (EMF PPE) at low frequencies is low, because EMF energy in a given volume from a source of a certain intensity depends on frequency.

The first difference between power transmission by radiation and induction is that the EMF “breaks away”, “leaves” from the source, losing contact with it, i.e. is emitted. If, for example, you give an impulse with a combat laser into space, and then turn off or destroy the source, then the packet of EMF oscillations will rush and rush in world space until it hits an obstacle and is absorbed by it or dissipates in the propagation medium. The consequence is that when power is transmitted by radiation, there is no reaction from the source to the receiver. A second-order consequence is that the ability of EMF to spontaneously concentrate is also absent, because the radiation itself tends to “spread” to the sides; to assemble it in a given area, special design and technical measures are needed. Unlike the induction method, the presence of ferromagnets in the transmitter coverage area reduces the power transfer coefficient, because ferromagnets “pull” EMF towards themselves, which should get into the receiver.

The efficiency of energy transfer by EMF radiation depends on the frequency of its oscillations, because There is no on-demand field pumping by the transmitter. What is “downloaded” into the emitted packet will be there. It is possible to add energy to the consumer only by continuing the radiation. Another feature is that the material that most effectively absorbs the flow of EMF power is not a conductive material, but, on the contrary, absorbs EMF energy; these properties are used in microwave ovens. A long insulated conductor of a certain configuration (for example, twisted into a spiral), which in this case represents a receiving antenna, can also be an absorber of EMF energy.

Both

In order to meet the requirements of minimum weight and dimensions and the absence of foreign ferromagnets near the radio path of the gadget, WPC developers had to increase the operating frequency of the system; After all, tablets also have transceivers for working in a Wi-Fi environment. As a result, WPC gained the ability to operate both in induction and radiation. This feature allows, in principle, to increase the range of the WPC to several meters, which is what some amateurs take advantage of. Such enthusiasts, apparently, either do not know at all about the biological effects of EMFs, or deliberately ignore such information.

In this case, it is impossible to say “the problems of the Indians are the problems of the Indians”, because “Indians” may turn out to be strangers, ignorant and uninvolved people, for example, neighbors behind the wall or their own children. Before you start making wireless charging yourself, you need to figure out under what circumstances it will be harmful or dangerous and how to avoid it.

However, a very definite intermediate conclusion can already be drawn - wireless charging must be selected upon purchase (see above) or done only by induction and spontaneously, without additional automation, switching without a receiver at the charging site to standby mode with the generator power reduced to a safe level. Of course, it’s completely convenient when the phone is lying around anywhere in the room and is still charging, but it’s healthy - you understand.

Note: There is no point in charging with a generator that turns off without a phone on charge. After all, then to charge the gadget you will have to turn it on, which reduces the convenience of wireless charging to almost nothing. Wireless charging must be done with a very sharp, as they say, acute, reaction of the generator to the receiver. There is also no point in integrating a mechanical or opto-sensor for the presence of a gadget into the charging; it can be triggered by something similar to it, but does not force the generator to reduce power.

Factors of harm and danger

The effect of EMF on living organisms also depends on the frequency of its oscillations. In general, it monotonically increases with frequency approx. up to 120-150 MHz, and then bursts and dips are observed. In one of them, visible light, we have adapted to live in the course of evolution; One of the others operates microwaves around 2900 MHz. But the microwave dip in EMF bioactivity is shallow, otherwise it will not be absorbed by the products, as long as it is technically possible and not very difficult to shield the oven from EMF radiation to the outside. Therefore, if you are planning to repair a microwave with your own hands, you need to know exactly how it is structured, how it works, what can be done there, what is permissible to do and what cannot be done so that the microwave does not siphon out, and know how to determine at home whether it is siphoning microwave. But let's get back to the topic.

The EMF PPE also increases with frequency, so the norms for its level are tied to the PPE. In addition, individual sensitivity to PPE EMF varies within a very wide range, approx. 1000 times. In countries with downright redneck labor and social legislation, acceptable levels of PES have been adopted to monstrous values, up to 1 (W*s)/sq. m. Approach in this case: were you warned when hiring? Do they pay for your additional medical insurance? Will they guarantee an increased pension for harmful activities after 10 (15, 20) years? The rest is Indian problems.

In PPE of this level, a person directly feels the effect of EMF: heaviness in the head, gentle warmth coming from the depths of the body. Gentle, but extremely dangerous: this is evidence of the beginning of plasmolysis of cells, which is why they can undergo malignant degeneration. “The device at half past six” is still the most terrible consequence of “picking up the bunny” PPE EMF.

In the USSR, the other extreme was in effect - 1 (μW*s)/sq. m, i.e. a million times less. The impact of such a PPE on the most sensitive subject will not affect either immediately or in the long term. Each citizen, or rather subject, of the “Council of Deputies” was actually the property of the state, but it also guaranteed his life, health and safety. At least formally.

For a market economy, such reinsurance will be unbearable, and in the current clogged airwaves, it is hardly technically feasible. Therefore, the generally accepted standard for the EMF PES level today is intermediate – 1 (mW*s)/sq. m. Such a PPE, which affects constantly and for a long time, will certainly give long-term consequences, but regular exposure to it for no more than a certain time per day is harmless and safe for the average person. Those who are overly sensitive are screened out by a medical examination during hiring, and the consequences of random deviations can already be compensated for without overtaxing social funds. Also, of course, a redneck approach, treating cancer in retirement instead of rest is not great pleasure, but at least within reason. Therefore, we will consider wireless charging potentially dangerous if it creates a PPE EMF of 1 (mW*s)/sq.m within a touch radius (approx. 0.5 m). m or more.

Safety calculation

Let's believe the advertising and buy a “super-duper” USB-powered charger (power consumption - 1.75 W), operating within a radius of 20 cm (0.2 m). The efficiency of a blogging generator (see below) of this power using a field-effect transistor is approx. 0.8; 1.4 W will go on air without a gadget lying on the site. The area of ​​a sphere with a radius of 0.2 m is 0.0335 sq. m. The PES on it will be 2.8/0.0335 = 41.8 (W*s)/sq. m(!). The PES value is inversely proportional to the square of the distance from the source. At what point in this case will it drop to the permissible 1 (mW*s)/sq. m? The calculation is simple: we take the square root of the ratio of the actual PES to the permissible one, and multiply the result by the initial radius of 0.2 m, i.e. divide by 5; we get... 20.4 m! This is what manufacturers' assurances of product safety are worth. Along with the power of Qi.

The above statement about the gadget on the site is not accidental. In this case, the charge at frequencies whose wavelengths are much greater than the gap between the emitter and the device will be inductive, if the receiver is suitable for it. The receiving coil of the gadget is uniquely suitable as an induction receiver. A gap of 3 cm (see above) will give a frequency of 10 GHz, which the generator is definitely not capable of producing; In reality the gap is even smaller. So the preliminary conclusion is confirmed: our charging should be only and only inductive. The EMF PES in the gap between the inductor and the device will then be many times greater, but this is no longer dangerous, because The EMF will naturally be drawn to the receiving coil, the diameter of which is approx. 5 cm. At a distance from it three times greater (more precisely, e times, e = 2.718281828...) the presence of EMF can only be detected by a sensitive detector, but calculations “on your fingers” cannot be done here; for the conclusion you need to use the means of mathematical physics .

Note: The fact that the WPC standard is not international makes it possible for manufacturers of wireless chargers to “go to extremes” based on safety assurances. You can refer to the safety standards of the country where production is taking place. Or the one where the company is registered, and there may be no regulation of PES at all; there are still such state entities left in some places.

About car chargers

From the calculation above it follows that wireless car charging is definitely dangerous: their range of action reaches 1 m. These marketers would be in such PPE for life... or at least until they feel the “device at half past six”... The justification given is the relative short duration of the impact and the need to protect an expensive gadget from damage due to the fact that it is dangling on a cord under the cigarette lighter. But wouldn’t it be smarter to simply extend the cord so that the gadget could be kept in the glove compartment or other convenient place? Driving a car with a phone in your hand is still risky, and in some places you can be fined for it.

If the gadget is without WPC

There are only 2 mandatory requirements for the WPC receiving coil: the number of turns is 25 and the wire diameter is designed for a current of 0.35 A, taking into account the skin effect at frequencies up to 30 MHz. Practically - from 0.35 mm for copper (without insulation). Thicker, when there is enough free space in the case, will only be better. Configuration – any according to location. Special care in manufacturing is not required (item 1 in the figure), but it is necessary that the ratio of the largest transverse dimension to the smallest does not exceed 1.5, otherwise the efficiency of the receiver will drop and the charge will be delayed.

If charging is done for an old plump phone or for a tablet without WPC, the coil is placed in the body of the gadget. A slight bend in place (item 2) will not affect the properties of the receiver. Suddenly there is not enough space inside (you still need to tuck the electronic components of the receiver somewhere), you will have to make a flat coil “like a branded one”, pos. 4. It is convenient to lay the wire in a flat spiral using tape placed on the substrate with the adhesive side up. To ensure that the Velcro does not wrap up and does not creep, it is fixed at the edges with strips of the same tape, applied with glue down. A round boss with a diameter of approx. is placed on the tape. 1 cm and lay turns around it, pressing the wire against the Velcro. When as many turns as necessary are laid, the boss is peeled off, the finished coil is dug to fix the turns with superglue or nitro varnish, pos. 3, and remove together with tape; its excess is trimmed off.

Doing exercises

Generators of homemade wireless charging and some of the factory ones are assembled according to the blocking generator circuit, or simply blocking, see figure:

We will do charging with a self-generator of harmonic oscillations according to an antediluvian circuit with weak inductive coupling. It fell out of use in industrial equipment back in the 20s of the last century, as soon as three-point generators, inductive and capacitive, were invented, precisely because of the very acute reaction to the load, but that’s what we need! And other shortcomings of a generator with a weak coupling are either eliminated by modern element base and circuitry, or are not fatal. So, at the beginning of a forced charge, the power consumption reaches 25 W, so a separate power source is needed. But the average long-term charge of a tablet with a 3500 mAh battery constantly turned on every night does not exceed 8 W, and in a month such charging will “wind up” as much as 5.75 kW/h.

But first of all, let's deal with the transmitting coil, because... this circuit is also sensitive to the parameters and quality of the frequency-setting nodes. To set up the generator (safety is worth something, nothing can be done) you will also have to hastily make a receiving coil, see above. You can use charging for its intended purpose only when the generator is set up, but then it works more stable and safer for the gadget than charging when blocked. Therefore, you can use any gadget with this charger: it is designed for 2 amperes of charging current or more. But an old phone with a 450 mAh battery will take from it no more than what the controller “prescribes” due to the same acute reaction to the load.

Transfer coil

Drawings of generator coils with weak inductive coupling are shown in Fig. below.:

On the left – contour L2 (see below); on the right - feedback coil L3 (in the middle) and charge indication circuit coil L1. They are etched on a plate made of 2-sided foil fiberglass laminate 100x100 mm, 1.5 mm thick, so-called. laser-iron technology LUT. There is nothing complicated about it, the idea and name are amateurish. LUT allows you to make printed circuit boards at home no worse than branded ones, signs with inscriptions, contour drawings, patterned panels, etc., see the video below:

Video: laser ironing technology

In addition to this, we can say that it is best to clean the blank for LUT with a regular school eraser. Then the scraps of copper are washed off with a cotton swab or a white, clean cotton rag, generously moistened with 96% alcohol or nitro solvent, and then, while the surface is wet, wiped dry with a microfiber cloth for cleaning glasses. The toner of any laser printer and even an inkjet printer from a template is firmly placed on the surface prepared in this way on a suitable (holding, but not absorbing ink) base.

Note: do not be confused by the width of the tracks in the drawing (0.75 mm for the contour coil). The permissible current density in a film conductor on a substrate is several times greater than in a round wire, and the skin effect is weaker. Thus, a track on a printed circuit board 10 mm wide and 0.05 mm thick can easily hold a current of 20 A, and this is far from the limit. Double-width feedback coil tracks are needed because... During the setup process, you will need to resolder the tap on it. In general, LUT allows you to obtain tracks up to 0.15-0.2 mm wide.

Circuit design

The diagram of a wireless charger on a generator with inductive coupling is shown in Fig.: on the left is the transmitter; receiver on the right. Its features, firstly, are the powerful active element VT3. It can only be an amplifying field-effect transistor. A generator based on a bipolar transistor will have low efficiency, and powerful field switches of the IRF, IRFZ, IRL series from computer power supplies or electronic ignition systems do not work in active mode.

The second is the auto bias circuit VD3 C3. For powerful amplifier field workers, the initial drain current can reach 100-200 mA or more. Without a blocking potential on the gate, it will be possible to configure the generator only for power or standby mode, but not for both, and the PES from the inductor within the contact radius will certainly exceed the permissible value. But it is also impossible to form an auto-bias by connecting a resistor to the source circuit, as in the cathode circuit in tube amplifiers: the generator will not reach full power, because As the source current increases, the displacement will also increase in absolute value. Therefore, the bias circuit is made nonlinear on the diodes: at low powers it increases in accordance with the source current, which ensures a soft start of the generator and its safety for any gadgets, and when the diodes enter saturation, the bias becomes close to fixed and allows the generator to “swing to its fullest.” The bias circuit is selected during the setup process from powerful rectifier diffusion RF diodes (PiN, KD213, KD2997 structure) and Schottky diodes (SMD structure) for a current of 6 A. The saturation voltage of the former in the current range of 0.7-5 A varies within 1- 1.4 V; second - 0.4-0.6 V.

Elements R1, VD1, VT1, VT2, C1, R2, VD2 and L1 make up the charge indication circuit. If the current transfer coefficient β VT1 is more than 80, then VT2 is excluded, and the R2 engine is connected to the VT1 base. Capacitor C3 must be film; Even better is the old paper one, because... It dissipates significant reactive power.

The receiver of this charger also has special features. The first is full-wave rectification of the received current, because harmonic vibrations. This does not prevent the use of this device for charging gadgets with built-in WPC, because in them, the received current is also rectified by a diode bridge for better use of the inductor radiation. The second is that ceramic C5 is connected in parallel with the storage electrolytic capacitor C4. “Electrolytes” have a large self-inductance and a significant dielectric loss tangent tgδ, which reduces the charge efficiency at operating frequencies. Bypassing the “electrolyte” with “ceramics” reduces the charging time by approx. by 7%. For a tablet with a 3500 mAh battery, this will be approx. half an hour. Agree, sometimes it’s significant.

Finally, the VD8 diode. It protects the gadget’s charge controller if it is placed on an inductor connected to wired charging. You never know what comes to mind. Maybe someone will think that double charging will charge the device faster. The charge controller will still not allow more current into the battery than it should, but it may not be able to withstand such abuse. If such a situation is excluded, then VD8 is also excluded; then VD7 is needed for a voltage of 5.6 V. Its operating current is indicated with a large margin, because the maximum charge current never passes through it due to the acute reaction to the generator load. Practically - set any low-power junk device to the required voltage. He holds it - well, let him hold it. If it gets hot, we install something more powerful and more expensive; The charge controller also has its own overvoltage protection.

Note: without VD7, the rectified voltage will be the maximum permissible in WPC 7.2 V, which allows you to charge tricky “alternative” gadgets. It can be reduced by re-soldering the hot end L2 (see below) closer to the center of the coil, but no more than 6-7 turns.

Setting up

Setting up the generator begins with setting its quiescent current Iп without excitation. To do this, L3 is turned off, and gate VT3 is connected to the common wire (item 1 in the figure), i.e. form a zero offset. Next, selecting the VD3 chain, set Ip within the specified limits. If the drain current at zero bias is less than 50 mA, IP can be set to 15-20 mA, the generator will become more economical and safer. Suddenly the initial drain current is less than 40 mA, even better, then C3 and VD3 are not needed.

The next stage is phasing the windings. To do this, you will need a probe from the receiving coil (see above) with an incandescent light bulb connected to it, pos. 2. The generator circuit is restored, turned on, and a probe is placed on L2. The light should light up. No - swap pins L2 or L3. The coils need to be phased so that the hot (farthest from the center) end L3, pos. 3. At the same stage, measure and record the operating current consumption Ip, pos. 4.

Now you need to set the safe standby current of the generator Id; The radiated power in standby mode will drop in proportion to the square of the ratio of the operating current to the standby current. Id is set by resoldering the hot lead L3 in the positions indicated in pos. 5 limits closer to the minimum value. The return to power is checked by placing a probe on L2. The installation procedure is quite tedious. To avoid tightening it and soldering until the track peels off, proceed as follows. instructions:

  • L3 is reduced by half (pos. 6);
  • Id turned out to be small, or the probe does not show a return to power - we return half of the discarded turns, pos. 7;
  • Id is still large - we discard half of the remaining half of L3, pos. 8;
  • situation according to point 2 - we return half of the turns discarded according to point 3, but not half of all discarded, pos. 9;
  • if necessary, continue the setup, following the same algorithm.

Thus, using the iteration method, setting Id takes very little time.

All that remains is to configure the charge indication circuit. To do this, assemble a receiver loaded with a resistor of such a size that the charge current is less than the forming current, but greater than the content current, pos. 10. The R2 engine is placed in the lower position, the receiver is placed on L2. By rotating the engine, you achieve the glow of VD1. They remove the receiver and see if VD1 goes out. No - the engine is turned back very smoothly and carefully until VD1 goes out.

Design

Further reduction of charging time and improvement of device safety parameters can be achieved by directing the energy flow from the inductor upward; this technique is used in some branded wireless chargers. These can be recognized by the inductor surrounded by a ring, unless very smart alternativeists just stuck it on for sales.

In fact, the radiation direction is created by shielding the inductor from the rear side. To do this, the generator is placed in an open-top housing made of thin, no more than 0.25 mm, sheet metal. If the height of the housing is indifferent to aesthetics, the generator power source is also placed in it. In this case, it must be equipped with a power frequency transformer on hardware: interference from a closely located UPS will disrupt the generator settings.

Steel is needed for magnetic shielding in addition to electrical shielding, and its thin thickness is needed to prevent losses due to eddy currents. For the same purpose, frequent thin vertical slits are made in the sides of the body, and the bottom is perforated in a checkerboard pattern, see fig. The ideal option is the walls and bottom of the housing made of fine-mesh steel mesh. Cover – any radio-transparent plastic without filler: glass, acrylic, fiberglass, fluorine paste, PET, PE, polypropylene, polystyrene. An option is colorless transparent acrylic or nitro varnish in 4-5 layers, but not paint or enamel. External design can be anything. It is with this design that you can keep wireless charging for your phone, smartphone, or tablet constantly on on your bedside table. Although in today’s extremely littered ether, it is still better to stay away from any known sources of EMF.

In order to equip your favorite smartphone with the flagship wireless charging function, you don’t need much.

Firstly, the base, also known as the charger. Most often it is made in the form of a small round platform with an outlet for a charger. For the experiment, let's take an unnamed model with a pleasant blue backlight. Powered by a 5 V, 2 A power supply (regular USB), powered via a standard microUSB port. At the output, the device produces a current with parameters of 5 V, 1 A, which is enough to charge most devices even in operating mode.

The second necessary element of modernization is the antenna, with the help of which the smartphone is charged from a distance. Usually this distance is minimal, by the way, but the convenience of using wirelessly can be significant for someone. For example, the base can be built into the dashboard of a car or placed on a chest of drawers near the bed: come, put it down, go to bed. And no searching for wires.

There are a lot of different universal antennas for smartphones on the market. They are also suitable for other equipment, but here you need to think about placement. The antenna (we have an unnamed Chinese copy) is a coil with a circuit board hidden in a paper-like envelope. A wire with a microUSB plug comes out of it, although if desired, it can be soldered to any other one. It is worth paying attention: the coil only works in one position in relation to the charger. Since the cable for connecting to a smartphone is flat, you may need to open the bag and flip the coil over for the antenna to work (as in our case). The coil should face the open side towards the charger.







Attention: the charging base shows the necessary parameters of the power supply (in the case of the used one - 5 V, 2 A). They need to be provided for. At lower current levels, charging will occur very slowly. For adequate operation, you may need to replace the cord included with the charger, since not every USB cable can pass a full 2 ​​A. As you can see,

With the announcement of integrated wireless charging in the Lumia 920, Nokia hopes that this technology will attract the attention of buyers and win some of them away from Apple. Nokia has joined HTC, Sony, Samsung and others in adopting QI, a proprietary standard interface created by the Wireless Power Consortium. Qi, pronounced "qi", comes from Chinese energy flow and is designed to power devices through magnetic induction. Let's look at what it is and what benefits it provides.

Operating principle

The term "wireless charging" usually refers to inductive charging. This technology uses a charging station that creates an alternating magnetic field. A device with a suitable induction coil will receive energy from the field induced by the field charging station, and thereby the energy can be transferred over a short distance. Everything is as the great Nikola Tesla said. Or maybe the Tunguska meteorite is really his doing?

Wireless toothbrushes have been using wireless charging for a long time. The technology has traditionally been plagued by problems of low efficiency and slow charging, but these weren't critical shortcomings for a toothbrush or electric razor that you only use for a few minutes every day. Using inductive charging is safer from the point of view that there is no wire to short out and you won't accidentally touch areas with poor insulation with wet hands. Inductive charging is not magic. It needs specific hardware, the hardware must be built into the device.

Disadvantages of wireless charging

Inductive charging depends on the magnetic field. They can be strong, of course, but still have a short range. This is the first drawback.

Charging speed and efficiency are the second drawback. Charging devices using inductive charging is not as efficient as using a direct, physical connection.

The third disadvantage is dimensions. Even though coils are small and getting smaller, a significant portion of the space available in a modern smartphone, tablet or ultrabook will still be coils. This is a problem that will decrease over time, but today it is still relevant.

The future of wireless charging

This inductive charging can be convenient, but the short range is a problem. This dramatically reduces the usability of this technology.
Will this change? May be. There has been a lot of research into the potential of wireless charging and there have been advances in range in various technologies. Lasers, microwave ovens, and more powerful inductive charging options have been able to achieve longer transmission distances. Disadvantages prevent the spread of this too powerful radiation of the above mentioned technologies. You might get burned or worse.

It is difficult to say who will take the palm in this market. The first candidate is Apple, because the company has patented a device that can supposedly charge from a distance of up to one meter. The Wireless Power Consortium is also constantly looking for better options. And then there's Intel, which recently announced that it's working on integrated magnetic device technology that will fit inside a laptop and distribute power to nearby smartphones and peripherals.

Conclusion

Wireless charging has huge potential. That's why people have been working on it for over a century. If we could transmit energy wirelessly, we could reimagine not only consumer electronics, but the infrastructure used by humanity. A list of smartphones that support wireless charging is presented

Nowadays, a person without a smartphone is a person cut off from life. It's hard to imagine that a few years ago a mobile phone was used only for communication. Now this little assistant gives us both access to the Internet and many applications, and wakes us up in the morning. The list of benefits provided by a smartphone can be continued endlessly. It is not surprising that a large number of gadgets have been invented for modern phones. One of them is a wireless charger, which we would like to talk about in more detail.

How can I tell if my phone supports wireless charging?

From the name it is clear that this is a gadget that allows you to charge your smartphone without using wires. It is a small stand connected to the network. There is an induction coil inside, which creates a small magnetic field around itself. If there is a smartphone within the radius of this field, it will receive electricity literally through the air. But there is one caveat - the smartphone must also have a built-in induction coil. It will serve as a kind of energy receiver from the charger.

The purpose of creating this device was to rid modern smartphones of charger connectors, and also to allow all devices in the house to be charged from one platform. The idea was a success, but why then don’t we see this technology in every home and don’t use it ourselves? The answer is simple - despite all the advantages, this miracle device also has disadvantages.

Pros and cons of a wireless charger

Wireless charging has a lot of advantages, but they all have their own cornerstone.

No wires

Without a doubt, this is a big plus. Wires have always been a weak point in chargers. With frequent kinks, the wire was easily damaged and tangled. Frequent recharging loosened the USB port on the phone, and sooner or later it required repairs. But there is also another side to the coin. Refusal of wires reduced the efficiency (efficiency factor) from 90% to 60–75%. Simply put, when using wireless charging, your smartphone will charge approximately 2-3 times longer.

Range of use

It would seem that there are no wires - there are no restrictions, and you can charge your phone simply while in the apartment. But no - the radius of use of the wireless charger is very modest (3–5 cm) and the phone will have to be placed on a stand. Another significant drawback will be the inability to use the smartphone while charging.

Price

The cost of a charger is quite variable, but it will always be more expensive than the usual charger.

Standards

I would like to talk about the standards that made the use of technology for transmitting electricity through the air possible.

Qi (“Qi”, after a term in Eastern philosophy) was developed by the WPC (Wireless Power Consortium). It is the most widespread and is supported by such giants of the mobile industry as Asus, Motorola, HTC, Huawei, LG, Nokia, Samsung, Blackberry, Sony and others. You can find out more about the standard and the list of supported devices on their official website.

The PMA standard also uses the principle of electromagnetic induction, but does not boast as large a list of manufacturers supporting their technology as Qi. It was developed by Powermat, which is currently trying to fight unhealthy competition from Qi.

This standard uses Rezence technology, which is fundamentally different from PMA and Qi. The strange thing is that the most unpopular standard has many advantages in comparison with its competitors. The advantages include:

  • the ability to charge through interference (if you put a book between the smartphone and the charger, nothing will change);
  • one platform can provide energy to several devices;
  • work in close proximity to metal objects, etc.

You can view the full list of smartphones that can use wireless charging right out of the box on the official website https://www.wirelesspowerconsortium.com. I would like to note that most manufacturers have made sure that their product supports the use of this technology.

What if your smartphone is not on the list of supported devices, but you need to use wireless charging? If you have this question, then most likely you are a happy user of Apple products. The iPhone does not yet have the ability to receive electromagnetic signals. However, there is an alternative - purchasing an auxiliary accessory that will do this for your phone. It fits under a standard case and does not cause any discomfort.

Is wireless charging harmful to health?

Like any new technology, wireless chargers raise many questions. One of the most pressing is whether it harms health. Let’s immediately dispel this far-fetched myth. It will do you no more harm than an electronic razor using the same technology. The developers of the WPC standard themselves claim this.

What is wireless charging for a smartphone, how does it work and how to choose it

Recently, more and more smartphones with wireless charging functionality have appeared on the mobile device market. In this article we will try to tell you a little about it, how it works, its pros and cons, how to use it and how to choose it. So let's get started!

Principle of operation

Let's start with the fact that this technology is based on the principle of electromagnetic induction, in which an electromagnetic field is formed around a current-carrying conductor. If another conductor is placed within the range of this field, current will also begin to flow through it. The radiation power can be adjusted using inductors, allowing the energy to be concentrated on the required area.

In our case, wireless charging technology is implemented through a special docking station (powered by a USB port or a regular outlet) and a receiving device - i.e. the smartphone itself. Each of them is equipped with an induction coil, which allows the Google Phone placed on the station’s stand to receive the station’s electromagnetic radiation and replenish the charge level of its battery.

Wireless charging standards

There are two standards of wireless charging technology in the consumer market today. The first of them (the most popular) is called Qi, the second is PMA. However, some manufacturers support both standards, which gives their gadgets some versatility.

You can find out which standard a particular smartphone supports from the documentation that came with it or from the description of its characteristics published on the manufacturer’s website.

How to choose a wireless docking station

1. Power

If you decide to purchase a docking station with fast charging functionality, be sure to check the charger specifications. So, for example, with an output voltage of five volts, the current can range from several hundred milliamps to one ampere and higher. In this case, the wired charger has an output current of one to two amperes. Thus, the most suitable model would be a model with an output current of one ampere or higher. If this value at the docking station is too low, then you will spend much more time charging your smartphone.

2. Number of charging circuits

It is also worth paying attention to the number of coils of the wireless charger you want. The fact is that most docking stations are equipped with only one coil, which is why they have a very limited range and require precise placement of the phone on the stand. At the same time, today on the market you can find stations with two or even three coils, thanks to which the accuracy of the gadget’s location on the platform has almost no effect on its charging speed.

3. Brand.

You should not buy completely “incomprehensible” devices. Chinese auctions today are replete with a huge number of various models of wireless chargers, but you need to understand that when buying a pig in a poke, you will not receive any guarantees that the output power will correspond to the declared indicators. And this is the most important indicator.

Today there are enough brands that produce good products, but not always for a lot of money: Samsung, Nokia, Belkin, Anker, Mophie, Skyway, etc.

  • Use the "correct" power supply, the power of which meets the manufacturer's recommended specifications.
  • For most chargers, especially those with single coils, the position of the device matters. These can be either drawn outlines of the recommended location of the smartphone, or specific recommendations in the instructions. If the charger is made in a docking station form factor, there are often only one or two possible positions (vertical and horizontal, if there are two coils)
  • Do not place anything between the smartphone and the charger. Magnetic mounts, magnetic cases, metal plates in car mount cases can all reduce the performance of the charger.
  • Also, do not forget to remove credit cards, electronic badges, and other things that have magnetic stripes or RFID chips from the case, because possible electromagnetic radiation can damage them.
  • A very thick case can also reduce charging efficiency by moving the device away from the charging circuit.
  • Vibrating the smartphone, for example when receiving a notification, can move the device from its original position, which can reduce efficiency
  • Slight heating during charging is normal. But only a small one.

Advantages and disadvantages

What are the pros and cons of wireless charging for smartphones? Let's start with its advantages:

Pros:

  • Convenience. I think no one will argue that this is much more convenient than connecting a cable. Especially if the device periodically has to be used during charging, for example, for calls.
  • You won’t have to connect the cable every time, which means the smartphone’s interface connector will last much longer.
  • Today, many establishments, including StarBucks and McDonalds, have equipped their customer tables with built-in Qi docking stations, which can be useful if you urgently need to charge your gadget and don’t have a charger on hand. Furniture has also already appeared (for example, in IKEA) with built-in charging panels, and automakers are increasingly installing them in premium cars.
  • While at home, you can keep your device on the docking station all the time, so it will always be fully charged. In this case, the controller built into the device will automatically stop charging as soon as its level reaches 100%.
  • Safe to use. Any cable begins to wear out with constant use, which can lead to damage and, as a result, a short circuit. Wireless charging has no such disadvantages.

Minuses:

  • Higher cost.
  • Most docking stations have a very limited range and require precise positioning of the phone on the stand.
  • Less energy efficient. On average, wireless charging takes 1.5-2.5 times longer than conventional charging.

What to do if your smartphone does not have wireless charging functionality?

The lack of wireless charging technology on a smartphone does not mean that it cannot be used. Today, to solve this problem, some manufacturers offer additional accessories that can add the missing function to the device.

One such method is plate receivers. This is a thin plastic card with a built-in inductor, which is connected to the smartphone using a special contact cable, after which it is placed under the cover. As a more comprehensive alternative, you can purchase a special charging case with a similar plate already built-in, which, after installation, replaces the rear panel of the gadget.