We looked at the circuit of a simple autonomous charger for mobile equipment, working on the principle of a simple stabilizer with a decrease in battery voltage. This time we will try to assemble a slightly more complex, but more convenient memory. The batteries built into miniature mobile multimedia devices usually have a small capacity, and, as a rule, are designed to play audio recordings for no more than several tens of hours when the display is turned off, or to play several hours of video or several hours of reading e-books. If a power outlet is unavailable or the power supply is turned off for a long period of time due to bad weather or other reasons, then various mobile devices with color displays will have to be powered from built-in energy sources.
Given that such devices consume considerable current, their batteries may be discharged before electricity is available from a wall outlet. If you do not want to immerse yourself in primitive silence and peace of mind, then to power your handheld devices, you can provide a backup autonomous energy source, which will help out both during a long journey into the wild, and in case of man-made or natural disasters, when your settlement may be on the verge of destruction. several days or weeks without power supply.
Mobile charger circuit without 220V network
The device is a linear voltage stabilizer of the compensation type with a low saturation voltage and a very low intrinsic current consumption. The energy source for this stabilizer can be a simple battery, rechargeable battery, solar or manual electric generator. The current consumed by the stabilizer when the load is off is about 0.2 mA at an input supply voltage of 6 V or 0.22 mA at a supply voltage of 9 V. The minimum difference between the input and output voltage is less than 0.2 V at a load current of 1 A! When the input supply voltage changes from 5.5 to 15 V, the output voltage changes by no more than 10 mV at a load current of 250 mA. When the load current changes from 0 to 1 A, the output voltage changes by no more than 100 mV at an input voltage of 6 V and by no more than 20 mV at an input supply voltage of 9 V.
A self-resetting fuse protects the stabilizer and battery from overload. The reverse-connected diode VD1 protects the device from reverse polarity of the supply voltage. As the supply voltage increases, the output voltage also tends to increase. To maintain the output voltage stable, a control unit assembled at VT1, VT4 is used.
An ultra-bright blue LED is used as a reference voltage source, which, while performing the function of a micro-power zener diode, is an indicator of the presence of output voltage. When the output voltage tends to increase, the current through the LED increases, the current through the emitter junction VT4 also increases, and this transistor opens more, and VT1 also opens more. which bypasses the gate-source of the powerful field-effect transistor VT3.
As a result, the resistance of the open channel of the field-effect transistor increases and the voltage across the load decreases. Trimmer resistor R5 can be used to adjust the output voltage. Capacitor C2 is designed to suppress self-excitation of the stabilizer as the load current increases. Capacitors C1 and SZ are blocking capacitors in the power supply circuits. Transistor VT2 is included as a micro-power zener diode with a stabilization voltage of 8..9 V. It is designed to protect against breakdown of the VT3 gate insulation by high voltage. A gate-source voltage that is dangerous for VT3 may appear when the power is turned on or due to touching the terminals of this transistor.
Details. The KD243A diode can be replaced by any of the KD212, KD243 series. KD243, KD257, 1N4001..1N4007. Instead of KT3102G transistors, any similar ones with low reverse collector current are suitable, for example, any of the KT3102, KT6111, SS9014, BC547, 2SC1845 series. Instead of the KT3107G transistor, any of the KT3107, KT6112, SS9015, VS556, 2SA992 series will do. A powerful p-channel field-effect transistor of the IRLZ44 type in a TO-220 package, has a low gate-source opening threshold voltage, a maximum operating voltage of 60 V. The maximum direct current is up to 50 A, the open channel resistance is 0.028 Ohm. In this design, it can be replaced with IRLZ44S, IRFL405, IRLL2705, IRLR120N, IRL530NC, IRL530N. The field-effect transistor is installed on a heat sink with a cooling surface area sufficient for a particular application. During installation, the terminals of the field-effect transistor are short-circuited with a jumper wire.
The autonomous charger can be mounted on a small printed circuit board. As an autonomous power source, you can use, for example, four pieces of series-connected alkaline galvanic cells with a capacity of 4 A/H (RL14, RL20). This option is preferable if you plan to use this design relatively rarely.
If you plan to use this device relatively often or your player consumes significantly more current even when the display is off, then it would be advisable to use a 6 V rechargeable battery, for example, a sealed motorcycle battery or from a large hand-held flashlight. You can also use a battery of 5 or 6 nickel-cadmium batteries connected in series. When hiking, fishing, to recharge batteries and power a handheld device, it may be convenient to use a solar battery capable of delivering a current of at least 0.2 A with an output voltage of 6 V. When powering the player from this stabilized energy source, it should be taken into account that the regulating transistor is turned on into the negative circuit, therefore, simultaneous power supply of the player and, for example, a small active speaker system is only possible if both devices are connected to the output of the stabilizer.
The purpose of this circuit is to prevent a critical discharge of the lithium battery. The indicator turns on the red LED when the battery voltage drops to a threshold value. The LED turn-on voltage is set to 3.2V.
The zener diode must have a stabilization voltage lower than the desired LED turn-on voltage. The chip used was 74HC04. Setting up the display unit involves selecting the threshold for turning on the LED using R2. The 74NC04 chip makes the LED light up when the discharge reaches the threshold that will be set by the trimmer. The current consumption of the device is 2 mA, and the LED itself will light up only at the moment of discharge, which is convenient. I found these 74NC04 on old motherboards, so I used them.
Printed circuit board:
To simplify the design, this discharge indicator may not be installed, because the SMD chip may not be found. Therefore, the scarf is specially placed on the side and can be cut along the line, and later, if necessary, added separately. In the future I wanted to put an indicator on the TL431 there, as a more profitable option in terms of details. The field-effect transistor is available with a reserve for different loads and without a radiator, although I think it is possible to install weaker analogues, but with a radiator.
SMD resistors are installed for SAMSUNG devices (smartphones, tablets, etc., they have their own charging algorithm, and I do everything with a reserve for the future) and they can not be installed at all. Do not install domestic KT3102 and KT3107 and their analogues; the voltage on these transistors was floating due to h21. Take BC547-BC557, that's it. Source of the diagram: Butov A. Radio constructor. 2009. Assembly and adjustment: Igoran .
Discuss the article MOBILE CHARGING FOR YOUR PHONE
Greetings, dear readers. In today’s article, we’ll talk about today’s hot technology – wireless charging for phones. You've probably heard how branded companies focus on it when introducing the next portable device with its support. Not wanting to spend their hard-earned money, many remain with their old mobile phone, never ceasing to dream of trying out wireless charging.
Do-it-yourself wireless charging is a very simple and fairly fast solution. Read the instructions and watch the video. Interesting, right? Then let's go in order. But be sure to read the advice at the end of the article!
Something new? No, the long-known “old”
When I first saw wireless charging, I thought that manufacturers had made a breakthrough by discovering some new technology. Fortunately, there is the Internet, which told me the truth. In fact, the advent of wireless energy transmission was made possible by the discovery of André Marie Ampere's law, which proved that electric current produces a magnetic field.
And this happened, for a moment, almost 200 years ago. In subsequent years, a number of scientists confirmed the existence of electromagnetic waves, and Nikola Tesla devoted years of his life to studying the possibility of transmitting energy over a distance. Using electromagnetic induction, the physicist was able to light an incandescent lamp from a distance.
Standard Qi
Of course, wireless energy transfer was of interest to many areas of human life, but for a long time it did not go beyond the walls of laboratories. Already in this century, companies that develop consumer electronics (tablets, smartphones) began to take initiatives to create wireless chargers. A huge contribution was made by the Wireless Power Consortium, which developed the Qi standard for low currents.
The standard specification was free and accessible, so it very soon began to be used in portable equipment. Three years later, Qi acquired a specification for medium currents. There are other standards, but they are more complex than Qi and less common. More recently, in 2015, scientists at the University of Washington discovered that energy can be transmitted via Wi-Fi networks. We are waiting for the smartphone to charge by connecting to the router.
How Qi wireless charging works
Well, already from the name of the device it becomes clear that the gadget does not require connecting wires to transfer energy. The operating principle is very simple. The charger has a built-in coil (copper), which takes on the role of creator and transmitter of the electromagnetic field already on the receiver coil placed in the smartphone (can be above the battery or back cover). Electromagnetic radiation occurs when a mobile phone with a receiver comes into close proximity to the transmitter (usually about 4 centimeters). Then the capacitors and rectifier (low-power semiconductor diode) get to work, which provide the battery with energy.
So, can I do wireless charging myself?
Yes, this doesn’t even require any special knowledge of electrical engineering. Moreover, enthusiasts have already conducted similar experiments before us, posting detailed instructions and diagrams for assembling wireless charging with their own hands. If all the necessary components are at hand, then creating the simplest wireless charging will not take even an hour. However, we recommend that you first practice on old “push-button” devices, and not rush to “invent” charging for a brand new iPhone. For example, you can assemble such a thing for your Nokia, whose charging socket has fallen off, resuscitating it in this way. So let's get started.
Instructions: how to make wireless charging for your phone with your own hands
The whole process can be divided into two parts: manufacturing the transmitter and the receiver. The first component will be a separate device, and the second will be installed on the phone.
The wireless charging circuit is very simple, consisting of two coils (transmitter and receiver), as well as a transistor and resistor.
Transmitter device:
- To begin with, we take a frame, the diameter of which should be 7-10 centimeters, but you can have another one - at your discretion.
- Now you will need copper wire with a diameter of 0.5 mm. This is what we wrap around the frame. It is necessary to make 20 turns, then make a tap and twist another 20 turns in the opposite direction.
- You will need a transistor. You can use any, be it polar or bipolar - there is not much difference. If there is direct conduction, then you will have to change the polarity. The transistor is connected to the end of the coil and the tap.
- We fasten the resulting structure with tape or another type of insulation. To make everything look “solid”, you can use DVD or CD boxes. Some craftsmen even bother cutting out, so to speak, wooden bodies.
- To provide power, you can use a standard 5 Volt power adapter that connects to the circuit.
- Everything, the device that will transmit electricity is ready.
Now let's move on to making the receiver:
- If making a transmitter takes a few minutes, then you will have to work hard with the receiver. First you have to make a coil, but a flat one. You will need copper wire, but with a smaller diameter - 0.3-0.4 mm. You will need to make 25 turns. For convenience, I advise you to use some kind of lining, for example a piece of plastic. We gradually strengthen the coils with superglue so that the structure does not fall apart - you will have to wind it again. At the end of the work, you must carefully tear the receiver away from the plastic on which it was wound.
- Now we connect our receiver to the battery via a high-frequency silicon diode, for example SS14. The coil should be on the top of the battery, closer to the cover. To stabilize the voltage, a capacitor should be used.
- You can connect the receiver either to the charging connector or directly to the battery. The latter option is perfect for users whose charging port has died.
- That's it, close the back cover so as not to move the coil.
For many users, I think a video on how to make wireless charging with your own hands would be helpful. So here you go:
With this, your DIY wireless charger is ready. To start using it, just place your phone on the transmitter. To date, more than a dozen instructions for assembling wireless chargers have accumulated on the Internet. The principle is approximately the same, but enthusiasts continue to improve this device, introducing something of their own. True, it is better for beginners to first practice with the simplest option presented in the instructions, so that they do not have to take the phone for repair.
Suitable for any device
The most important advantage of DIY wireless charging is the ability to make it for almost any device: smartphone, regular phone, camera, radio, and so on. The power principle of all these gadgets is similar, so charging follows the same scenario.
True, I strongly do not recommend trying to make wireless charging with your own hands for expensive smartphones. Firstly, you will have to disassemble the case in order to connect the receiver coil, since modern models are often made non-separable (it is not possible to simply remove the cover). Secondly, if you mix something up, you risk damaging the device, especially for beginners. Thirdly, most modern smartphones support wireless charging from the factory or provided by other manufacturers.
Disadvantages of DIY wireless charging
do you need it? Smoothly we come to a very important point - the disadvantages of homemade wireless chargers. Yes, the opportunity to make an interesting and useful device at no extra cost is great, but let’s not forget about the risks you are taking.
- Errors during manufacturing will, at best, lead to the fact that wireless charging will not work; at worst, the phone will not work.
- Don't expect your smartphone to charge quickly. Even factory wireless chargers still lag behind conventional chargers in terms of charging speed, let alone those made by yourself.
- I don’t think that every house has a coil of wire, a diode and a couple of transistors. You will have to buy all this, spending an amount comparable to that required to buy a ready-made, albeit Chinese, device.
What can I add? Do-it-yourself wireless charging is more of a way to visually look at the principle of operation of the electromagnetic field. To assemble a truly worthwhile and beautiful device, you will need to spend a lot of time and money. It is more profitable to order a ready-made kit without wasting time on winding the circuit. Of course, if you are a fan of creating something unusual with your own hands, then be sure to start developing “your own” wireless charger.
Photo: Koolpad Qi What should those who don’t want to spend time assembling wireless charging do it themselves? It’s simple – we order a ready-made kit, which is already more or less well assembled at the factory. The cost, as a rule, does not exceed 300 rubles, and the kit already includes both a transmitter and a receiver. Wireless chargers are sold in electronics stores, but it is more profitable to order from Chinese online stores.
Please note that many modern smartphones are equipped by the manufacturer with a receiver (receiver). Therefore, owners of these models do not need to purchase anything additional (in exceptional cases, sellers may not include a docking station (transmitter) in the kit). The list of such devices is quite extensive:
- Samsung (Note 5, S6/S6 Duos and later models)
- Google Nexus 4/5/6/7
- LG G3 and new flagships
- Blackberry 8900
- Nokia Lumia (810-930)
- Yotaphone 2
The list includes the most common models, but not all. In addition, it is regularly updated with new devices. To find out if your smartphone supports wireless charging, look for the “Qi” designation in the model specifications. Information must also be present on the manufacturer’s website.
My smartphone does not support wireless charging
If your device does not have a built-in receiver, do not rush to get upset - Chinese “friends” have taken care of users by releasing both special receivers for certain models and universal receivers. About the first type, I think everything is clear. Usually, they indicate which smartphone model it is intended for. But the second type of receiver is more interesting. Such receivers are not tied to a specific smartphone, so they can be installed in almost any one. However, it should be taken into account that universal receivers are divided into several classes:
- Film with special contacts. Fits under the phone cover without affecting functionality. The device must have contacts near the battery for its installation. The main advantage is that the charging socket remains free.
- Apple receiver. This type is intended for Apple devices with a Lightning connector, that is, all current models.
- Android receiver. Designed for smartphones with a microUSB connector. Since there are plenty of Android smartphones, and the manufacturer places the charging socket however he wants (and where he wants), you should look at the specific model. As a rule, microUSB is located on the lower or upper end, and is of type “A” (connector in the form of a regular trapezoid, when looking at the smartphone with the screen up), “B” (irregular trapezoid) or “C” (oval).
The docking station (transmitter) does not play a special role - you can even use more than one kit or a completely different form. Therefore, the receiver and charging pad can be purchased separately, which will help save a little more.
In addition to receivers that need to be mounted on a lid or hidden under it, cases with a built-in receiver are available for sale. Of course, they are not universal, so you can’t find one for every smartphone. And they don't look the best. Be that as it may, many may still be interested in this look.
Models of ready-made wireless chargers
So, we come to buying a wireless charger from Chinese online sites. You can, of course, go to an electronics store that sells better models, but you will have to pay significantly more. Therefore, we go to one of the stores on the Internet, where we look for something like “universal wireless chargers.” Here you will meet a bunch of models. Then you have several options:
- Purchasing a complete set. In this case, you get both a receiver (receiver) and a charging pad. Upon receipt, all you have to do is connect everything.
- Purchasing parts separately. Perhaps you already have a receiver, but the docking station is broken (or vice versa). In order not to waste money, you can order only what you need.
- Purchasing components for self-assembly. Some sellers provide the base (coils, boards, transistors, etc.) so that the user can assemble whatever his heart desires.
You can’t single out popular companies because sellers don’t even list them. And if the manufacturer is indicated, then the name says absolutely nothing (some kind of Chinese company). And it’s stupid to bother finding a good manufacturer - the cost of wireless charging is usually ridiculous. Plus, customer reviews indicate that the defect rate is quite low.
Prologue
The idea to build this design was inspired by a flight on an Airbus A380 aircraft, in which there is a USB connector under the armrest of each seat, designed to power USB-compatible devices. But such luxury is not available on all planes, and even more so it cannot be found on trains and buses. And I have long dreamed of rewatching the series “Friends” from beginning to end. So why not kill two birds with one stone - watch the series and brighten up your travel time.
An additional incentive to build this device was the discovery.
Technical task
The Portable Charger must provide the following capabilities.
- Battery operating time under rated load is at least 10 hours. High-capacity lithium-ion batteries are ideal for this purpose.
- Automatic switching on and off of the charger depending on the presence of load.
- Automatic shutdown of the charger when the battery is critically discharged.
- The ability to force the charger to turn on when the battery is critically discharged, if necessary. I believe that on the road a situation may arise when the battery of a portable charger is already discharged to a critical level, but the phone needs to be recharged for an emergency call. In this case, you need to provide an “Emergency power-on” button to use the energy still available in the battery.
- The ability to charge the batteries of a portable charger from a network charger with a Mini USB interface. Since you always take a phone charger with you on the road, you can also use it to charge the batteries of a portable power supply before the return journey.
- Simultaneous charging of charger batteries and recharging of a mobile phone from the same mains charger. Since the network charger from a mobile phone cannot provide sufficient current to quickly charge the battery of a portable charger, the charge can take a day or more. Therefore, it should be possible to connect the phone to charge directly while the battery of the portable power supply is charging.
Based on this technical specification, a portable charger using lithium-ion batteries was built.
Block diagram
The portable memory consists of the following components.
- Converter 5 → 14 Volt.
- A comparator that turns off the charge converter when the voltage on the lithium-ion battery reaches 12.8 Volts.
- Charge indicator – LED.
- Converter 12.6 → 5 Volts.
- A 7.5 Volt comparator that turns off the charger when the battery is deeply discharged.
- A timer that determines the operating time of the converter when the battery is critically discharged.
- Converter operation indicator 12.6 → 5 Volts - LED.
Switching voltage converter MC34063
It didn’t take long to choose a driver for the voltage converter, since there wasn’t much to choose from. At the local radio market, at a reasonable price ($0.4), I found only the popular MC34063 chip. I immediately bought a couple to find out if it was possible to somehow forcibly turn off the converter, since the datasheet for this chip does not provide for such a function. It turned out that this can be done by applying supply voltage to pin 3, intended for connecting the frequency-setting circuit.
The picture shows a typical circuit of a step-down pulse converter. The forced shutdown circuit, which may be needed for automation, is marked in red.
In principle, having assembled such a circuit, you can already power your phone or player if, for example, the power is supplied from ordinary batteries (batteries).
I will not describe in detail the operation of this microcircuit, but from the “Additional Materials” you can download both a detailed description in Russian and a small portable program for quickly calculating the elements of a step-up or step-down converter assembled on this chip.
Lithium-ion battery charge and discharge control units
When using lithium-ion batteries, it is advisable to limit their discharge and charge. For this purpose, I used comparators based on cheap CMOS chips. These microcircuits are extremely economical, as they operate on microcurrents. At the input they have field-effect transistors with an insulated gate, which makes it possible to use a microcurrent Reference Voltage Source (RPS). I don’t know where to get such a source, so I took advantage of the fact that in microcurrent mode, the stabilization voltage of conventional zener diodes decreases. This allows you to control the stabilization voltage within certain limits. Since this is not a documented inclusion of a zener diode, it is possible that in order to provide a certain stabilization current, the zener diode will have to be selected.
To provide a stabilization current of, say, 10-20 µA, the ballast resistance should be in the region of 1-2 MOhm. But, when adjusting the stabilization voltage, the resistance of the ballast resistor may turn out to be either too small (several kiloohms) or too large (tens of megaohms). Then you will have to select not only the resistance of the ballast resistor, but also a copy of the zener diode.
The digital CMOS chip switches when the input signal level reaches half the supply voltage. Therefore, if you power the ION and the microcircuit from a source whose voltage you want to measure, then a control signal can be obtained at the output of the circuit. Well, this same control signal can be applied to the third pin of the MC34063 chip.
The drawing shows a comparator circuit based on two elements of the K561LA7 microcircuit.
Resistor R1 determines the value of the reference voltage, and resistors R2 and R3 determine the hysteresis of the comparator.
Charger switching and identification unit
In order for a phone or player to start charging from a USB connector, it needs to be made clear that this is a USB connector, and not some kind of surrogate. To do this, you can apply a positive potential to contact “-D”. In any case, this is enough for Blackberry and iPod. But, my branded charger also supplies positive potential to the “+D” contact, so I did the same.
Another purpose of this node is to control the switching on and off of the 12.6 → 5 Volt converter when a load is connected. This function is performed by transistors VT2 and VT3.
The design of the portable charger also includes a mechanical power switch, but its purpose is more likely to correspond to the “mass switch” of the battery in a car.
Electrical circuit of a portable power supply
The figure shows a diagram of a mobile power supply.
C1, C3 = 1000µF
C2, C6, C10, C11, C13 = 0.1µF
C14 = 20µF (tantalum)
IC1, IC2 – MC34063
| DD1 = K176LA7 | R3, R12 = 1k | R27 = 44M |
| DD2 = K561LE5 | R4, R7 = 300k | R28 = 3k |
| FU=1A | R5 = 30k | VD1, VD2 = 1N5819 |
| HL1 = Green | R6 = 0.2 Ohm | VD3, VD6 = KD510A |
| HL2 = Red | R8, R15, R23, R29 = 100k | VT1, VT2, VT3 = KT3107 |
| L1 = 50mkH | R10, R11, R13, R26 = 1M | VT4 = KT3102 |
| L2 = 100mkH | R16, R24 = 22M | Are being selected |
| R0, R21 = 10k | R17, R19, R25 = 15k | R14* = 2M |
| R1 = 180Ohm | R18 = 5.1M | R22* = 510k |
| R2 = 0.3Ohm | R20 = 680Ohm | VD4*, VD5* = KS168A |
Purpose of circuit nodes.
IC1 is a step-up voltage converter 5 → 14 Volts, which is used to charge the built-in battery. The converter limits the input current to 0.7 Amps.
DD1.1, DD1.2 – battery charge comparator. Interrupts the charge when the battery reaches 12.8 volts.
DD1.3, DD1.4 – indication generator. Makes the LED flash while charging. The indication is made by analogy with Nikon chargers. While charging is in progress, the LED flashes. The charge is complete - the LED is constantly on.
IC2 – step-down converter 12.6 → 5 Volts. Limits output current to 0.7 Ampere.
DD2.1, DD2.2 – battery discharge comparator. Interrupts battery discharge when the voltage drops to 7.5 Volts.
DD2.3, DD2.4 – timer for emergency switching on of the converter. Turns on the converter for 12 minutes, even if the battery voltage drops to 7.5 Volts.
Here the question may arise, why such a low threshold voltage was chosen if some manufacturers do not recommend allowing it to drop below 3.0 or even 3.2 Volts on the bank?
I reasoned like this. Traveling does not happen as often as we would like, so the battery is unlikely to have to go through many charge-discharge cycles. Meanwhile, in some sources describing the operation of lithium-ion batteries, a voltage of 2.5 Volts is called critical.
But, you can limit the discharge limit to a higher voltage level if you plan to use such a charger frequently.
Construction and details
I express my gratitude to Sergei Sokolov for his help in finding the design components!
Printed circuit boards (PCBs) are made of foil-coated fiberglass laminate with a thickness of 1 mm. The dimensions of the PP were selected based on the dimensions of the purchased case.
All elements of the circuit, except the battery, are placed on two printed circuit boards. Moreover, on the smaller one there is only a Mini USB connector for connecting an external charger.
The power supply units were placed in a standard Z-34 polystyrene housing. This is the most expensive part of the design, for which we had to pay $2.5.
The power switch pos. 2 and the forced power button pos. 3 are hidden flush with the outer surface of the case to avoid accidental pressing.
The Mini USB connector is located on the rear wall of the case, and the USB connector pos. 4 together with indicators pos. 5 and pos.6 to the front.
The size of the printed circuit boards is designed to fix the batteries in the body of the portable power supply. Between the batteries and other structural elements, a 0.5 mm thick electrical cardboard gasket, bent in the shape of a box, is inserted.
This movie requires Flash Player 9 |
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And this is a portable power supply unit in assembled form. Drag the image with the mouse to view the power supply from different angles.
Settings
Setting up a portable charger came down to selecting instances of zener diodes and ballast resistors for each of the two comparators.
How it works? Video illustration.
The three-minute video shows how this homemade product works and what is inside. Video format – Full HD.
Over time, smartphone batteries lose their capacity, so they become uncomfortable to use and have to be replaced. But you shouldn’t throw away such batteries either. Once you have enough of them, you can build a portable charger. It will turn out to be massive (since there will be much less useful charge in it than in a new one) but very cheap.
What you will need:
Small box
- One or more batteries
- Boost voltage converter (eg 0.9-5 to 5V)
- Battery charging board
- Switch
- Soldering iron and wires, hot glue and gun
Choose a box of a size that will accommodate all the batteries, as well as the voltage converter and charging board.
Connect the battery contacts in series. This will maintain their original voltage (usually less than 5 V) and increase the total capacity. Connect this structure to a voltage converter. It will increase the voltage supplied from batteries to 5V, which are used to charge smartphones.
Assemble the components according to this diagram. The switch and diode are needed so that when charging, the current flows to the charging board and batteries, and not to the step-down converter.
Place the batteries and circuit boards in the case, fill them with hot glue so that they do not dangle, and put a port for charging the batteries and an output port for charging the smartphone on the case.
Keep in mind that not all smartphone batteries will be able to work harmoniously in such a circuit. In some cases, they will begin to charge each other and run out of energy when all the energy is used up due to heating and losses in the electronics. In addition, the maximum capacity of a prefabricated battery may be limited by the capacity of the weakest battery. Therefore, it is recommended to use one battery (although in this case it will not be enough to fully charge the smartphone) or batteries of the same brand.
Making your own solar USB charger for your phone is one of the most interesting and useful projects on. Making a homemade charger is not too difficult - the necessary components are not very expensive and are easy to obtain. Solar USB chargers are ideal for charging small devices such as a phone.
The weak point of all homemade solar chargers is the batteries. Most are assembled on the basis of standard nickel-metal hydride batteries - cheap, accessible and safe to use. But unfortunately, NiMH batteries have too low voltage and capacity to be seriously considered in quality, the energy consumption of which is only growing every year.
For example, the iPhone 4's 2000 mAh battery can still be fully recharged from a homemade solar charger with two or four AA batteries, but the iPad 2 is equipped with a 6000 mAh battery, which is no longer so easy to recharge using a similar charger.
The solution to this problem is to replace nickel-metal hydride batteries with lithium ones.
From this instruction you will learn how to make a solar USB charger with a lithium battery with your own hands. Firstly, compared to this, a homemade charger will cost you very little. Secondly, it is very easy to assemble. And most importantly, this lithium USB charger is safe to use.
Step 1: Required components to assemble the solar USB charger.
Electronic components:
- 5V or higher solar cell
- 3.7V Li-ion battery
- Li-ion battery charging controller
- USB DC boost circuit
- Panel mount 2.5mm jack
- 2.5 mm jack with wire
- Diode 1N4001
- The wire
Construction materials:
- Insulating tape
- Heat shrink tubing
- Double Sided Foam Tape
- Solder
- Tin box (or other enclosure)
Tools:
- Soldering iron
- Hot glue gun
- Drill
- Dremel (not required, but recommended)
- Wire cutters
- Wire stripper
- Help from a friend
This tutorial shows you how to make a solar powered phone charger. You can refuse to use solar panels and limit yourself to making a regular USB charger using lithium-ion batteries.
Most of the components for this project can be purchased at online electronics stores, but the USB DC boost circuit and lithium-ion battery charge controller will not be so easy to find. Later in this guide, I'll tell you where you can get most of the required components and what each of them does. Based on this, you can decide for yourself which option suits you best.
Step 2: Benefits of lithium battery chargers.
You may not realize it, but most likely a lithium-ion battery is in your pocket or on your desk right now, or maybe in your wallet or... Most modern electronic devices use lithium-ion batteries, characterized by high capacity and voltage. They can be recharged many times. Most AA batteries are nickel-metal hydride in chemical composition and cannot boast of high technical characteristics.
From a chemical standpoint, the difference between a standard AA NiMH battery and a Lithium-Ion battery lies in the chemical elements contained within the battery. If you look at the periodic table of elements, you will see that lithium is in the left corner next to the most reactive elements. But nickel is located in the middle of the table next to chemically inactive elements. Lithium is so reactive because it only has one valence electron.
And it is precisely for this reason that there are many complaints about lithium - sometimes it can get out of control due to its high chemical reactivity. Several years ago, Sony, a leader in laptop battery production, produced a batch of low-quality laptop batteries, some of which spontaneously caught fire.
This is why when working with lithium-ion batteries, we must take certain precautions - very accurately maintain the voltage during charging. This instruction uses 3.7 V batteries, which require a charging voltage of 4.2 V. If this voltage is exceeded or decreased, the chemical reaction can get out of control with all the ensuing consequences.
This is why extreme caution must be exercised when handling lithium batteries. If you handle them carefully, they are quite safe. But if you do inappropriate things with them, it can lead to big trouble. Therefore, they should be used only strictly according to the instructions.
Step 3: Selecting a lithium-ion battery charge controller.
Due to the high chemical reactivity of lithium batteries, you must be one hundred percent sure that the charge voltage control circuit will not let you down.
Although you can make your own voltage control circuit, it is better to simply buy a ready-made circuit that you will be confident in its performance. There are several charge control schemes available to choose from.
Adafruit is currently in its second generation of charge controllers for lithium batteries with several available input voltages. These are pretty good controllers, but they are too large. It is unlikely that it will be possible to assemble a compact charger using them.
You can buy small lithium battery charging controller modules on the Internet, which are used in this manual. Based on these controllers, I also assembled many others. I like them for their compactness, simplicity and LED battery charge indicator. As with Adafruit, when there is no sun, the lithium battery can be charged via the controller's USB port. The ability to charge via a USB port is an extremely useful option for any solar charger.
Regardless of which controller you choose, you should know how it works and how to operate it correctly.
Step 4: USB port.
Most modern devices can be charged via the USB port. This is the standard all over the world. Why not just connect the USB port directly to the battery? Why do you need a special circuit for charging via USB?
The problem is that the USB voltage is 5V, but the lithium-ion batteries we will be using in this project are only 3.7V. So we will have to use a USB DC boost circuit that increases the voltage to sufficient to charge various devices. Most commercial and homemade USB chargers, on the contrary, use step-down circuits, since they are assembled on the basis of 6 and 9 V batteries. Step-down circuits are more complex, so it is better not to use them in solar chargers.
The scheme used in this manual was chosen as a result of lengthy testing of various options. It's almost identical to Adafruit's Miniboost circuit, but costs less.
Of course you can buy an inexpensive USB charger online and take it apart, but we need a circuit that converts 3V (the voltage of two AA batteries) to 5V (the voltage on the USB). Disassembling a regular or car USB charger will not do anything, since their circuits work to reduce the voltage, but on the contrary, we need to increase the voltage.
In addition, it should be noted that the Mintyboost circuit and the circuit used in the project are capable of working with Apple gadgets, unlike most other USB charging devices. Apple devices check the information pins on the USB to know where they are connected. If the Apple gadget determines that the information pins do not work, then it will refuse to charge. Most other gadgets do not have such a check. Believe me - I tried many cheap charging circuits from eBay - none of them managed to charge my iPhone. You don’t want your homemade USB charger to be unable to charge Apple gadgets.
Step 5: Battery selection.
If you Google a little, you will find a huge variety of sizes, capacities, voltages and prices. At first, it will be easy to get confused in all this diversity.
For our charger we will be using a 3.7V lithium polymer (Li-Po) battery, which is very similar to an iPod or cell phone battery. Indeed, we only need a 3.7 V battery, since the charging circuit is designed for this voltage.
The fact that the battery should be equipped with built-in protection against overcharge and overdischarge is not even discussed. This protection is usually called "PCB protection". Search eBay for these keywords. It is just a small printed circuit board with a chip that protects the battery from overcharging and discharging.
When choosing a lithium-ion battery, look not only at its capacity, but also at its physical size, which mainly depends on the case you choose. I used an Altoids tin box as the case, so I was limited in my choice of battery. At first I thought of buying a 4400 mAh battery, but due to its large size, I had to limit myself to a 2000 mAh battery.
Step 6: Connecting the solar panel.
If you are not going to make a charger that can be recharged from the sun, you can skip this step.
This tutorial uses a 5.5V, 320mA hard plastic solar cell. Any large solar panel will work for you. For the charger, it is best to choose a battery designed for a voltage of 5 - 6 V.
Take the wire by the end, divide it into two parts and strip the ends a little. A wire with a white stripe is negative, and an all-black wire is positive.
Solder the wires to the corresponding contacts on the back of the solar panel.
Cover the solder joints with electrical tape or hot glue. This will protect them and help reduce stress on the wires.
Step 7: Drill the tin box or housing.
Since I used an Altoids tin as the body, I had to do a little drill work. In addition to the drill, we will also need a tool such as a dremel.
Before you start working with a tin box, put all the components in it to make sure in practice that it suits you. Think about how best to place the components in it, and only then drill. You can mark the locations of the components with a marker.
After designating the places, you can get to work.
There are several ways to remove the USB port: make a small cut right at the top of the box, or drill a hole of the appropriate size on the side of the box. I decided to make a hole on the side.
First, attach the USB port to the box and mark its location. Drill two or more holes inside the designated area.
Sand the hole with the Dremel. Be sure to follow safety precautions to avoid injuring your fingers. Do not hold the box in your hands under any circumstances - clamp it in a vice.
Drill a 2.5mm hole for the USB port. If necessary, widen it using a Dremel. If you don't plan to install a solar panel, then the 2.5mm hole is not necessary!
Step 8: Connecting the charging controller.
One of the reasons I chose this compact charge controller is its reliability. It has four contact pads: two in front next to the mini-USB port, where constant voltage is supplied (in our case from solar panels), and two in the back for the battery.
To connect a 2.5 mm connector to the charging controller, you need to solder two wires and a diode from the connector to the controller. In addition, it is advisable to use heat-shrinkable tubing.
Fix the 1N4001 diode, charge controller and 2.5mm jack. Place the connector in front of you. If you look at it from left to right, the left contact will be negative, the middle one will be positive, and the right one is not used at all.
Solder one end of the wire to the negative leg of the connector, and the other to the negative pin on the board. In addition, it is advisable to use heat-shrinkable tubing.
Solder another wire to the diode leg, next to which there is a mark. Solder it as close to the base of the diode as possible to save more space. Solder the other side of the diode (without the mark) to the middle pin of the connector. Again, try to solder as close to the base of the diode as possible. Finally, solder the wires to the positive contact on the board. In addition, it is advisable to use heat-shrinkable tubing.
Step 9: Connecting the battery and USB circuit.
At this stage, you only need to solder four additional contacts.
You need to connect the battery and USB circuit to the charge controller board.
First cut some wires. Solder them to the positive and negative pins on the USB circuit, which are located on the bottom of the board.
After that, connect these wires together with the wires coming from the lithium-ion battery. Make sure you connect the negative wires together and connect the positive wires together. Let me remind you that the red wires are positive and the black wires are negative.
Once you have twisted the wires together, weld them to the terminals on the battery, which are on the back of the charge controller board. Before soldering, it is advisable to thread the wires into the holes.
Now we can congratulate you - you have 100% completed the electrical part of this project and can relax a little.
At this stage, it is a good idea to check the functionality of the circuit. Since all electrical components are connected, everything should work. Try charging your iPod or any other gadget equipped with a USB port. The device will not charge if the battery is low or defective. In addition, place the charger in the sun and see if the battery will charge from the solar panel - the small red LED on the charge controller board should light up. You can also charge the battery via a mini-USB cable.
Step 10: Electrically isolate all components.
Before placing all the electronic components in the tin box, we must be sure that it cannot cause a short circuit. If you have a plastic or wooden case, then skip this step.
Place several strips of electrical tape on the bottom and sides of the tin box. It is in these places that the USB circuit and charging controller will be located. The photos show that my charging controller was left loose.
Try to carefully insulate everything so that a short circuit does not occur. Make sure the solder joints are secure before applying hot glue or tape.
Step 11: Placing the Electronic Components in the Case.
Since the 2.5mm jack needs to be secured with bolts, place it first.
My USB circuit had a switch on the side. If you have the same circuit, then first check whether the switch that is needed to turn the “charging mode” on and off works.
Finally, you need to secure the battery. For this purpose, it is better to use not hot glue, but several pieces of double-sided tape or electrical tape.
Step 12: Operate your homemade solar charger.
In conclusion, let's talk about the correct operation of a homemade USB charger.
You can charge the battery via a mini-USB port or from the sun. The red LED on the charge controller board indicates the charging process, and the blue LED indicates a fully charged battery.
