Stabilized voltage converter on the YX8018 microcircuit. Boost converter with MPPT charge controller for solar panels Boost-voltage converter for solar panels

Poonam deshpande

Electronic Design

An uncomplicated combination of a solar panel, several LEDs and a small DC / DC regulator allows you to illuminate dark corners of the room during the daytime and at the same time provide a stabilized power supply to a low-power load

A solar-powered lamp only during the day may seem almost useless, but there are many areas in homes and offices that remain relatively dark even during the day. This "daylight lamp" glows from a nearby solar panel, and in addition, has an additional stabilized 0.5 W source, capable of powering small loads such as a VHF receiver.

A photovoltaic panel with a rated power of 10 W is used to power the daylight lamp (Figure 1). Its voltage, at the point of maximum power equal to 17.3 V, powers two identical LED chains (LED1… LED5 and LED6… LED10). Each string consists of five 1W white LEDs. Series 22 Ohm resistors R1 and R2 with allowable dissipation power of 2 W set the chain currents.

The output of the photovoltaic panel through the switch is connected to the input pulse stabilizer voltage (ISN) (Figure 2). The capacitor at the input of the converter microcircuit reduces the dependence of the brightness of the LEDs on the change in the load current, which depends on the level of the audio signal at the output of the VHF receiver.

There are quite a few cheap switching voltage converters ICs that are well suited for this application, and three of them are very similar in prevalence, switching frequency, output voltage, L and C values, and load impedance. These are LM3524, MC34063 and LM2575. All other things being equal, the chip-based converter loses less battery voltage due to lower current consumption and more low voltage saturation of the power switch. It is clear that this particular microcircuit was chosen for the power supply.

The input supply voltage (V IN) is supplied to pin 6 of the MC34063 DC / DC converter through switch SW (Figure 3). Smoothing capacitor C1 with a capacity of 2200 μF, connected after the switch, is designed to minimize voltage fluctuations caused by changes in lighting intensity. Capacitor C2 with 100 pF at pin 5 sets the converter switching frequency to 33 kHz.

The output voltage is filtered by elements L1 and C3. An inductance of 220 μH was made by ourselves by winding 48 turns of wire on a toroidal core, which can be used as a core with a diameter of 10 mm and a height of 20 mm, extracted from an old computer cable. The resistances of the resistors R1 and R2 are selected so that the output voltage is 5 V. If the output should be a different voltage, you must change the resistance of the resistor R1. For example, for an output voltage of 6 V, the resistance R1 should be 27 kOhm, and for 4.5 V, it should be about 39 kOhm. Assembled circuit is shown in Figure 4, and complete system- in Figure 5.

To get more light, you can make a daylight lamp with two solar panels connected in series (Figure 6). However, in this case, the maximum output voltage of the photovoltaic source can exceed 40 V, which is the limit value set for the MC34063. To solve this problem, the DC / DC converter is not connected directly to the output of the solar panel, but to one of two LED strings. Each string consists of ten LEDs with a maximum forward voltage of 3.5 V. Thus, the voltage on the string does not exceed 35 V.

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Pulse converters direct current(DC / DC) DC DC CONVERTER CONTROL CIRCUITS

• Super!!! Illuminate during the day, darken at night !!! All ingenious is simple !!! Now I finally understood what a "fluorescent lamp" is !!!
• The above is not our way! Our people are much more economical! Our, domestic young technician, a 5th grade student. buys a dynamo flashlight for 19 UAH. (40-45 rubles. RF) and ... just puts it in his pocket. Savings - $ 20 for the purchase of a solar panel and all kinds of diode resistors from foreign capitalists. http://www.leroymerlin.ua/p/%D0%9B%D...4-307ee51a3035. Say - uncomfortable? Under the guidance of a pensioner - a former physics teacher from the school circle "Crazy Hands", the student, having learned the multiplication table by the 5th grade, calculates the work that his grandmother does when opening the door to the dark pantry: he multiplies 2 kgf of effort by 1 meter of moving the edge doors and gets 20 joules. Looking at the school physical office, the student learns that 2 LEDs of the mentioned flashlight with a voltage of 2 volts and a current of 10 milliamperes have a power consumption of only 20 mW! By opening the door just 1 time, you can illuminate the pantry for 50 seconds - the energy in the flashlight does not disappear, but it charges the battery built into the Chinese flashlight! Now the whole family of the young talent opens and closes the door to the pantry during the morning exercises - the student's dad has attached a dynamo flashlight to the door to the pantry during the break of a football match! And the younger brother of our schoolchild attached a switch to the same door from the door of the old refrigerator - when the pantry is closed, there is no light in the closet - the flashlight battery does not discharge. They are already collecting signatures for petitions to the Government. If each of the 100 million inhabitants saves only 100 watts of electricity, it will be possible to permanently close all the power plants in the country! Details and next steps - https://www.youtube.com/watch?v=WVMolYlx-h8.
• A. Raikin wanted to tie a dynamo to the ballerina ...
• what for a goat accordion and a priest accordion? the receiver can be powered free energy and nafig that solar panel
• Give a working example ... a detector receiver, mind you, don't suggest.

The device is a simple step-up converter and voltage limiter that charges 12V batteries from a 6V solar panel. The device also has an MPPT (Maximum Power Point Tracking) function. When we think of MPPT, we usually think of microcontrollers and complex computational power algorithms. However, such algorithms are not really needed.

The article presents two schematic solutions. The first diagram is simply illustrating a boost pulse converter, while the second one demonstrates a homemade working scheme devices. It is recommended for more advanced experimenters who have an oscilloscope at their disposal. The circuit may also be of interest to students and those who simply want to expand their knowledge of electronics.

Boost converter topology diagrams and homemade solar converter circuit

TheoreticalintelligenceOraisingconverter

In the boost converter topology diagram, L1 is charged when Q1 is on. When Q1 is off, L1 is discharged to the battery via Zener diode D1. Performing this operation several thousand times per second will result in significant output current. This process is also called inductive discharge. For its functioning, it is necessary that the input voltage is lower than the output. Also, if a solar panel is available, it is necessary to use an energy storage element - a capacitor (C1), which will allow the solar panel to continuously output current between cycles.

Description schematic diagram boost converter

The circuit consists of three main blocks, including a 555 MOS-based gate generator, a 555 PWM modulator, and an op-amp with a voltage limiter. The 555 series with cascade output can provide up to 200mA current and makes an excellent low-power pulse generator. The 555 PWM modulator is a classic oscillator circuit based on the 555 series. To adjust the discharge time of the capacitor C3 (coil charge time), a voltage of 5V is applied to pin 5.

Limitationstresses

Operational amplifier U1A calculates the battery voltage signal when the divided voltage setpoint is compared with a 5V reference voltage. When the voltage exceeds the set value, the output switches in the negative direction, thus reducing the pulse frequency of the PWM generator and limiting any subsequent charge. This effectively prevents overcharging.

Powering the circuit from a solar panel

To prevent unnecessary battery discharge when the sun is not shining, all circuits are powered through the solar panel, except for the voltage divider with feedback, which consumes about 280μA.

MOSFET logiclevel

Since the circuit must operate at low voltage levels (this circuit operates on an input voltage of at least 4V), the MOSFET must be set to logic level. It will open at 4.5V. For this purpose, I used a powerful MOSFET MTP3055.

Voltage clamping using a zener diodeD2

In this circuit, DO NOT DISCONNECT the battery, otherwise the MOSFET will burn out. Therefore, to protect it, I installed a 24V Zener diode D2. Without this zener diode, I myself have burned out a lot of MOSFETs.

MPPT function

As the voltage / current of the solar panel increases, the PWM generator increases the pulse frequency, which in turn increases the output current. At the same time, additional voltage is applied to the coil, thus increasing its charging current. As a result, the boost converter actually "exerts more force" when the voltage rises, or "fades" when the voltage decreases. For maximum energy transfer in bright sunlight, potentiometer R8 is adjusted so that the battery charging current is maximum - this will be the maximum power point. If the circuit is working correctly, there will be a very flat peak when R2 is rotated. Diode D3 performs automatic MPPT adjustment more accurately by subtracting a fixed voltage from the voltage difference between the battery and the average voltage across capacitor C3. In low light conditions you will find that R3 is not optimal, however it will not be completely removed from the chain. Note that smart MPPT controllers can also perform better at full range, but this improvement is extremely ineffective.

Component ratings

The circuit is set to a voltage of 9V, a solar panel to a power of 3W. Boost converters are very finicky and will not work in wide range conditions - if your system uses a different power rating for the solar panel, then expect a problem. The only components that need tuning are coil L1 and capacitor C3. I was surprised that the repetition rate was very low (around 2kHz). I started with a 100μH coil, however the circuit works better with 390μH inductance - I originally wanted to get around 20kHz. For best work charge the coil 5 to 10 times the solar panel current, then allow an extended period of time (3X) to allow the coil to fully discharge. This will provide acceptable performance when the power supply voltage is close to the battery voltage. Note that low impedance coils provide the best efficiency. The largest loss actually occurs in the Schottky diode, and the smallest loss is what these diodes are for.

Work at high frequency usually preferred. This will minimize the coil size. However, for experiment, use the coil that works best.

The suggested components are shown in the diagram. Naturally, Charger can be adapted according to your requirements.

Oscillograms

List of radioelements

MySKU sometimes has solar panel reviews. I also decided to join the "green" energy. Re-read the stack different materials by solar panels and controllers. I didn’t become an expert, but I gained a small bag of knowledge. I will share with you a piece of knowledge today.

For the implementation of autonomous lighting in the bathhouse in the country and acquaintance, I chose a small panel with a nominal output power of 30 W and a voltage of 12 V, and a simple popular controller for charging a lead-acid battery.

Planned connection diagram:

The solar panel

The solar panel arrived unexpectedly quickly. A courier called, which I did not expect. Due to the large weight Banggood store sent the panel via EMS, but the controller was sent by regular mail for the standard three and a half weeks.

The panel was packed well, but the most vulnerable part was the corners of the aluminum profile. It's okay, but for the future you need to ask the seller to additionally protect the corners in the package.




The panel is large enough. Real size 650x350x25 mm, weight 2.5 kg.


The photocells are located between a thick sheet of transparent plastic and a thin sheet of white plastic. The sandwich is inserted into an aluminum profile and treated with a sealant. The aluminum profile is covered with a transport foil. The degree of protection is not indicated anywhere. The face plastic feels durable. How he will withstand the hail, I do not know.

On back side the panel contains a protective cover / box for connection. A wire comes out of it.


The wire is long - 4.5 meters, 2 x 0.75 mm.


At the ends of the wire "crocodiles". Of course, during the final installation, the crocodiles and most of the wire will need to be cut off, but they will come in handy for the test.

There is a shunt diode inside the box. It is only needed for the serial connection of several panels (so that when one of the panels goes into the shade, the whole system continues to work), for one panel it does not play any role.

Specification sticker:


Manufacturer not specified. Specifications:

As you can see, the solar panel outputs a maximum voltage of 21 V without load (in reality, measured by 22 V), and not 12 V, as stated. There is no need to be afraid. This is normal, usually the operating voltage of the system for which the solar panel is intended is indicated, and this is 12 V (in fact, this is a formality, in reality it all depends on the charge controller). For example, solar panels for 24V systems can be up to 45V.

To make the panel parameters clearer, take a look at the graph (it refers to a 230 W, 24 V panel):


The horizontal axis is voltage, the vertical axis is current and power. See how the panel current changes (red graph). As the current increases, the panel voltage decreases. Now look at the power graph (blue, IxU). As you can see, the maximum power is reached at a certain point. This point is called the panel's maximum power point and is characterized by the Vmp and Imp values. During operation, mainly due to changes in the temperature of the photocells, this point may shift.

The panel from the review has Vmp = 18 V and Imp = 1.67 A. It is at this point that a power of 30 W is achieved (in the most ideal conditions). If you load the panel more, the amperage will rise slightly and the voltage and power output will drop. If you load the panel less, the current will drop, the voltage will rise, and the power will drop again. Those. the efficiency of the panel decreases from the point of maximum power. Later, I will return to the point of maximum power.

Controller

The CMTP02 controller comes in a small box.


Inside the controller itself and a short instruction.

The controller is designed for currents up to 15 A. gives a current to the battery and to the load up to 15 A. These are "Chinese" 15 A. In reality, of course, less. I have a panel with a maximum amperage of 1.75 A - you don't have to worry at all. The controller can operate with 12V and 24V batteries.

Unscrew 4 screws and remove the metal cover. On the underside of the board are three MOSFET transistors with erased markings. The transistors are covered with insulation. Maybe it plays the role of a thermal substrate for dissipating heat to the metal cover, but the material is solid and only one transistor fits tightly to the cover. If you plan to use a controller with a current greater than 5 A, it is better to replace this insulation with a silicone thermal pad (100x100x3 mm costs a couple of dollars).

On the reverse side of the board is an operational amplifier and controller, and many SMD components in a harness.


There are many varieties of such a controller with additional functionality on the market. The board has a place for wiring a USB output (5 V), a stabilized voltage of 12 V, etc.

This PWM / PWM controller is the simplest one, without the possibility of any configuration. You just need to connect the battery, solar panel and load. It is important to follow the connection sequence. Battery> solar panel> load. Disconnection in reverse order... The controller does not work without a battery.

Although the instructions indicate that the controller can work with GEL batteries, it is better not to do this, because it is this controller that does not have a choice of the type of battery, which means that the voltage is the same for all types of batteries. For GEL, it should usually be lower.

The market for solar charging controllers can be formally divided into two types. MPPT and not MPPT (sometimes called PWM / PWM). MPPT - maximum power point tracking. Remember I wrote about the maximum power point? So, the MPPT controller monitors (there are different algorithms) the maximum power point and at the input tries to keep the voltage at a level that corresponds to this point until the next measurement. Many MTTP controllers can work without problems with high voltage (for example, series-connected panels with a voltage of 90 V for low losses due to wire resistance), and at the output they can charge ordinary 12 V batteries.

The PWM controller does not monitor the maximum power point. For example, at the stage of bulk charge (CC - constant amperage), the voltage of the solar panel is equalized with the voltage of the battery and gradually increases at this stage. Let's take a look at another graph.


Pay attention to the gray area and black graph of the solar panel power output - this is the power output when using the PWM controller, and the Pmpp point is the output power when using the MTTP controller.

MPPT controllers are more expensive and more efficient. But a significant gain is obtained only when using powerful panels. You also need to know that many cheap Chinese controllers, on which MPPT is written, in fact, are not.

Let's go back to CMTP02. For its initial test, I will use: AGM battery, EBD-USB tester to create a load, a simple USB tester with high voltage support


The Solar indicator is on when there is voltage from the solar panel. Flashes when the voltage exceeds the norm for this controller(more than 45 V). The controller has reverse current protection - from the battery to the solar panel.

The Load indicator is on when there is no problem. Does not light up if the battery voltage is below 11.2 V - in this case, no current flows to the load. Flashes quickly when short-circuited.

As long as there is enough power from the solar panel to power the load, the battery is being charged. Those. the current goes to both the battery and the load. As soon as the load power begins to exceed the output power of the solar panel, the battery charging is stopped and the shortage of current is compensated by the battery. The whole process works like a clock. As soon as the solar panel stops generating energy (for example, the sunny day is over), the load is powered only by the battery.

As I already wrote, the controller is the simplest, but it does its job. There are many models of controllers on the market for any task, power and wallet.

If you have a simple task, for example, you want a fountain in the country that works only during the day, then there is nothing easier. Such interesting converters with manual setting maximum power voltage:


Such devices cost from $ 6. No battery needed, just connect the inverter directly to the solar panel and pump. Using the MPP potentiometer, you set the input voltage to the maximum power, additionally set the voltage for the pump at the output. Simple and effective.

Solar panel testing

In order to clearly know how much energy the panel will generate per day, to build daily charts, etc., there are several options. The simplest and most private is to connect a tester between the controller and a discharged battery. Universal is to use a load that supports Constant Voltage mode. The essence of this load is as follows - you set the voltage, and the load begins to increase the amperage until the voltage stabilizes at the given value. As soon as the voltage starts to drop or rise, the load instantly decreases or increases the current consumption. Thus, the energy source, the solar panel, gives out everything that it can at a particular moment in time at a given voltage.

I decided to use a load with CV mode, which will be connected directly to the panel.

The problem is that such a mode is very rarely in demand, it is not always available in electronic loads. I asked my friends, none of them turned out to be like that. I began to study the diagrams on the Internet. ... Not without the help of a friend. But everything worked out.


The circuit uses an LM358 operational amplifier (U1) and a field-effect transistor (N-channel, Q1). There was another operational amplifier available, for which it was necessary to add another stabilizer to the circuit. The finished product does not look quite presentable, but the main thing is that it contains blue electrical tape and is completely suitable for use.




The potentiometer can be used to adjust the load voltage. Because the load is made of improvised components, then there is a certain voltage drop when the current strength changes. The test bench looks like this:


Because the current is small in my panel, then thin short wires can be used. To measure, I will use an EBD-USB tester in monitoring mode. The load is connected to the solar panel through EBD-USB, which in turn is connected to the computer. The first revision of EBD-USB supports voltage measurement up to 13.65 V (operation up to 20 V). It plays into my hands, tk. with the battery connected, the voltage range will be 11.2 - 14.6 V. With the potentiometer on the load, I will set the voltage to a little more than 12 V.

March 27, time period 9.00 - 9.05, cloudless weather.

Bursts - I was covering the solar panel, watching the graph change. For 5 minutes of operation, the solar panel produced 1.5 Wh. The output power was 19 W. When the voltage is set to about 18 V, the maximum power point (I already looked at this with replacing EBD-USB with normal USB tester with support high voltage), the power was 21 W. And this is only the morning at the end of March. In summer, when the sun is at its zenith, the panel may well give out the declared 30 watts. But we will focus on the available data. If you roughly estimate that the sun will shine for 5 hours a day, then I get 1.5 x 12 x 5 = 90 Wh per day. Summer daylight hours are longer, the coefficient "summer / spring" in the central region is 1.5. Those. in summer it will be 135 Wh. The efficiency of a lead-acid battery is 75%. The energy stored per day will be 100 Wh. The battery (14.5 Ah) will be fully charged in 2 daylight hours. In the barn and in the bath, I can hang 4 lamps of 7 W each (with a luminous flux of 500 lm, equivalent to 55 W). And every day / evening I can use them for up to 3 hours at a time. It suits me.

Of course, this is a rough estimate based on short term tests. I will conduct detailed testing with measurements and charts of the whole day in May already at the site of the panel.

While I was experimenting with the panel, the load radiator got very hot - after all, it dissipated 20 watts. For measurements of my panel, it is quite enough, but more powerful it is already necessary to put a larger radiator and active cooling.

Here's another one froze. March 31, time period 9.00 - 9.05. The weather is cloudy with haze and clouds in the sky. The sun comes out and disappears.


The output power ranged from 3W to 17W. For 5 minutes of operation, the solar panel produced 1 Wh. For this kind of weather, the panel does an excellent job.

I liked the experiments with the solar panel, I will continue them. If someone has sensible and useful tips feel free to share them in the comments. I think that many will be interested.

The ginger bandit is also charging from the sun:

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