Boost converter with MPPT charge controller for solar panels. The solar panel powers the “day lamp” and the VHF receiver. The circuit is powered by the solar panel.

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

The article presents two schematic solutions. The first circuit simply illustrates a boost switching converter, while the second shows a homemade working circuit of the device. 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 diagram

TheoreticalintelligenceOincreasingconverter

In the boost converter topology diagram, coil L1 is charged when transistor Q1 is on. When transistor Q1 is turned off, coil L1 discharges to the battery through zener diode D1. Performing this operation several thousand times per second will result in a significant output current. This process is also called inductive discharge. For it to function, the input voltage must be lower than the output voltage. Also, if you have a solar panel, you must use an energy storage element - a capacitor (C1), which will allow the solar panel to continuously output current between cycles.

Description of the boost converter circuit diagram

The circuit consists of three main blocks, including a 555 MOS gate generator, a 555 PWM modulator, and an operational amplifier with a voltage limiter. The 555 series with cascaded output can provide a current of about 200mA 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 capacitor C3 (coil charging time), a voltage of 5V is applied to pin 5.

Limitationvoltage

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

Powering the circuit from a solar panel

To prevent unnecessary battery drain when the sun is not shining, all circuits are powered through the solar panel, with the exception of the closed-loop voltage divider, which draws about 280uA.

MOSFET logiclevel

Since the circuit must operate at low voltage levels (this circuit operates from an input voltage of at least 4V), it is necessary to install a logic level MOSFET. It will open at a voltage of 4.5V. For this purpose I used a power MOSFET transistor MTP3055.

Voltage clamping using a zener diodeD2

In this circuit, DO NOT DISCONNECT the battery, otherwise the MOSFET transistor will burn out. Therefore, to protect it, I installed a 24V zener diode D2. Without this zener diode, I myself have burned out many MOS transistors.

MPPT function

When the solar panel voltage/current increases, the PWM generator increases the pulse frequency, which in turn causes the output current to increase. At the same time, additional voltage is applied to the coil, thus increasing its charging current. The result is that the boost converter actually "goes hard" when the voltage goes up, or "goes hard" when the voltage goes down. To maximize energy transfer in bright sunlight, potentiometer R8 is adjusted so that the battery charging current is maximum - this will be the point of maximum power. If the circuit is working correctly, there will be a very flat peak when R2 is rotated. Diode D3 performs automatic MPPT regulation more accurately by subtracting a fixed voltage from the voltage difference between the battery and the average voltage through capacitor C3. In low light conditions you will find that resistor 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 configured for a voltage of 9V, the solar panel for a power of 3W. Boost converters are quite finicky and won't work over a wide range of conditions - if your system uses different power rating limits for the solar panel, then expect a problem. The only components that require adjustment are coil L1 and capacitor C3. I was surprised that the repetition rate was very low (about 2kHz). I started with a 100µH coil, but the circuit works better at 390µH - I originally wanted around 20kHz. For best performance, charge the coil 5 to 10 times the solar panel current, then allow a long period of time (3X) to allow the coil to fully discharge. This will ensure acceptable operation when the power supply voltage is close to the battery voltage. Note that low impedance coils provide the best efficiency. The greatest loss really occurs in a Schottky diode, and the least loss is what these diodes are designed for.

High frequency operation is usually preferred. This will minimize the size of the coil. However, for experimentation, use the coil that will work best.

The proposed components are indicated in the diagram. Naturally, the charger can be adapted to suit your requirements.

Oscillograms

List of radioelements

Power supply systems with the simultaneous use of traditional current supply and electricity from the sun are an economically feasible solution for private households, cottage and holiday villages and industrial premises.

An indispensable element of the complex is a hybrid inverter for solar panels, which determines the voltage supply modes, ensuring the uninterrupted and efficient operation of the solar system.

For the system to work effectively, you need not only to choose the optimal model, but also to connect it correctly. And we will look at how to do this in our article. We will also consider existing types of converters and the best offers on the market today.

Using renewable solar energy in combination with centralized power supply provides a number of advantages. The normal functioning of the solar system is ensured by the coordinated operation of its main models: solar panels, battery, and one of the key elements - the inverter.

Solar system inverter is a device for converting direct current (DC) coming from photovoltaic panels into alternating electricity. It is on a current of 220 V that household appliances operate. Without an inverter, energy production is meaningless.

System operation diagram: 1 – solar modules, 2 – charge controller, 3 – battery, 4 – voltage converter (inverter) with alternating current (AC) supply

It is better to evaluate the capabilities of a hybrid model in comparison with the operating features of its closest competitors - autonomous and networked “converters”.

Network type converter

The device operates on the load of the general electrical network. The output from the converter is connected to electricity consumers, the AC network.

The scheme is simple, but has several limitations:

• operability when AC power is available in the network;
• The mains voltage must be relatively stable and within the operating range of the converter.

This variety is in demand in private homes with a current “green” tariff for electrification.

Solar Inverter Selection Parameters

The efficiency of the converter and the entire power supply system largely depends on the correct choice of equipment parameters.

In addition to the characteristics described above, you should evaluate:

• output power;
• type of protection;
• operating temperature;
• installation dimensions;
• availability of additional functions.

Criterion #1 – device power

The rating of the solar inverter is selected based on the maximum load on the network and the expected battery life. In start-up mode, the converter is capable of delivering a short-term increase in power at the time of commissioning capacitive loads.

This period is typical when turning on dishwashers, washing machines or refrigerators.

When using lighting lamps and a TV, a low-power inverter of 500-1000 W is suitable. As a rule, it is necessary to calculate the total power of the equipment being used. The required value is indicated directly on the device body or in the accompanying document.

Overview of the capabilities, operating modes and efficiency of using the 3 kW InfiniSolar multifunction converter:

Designing a solar power supply system is a complex and responsible task. It is best to entrust the calculation of the necessary parameters, selection of solar complex components, connection and commissioning to professionals.

Mistakes made can lead to system failures and ineffective use of expensive equipment.

Are you choosing the best converter option for operating an autonomous solar energy supply system? Do you have questions that we did not cover in this article? Ask them in the comments below - we will try to help you.

Or maybe you noticed inaccuracies or inconsistencies in the material presented? Or do you want to supplement the theory with practical recommendations based on personal experience? Write to us about this, share your opinion.

There are different opinions and different numbers about the efficiency of PWM and MPPT controllers. For some, the PWM controller is more effective in cloudy weather, and MPPT works better in sunny weather. For others, the MPPT controller works better in all respects, and there are those who claim that PWM is much better. But you shouldn’t believe everything at once and take an unambiguous point of view; in each case you need to separately understand why and how it works. There are people who don’t even really know how to use their controllers and then say that they are worse or better.

Conventional PWM (PWM) controllers work very simply and the current from the solar panels passes through them almost directly, the power drop on the power transistors is very small. Therefore, as soon as the solar battery voltage exceeds the battery voltage by about 0.5-1 volts, the battery begins charging. But these controllers do not know how to extract all the power from the solar panel. For solar panels, the maximum current cannot exceed its maximum, for example, for a 12 volt solar panel with a power of 100 watts, the load current is no more than 5.7A. And when our battery voltage is about 13-14 volts, then the power going to the battery will be 14 * 5.7 = 79.8 watts, if the battery is discharged to 12 volts, then the power will be even less. In this case, more than 80% of the maximum power of the solar panel cannot be obtained.

But if the battery voltage were not 13-14 volts, but for example 17 volts, then 18*5.7=96.9 watts. In general, in order to extract all the power from a solar panel in the sun, it is enough for it to have 30 elements, and not 36, but then in cloudy weather such a panel will practically not work, which is why they make panels with a standard 36 elements for a 12V battery, and at idle the voltage is about 21-22 volts for such panels. But in the characteristics they write the full power of the panel, and not when operating on a 12 volt battery through a PWM controller.

MPPT controllers work differently, they have a DC-DC converter that converts high voltage to lower voltage, increasing the charge current. The controller scans the voltage and current of the solar panel, and removes power at the point where the maximum voltage of the solar panel is at maximum current, and then converts it to a low voltage to charge the battery. For example, if the panel is 12 volts, then its maximum power will be at 17-18 volts.

But since in MPPT controllers the work occurs through a DC-DC converter, it has its own efficiency, which is usually 90-96%, depending on the operating mode. The DC-DC module itself, in active mode, consumes its energy no matter how much the battery transmits. This is like the inverter has consumption at idle, and DC-DC also has its consumption. This suggests that if in cloudy weather the power from the solar panels is too small, then simply DC-DC operation can consume all this power and nothing will get into the battery, or much less than directly through the PWM controller.

For DC-DC to work, the voltage must be higher than the output by about 1.5-2 volts, this means that when the voltage on the solar panel drops to 15 volts, charging will stop. But now there are different MPPT controllers, some switch to PWM mode when the voltage and current are very small. There are some that stop working at low power and do not charge the battery. Some simply cannot determine the MPPT point at low power and constantly search for it, wasting energy from the battery, that is, they do not charge, but rather discharge it for the useless operation of the DC-DC module.

I now have two controllers, Solar 30 and Photon 100 50, and I compared how they work from dawn until the sun appears. I filmed all this, and this is what I got:

This test showed a clear victory for a specific MPPT controller over a specific PWM controller. Although Solar 30 says that it is MPPT, this is nothing more than a marketing ploy, it is just a PWM controller.

In the end, what can we say about all this? Even in cloudy weather, a good MPPT is not inferior to PWM, and as soon as conditions allow you to take more from the solar panel, the MPPT controller works much better. Well, if the power from a solar panel or an array of panels in cloudy weather is even theoretically 1-2% of the nominal, then there is no point in fighting for these drops. It's better to shoot up to 20% more in brighter light.

The YX8018 chip is widely used in inexpensive LED lawn lights, where an unstabilized step-up voltage converter is built on it. It powers the lighting LED(s) from a Ni-Cd battery. The current through the LED (from fractions to several milliamps) is set by the inductance of the storage choke in the converter. Therefore there is no need to stabilize the voltage. A special feature of the YX8018 and similar microcircuits is the presence of a control input, with which you can also turn on the voltage converter switch. It is this input that is used in LED lawn lights to automatically turn them on after dark. The same input can be used to build a stabilized boost voltage converter.

The circuit of such a converter on the YX8018 chip is shown in Fig. 1. It can be used to power from one Ni-Cd, Ni-Mh battery or galvanic cell of various radio-electronic devices requiring a supply voltage of 2 to 5 V. In the initial state, there is a voltage close to the voltage at the CE input (pin 3) of the microcircuit nutrition. This is due to the presence of a built-in resistor connecting this pin to the power supply positive. Therefore, the converter turns on, the voltage pulses at its output L (pin 1) are rectified by the diode VD1, and the smoothing capacitors C2 and C3 are charged - the output voltage increases. When the gate voltage of transistor VT1 reaches a threshold value (about 2 V), the resistance of the transistor channel will decrease and the voltage at its source (and the CE input of the microcircuit) will also decrease - the converter will turn off. The output voltage will begin to decrease, which will lead to the closing of the field-effect transistor and turning on the converter.

Thus, the converter periodically turns on and off, maintaining the output voltage set by trimming resistor R1. The operating frequency of the converter is about 200 kHz, and the on/off frequency depends on the output current and the capacitance of capacitor C2 (the higher the current and the smaller the capacitor capacitance, the higher the frequency) and can range from several hertz to tens of kilohertz. The dependences of the output voltage of the converter (2.7 V) on the input voltage for different values ​​of the load current and the limit values ​​of the load current are presented in Fig. 2. The ripple amplitude is about 10 mV, remains almost unchanged and depends within small limits on the output voltage and parameters of the field-effect transistor. The ripple frequency depends on the operating frequency of the converter and the frequency of switching on/off the converter and can vary within wide limits. Thermal stability is determined primarily by the parameters of the field-effect transistor. In this case, the temperature coefficient of voltage is negative and amounts to several millivolts per degree Celsius.

All elements can be mounted on a single-sided printed circuit board made of foil fiberglass, its drawing is shown in Fig. 3. A tuning resistor SP3-19 was used, the oxide capacitor was imported, the rest were K10-17. Instead of the 1N5817 diode, low-power pulsed or detector germanium diodes or Schottky diodes can be used. The inductor is wound on a ferrite ring with a diameter of 6...9 mm from the electronic ballast transformer of a compact fluorescent lamp and contains 5 turns of PEV-2 0.4 wire. The output voltage in the range of 2.2.5 V is set with a trimming resistor; it can be replaced with a resistive divider with a total resistance of at least 1 MOhm. To reduce ripple with a frequency of 200 kHz between capacitors C2 and C3, you need to install a choke, for example EC24, with an inductance of 470...1000 μH in the positive power line.

Publication date: 07.05.2014

Readers' opinions

• Sergey (other) / 04/14/2019 - 14:49
  And garden lamps don’t need to “shine all night.” They need it to “shine all evening and part of the night.” They are also a “decorative element”. For lighting and other beauty. And not at all for illuminating anything with “bright light”. They don't have to keep the light on all night.
• Sergey / 08/13/2018 - 12:12
  The problem with garden lamps is that the sun is weak; it doesn’t feed the battery enough, and therefore it’s not enough even for the night. I paralleled two solar ones - now after a day there is 18 hours of sunshine.
• clim / 06/09/2018 - 07:25
  in the datasheet there are just 2 options - from 1 and from 2 batteries
• clim / 06/09/2018 - 07:24
  I checked the lawn lamp, the solar battery is 4*4 cm, in the bright sun it gives up to 10 mA, not microamperes, so everything is ok, it can be fully charged in a day (solar)
• badgers / 01/05/2018 - 08:18
  I looked through all the “data-seets” - nowhere is the MAXIMUM input voltage for the YX8018 specified, specifically is it possible to give 3.2 V (when powering the flashlight from two elements), in practice it seems to work, but I would like to act according to legal specifications, I am trained as a designer ...
• z123 / 12/10/2017 - 00:36
  The solar cell provides a microampere current and cannot in any way charge a battery that requires at least tens of MILLIAMPS. Support (so that she lives longer) - maybe. But don't charge. Therefore, circuits where only this YX8018 + battery, resistor, switch, LED and solar element = this is a circuit for a short time, then the battery dies and that’s it. Either dispose of it (for spare parts) or convert it into something completely different. Those who make and sell this are cheaters. Counting on fools to fool and swindle. And then it doesn’t matter anymore.
• Grandfather Sergey / 10/07/2017 - 00:04
  No, for some this topic is really relevant, there is no need to laugh in vain. I also have this problem - there are a lot of batteries left with a resource of 10-30%. They are no longer suitable for a flashlight; for other devices, it is better to buy new ones. But the YX1808 for night lighting of my apartment, as long as I don’t fit my forehead into the door in the dark, is the absolute ONE! And, if the LED in THIS device has already gone out, then THIS battery is truly dead. No other device will suck anything out of it! You can safely say thank you to her for her cooperation and, saying goodbye, dispose of it.
• Danil / 05/30/2017 - 14:28
  How to charge a phone using this chip? What would be powered by the sun and charge your phone?
• Dmitry / 05/16/2017 - 23:36
  Yuri, the end of the wire that comes from the middle of the resistor should continue to the transistor at control input 3. In the picture it is cut off. According to the logic of work, it should be like this. I bought a lamp with such a converter and immediately disassembled it. The plus of the solar cell is soldered to input 3. It is not for charging, but just a light sensor. You need to charge the AAA battery yourself by removing it from the lamp.
• Andrey / 05.25.2016 - 16:32
  Fixed prices sell garden night lights. Inside there is a 4-pin YX8018 microcircuit, an LED, a nickel tablet, a solar panel, a switch and, like, a choke for a resistor type. It charges during the day, and if you cover the diesel fuel (or in the evening), the diode lights up. Googled it a bit. 8018 is a DC-DC converter for solar panel
• Yuri / 03/22/2015 - 18:05
  Is the author mistaken about the internal resistor at pin 3? Most likely it is connected to ground.
• TL494 / 12/16/2014 - 13:10
  And if you calculate how much a kW/hour stored in HIT costs? Everything is quite natural. Although at home I recycle old batteries in batches of 2-3, to zero, without any diagrams.
• Vladislav / 06.12.2014 - 15:25
  Dear I Nechaev, Thank you for your publication, it is relevant for me, since I am looking for a low-cost circuit for recycling voltage of about 1 volt at XX, there is something to recycle in large quantities. In garden lanterns, a similar circuit, such as JD 1803B, probably works most likely. THESE CHARACTERISTICS CAN NOT BE FOUND ON IT, on some of these flashlight controllers there are no markings at all, THERE IS ANALOGUE ANA 608-6, ANA 618 BUT there are Chinese symbols, there are other controllers like max 1724 or 1722 and others that work from 0.7 - 0.8 volts with an output voltage of up to 5.5 volts at a current of 150 to 300 mA, since I am not a strong electronics engineer, I need additional. discussing the circuit design, my skype vladislav14211 mail [email protected] I will be glad to cooperate and discuss the technical solution I need based on your scheme
• Sergey / 05/10/2014 - 07:18
  Get several ma at 9...15 volts from one element a larger capacity is sufficient - this is understandable. For example, to power a multimeter. I assembled similar circuits myself if necessary. But from the voltage that 1 element gives you get 2 volts, this is strong, guys!!! This is more likely due to an excess of time. I understand a man who finds himself in the heat of the “promised homeland” (look at this site) But in the imperial capital, when you spit, you end up in a store or kiosk where there is a heap of batteries.

Reviews of solar panels sometimes pop up on mySKU. I also decided to join the “green” energy. I re-read a stack of different materials on solar panels and controllers. I didn’t become an expert, but I gained a small bag of knowledge. I will share a piece of knowledge with you today.

To implement autonomous lighting in a bathhouse at the dacha and get acquainted, 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:

A solar panel

The solar panel arrived unexpectedly quickly. The courier called, which I didn't expect. Due to the heavy weight, the Banggood store sent the panel via EMS, but the controller took the standard three and a half weeks by regular mail.

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




The panel is quite large. Actual size 650x350x25 mm, weight 2.5 kg.


The photocells are sandwiched between a thick sheet of clear plastic and a thin sheet of white plastic. The sandwich is inserted into an aluminum profile and treated with sealant. The aluminum profile is covered with transport film. The degree of protection is not indicated anywhere. The front plastic feels durable. How it will withstand hail, I don’t know.

On the back of the panel there is a protective casing/connection box. There is a wire coming out of it.


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


There are “crocodiles” at the ends of the wire. Of course, during the final installation the crocodiles and most of the wire will need to be cut off, but they will be useful for the test.

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

Specifications sticker:


Manufacturer not specified. Specifications:

As you can see, the solar panel produces a maximum voltage of 21 V without load (in reality, according to measurements, 22 V), and not 12 V, as stated. There is no need to be afraid. This is normal, the operating voltage of the system for which the solar panel is intended is usually 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 have voltages up to 45V.

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


The horizontal axis is voltage, the vertical axes are 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, maximum power is reached at a certain point. This point is called the maximum power point of the panel, characterized by the values ​​Vmp and Imp. During operation, mainly due to changes in the temperature of the photocells, this point may shift.

The panel in the review has Vmp = 18 V and Imp = 1.67 A. It is at this point that the power of 30 W is achieved (in the most ideal conditions). If you load the panel more, the current will increase 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 panel's efficiency decreases as it moves away from the maximum power point. A little later I will return to the point of maximum power.

Controller

The CMTP02 controller comes in a small box.


Inside is the controller itself and brief instructions.

The controller is designed for current up to 15 A. That is. supplies a current of up to 15 A to the battery and the load. This is the “Chinese” 15 A. In reality, of course, it is less. I have a panel with a maximum current of 1.75 A - no need to worry at all. The controller can work with 12 V and 24 V batteries.

Unscrew the 4 screws and remove the metal cover. On the bottom side of the board are three MOSFET transistors with erased markings. The transistors are insulated. Maybe it plays the role of a thermal substrate to remove heat to the metal cover, but the material is hard 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 substrate (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 the harness.


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

This PWM/PWM controller is the simplest, 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. Switching off in reverse order. Without a battery, the controller does not work.

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

The solar panel charging controller market can be formally divided into two types. MPPT and non-MPPT (they are also sometimes called PWM/PWM). MPPT - maximum power point tracking, tracking the maximum power point. Remember when I wrote about the maximum power point? So, the MPPT controller monitors (there are different algorithms) the maximum power point and tries to keep the voltage at the input at a level that corresponds to this point until the next measurement. Many MTTP controllers can operate with high voltage without problems (for example, series-connected panels with a voltage of 90 V for low losses due to wire resistance), and charge conventional 12 V batteries at the output.

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


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

MPPT controllers are more expensive and more efficient. But significant gains are obtained only when using powerful panels. You also need to know that many cheap Chinese controllers that say MPPT are not actually MPPT.

Let's return 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 lights up when there is power 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 there is a short circuit.

As long as there is enough power from the solar panel to power the load, the battery is charged. Those. Current flows to both the battery and the load. As soon as the load power begins to exceed the output power of the solar panel, charging the battery stops and the lack of current is compensated from the battery. The whole process works like clockwork. As soon as the solar panel stops producing 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 budget.

If you have a simple task, for example, you want a fountain in your country house that works only during the day, then nothing could be simpler. The following interesting converters with manual adjustment of the maximum power voltage are available on the market:


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

Solar panel testing

To clearly know how much energy the panel will produce per day, build daily charts, etc., there are several options. The simplest and most private is to connect the tester between the controller and the discharged battery. Universal is to use a load that supports Constant Voltage mode. The essence of this load is the following - you set the voltage, and the load begins to increase the current until the voltage stabilizes at the specified value. As soon as the voltage begins to sag or rise, the load instantly reduces or increases the current consumption. Thus, the energy source, the solar panel, produces everything 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 this mode is very rarely in demand; it is not always available in electronic loads. I asked my friends, but no one had one. I started studying diagrams on the Internet. . It couldn't have happened 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 very presentable, but the main thing is that it contains blue electrical tape and is completely suitable for use.




Using a potentiometer, you can adjust the load voltage. Because Since the load is made from improvised components, there is some voltage drop when the current changes. The test bench looks like this:


Because The current is low on my panel, so you can use thin short wires. For measurements I will use an EBD-USB tester in monitoring mode. The load is connected to the solar panel via 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). This works to my advantage, because... with the battery connected, the voltage range will be 11.2 - 14.6 V. Using the potentiometer on the load, I will set the voltage to slightly more than 12 V.

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

Bursts - I was covering the solar panel, looking at the change in the graph. In 5 minutes of operation, the solar panel produced 1.5 Wh. The output power was 19 W. When the voltage was set to about 18 V, the point of maximum power (I already looked at this by replacing the EBD-USB with a regular USB tester with high voltage support), the power was 21 W. And this is only a morning at the end of March. In summer, when the sun is at its zenith, the panel can easily produce the stated 30 W. But we will focus on the available data. If I roughly estimate that the sun will shine for 5 hours a day, then I will get 1.5 x 12 x 5 = 90 Wh per day. Summer daylight hours are longer, the summer/spring coefficient 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 light days. In the barn and in the bathhouse I can hang 4 lamps of 7 W (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 graphs for the whole day in May already at the panel location.

While I was experimenting with the panel, the load heatsink got very hot - after all, it was dissipating 20 W. It’s quite enough for measuring my panel, but if it’s more powerful, you’ll need to install a larger radiator and active cooling.

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


The output power ranged from 3 W to 17 W. In 5 minutes of operation, the solar panel produced 1 Wh. The panel copes well for this weather.

I liked the experiments with the solar panel, I will continue them. If anyone has practical and useful advice, do not hesitate to share them in the comments. I think that many will be interested.

The red-haired bandit also charges from the sun:

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