Homemade controller for a solar panel. Solar battery charge controller DIY charge controller for solar panels

This time I decided to make an automatic machine that automatically turns on the LED lighting in the garden gazebo. Since there is no outlet nearby, and constantly pulling an extension cord is quite tedious, I decided to power the LEDs from a battery with recharging from solar cells.

A very similar one was previously described, which illuminates a glass shelf in a closet. Using this driver would pose a problem because we need more light to illuminate a gazebo than to illuminate a glass shelf. Also, the use of a more powerful light source will quickly discharge the battery, which can fail as a result of deep discharge of the elements in the battery.

To prevent this, I decided to create a simple driver with protection against too deep battery discharge based on . In turn, the solar cells also serve as a light sensor, which greatly simplifies the entire circuit.

The printed circuit board measures 40mm by 45mm. Additionally, two mounting holes have been added. The entire device is powered by three Ni-MH batteries (1.2V/1000mAh). A solar battery with a nominal voltage of 5 volts and a maximum output current of up to 80 mA is used for charging. The solar battery charges the batteries through the rectifier diode D1. The circuit does not have protection against overcharging the battery due to the fact that in such a configuration, overcharging is simply impossible.

A fully charged battery should have a voltage of about 4.2-4.35 V. The solar cell produces a voltage of 5 V, but there is a drop in the rectifier diode of about 0.7 V, which gives us a voltage of 4.3 V. Transistor Q1 is responsible for turning on the light night time and turn it off during the day. The base of this transistor is connected through a 2.2 kOhm resistor to the positive pole of the solar cell.

When the solar cell is not producing electricity or is too small, transistor Q1 is turned off. Then the current from the pin ("REF") of the zener diode TL431 will flow only through resistor R4, which creates a voltage divider together with resistors R2 and R3. Transistor Q2 controls the load in the form of LEDs. For the circuit to work correctly, we cannot ignore resistor R5, whose task is to pull the base of transistor Q2 to the positive of the power supply.

According to calculations for the available voltage, it turns out that the resistor should have a resistance of 100 Ohms. With such resistance, the circuit switches very quickly. But the problem is that this resistor has a fairly small value, and a very large current flows through it. The total current consumption is about 23 mA! I decided to replace this resistor with a resistor of a larger value. In the end, I installed a 1 kOhm resistor. Now the load shedding is not so fast, but the current consumption has been reduced to 8mA.

Of course, the current 8mA is only consumed when the solar cell is in a dark place - that is, only at night when the LEDs are on. And this is the same maximum current (8 mA) that comes from the battery at a voltage of 4.2 V. I set the load cut-off voltage to 2.9 V. The maximum voltage for one cell is 0.9 V, which when connecting three in series gives us 2.7 V, and therefore we still have 0.2 V left.

The circuit, after disconnecting the load (i.e. at 2.9 V and below), consumes only 50 μA. The same current will flow when the solar panel charges the batteries. The device is very responsive to light, but not so much that street lighting would interfere with twilight detection. From the moment sunset is detected until the LEDs turn on 100%, it takes approximately 2 minutes.

By removing transistor Q1, resistor R1 and rectifying diode D1 from the system, we obtain a simple circuit for protecting the battery from deep discharge. A similar circuit can be used to disconnect a Li-Ion or Li-Pol battery from charging. It can be used, for example, in a flashlight. It is also possible to create similar protection for other voltages; to do this, you need to calculate the voltage divider. There are formulas and an example of calculation

One of the most important components of a home solar power plant is the battery charge controller. It is this device that monitors the charging/discharging process of batteries, maintaining their optimal operating mode. There are many controller schemes for solar panels - from the simplest, sometimes made in a homemade way, to the very complex, using microprocessors. Moreover, homemade charge controllers for solar batteries often work better than similar industrial devices of the same type.

What are battery charge controllers for?

If the battery is connected directly to the terminals of the solar panels, it will be charged continuously. Eventually, a battery that is already fully charged will continue to receive current, causing the voltage to increase by several volts. As a result, the battery is recharged, the temperature of the electrolyte rises, and this temperature reaches such values that the electrolyte boils, and a sharp release of vapors occurs from the battery cans. As a result, complete evaporation of the electrolyte and drying out of the cans may occur. Naturally, this does not add “health” to the battery and sharply reduces its service life.

Controller in a solar battery charging system

So, in order to prevent such phenomena, in order to optimize the charge/discharge processes, controllers are needed.

Three principles for designing charge controllers

Based on the principle of operation, there are three types of solar controllers.
The first, simplest type is a device made on the “On/Off” principle. The circuit of such a device is a simple comparator that turns the charging circuit on or off depending on the voltage value at the battery terminals. This is the simplest and cheapest type of controller, but the way it produces the charge is also the most unreliable. The fact is that the controller turns off the charging circuit when the voltage limit at the battery terminals is reached. But at the same time the cans are not fully charged. The maximum charge achieved is no more than 90% of the nominal value. This constant lack of charge significantly reduces the performance of the battery and its service life.

Current-voltage characteristics of the solar module

Second type of controllers- These are devices built on the PWM (pulse width modulation) principle. These are more complex devices, in which, in addition to discrete circuit components, there are also microelectronic elements. Devices based on PWM (English - PWM) charge batteries in stages, choosing optimal charging modes. This selection is made automatically and depends on how deeply discharged the batteries are. The controller increases the voltage while simultaneously decreasing the current, thereby ensuring the battery is fully charged. The big drawback of the PWM controller is noticeable losses in battery charging mode - up to 40%.

The third type is MPPT controllers, that is, working on the principle of finding the point of maximum power of the solar module. During operation, devices of this type use the maximum available power for any charging mode. Compared to others, devices of this type provide approximately 25% - 30% more energy to charge batteries than other devices.

The battery is charged with a lower voltage than other types of controllers, but with a higher current. The efficiency of MPPT devices reaches 90% - 95%.

The simplest homemade controller

When making any controller yourself, it is necessary to comply with certain conditions. Firstly, the maximum input voltage must be equal to the battery voltage without load. Secondly, the ratio must be maintained: 1.2P

This device is designed to operate as part of a low-power solar power plant. The principle of operation of the controller is extremely simple. When the voltage at the battery terminals reaches the specified value, the charge stops. Subsequently, only the so-called drop charge is produced.

PCB mounted controller

When the voltage drops below the set level, the supply of energy to the batteries is resumed. If, when operating a load in the absence of a charge, the battery voltage is below 11 volts, the controller will turn off the load. This prevents the batteries from discharging when there is no sun.

Analogue controller for low power helium systems

Analog devices are used mainly in helium systems that have low power. In powerful systems, it is advisable to use digital serial devices of the MPPT type. These controllers interrupt the charging current when the battery is fully charged. The proposed analog controller circuit uses a parallel connection. With this connection, the solar module is always connected to the battery through a special diode. When the battery voltage reaches a predetermined value, the controller, in parallel with the solar module, turns on a load resistor circuit, which absorbs excess energy from the module.

This device was designed and assembled for a specific system consisting of a solar panel with 36 cells, with an open circuit voltage output of 18 volts and a short circuit current of up to one ampere. Battery capacity is up to 50 ampere-hours, at a nominal voltage of 12 volts. Before including the assembled device in the working configuration of the system, it is necessary to configure it. For quick setup, you need to take a pre-charged battery. The solar battery, observing the polarity, must be connected to the PV terminals according to the diagram, and the battery – to the VAT terminals. A digital voltmeter must also be connected to the battery terminals.

Now to get the most out of the solar panel, you need to orient it towards the sun. After this, slowly turn the screw of a twenty-turn variable resistor with a nominal value of 100 kOhm. The screw is rotated until the LED starts flashing. After flashing begins, the screw should continue to be turned slowly until the voltmeter shows the desired voltage at the battery terminals. This completes the device setup.

During operation of the system, when the voltage at the battery terminals reaches a limit value, the LED begins to emit short light pulses with long intervals. As the battery continues to charge, the duration of the light pulses increases, and the interval between them, on the contrary, decreases.

Of course, if you have certain knowledge and skills, you can assemble a more complex device, for example, MPPT, but if it comes to buying expensive equipment for a home power plant, then it probably makes sense to buy an industrial device, which is also covered and manufacturer's warranty. And do not expose batteries to the risk of damage.

In power plant systems powered by solar panels, various connection schemes are used to supply the received energy, which are made using different algorithms based on microprocessor electronics technology. Based on such circuits, devices called solar panel controllers have been created.

Operating principle

There are several methods for transferring electricity from solar cells to a battery:

Without the use of switching and adjustment devices, directly.
Through controllers for

The first method causes the passage of electric current from the source to the batteries to increase their voltage. First, the voltage will rise to a certain limit value, which depends on the type and design of the battery and the ambient temperature. Will further exceed this level.

During the initial period, the batteries charge normally. Then processes begin that are characterized by negative aspects: the charging current continues to flow, causes an increase in voltage above the permissible value, overcharging occurs, and as a result, the temperature of the electrolyte increases. This causes it to boil and release water vapor with significant intensity from individual battery cells. This process can continue until the cans dry. It is clear that the battery life of the batteries does not increase due to this phenomenon.

To limit the charge current, they use special devices - charge controllers, or do it manually. Almost no one uses the latter method, since it is inconvenient to monitor the voltage level on devices, make switches by hand, and it is necessary to assign a special worker for this to service the controllers for solar panels.

Controller operation during charging

Controllers for solar panels are manufactured in various modifications based on the principles and complexity of the voltage limiting method:

Easy to turn off and on. The controller switches the charger to the battery depending on the voltage value at the terminals.
Transformations.
Maximum power control.

First principle of simple switching

This is the simplest type of work, but it is less reliable. The main disadvantage of the method is that when the voltage at the battery terminals increases to the maximum value, the final charge does not occur. The charge reaches 90% of the nominal value. Batteries are constantly in a state of undercharging. This has a detrimental effect on their service life.

Pulse width principle

Such devices are manufactured on the basis of microcircuits. They control the power unit to maintain the input voltage within a certain range using feedback signals.

Controllers with pulse width control have the following capabilities:

Measure the temperature of the electrolyte in a remote or built-in battery.
Compensate the temperature with the charging voltage.
Adjust to the properties of a specific type of battery with different values according to the voltage graph.

The more functions built into solar panel controllers, the higher their reliability and cost.

Solar battery operation schedule

Voltage limitation based on peak power point

These devices can also operate using the pulse width method. Their accuracy is high, since the maximum value of power supplied by the solar battery is taken into account. The power value is calculated and stored.

For solar batteries with a voltage of 12 volts, the maximum power is at 17.5 volts. A simple controller will turn off the battery charge already at 14 V, and a controller with special technology allows you to use a solar battery reserve of up to 17.5 volts.

The more the battery is discharged, the greater the energy loss from solar cells; controllers for solar panels reduce these losses. As a result, controllers, using pulse-width transformations, increase the energy output of the solar battery during all charging cycles. The savings percentage can reach up to 30%, depending on various factors. The output current of the battery will be higher than the input current.

Properties

When choosing the type of controller, you need to pay attention not only to the principles of operation, but also to the conditions intended for its operation. These device indicators are:

Input voltage value.
The value of the total power of solar cells.
Type of load.

Voltage

The controller circuit can receive voltage from several batteries that are connected in different ways. For the device to function properly, it is necessary that the total voltage value, including no-load voltage, does not exceed the limit specified by the manufacturer in the instructions.

Let's name some factors due to which it is necessary to make a 20% voltage reserve:

It is necessary to take into account the factor of advertising overestimation of controller data.
The processes occurring in photocells are unstable; with excessive solar flares of light, the energy that creates the battery's no-load voltage can be exceeded.

Solar power

This value is important in the operation of the controller, since the device must have sufficient power to transfer it to the batteries; if there is not enough power, the device circuit will fail.

To calculate the power, the value of the output current from the controller is multiplied by the voltage that is generated, not forgetting the 20% reserve.

Type of load

The controller must be used for its intended purpose. There is no need to use it as a regular voltage source or connect various household devices to it. Maybe some of them will work normally and will not damage the controller.

Another question is how long this will last. The device operates on the principle of pulse-width type transformations and uses microprocessor production technologies. These technologies take into account the load inherent in the properties of the battery, and not various types of consumers that have peculiar behavior properties when the load changes.

How to make a controller with your own hands

To make such a device, it is enough to have some knowledge of electrical engineering and electronics. A homemade device will be inferior to an industrial model in terms of functionality and efficiency, but for simple networks with low power, such a homemade controller is quite suitable.

A homemade controller must have the following parameters:

1.2 P ≤ I × U. In this expression, the designations used are the total power of the sources (P), the controller output current (I), and the voltage when the battery is discharged (U).
The highest controller input voltage should correspond to the total voltage of the batteries at idle without load.

A simple diagram of a homemade controller module:

Self-assembled solar panel controllers have the following properties:

The charging voltage is 13.8 volts, varies depending on the rated current.
The switching voltage is 11 volts, can be adjusted.
Switching voltage is 12.5 volts.
The voltage drop on the keys is 20 millivolts at a current of 0.5 A.

Controllers for solar panels are included in any solar systems, as well as systems based on solar panels and wind generators. They make it possible to create a normal charging mode for batteries, increase efficiency and reduce wear, and can be assembled on their own.

Analysis of the controller circuit for hybrid power

For example, we will consider a source of emergency lighting or security alarm operating 24 hours a day.

The use of solar battery energy allows you to reduce the consumption of electrical energy from the central power supply network, as well as protect electrical devices from the possibility of rolling power outages.

In the dark, when there is no sunlight, the system switches to 220 volt mains power. The backup source was a 12-volt battery. This system operates in any weather.

Circuit of the simplest controller

The photoresistor controls transistors T1 and T2.

During the day, when there is sunlight, the transistors turn off. A voltage of 12 volts is supplied to the battery from the panel through diode D2. It prevents the battery from being discharged through the panel. When there is sufficient lighting, the panel produces a current of 15 watts, 1 ampere.

When the batteries are fully charged to 11.6 volts, the zener diode opens and the red LED turns on. When the voltage at the battery contacts drops to 11 volts, the red LED turns off. This indicates that the battery requires charging. Resistors R1 and R3 limit the current of the LED and Zener diode.

At night, or in the dark, when there is no light from the sun, the resistance of the photocell decreases, transistors T1 and T2 are connected. The battery receives charge from the power supply. The charging current from the 220 volt power line is supplied to the battery through a transformer, rectifier, resistor and transistors. Capacitance C2 smoothes out network voltage ripples.

The luminous flux limit at which the photosensor turns on is adjusted with a variable resistor.

In our progressive times, when technologies are constantly improving and production capacity is constantly increasing, materials and components that previously could only be dreamed of are becoming increasingly accessible to the simple home-made worker. One such component is solar photovoltaic cells. An increasing number of homegrown Kulibins are creating their own from photovoltaic cells purchased at a reasonable price on Ebay, Dealextreme or other places.

But as you know, the introduction of a new technical device, such as a solar battery, provokes the creation of a control device for this useful device. If earlier the simplest circuits with limiting diodes or relays were used for this, now more and more progressive devices are being developed. We suggest that you familiarize yourself with one of these devices, charge controllers for a solar battery, the manufacture of which is quite feasible even for beginners. The essence of the operation of all charge controllers (both factory-made and home-made) is as follows: the load of the solar battery is most often the battery, which accumulates the received solar energy, and in order to comply with all battery charging parameters, prevent it from overcharging (and thus extend the life its service) and utilize “extra” energy. So, let's look at the charge controller circuit for a solar battery.

It is designed to charge a sealed lead-acid (gel) battery at 12V from a low-power solar panel, with a return current of up to several amperes. The series protective diode, which was previously installed to prevent batteries from discharging at night, is replaced here by a field-effect transistor, which in turn is controlled by a comparator.

A higher quality printed drawing is in the archive. The controller stops charging the battery when the voltage on it reaches a predetermined limit and switches the panel to an additional consumer (load) to utilize excess energy. When the battery voltage drops below a preset limit, the controller switches the solar panel from load to battery charge. Main characteristics of the scheme:

Charge voltage Vbat=13.8V (adjustable), measured in the presence of charge current;
-The load is turned off when Vbat is less than 11V (configurable), the load is turned on when Vbat = 12.5V;
-Temperature compensation of charge mode;
-The economical comparator TLC339 can be replaced with the more common TL393 or TL339;
-The voltage drop across the keys is less than 20mV when charging with a current of 0.5A.

It is better to configure the device to turn the charge on/off based on the passport data for the battery used; The charging current is limited only by the capabilities of the solar battery - the controller circuit does not affect it in any way. This device was used by the author for a year. During this time, no complaints or irregularities in work were identified. In the photo of the device's printed circuit board, in addition to the wiring directly under the controller itself (on the right), there are also places for 3 DC/DC converters for 3.6 and 9 volt outputs.

Photo of the finished device with all components, including batteries, controller, converters and an additional display and switching unit. Controller designer - Oscar den Uijl.

One of the most important components of a solar system is the charge controller. It can be supplied separately or complete with an inverter. As the name implies, this device is designed to control battery charge, that is, charge controllers for solar batteries monitor the voltage level on the battery and serve to prevent complete discharge or overcharging of the battery.

The age of global accessibility, when you can find absolutely any product and information, allows you not only to purchase controllers in any specialized store, but also to assemble it yourself. To do this, you will need a diagram of the device that you plan to manufacture, in our case it is a charging controller, and the ability to understand electronics. We will try to provide you with both.

Charging controllers for solar power: a brief description

There are several varieties of the described device. The simplest of them perform only one function: turns the batteries on and off depending on their charge. More “advanced” models are equipped with a function for tracking the maximum power point, which provides a higher output current compared to the current of the solar battery. And this, in turn, increases the efficiency of the entire installation as a whole.

More advanced models are capable of reducing the voltage on the solar panel and maintaining it at the required level. The presence of this function helps to charge the battery more fully.

Any controller, including homemade ones, must meet certain requirements:

1.2P ≤ I×U, where P is the total power of solar panels of the entire system; I – controller output current; U – system voltage with discharged batteries.
1.2 Uin = Ux.x, where Uin is the maximum permissible input voltage, Ux.x is the total open-circuit voltage of all solar panels in the system.

If you can't buy...

Of course, often a device assembled by yourself will be worse than a similar device produced in a factory. But today few people can be trusted. And cheap solar panel controllers supplied from China could also be assembled in a utility room. So why buy a device whose quality you are not sure of, if you have the opportunity to build it at home.

Figure 1 shows the simplest circuit, using which you can assemble your own controller suitable for charging a 12 V lead-acid battery using a low-power SB with a current of several amperes. By changing the values of the elements used, you can adapt the assembled device to a battery with other technical characteristics. It should be noted that this circuit involves using a field-effect transistor controlled by a comparator instead of a protective diode.

Video to help you:

The principle of operation is quite simple: when the voltage on the battery reaches the specified value, the controller will stop charging; if it drops below the threshold value, charging will be turned on again. When the voltage is less than 11 V, the load will be disconnected, and when the voltage is more than 12.5 V, on the contrary, it will be connected to the battery. This small device will save your battery from spontaneous discharge in the absence of sun. Figure 2 shows an already assembled kit, consisting of two batteries, DC/DC converters and an indication.

Solar battery charge controllers, assembled with your own hands using more complex circuits, can guarantee you reliable and stable operation. Therefore, if you feel strong, then another diagram is presented below. It consists of a larger number of components, but it functions without “glitches” (Figure 3).

A homemade controller assembled according to this scheme is suitable for an energy supply system operating both from a solar power system and from a wind generator. The signal that comes from the alternative energy source used is switched by a relay, which in turn is controlled by a field-effect transistor switch. Trimmer resistors are used to adjust the mode switching thresholds.

Don’t be afraid to experiment, because the best minds of humanity also made mistakes and failures, so if the first time you weren’t able to assemble a reliable controller with your own hands, don’t despair. Try again, and perhaps you will succeed the second time. But you will be “warmed” by the very knowledge that you did it yourself.

The article was prepared by Abdullina Regina

How to modify the charge control device: