Solar battery charge controller: circuit, operating principle, connection methods

Solar energy is so far limited (at the household level) to the creation of photovoltaic panels of relatively low power.But regardless of the design of the photoelectric converter of solar light into current, this device is equipped with a module called a solar battery charge controller.

Indeed, the solar photosynthesis installation includes a rechargeable battery - a storage device for the energy received from the solar panel. It is this secondary energy source that is primarily served by the controller.

In the article we present, we will understand the design and operating principles of this device, and also consider how to connect it.

Solar Controllers

An electronic module called a solar controller is designed to perform a number of control functions during the charging/discharging process solar battery battery.

When sunlight falls on the surface of a solar panel installed, for example, on the roof of a house, the device's photocells convert this light into electric current.

The resulting energy, in fact, could be supplied directly to the storage battery. However, the process of charging/discharging a battery has its own subtleties (certain levels of currents and voltages). If you neglect these subtleties, the battery will simply fail in a short period of operation.

To avoid such sad consequences, a module called a charge controller for a solar battery is designed.

In addition to monitoring the battery charge level, the module also monitors energy consumption.Depending on the degree of discharge, the solar battery charge controller circuit regulates and sets the current level required for the initial and subsequent charge.

Depending on the power of the solar battery charge controller, the designs of these devices can have very different configurations

In general, in simple terms, the module provides a carefree “life” for the battery, which periodically accumulates and releases energy to consumer devices.

Types used in practice

At the industrial level, two types of electronic devices have been launched and are being produced, the design of which is suitable for installation in a solar energy system:

1. PWM series devices.
2. MPPT series devices.

The first type of controller for a solar battery can be called “old man”. Such schemes were developed and put into operation at the dawn of the development of solar and wind energy.

The operating principle of the PWM controller circuit is based on pulse width modulation algorithms. The functionality of such devices is somewhat inferior to the more advanced devices of the MPPT series, but in general they also work quite effectively.

One of the popular solar station battery charge controller models in society, despite the fact that the device circuit is made using PWM technology, which is considered outdated

Designs using Maximum Power Point Tracking technology (tracking the maximum power limit) are distinguished by a modern approach to circuit solutions and provide greater functionality.

But if we compare both types of controller and, especially, with a bias towards the domestic sphere, MPPT devices do not look in the rosy light in which they are traditionally advertised.

MPPT type controller:

• has a higher cost;
• has a complex configuration algorithm;
• gives a gain in power only on panels of a large area.

This type of equipment is more suitable for global solar energy systems.

A controller designed for operation as part of a solar power installation. It is a representative of the class of MPPT devices - more advanced and efficient

For the needs of an ordinary user from a domestic environment, who, as a rule, has small-area panels, it is more profitable to buy and operate a PWM controller (PWM) with the same effect.

Block diagrams of controllers

Schematic diagrams of PWM and MPPT controllers to consider them with a layman's eye are too complex a point associated with a subtle understanding of electronics. Therefore, it is logical to consider only structural diagrams. This approach is understandable to a wide range of people.

Option #1 - PWM devices

The voltage from the solar panel travels through two conductors (positive and negative) to the stabilizing element and the separating resistive circuit. Due to this piece of the circuit, potential equalization of the input voltage is obtained and, to some extent, they organize protection of the controller input from exceeding the input voltage limit.

It should be emphasized here: each individual device model has a specific input voltage limit (indicated in the documentation).

This is approximately what the block diagram of devices made on the basis of PWM technologies looks like.For operation as part of small household stations, this circuit approach provides quite sufficient efficiency

Next, the voltage and current are limited to the required value by power transistors. These circuit components are in turn controlled by the controller chip through the driver chip. As a result, the output of a pair of power transistors sets the normal value of voltage and current for the battery.

The circuit also contains a temperature sensor and a driver that controls the power transistor, which regulates the load power (protection against deep discharge of the battery). The temperature sensor monitors the heating status of important elements of the PWM controller.

Usually the temperature level inside the case or on the heatsinks of power transistors. If the temperature goes beyond the limits set in the settings, the device turns off all active power lines.

Option #2 - MPPT devices

The complexity of the circuit in this case is due to its addition to a number of elements that build the necessary control algorithm more carefully, based on operating conditions.

Voltage and current levels are monitored and compared by comparator circuits, and based on the comparison results, the maximum output power is determined.

Circuit design in structural form for charge controllers based on MPPT technologies. A more complex algorithm for monitoring and controlling peripheral devices is already noted here.

The main difference between this type of controller and PWM devices is that they are able to adjust the solar energy module to maximum power, regardless of weather conditions.

The circuitry of such devices implements several control methods:

• disturbances and observations;
• increasing conductivity;
• current sweep;
• constant voltage.

And in the final segment of the overall action, an algorithm for comparing all these methods is also used.

Controller connection methods

Considering the topic of connections, it should immediately be noted: for the installation of each individual device, a characteristic feature is working with a specific series of solar panels.

So, for example, if a controller is used that is designed for a maximum input voltage of 100 volts, a series of solar panels should output a voltage no greater than this value.

Any solar power installation operates according to the rule of balancing the output and input voltages of the first stage. The upper limit of the controller voltage must correspond to the upper limit of the panel voltage

Before connecting the device, you need to decide on the location of its physical installation. According to the rules, the installation location should be chosen in dry, well-ventilated areas. Avoid the presence of flammable materials near the device.

The presence of sources of vibration, heat and humidity in the immediate vicinity of the device is unacceptable. The installation site must be protected from precipitation and direct sunlight.

Connection technology for PWM models

Almost all manufacturers of PWM controllers require that the devices be connected in the exact sequence.

The technique of connecting PWM controllers to peripheral devices is not particularly difficult. Each board is equipped with labeled terminals. Here you simply need to follow the sequence of actions

Peripheral devices must be connected in full accordance with the designations of the contact terminals:

1. Connect the battery wires to the battery terminals of the device in accordance with the indicated polarity.
2. Switch on the protective fuse directly at the point of contact of the positive wire.
3. Attach the conductors coming from the solar panel battery to the controller contacts intended for the solar panel. Observe polarity.
4. Connect a test lamp of the appropriate voltage (usually 12/24V) to the load terminals of the device.

The specified sequence must not be violated. For example, connecting solar panels first when the battery is not connected is strictly prohibited. By doing this, the user runs the risk of “burning” the device. IN this material The diagram for assembling solar panels with a battery is described in more detail.

Also, for PWM series controllers, it is not permissible to connect a voltage inverter to the controller load terminals. The inverter should be connected directly to the battery terminals.

Procedure for connecting MPPT devices

The general physical installation requirements for this type of device do not differ from previous systems. But the technological setup is often somewhat different, since MPPT controllers are often considered more powerful devices.

For controllers designed for high power levels, it is recommended to use large cross-section cables equipped with metal end caps for power circuit connections.

For example, for powerful systems, these requirements are supplemented by the fact that manufacturers recommend using a cable for power connection lines designed for a current density of at least 4 A/mm². That is, for example, for a controller with a current of 60 A, you need a cable to connect to the battery with a cross-section of at least 20 mm².

Connecting cables must be equipped with copper lugs, tightly crimped with a special tool. The negative terminals of the solar panel and battery must be equipped with adapters with fuses and switches.

This approach eliminates energy losses and ensures safe operation of the installation.

Block diagram of connecting a powerful MPPT controller: 1 – solar panel; 2 – MPPT controller; 3 – terminal block; 4.5 – fuses; 6 – controller power switch; 7.8 – earth bus

Before connecting solar panels When connecting to the device, make sure that the voltage at the terminals corresponds to or is less than the voltage that can be supplied to the controller input.

Connecting peripherals to the MTTP device:

1. Switch the panel and battery switches to the “off” position.
2. Remove the protective fuses on the panel and battery.
3. Connect the battery terminals with a cable to the controller terminals for the battery.
4. Connect the terminals of the solar panel with a cable to the controller terminals indicated by the corresponding sign.
5. Connect the ground terminal to the ground bus with a cable.
6. Install the temperature sensor on the controller according to the instructions.

After these steps, you need to reinsert the previously removed battery fuse and turn the switch to the “on” position. A battery detection signal will appear on the controller screen.

Next, after a short pause (1-2 minutes), replace the previously removed solar panel fuse and turn the panel switch to the “on” position.

The device screen will show the voltage value of the solar panel. This moment indicates the successful launch of the solar energy installation.

Conclusions and useful video on the topic

The industry produces devices that are multifaceted in terms of circuit designs. Therefore, it is impossible to give unambiguous recommendations regarding the connection of all installations without exception.

However, the main principle for any type of device remains the same: without connecting the battery to the controller buses, connection to photovoltaic panels is unacceptable. Similar requirements apply for inclusion in the scheme voltage inverter. It should be considered as a separate module connected to the battery via direct contact.

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