Solar power control unit. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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There is an opinion that solar panels will someday be able to significantly supplement and even replace traditional energy sources. Then the time will come for a real test of the possibilities of solar cells.

In this chapter, we will take a little look into the future and test the potential of photovoltaics to bring real benefits. No more souvenirs, no more toys, just a modest, mundane job.

In this chapter, the reader expects to know how solar energy will help us with our daily household chores, including powering a powerful saw, lighting in the room, providing power to various entertainment devices, and much more. This is the future of solar energy.

However, the details of such systems will not be described in this book. Instead, it will show how to control an already completed photovoltaic system. This purpose is served by the power control unit.

Power control unit

This unit is designed to fully control the life of solar panels. From the remote control of this unit, you can easily control the power supply to up to four energy consumers. In addition, a fuse is provided to protect each consumer.

But that is not all. Since the performance of the system certainly depends on the state of charge of the lead-acid batteries, a battery condition monitoring unit is directly integrated into this device. By looking at the control panel, you can immediately assess the working condition of the energy source. And if it is unsatisfactory, the energy supply reaches a dangerous level, a warning signal (buzzer) is given.

What more could you want from a controller?

Power distribution control and management device

The main task of the power control unit is to distribute photovoltaic energy between different parts of the system. It is also designed to save energy in reserve.

Consider, for example, the operation of a voltage converter, which converts the 12 V DC voltage generated by solar panels into 110 V AC voltage. This voltage is necessary for the operation of certain devices, such as a power saw.

But the voltage converter consumes power all the time, even when no load is connected to it. This wastes energy that could be better spent. Therefore, it is necessary to provide a toggle switch in the power control unit to turn off the inverter.

This block provides the ability to turn off any load that is equipped with its own toggle switch. To disconnect any load from the power source, simply "flick" the switch.

Considering fig. 1, it can be found that the block has four separate circuits, each with a toggle switch mounted on the front panel. Above each toggle switch there is a small LED. When the circuit is energized, the corresponding LED illuminates to indicate that power is being supplied to the selected load.

Ris.1

However, control over the supply of energy to the load is not enough. For safety reasons, it is necessary to monitor the current strength in the circuit.

That is why not ordinary toggle switches are used as switches, but special breakers. Unlike conventional breakers, which wear out quickly when used as breakers, these breakers are designed to function both as a limiter and as a switch.

Battery voltage and state of charge monitoring device

The control unit contains a voltage monitoring device that indicates the state (degree of charge) of the batteries.

As shown in Chap. 6, the voltage of a lead-acid battery depends on the charge stored in its cells. This is clearly seen from Fig. 2, which shows the relationship between voltage and battery state of charge. It follows from the dependence that a fully charged battery has a voltage of 13,2 V, and a fully discharged one - 10,5 V. To determine the degree of charge of the battery cells, it is necessary to measure the voltage on the battery and compare it with the value in fig. 2.

Ris.2

This is what the battery monitor does. However, it uses a light strip instead of a meter to indicate voltage. The voltage of the monitored battery is displayed by 10 LEDs. The reading scale is constructed so that each subsequent diode lights up with an increase in voltage by 0,5 V. If the first diode is on, the voltage is 10,5 V, if the second is 11 V, if the third is 11,5 V, etc. up to up to 15 V.

The display unit is made on a separate integrated circuit LM3914. Inside it there are a number of comparators that compare the input voltage with the reference voltage of the source and turn on the light bulb corresponding to the ratio of the mentioned voltages.

The principle of operation of the indication circuit is clear from Fig. 3. Resistors R1, R2, R3 form a voltage divider that reduces the 12V input (from battery) to the 2,5V needed to power IC1. The voltage conversion scale of IC1 is set by variable resistor VR1. Now the input voltage from the battery goes to the comparators inside IC1, which decide on its true value. This value is then indicated by one of the 10 LEDs.

Ris.3

The battery status is displayed in two ways using color-coded LEDs. For example, a 13V diode is green. It is believed that a battery with a voltage of 12-14 V is operational, therefore, the diode is green.

However, if the battery voltage drops to 11,5 V and then to 11 V, then the charge is depleted. These diodes are yellow, indicating a problem that may be encountered in the future.

The last 10,5V diode is red. If the battery voltage drops to this level, there is little (or no) stored energy in the battery. A simple glance is enough to find out not only the exact value of the battery voltage, but also its state of charge (by color change). In table. 1 is a list of LEDs with their colors and the information they display.

Table 1. Information displayed by the LEDs

Battery monitor

The battery voltage monitor also allows you to check the state of the charging circuit. Under normal conditions, the charging voltage should not exceed 15,5 V, otherwise the battery may be damaged.

Therefore, a red light is reserved for the 15-volt indicator device. When it lights up, it doesn't necessarily mean something has happened, just that the charging voltage is excessively high for some reason.

alarm

And that's not it! Did you know that letting the battery charge below 10,5V can damage the battery. Plate sulfation will occur, and it is imperative that this does not happen.

An alarm has been added to the circuit. If for any reason the system voltage drops below 10,5V, an alarm will sound. I also connected the 15-volt output of the indicator to the alarm so that the signal was also given in the event of a battery overcharge.

The signal is controlled by two logic elements of the IC2 chip. Power is supplied to the microcircuit from diode D1

Design

The battery voltage monitoring device is made using printed wiring. Figure PCB is shown in fig. 4. Remember that the parts list contains the address of the supplier of the finished circuit board for this device.

Ris.4

Circuit elements are placed according to fig. 5. When soldering radio components, pay attention to the following points.

Ris.5

First, to connect the LEDs. Polarity must be observed, it is not always easy to determine which diode terminal is the anode and which is the cathode. If you connect the LEDs in reverse polarity, they will not glow. It is also necessary to pay attention to the color matching of the LEDs before soldering and do not shorten their leads.

Secondly, to observe the polarity of the inclusion of the IC1 microcircuit, since an erroneous inclusion will lead to its failure. The microcircuit is a CMOS chip, which is very sensitive to electrostatic charge, so you need to pay attention to this point.

Automatic breakers are placed on the front panel of the aluminum case. The breakers mentioned in the parts list require holes with a diameter of 10 mm.

It is necessary to select circuit breakers for the system that constantly pass the required current, but trip when overloaded. Breakers with too high threshold must not be used.

The LEDs are placed exactly above the breakers. Holes with a diameter of 6 mm are drilled under their chrome-plated holder case. The wiring diagram of the entire power control unit is shown in fig. 6.

Ris.6

Resistors are connected in series with four LEDs. They are simply soldered between the cathodes of the LEDs and the disconnected outputs of the breakers.

To connect external devices, an adapter block is placed on the rear wall of the case. External devices include solar panels and switched appliances. Make sure that the power supply circuits use a wire of sufficient diameter. The conductors leading to the battery voltage monitor may be smaller in diameter.

The battery voltage monitor is located under the breaker. The printed circuit board is mounted on plastic racks parallel to the bottom of the case.

The LED leads are bent so that the LEDs protrude beyond the edge of the board, being in the same plane. Then the LEDs are pulled out of the slot cut under the breakers.

If there is a desire, we will make inscriptions under the switches, you can use a translated font for this purpose.

Checking and setting

Checking the device is quite simple, you just need to connect a 12-volt battery to the input. You don't need to connect anything else to check.

Click on the breaker and check the operation of the LED. The LED should glow when the breaker is on and go out when it is off.

The battery voltage monitor must first be calibrated. By connecting a voltmeter to the battery input, it is necessary to measure its voltage. Then, by rotating the variable resistor VR1, the LED glows corresponding to the measured voltage. This completes the calibration.

Author: Byers T.

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