The photocell circuit and connection rules

Automation of lighting in the apartment, in the house or on the street is achieved through the use of a photo relay. If properly configured, it will turn on the light when darkness comes and turn it off during daylight. Modern devices contain a setting, through which you can set the trigger depending on the light. They are an integral part of the "smart house" system, which takes on a significant part of the duties of the owners. The photo-relay circuit, first of all, contains a resistor changing the resistance under the action of light. It is easy to assemble and set up by yourself.

Operating principle

The connection diagram of the photocover for street lighting includes a sensor, an amplifier and an actuator. The photoconductor PR1 under the action of light changes the resistance. In this case, the magnitude of the current passing through it varies. The signal is amplified by the compound transistor VT1, VT2 (Darlington circuit), and from it goes to the actuator, which is the electromagnetic relay K1.

In the dark, the resistance of the photosensor is several mΩ. Under the influence of light it decreases to a few kOhm. This opens the transistors VT1, VT2, including the relay K1, the control load circuit through the contact K1.1. The diode VD1 does not pass the self-induction current when the relay is switched off.

Despite the simplicity, the photo-relay circuit has a high sensitivity. To set it to the required level, the resistor R1 is used.

The supply voltage is selected according to the relay parameters and is 5-15 V. The winding current does not exceed 50 mA. If you want to increase it, you can use more powerful transistors and relays. The sensitivity of the photocell rises with increasing supply voltage.

Instead of a photoresistor, you can install a photodiode. If a sensor with increased sensitivity is required, circuits with phototransistors are used. Their use is advisable in order to save electricity, since the minimum limit of operation of a conventional device is 5 lux, when the surrounding objects are still distinguishable. The threshold of 2 lux corresponds to a deep twilight, after which, after 10 minutes, darkness sets in.

The photorelay is advisable to use even with manual lighting control, since you can forget to turn off the light, and the sensor will "take care" of it yourself. It is not difficult to install, and the price is quite affordable.

Characteristics of photocells

The choice of a photo relay is determined by the following factors:

• Sensitivity of the photocell;
• supply voltage;
• Switched power;
• external environment.

The sensitivity is characterized as the ratio of the resulting photocurrent to the magnitude of the external light flux and is measured in μA / lm. It depends on the frequency (spectral) and the intensity of light (integral). To control lighting in everyday life, the last characteristic, depending on the total luminous flux, is important.

The value of the rated voltage can be found on the housing of the device or in the accompanying document. Devices of foreign manufacture can have other standards of supply voltage.

The power of the fixtures to which the photo relay is connected depends on the load on its contacts. Lighting relays can include direct switching of lamps through the sensor contacts or via the starters when the load is high.

In the open air, the twilight switch is placed under the sealed transparent cover. It is a protection against moisture and precipitation. When working in the cold period, heating is used.

Factory-made models

Previously, the photo-relay circuit was self-assembled. Now this is not necessary, since the devices have become cheaper, and the functionality has expanded. They are used not only for external or internal lighting, but also for watering plants, ventilation systems, etc.

1. Photo-relay FR-2

Factory-made models are widely used in automation devices, for example, for controlling street lighting. It is often possible to see the burning lights in the afternoon, which they forgot to turn off. If there are photo sensors, there is no need to manually control the lighting.

The scheme of photo relay fr-2 of industrial manufacture is used for automatic control of street lighting. Here, also the switching device is relay K1. A photoresistor FSK-G1 with resistors R4 and R5 is connected to the base of transistor VT1.

The power is supplied from a single-phase 220 V network. When the illumination is small, the resistance of FSK-G1 is large and the signal based on VT1 is not enough to open it. Accordingly, the transistor VT2 is also closed. Relay K1 is on, and its working contacts are closed, keeping the light bulbs burning.

When the illumination increases to the pickup threshold, the resistance of the photoresistor is reduced and the transistor wrench opens , after which the relay K1 switches off, breaking the power supply circuit of the lamps.

2. Types of photo relays

The choice of models is large enough so that you can choose the right one:

• With a remote sensor located outside the body of the product, to which 2 wires are connected;
• Lux 2 - a device with high reliability and quality level;
• A photo relay with a power supply of 12 V and a load not exceeding 10 A;
• Module with a timer, mounted on the DIN-rail;
• Devices IEK of the domestic manufacturer with high quality and functionality;
• AZ 112 - automatic with high sensitivity;
• ABB, LPX - reliable manufacturers of devices of European quality.

Ways to connect a photocell

Before purchasing the sensor, it is necessary to calculate the power consumed by the luminaires and take 20% with a margin. With a significant load, the street photocell circuit provides for an additional installation of an electromagnetic starter, the winding of which must be switched through the contacts of the photo relay, and the power contacts to switch the load.

For the home, this method is rarely used.

Before installation, the mains supply voltage is checked ~ 220 V. The connection is made from the circuit breaker. The photosensor is installed in such a way that the light from the flashlight does not fall on it.

The device uses terminals for connecting wires, which makes installation easier. If they are missing, a junction box is used .

Due to the use of microprocessors, the connection circuit of a photo relay with other elements has acquired new functions. In the algorithm of actions, we introduced a timer and a motion sensor.

It is convenient, when the lamps are automatically switched on when a person passes through the staircase or along the garden path. And the trigger occurs only at night. Due to the use of the timer, the photo relay does not respond to the headlights from passing cars.

The simplest scheme for connecting a timer with a motion sensor is a serial one. For expensive models, special programmable circuits have been developed that take into account different operating conditions.

Photo-relay for street lighting

To connect the photocell, the circuit is applied to its housing. It can be found in the documentation for the device.

Three wires are coming out of the device.

1. Zero conductor - common for fixtures and photocells (red).
2. Phase - is connected to the input of the device (brown).
3. Potential conductor for supplying voltage from the light switch to the luminaires (blue).

The device operates on the principle of interrupting or switching on the phase. Color marking from different manufacturers may vary. If the network has a conductor "earth", it is not connected to the device.

In models with a built-in sensor, which is located inside a transparent case, the work of street lighting is autonomous. You only need to bring food to it.

Variants with sensor removal are used in case when the electronic stuffing of the photocell is conveniently placed in the control panel with other devices. Then there is no need for a stand-alone installation, power wiring and maintenance at altitude. The electronic unit is placed indoors, and the sensor is brought out.

Features of the photo-relay for street lighting: scheme

When installing a photo relay on the street, some factors should be taken into account.

1. The presence of a supply voltage of 220 V and the matching of the powers of the contacts and the load.
2. Do not install appliances near inflammable materials or in an aggressive environment.
3. The base of the device is placed below.
4. Before the sensor, there should be no swinging objects, for example, branches of trees.

The wires are connected through a junction box for the street. It is fixed next to the photo relay.

Selecting a Photo Relay

1. The ability to adjust the trigger threshold allows adjustment of the sensitivity of the sensor depending on the time of year or in cloudy weather. As a result, electricity is saved.
2. Minimum labor is required when installing a photocell with a built-in sensor. It does not require special skills.
3. Relay with a timer is well programmed for its needs and work in the established mode. You can set the device to turn off at night. The display on the body of the device and the push-button control make it easy to configure.

Conclusion

The use of the photocell allows you to automatically control the switching period of the lamps. Now the need for a lamplighter's profession has already disappeared. The scheme of the photo relay without the participation of a person in the evenings lights the light on the streets and turns it off in the morning. Devices can control the lighting system, which increases its life and makes operation easier.