Automation of the supply of lighting in an apartment, in a house or on the street is achieved through the use of a photo relay. When properly configured, it will turn on the light when it gets dark and turn it off during daylight hours. Modern devices contain a setting, due to which you can set the response depending on the light. They are an integral part of the system of "smart home", taking on a significant part of the responsibilities of the owners. The photorelay circuit, first of all, contains a resistor that changes the resistance under the influence of light. It is easy to assemble and configure with your own hands.
Operating principle
The photo relay connection scheme for street lighting includes a sensor, an amplifier and an actuator. Photoconductor PR1 changes the resistance under the influence of light. In this case, the magnitude of the electric current passing through it changes. The signal is amplified by a composite 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 milliohms. Under the influence of light, it decreases to a few kOhm. In this case, the transistors VT1, VT2 are opened, including the relay K1, which controls the load circuit through the contact K1.1. The diode VD1 does not pass the self-induction current when the relay is turned off.
Despite its simplicity, the photorelay circuit is highly sensitive. To set it to the required level, a resistor R1 is used.
The supply voltage is selected according to the parameters of the relay and is 5-15 V. The winding current does not exceed 50 mA. If you need to increase it, you can use more powerful transistors and relays. The sensitivity of the photo relay increases with increasing supply voltage.
Instead of a photoresistor, you can install a photodiode. If a sensor with increased sensitivity is needed, circuits with phototransistors are used. Their use is advisable in order to save electricity, since the minimum response limit of a conventional device is 5 lux, when the surrounding objects are still distinguishable. The threshold of 2 lux corresponds to deep twilight, after which darkness sets in after 10 minutes.
It is advisable to use a photorelay even with manual lighting control, since you can forget to turn off the light, and the sensor will “take care” of it on its own. Installing it is easy, and the price is quite affordable.
Photocell Features
The choice of photo relay is determined by the following factors:
- photocell sensitivity;
- supply voltage;
- switched power;
- external environment.
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 light intensity (integral). To control lighting in everyday life, the last characteristic, depending on the total luminous flux, is important.
The rated voltage can be found on the instrument housing or in the accompanying document. Foreign-made devices may have different supply voltage standards.
The load on its contacts depends on the power of the lamps to which the photo relay is connected. Light photo relay circuits may provide for the direct inclusion of lamps through the sensor contacts or through starters when the load is high.
Outdoors, the twilight switch is placed under a sealed transparent cover. It is protected against moisture and precipitation. When working in the cold period, heating is used.
Factory Models
Previously, the photo relay circuit was assembled with your own hands. 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 controlling plant irrigation, ventilation system, etc.
1. Photorelay FR-2
Factory-made models are widely used in automation devices, for example, to control street lighting. You can often see burning lanterns during the day that you forgot to turn off. In the presence of photosensors there is no need for manual control of lighting.
The scheme of the FR-2 photorelay industrial production is used for automatic control of street lighting. Here also the switching device is relay K1. The FSK-G1 photoresistor with resistors R4 and R5 is connected to the base of transistor VT1.
Power is supplied from a single-phase network of 220 V. When the illumination is low, the resistance of the 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 turned on and its operating contacts are closed, keeping the lighting lamps lit.
When the illumination increases to the threshold, the resistance of the photoresistor decreases and the transistor switch opens , after which the relay K1 is turned off, opening the lamp power circuit.
2. Types of photo relay
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 supplied;
- Suite 2 - a device with high reliability and quality level;
- photo relay with a power supply of 12 V and a load of not more than 10 A ;
- DIN rail mounted module with timer;
- IEK devices of a domestic manufacturer with high quality and functionality;
- AZ 112 - machine with high sensitivity;
- ABB, LPX - reliable manufacturers of devices of European quality.
Methods for connecting a photo relay
Before purchasing a sensor, it is necessary to calculate the power consumed by the fixtures and take with a margin of 20%. With a significant load, the street photo relay circuit provides for the additional installation of an electromagnetic starter, the winding of which must be switched on via the photo relay contacts, and the load must be switched by power contacts.
For home, this method is rarely used.
Before installation, the voltage of the power supply ~ 220 V is checked. Connection is made from a circuit breaker. The photosensor is installed so 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 photorelay connection scheme with other elements has acquired new functions. A timer and a motion sensor were added to the algorithm of actions.
It is convenient when the lamps automatically turn on when a person passes along the landing or along the path of the garden. Moreover, the operation occurs only in the dark. Due to the use of a timer, the photo relay does not respond to headlights from passing cars.
The simplest connection scheme for a timer with a motion sensor is serial. For expensive models, special programmable schemes have been developed that take into account various operating conditions.
Photorelay for street lighting
To connect the photo relay, the circuit is applied to its housing. It can be found in the documentation for the device.
Three wires come out of the device.
- Zero conductor - common for fixtures and photorelay (red).
- Phase - connects to the input of the device (brown).
- Potential conductor for supplying voltage from the photorelay to the fixtures (blue).
The device operates on the principle of interrupting or switching on the phase. Color coding may vary by manufacturer. If the network has a ground conductor, 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 just need to bring power to it.
Variants with a remote sensor are used when it is convenient to place the electronic filling of the photo relay in the control panel with other devices. Then there is no need for an autonomous installation, pulling out power wiring and maintenance at altitude. The electronic unit is located indoors, and the sensor is carried out.
Features of the photo relay for street lighting: scheme
When installing a photo relay on the street, several factors must be taken into account.
- The presence of a supply voltage of ~ 220 V and the correspondence of the power of the contacts and the load.
- Do not install appliances near flammable materials or in aggressive environments.
- The base of the device is located below.
- There should be no swaying objects in front of the sensor, such as tree branches.
The wires are connected through the junction box for the street. It is fixed next to the photo relay.
Photo relay selection
- The ability to control the threshold allows you to adjust the sensitivity of the sensor depending on the time of year or in cloudy weather. The result is energy savings.
- A minimum of labor is required when installing a photo relay with an integrated sensor element. No special skills are required.
- The timer relay is well programmable for its needs and operation in the set mode. You can configure the device to turn off at night. Indication on the device body and button control make it easy to configure.
Conclusion
The use of a photo relay allows you to automatically control the period of the lamp on. Now the need for the profession of a lamplighter has already disappeared. A photo relay circuit without human involvement in the evenings lights up the streets and turns it off in the morning. Devices can control the lighting system, which increases its resource and makes operation easier.