With the help of photosensors built into certain electronic devices, it is possible to provide effective control of the light flux. In this article, a photorelay will be considered with your own hands: circuits, device and application.
Appointment
This device is designed to turn on lighting when it is dark and turn it off when dawn arrives. When assembling with your own hands, the photorelay circuit should include a phototransistor or photoresistor, which change their parameters under the dynamics of illumination. The power circuit is open as long as the required amount of light is incident on these devices. As soon as darkness sets in (its parameters can be set), the circuit closes. As morning approaches, the process goes in the opposite direction.
Specifications
A do-it-yourself photo relay circuit should provide for whether the light sensor will be used: built-in or remote. The latter is characterized by small dimensions, can be protected from the backlight and located in the shield. The photorelay equipped with the built-in sensor are located near the lamp. In this case, the light on the photocell should not have an effect. This option is acceptable for solar-powered luminaires.
Exploitation
The DIY photo relay circuit of 220 V or 12 V (voltage) provides that it depends on the latter, from which the street lighting is powered . The creation of this device should provide for its operation in various extreme conditions of the region of residence.
Housing protection must be at least IP23 for home and IP44 for street. The last protection class shows that water splashes and solid particles having a size exceeding 1 mm will not get into the case.
These specifications are relevant for industrial designs. It is quite difficult to achieve that the DIY photorelay assembled according to the scheme has the same characteristics. The maximum load power should be 20% more than the total load from those devices that are connected.
FR models
Before looking at the photo relay circuitry with our own hands, we will focus on the most popular industrial models - FR-601 and FR-602.
They are as simple as possible to connect even by an unprepared user and differ only in the maximum possible cross-section of the connected conductors, which also determines the differences in the rated load current (10 and 20 A, respectively). The photocell of these models is built-in, and is adjustable from 0 to 50 lux.
You can repeat such devices at home on your own. This is of greatest relevance if it is necessary to connect a large number of lighting devices. DIY photocell circuit is shown in the figure.
For manufacturing you will need:
relay SHA-24VDC-SA (Rel1);
photocell (PH, up to 100 kOhm);
bipolar transistors BC857A (2 pcs. Q1 and Q2 or domestic KT3107B instead of the latter);
resistors (R2, R4 – R9: 1.5; 1 MΩ, 560, 200, 100, 75 and 33 kΩ; power 0.125 W) and R3, 220 Ohm, 2 W;
tuning resistor (WL, 2.2 mOhm);
rectifier diodes 1N4007 - 5 pcs. and one 1N4148 zener diode 1N4749 or three connected in series D814A or two D814D;
capacitor (C2, 0.7 uF 400 V);
electrolytic capacitors (C4 – C5, 100 μF 50 V and 47 μF 25 V).
The disadvantages of self-assembled RF can be described as follows. From a technical point of view, this photo relay does not differ from the factory assembly. The main differences will be that it is very difficult to achieve the IP44 protection standard for the photo relay according to the scheme for street lighting with your own hands, which corresponds to the industrial design. The latter also has a larger operating temperature range. A home-made photo relay may stop working in the cold if even one connection is made poorly.
High power devices
These include the FR-7 model. It does not have moisture protection, the power consumption is quite high, the contact clamps are open, and the trimmer resistor located on the front panel has no protection. However, this device can work in networks with a voltage of 220 V. A specialist can set the adjustment to 10 lux, since it is very difficult to achieve this independently.
Self-locking alarm photo relay
It can be used as a light detector. If there is no light on the photoresistor PR1, the HL1 LED lights up. This helps to control the security zones of a building or summer cottage. As long as PR1 is lit, it has a small current resistance, which is constant, and the voltage drop does not lead to the unlocking of the thyristor VS1. When the flow of light going to the photosensor is interrupted, the resistance of the photoresistor increases to 1-5 MΩ, in this case, the capacitor C1 will receive energy from the power source, which contributes to the unlocking of VS1 and, as a consequence, the inclusion of the LED.
Thus, in a do-it-yourself photorelay circuit, switching on when dark is provided. Returning the device to its original state is carried out by button S1. Instead of the above LED and the limiting resistor R2, analogues can be used - low-power EM relays having a response current of 15-30 mA.
A substitute for the thyristor brand under consideration can be similar devices of the KU101 series. The PR1 photo relay includes two SFZ-1 photoresistors connected in parallel. Models of capacitors used: C1 type MBM or other similar. LEDs and button S1 can be used by anyone. Fixed resistors are used type MLT-0/25.
Photorelay with universal timer
This device is automatic and can be operated in any settlements, as well as in household plots. Contact with a photoresistor or two SFZ-1 devices connected in parallel for better sensitivity even of weak natural light closes the transistor VT1. As the illumination of their working surface decreases, the resistance between the emitter of the transistor and the base reaches values exceeding 100 kOhm.
The transistor opens at low resistance between the positive terminal of the supply source and the base VT1. Relay K1 is activated, which helps to connect the output of the thyristor anode to the pole with a positive charge in the supply source. Next, the DA1 KR1006VI1 timer is connected with a voltage of 10.5 V installed at the output. It is possible to connect low-power relays to the DA1 output without using a key transistor cascade.
Relay K1 is activated, due to which the lamp HL1 is kept on. Thyristor analogs - KU101A-KU101G, KU221, regardless of the letter. Analogs of the transistor VT1 are KT312A, B, C and others in electrical characteristics. At the same time, its current gain h21e should not be less than 40. The response current of the relay is 15-30 mA at a voltage of 12 V, that is, it must be low-power.
Types of fixed resistors MLT-0.125. Types of capacitors C1 KM, C2-K50-20. In this case, the operating voltage must exceed 16 V. Using the diodes VD1, VD2, the transition of the transistor VT1 and the output of the DA1 chip are protected from sudden fluctuations in the alternating current, which prevents the relay contacts K1 and K2 from bouncing when they trip. The first can be replaced by others included in the KD522 series.
The last two circuits do not require special supply voltage, they can work with low-power relays, with transformerless and transformer stabilizers having an output voltage of 10-16 V.
Finally
As can be seen from this article, there are various do -it-yourself photorelay schemes . They can operate with a voltage of 12 V, as well as 220 V. You can create your own devices that are not inferior in technical characteristics to the quality of industrial designs. The most difficult thing is to achieve the same level of protection.