The most widely used solid-state relay found in industry. Here it is used to create equipment that should be small and reliable. The abbreviation in Cyrillic looks like TTR, and in Latin SSR. The main disadvantage of these devices is called the price. But within the framework of the article, we will talk exclusively about the features and advantages that a solid-state relay has.
The principle of work and construction
Let's first look at how a regular relay works. It is a device in which there are contacts and a control coil. For the device to work, we need a voltage with which it will be affected. It will cause the contacts to open or close while it is being fed to the coil. A solid state relay works in a similar way. Only instead of contacts,
semiconductor devices are used. The most common are triacs, thyristors (to switch
alternating current) and transistors (for direct). Solid state relays also use
galvanic isolation between the voltages on the power contacts and the coil. This is achieved due to the presence of an optocoupler at the input. If the functional is implemented through thyristors and triacs, then they say that we have solid-state AC relays.
Comparison
In general, each key transistor can be represented as a solid state relay. Let's recall how most motion or light sensors work. After all, they are created according to the principle according to which a transistor supplies voltage to a conventional relay. Coil and semiconductor element as contact. As for the use of triacs and thyristors, they can pass current in both directions (which is not available to the transistor). If we continue our comparison further, it is worth noting that solid-state relays are consumed and much less energy is lost during operation. They also have small dimensions, high speed, long service life and absolute noiselessness. But, despite all the advantages, it is impossible to say that we can refuse conventional relays in the near future.
Intraspecific differences
There are solid state relays:
- Three-phase current commutates in the range from 10 to 120 Amperes immediately in 3 phases.
- Reversible. Semiconductor devices that can conduct non-contact switching of direct and alternating currents. By their main task they coincide with single-phase relays. There must be a control circuit that provides protection against false switching. Reversing relays are characterized by three-phase operation and a long service life. This is possible thanks to the high-quality control and isolation mechanism that are provided constructively for this type of device. When operating these devices, there is no acoustic noise, bounce when switching and sparking.
- Single-phase provides switching current when it passes through zero. The solid-state single-phase relay operates in the range from 10 to 500 Amps. Management can be done in four ways.
Areas of use
Solid state relays are used where it is necessary to adhere to the principle of installed and forgot about it. For comparison, consider an example. But before that, we consider an excerpt from the instructions for ordinary contacts: even the manufacturer recommends cleaning them after several thousand cycles of closures.
But now about an example. The company has a machine on which solenoid valves are installed . Food on them - 24VDC 2A. They are connected in parallel. Turn off / on about once per second. Power is supplied via a relay. Even if it can withstand 10 amperes of inductive load, then it will be necessary to change it once a month or a second. While a solid-state relay will forget about it for years. Although the conduct of the planned technical inspection has not been canceled. In this regard, it is advisable to focus on the recommendations received from the manufacturer in the accompanying documentation.
Indications for use
If ordinary contacts do not cope with their duties, burn like candles, then this is the best recommendation for use. Solid state relays can provide reliable performance. They can easily handle commutation of inductive loads. Also, if you need to make sure that the contacts do not stick, or if there is a strict size limit, solid-state relays will come to your aid.
What types of solid state relays are there?
They are divided by their device, as well as the principle of operation. For ease of understanding, I propose the following classification:
- Depending on the type of control voltage:
- Constant (discrete).
- Variable.
- Depending on the type of switched voltage:
- The variables.
- Permanent.
- Depending on the number of phases of alternating voltage:
- Solitary.
- Triple. There is still the possibility of dividing by the presence or absence of a reverse.
- By design features (where installation is carried out):
- On the surface.
- On a DIN rail.
Choosing a Solid State Relay
Some features should be noted. So, conventional relays can withstand short-term overloads without any problems, the value of which will be 150% or even 200% of the nominal value. If everything is done correctly, then cleaning contacts can be dispensed with in all cases. With a solid state relay, this is not possible. So, if you exceed the figure by 150%, you can safely discard the device. Therefore, for an active load, a margin of 2-4 times should be provided for at rated current. If a solid-state relay will be used to start induction motors, this figure will need to be increased by 6-10 times. Such a reserve, although it makes us choose more expensive parts, at the same time allows us to guarantee a long service life of the device to which the device is connected.
Add-ins for correct operation
When interacting with inductive load, structures can function with certain problems. Therefore, when working with transformers, electric bells, coils with magnetic circuits and similar devices, it is necessary to turn on the RC circuit in parallel to reduce the effect of counter-EMF. It will also reduce the overall inductance of the load, and the solid state relay will be easier to operate.
Short circuit protection
Manufacturers in this case recommend the use of special fuses, which were developed for solid-state devices. Here is their classification:
- gR - fuses operating with the entire range of operating currents. They are used to protect semiconductor elements. They are considered very fast.
- gS - work with the entire range of operating currents. Used when the line is experiencing increased load, as well as as protection for semiconductor elements.
- aR - fuses that work with the entire range of operating currents. Used to protect semiconductor elements from short circuits.
It should be noted that fuses are quite expensive. Therefore, as an alternative, circuit breakers are used (class B).
Where can I get it?
You can buy AC solid state relays at your local electronics store. But this applies, as a rule, to those cases when the place of residence of the reader is a large city. If this is not the case, you can recommend using the services of online stores. They usually provide delivery to the recipient for a certain amount or free of charge.
And what can we say directly about the cost that a solid-state relay has? The price of these devices ranges from 600 rubles to several thousand.
Solid State Relay Connection
There is nothing complicated in this action. So that the device works, the input, observing the polarity, it is necessary to apply a control voltage. Let's talk about the features of this process:
- Connections are preferably carried out by screw, rather than by soldering.
- To avoid damage to the device, it is necessary to check the absence of dust, as well as elements of metallic nature.
- Try to do everything possible so that there are no unacceptable external influences on the device case (both during operation and in the off state).
- Do not touch the relay while it is operating, to avoid burns. Also check that the device is not located near flammable materials.
- When connecting, make sure that the correct connection is made.
- If the device heats up more than 60 degrees during its operation, it is necessary to get a cooling radiator for it.
- Care should be taken not to cause a short circuit at the output of the device. In the opposite case, it simply fails.
Solid state relays can be directly controlled using a circuit in which various options are provided. It is mounted on the plus-entrance.
Conclusion
We examined the solid state relay, the principle of operation, control, types, protection - everything that matters. Of course, this is not enough to independently install such a device in most cases.