To make a solid-state relay with your own hands is possible even for a beginner radio amateur. There is nothing complicated in the design of this device, but you still need to understand the circuitry, application and connection features. A solid state relay is an element made on the basis of semiconductors. In its design, there are power switches on triacs, thyristors or transistors. These noiseless relays are a good replacement for contactors and starters. With their help, devices are connected more reliably and securely.
Simple relay circuit
In power electronics, it is often necessary to use a single or 3 x phase solid state relay. You can make this device with your own hands according to one of the schemes presented in the article.
The advantage of a solid-state relay over mechanical contactors is obvious - they have a much higher resource. And this is due to the fact that they do not have a single mechanical component, namely they are the most vulnerable.
For the manufacture of a solid-state relay, you can use chains consisting of a control circuit and a triac. Galvanic isolation is carried out by a triac optocoupler. The following elements are used in the scheme:
- Optocoupler type MOS3083.
- Triac VT139-800 16A with an anode.
- A limiting resistor that reduces the current passing through the LED.
- LED to indicate device operation.
- A resistor of 160 Ohms is connected to the control electrode of the triac.
And now let's look at the device manufacturing process in more detail.
Features of the manufacturing process
It is recommended that all circuit elements be enclosed in a metal casing so that cooling is much better. For reliability, you need to fill the box with a glue gun. The main thing at work is to choose the right metal substrate to ensure the best heat dissipation. For the manufacture of formwork is used, which is a solid-state relay DC. With your own hands it can be made from any material.
A plastic box or pipe section is ideal. It all depends on what size the product is. The metal substrate must be placed in this formwork. Carefully it is necessary to fill in with glue all elements of the circuit, openings in the housing to ensure high-quality insulation. Please note that in triacs, conclusions are usually ambiguously determined, so they need to be checked in advance. To check the opening of the triac, you must use a megger. As soon as the triac opens, the resistance will change from several tens of megaohms to 1-2 kOhm.
Solid State Relay Features
Regardless of the manufacturer of the solid-state relay, the element base is constant - in rare cases, slight differences can be found. A resistor is usually installed at the input, it is connected in series with an optical device. Sometimes resistance is made according to a complex design, which includes reverse polarity protection and a current regulator. It is necessary to highlight the following properties of solid-state relays:
- Using optical isolation provides isolation of various circuits of the electronic device.
- Using a switching circuit, it is possible to supply a load with a supply voltage.
- Using the trigger circuit, the input signal is processed and it switches to the output.
Industrial Design Siemens V23103-S2232-B302
The solid-state circuit is shown in the figure:
According to this scheme, a self-made solid-state relay can be fabricated quite quickly, without any difficulties. The main thing is to find the necessary components or analogues. Protection can be located either inside the relay housing or separately. Now you need to consider additional devices that must be used in conjunction with the relay.
Protective circuit features
As you can see, there are no difficulties in manufacturing. If you doubt your abilities, then it is better, of course, to purchase an industrial design of the device. You can highlight the key features of self-made relays:
- The control voltage is 3..30 V, direct current.
- It is allowed to connect 115..280 V sources to the output.
- The output power is about 400 watts.
- The minimum current at which the device operates is about 50 mA.
If the device is used for switching low currents (up to 2 A), then there is no need to install a radiator. But if the currents are high, a strong heating of the elements will occur. Therefore, you need to take care of cooling - install an additional radiator and cooler (if it is possible to arrange power for it).
Please note that when controlling asynchronous motors, you need to increase the current reserve by about 10 times. When starting, the motor “draws” current from the mains, which is several times higher than the operating value. For this reason, it is necessary to use power elements with a significant current margin.
Features and relay switching schemes
When making a solid-state relay on a field effect transistor with your own hands, it is important to take into account the parameters of the circuit in which it will be used. But let's, to understand the features of the operation of solid-state elements, consider conventional electromagnetic relays. In them, when voltage is applied to the winding, a magnetic field is generated. With its help there is an attraction of contacts.
In this case, the circuit either opens or closes. There is one drawback of such a mechanism - there are many moving elements in the design. Solid state ones do not, and this is the main advantage. You can also highlight the following features:
- Switching the load on and off only occurs when the voltage passes through zero.
- During operation, the appearance of electrical noise does not occur.
- A sufficiently large voltage range at which the device operates.
- Between control circuits and load, high-quality insulation.
- High mechanical strength of the product.
And even during operation, not a single sound is made - the semiconductor junction simply opens and closes.
Solid State Relay Connection Example
You know how to make a solid state relay yourself. Analogs of such a device are on sale quite often. You can use both amateur circuits and industrial ones - it depends on what opportunities you need to get from the device. With the help of such a device, the contact of the high-voltage and low-voltage circuits is ensured.
Most industrial devices and homemade products have a similar structure. The differences are insignificant, they do not affect the work in any way. It’s easy to make sure. The figure shows the simplest relay switching circuit:
Device structure:
- Optical isolation of chains.
- Trigger chain (may be several).
- Protective devices and switches.
- Inputs
An input is a primary circuit in which a constant resistance is established. The input function is to receive a signal and transmit the desired command to a device that performs load switching.
Optical isolation
Optical isolation is a device that isolates inputs and outputs. When signal processing arrives at the input, it is imperative to use a trigger circuit. This is a separate component, but sometimes it is included in the design of optical isolation. The switching circuit is used when it is necessary to supply voltage to the load.