Solid State Relays vs Electromechanical Relays

Solid State Relays vs Electromechanical Relays

Now, let's compare these two types of relays.

Solid State Relays Electromechanical Relays

There is no physical contact inside the relay action. There is a phenomenon of physical contact inside, which is used for the activation of the relay.

Relays have no wear issues due to no physical contact Relays can withstand wear due to physical contact

Its longevity is high. it has a short lifespan

it provides higher efficiency it provides lower efficiency

more expensive cheaper

Small vibration High vibration

Due to their superiority, solid state relays have replaced electromechanical relays in many applications.

Design of Solid State Relays

solid state relay

External structure of solid state relay

The diagram shown here is the external structure of the DC SSR. You can see it consists of 4 ports/pins for connections. Ports 1 and 2 are output ports. Again, ports 3 and 4 are input ports. We need to provide 4 to 32 VDC at the input port. The relay activates when a given range of input DC voltage is supplied. Therefore, the LED on the relay lights up. This input voltage is also known as the coil voltage or pickup voltage.

After activating the relay, you can supply 24 to 480 VAC at the output port. Also, the current limit for a given relay is 16A. However, this value can be changed from one solid state relay to another. Now the load connected to the output port starts working.

In the case of AC SSR, you can provide AC voltage as input and DC voltage as output. Others are the same as the DC SSR in the figure.

How solid state relays work

Once the photodetector receives light from the LED, it is activated. So current starts to flow at the output.

Using this basic principle, it has been used in many applications such as zero crossing. The design or construction of the zero-crossing circuit diagram is shown in the following figure.

Advantages of SSR

Solid state relays have many advantages. Some of them are as follows.

Not subject to wear and tear.

A higher service life has been achieved.

very effective.

Since there is no physical contact inside, no vibration of any kind occurs.

Features higher switching capability with 1 microsecond on time and 0.5 microsecond off time.

It requires low power consumption to operate (5 mA at 5 VDC).

Can operate in various modes, such as zero adjustment, instant start, etc.

Since it can operate from a small voltage input, it can be used in many applications from heaters to microcontrollers.

Disadvantages of SSR

Although this relay is superior to traditional relays, it also has some disadvantages. Some of them are as follows.

The voltage drop across the relay is the source of heat generation. So you may need to add a heatsink at the same time as the solid state relay.

Leakage current may occur even when the relay is closed.

It's quite expensive.

Typically, a single relay provides the opportunity to make a single contact with the load.

Even a small amount of input voltage can turn it on. Therefore, there may be risks at times.

test

There are several ways to check the condition of solid state relays.

You can only check solid state relays with a multimeter. For this, use a relay and a multimeter. Then set the multimeter to resistance mode. Now check the resistance of the input and output ports. In both cases, the result should be in megohms. Otherwise, the relay may be faulty.

You can supply voltage at the input port of the solid state relay. The relay's LED will then light up. That means it's activated and probably not faulty. Now, when activated, the resistance of the output port will decrease. You can check it by measuring the resistance. Resistance will drop from megohms to kiloohms.

The best way is to add load to the system. To do this, supply the appropriate voltage to the input terminals. Then connect the load to the output port and check the condition of the load.

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