Electromechanical Relay vs Solid State Relay: Which Should You Use?

Relays are electronic components that act as electrically operated switches and are essential in the operation of most of the electronic devices we use every day, such as cars and computers. 

There are different types of relay and people have been discussing whether electromechanical or solid state relays are better for some time now. However, there isn’t a clear winner for use in all situations. Here are the facts concerning the electromechanical relay vs solid state relay debate.

 

What is an electromechanical relay?

There are several different types of electromechanical relay (EMR) for use in different situations, but all of them operate as a switch to complete or interrupt a circuit. This is achieved through the physical movement of the armature opening and closing, with a set of electrical contacts that transfer the power. They are used in many modern household appliances but also in aerospace, aviation and wireless technologies.

 

Advantages and disadvantages of electromechanical relays

Many EMRs come with multiple poles and therefore have the ability to control multiple circuits simultaneously, as well as being able to switch any AC or DC load up to their maximum rating. EMRs are effective at controlling large power loads as well as operating at full load across a range of temperatures. Unlike SSRs, they also do not need to be mounted on heat sinks, as higher loads reduce the resistance between contacts.

EMRs are best where heavy surge or spike voltages are anticipated as they won’t short like an SSR. They are also the best choice when used in a circuit that must be completely off when not in use.

On the other hand, because EMRs arc when they interrupt a current, they may cause the failure or malfunction of any nearby devices or equipment that is sensitive to radio frequency interference. They can also cause electromagnetic interference to sensitive equipment if it is installed close by.

 

What is a solid state relay?

Solid state relays, or SSRs, aren’t technically relays (they are electronic circuits) but they perform the same function as a relay. They have no moving parts but instead use semiconductors to switch between an ‘on’ and ‘off’ state. The most common type of SSR is the zero-switching SSR, which turns on the load when the voltage is applied and exceeds the set threshold. When the voltage is removed and falls below, the load is turned off.

SSRs are commonly used in many of today’s electrical devices as they can handle much higher levels of voltage than earlier models. They may also be used for phase-controlled applications such as event lighting and motor speed controls.

 

Advantages and disadvantages of solid state relays

One of the advantages of SSRs is that they have no moving parts, which means that their functionality is unaffected by external factors such as altitude, vibration or physical shock, ultimately making them more durable. They also don’t emit any noise which can be preferable in certain applications.

SSRs can also operate at a range of voltage levels whilst using relatively low power and they don’t produce any arc. This means that they are a better choice of relay for hazardous environments or ones where radio frequency interference could be an issue.

The downside of SSRs is that semiconductors are never truly on or off. When they are ‘on’, there is enough resistance that a significant amount of heat can be generated when the current is flowing. In order to counteract this, SSRs must be mounted on heat sinks and operated on a lower power when used in hot environments.

Another problem with SSRs is that, whilst they rarely fail, you may not know if they do. This is because SSRs can continue to conduct for a limited time after a surge or voltage spike has caused it to short.

 

Ultimately, the electromechanical relay vs solid state relay debate cannot be satisfactorily resolved. Each is suited to different types of applications. 

Whenever a relay is needed, several factors need to be considered, such as the amount of voltage that will be used, whether the device will be subject to movement or agitation, and what other devices will be in use nearby. The answer to these questions will point you more accurately towards either an EMR or SSR for that particular application.

You can take a look at our range of electromechanical components here.

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