Advantages and disadvantages of relays

Relays are used as interface modules. They perform different tasks. Using relays has advantages and disadvantages. Let’s check them one by one.

Advantages of relays

Whether switching, separating, amplifying, or multiplying relays perform different tasks in industrial control applications. They have specific characteristics and they are available in almost innumerable varieties on the market. Relays have many benefits for the systems and users. Some of them are:

Simple and effective operation

The operating principle of a relay is really simple. The current flowing through the coil of the relay creates a magnetic field that attracts a lever and changes the switch contacts. Thus, it allows controlling a device remotely. A relay is activated with a low current; however, it can switch large circuits with a small amount of energy.

Circuit multiplication

Relays can switch many contacts at once. A single voltage signal may be used to simultaneously perform up to four different switching operations. Each output contact of a relay can be used to switch load circuits with different voltage and current levels.

Galvanic isolation

Relays are excellently suited to ensure safe galvanic isolation. Relays separate control circuit from load circuit. Even in case of failures, flash-overs between contacts and coil are rare. Relays are not only a control device but also a safety device.

Voltage conversion

Relays allow for small voltage signals to switch much larger loads. For example, a 24 V DC 10 mA signal can be used to switch a 230 V AC 16 A load. Larger loads can be controlled with a small amount of energy.

Accessory options

The complete relay body comprises a pluggable interface relay, socket, holder, and/or functional module. Each accessory has different functions and this helps to increase the performance of the relay.

For example

An effective contact protection circuit can increase the service life of the contacts by 5 to 10 times compared to inductive loads that are not or unfavorably protected. The freewheeling diodes are preferably suitable for this purpose.

AC or DC contact switching

A wide variety of relays may be used for switching AC or DC loads. They can be used for both ac and dc systems for the protection of ac and dc equipment. Besides, relays are offered across a wide spectrum of coil voltages, with a variety of optional function modules. Warehousing and logistics play an important role in the assessment of total costs. With relays, you can significantly reduce your logistic expenses. For example, by using products with multi-voltage inputs, you can reduce the width of your stock.

Compact size and low cost

The relays combine lower cost with higher value and performance by offering essential functions in space-saving housing. Despite rising raw material prices, they are still very inexpensive and can be easily integrated into a wide variety of circuit types.

Terminal connection

A variety of sockets are available for relays to meet the needs of different applications such as vibration-intensive environments. The space-saving design and different connection terminal possibilities optimize your panel installation. There are many terminal connection options available such as screw, spring, and fork type.

Some special relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.

Easy to install and troubleshoot

Relays are easy to mount by snapping onto a DIN-rail. You can also use jumper bars to make your connection easier. Troubleshooting usually requires isolation or removal of the component, and a bench setup to verify operation. Many models of the relay have a switch on the top that allows the technician to switch the contacts on and off, even with no power to the coil. This can isolate problems to either the input or output side instantly, never requiring a single wire to be removed.

Led indication and test button

Relays indicate the position of the contacts via an optional led module. The switching state is partially visible to the naked eye. Some type of relays has an optional test button. When the test button is pushed, the contacts operate. When the test button is released, the contacts return to their former state.

High resistance

Relays have a high resistance to voltage transients. With RC modules, voltage peaks are compensated via a capacitor. Besides, they can withstand short-term overload on both input and output sides without losing functionality.

Maintenance-free and long lifespan

Regardless of the application and environment, maintenance and repairs are unavoidable and must be carried out at regular intervals. With relays, you can considerably reduce the required effort. This makes work easier, faster, more cost-effective, and safer. The electrical lifetime of a high-quality relay is around 1 million operating cycles. It is long compared to other switching devices. But in rapid switching applications, the lifetime of the relay decreases. This should also be considered.

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Disadvantages of relays

Relays have some drawbacks for the users and systems. Some of them are:

Contact wear

Due to their design, relay modules are subject to mechanical and electrical wear, which must be taken into account when relay circuits are set up.

Used only low current applications

Relays are suitable for control voltages from 12 V to 230 V (generally), as well as for switching currents from 6 A to 16 A, and therefore they cannot be used for switching high currents like contactors.

Humming

They generate a lot of noise with the activation and deactivation of the contacts. Humming could be disturbing if you use lots of relays in your automation panels.

Low speed of operation

Relays cannot switch rapidly. Operation speed for a relay is limited by the mechanical inertia of the component. Their response time and switching cycles are lower than transistors.

Change in characteristics due to aging

Relay operation can be affected due to aging of the components and dust, pollution resulting in false trips. As time passes, the springs and the components inside the relay grow weak.

Poor performance in high inrush currents and microelectronic circuits

Relays cannot withstand high inrush currents as contactors do. The performance of the relay decreases when switching high inrush currents.

The coil of a relay needs a fairly high current to energize. High coil consumption is a disadvantage in some microelectronic circuits because these circuits can’t drive them directly without additional circuitry.

Low performance in vibrated environments

Many relays are designed for industrial operation and claim high-performance ratings. Circumstances in railway vehicles differ greatly from typical industrial applications, though. Extreme vibration, frequent and wide temperature cycles and oily, corrosive, and damp environments are all stress components, including relays. This may result in a disappointing performance when industrial relays are used in vehicles.

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