What is a solid state relay used for?

In this article we are going to discuss about the Solid State Relay, which is mostly known as SSR, and especially their applications.
Solid-state relays are the semiconductor equivalents of the electromechanical relays, and therefore can be used to control electrical loads.
The solid-state relay is a fairly complex device, but it has a simple purpose – to activate a single output load when energized. They are efficient and effective at the job, allowing in some cases, extremely large loads to operate with very precise control voltages.

In our last blog article we have mentionned the key advantages of using Solid State Relays. For large load devices like heaters and motors, solid-state relays can be a huge advantage over traditional mechanical relays. To sum up Solid-state relays are the preferred option when very precise high-speed switching ; they are efficient, and have a long operational life. So you clearly understand that SSRs are the way to go for many applications, we will discover which ones.

First we will discover the types of load applications, and then we will see in which industries you can find Solid State Relays.

1-Load Types

There are hundreds of possible uses for Solid State Relays. Most can be categorized into the following type of load applications :

Heating Elements

« Heater Load » is also known as « Resisitive Load ».

Solid State Relays enable high-precision, high-frequency temperature control. Heating control applications include :

  • Commercial food processing machines
  • Plastic injection molding / extrusion
  • Furnaces
  • HVAC
  • Textile
  • Residential heating
  • Infrared heating
  • Drying
  • Thermoforming
  • Soldering equipment

A resistive load has no inrush current. The SSR is generally used together with a pulse-voltage-output in temperature controller for heater ON/OFF switching. When using an SSR with the zero cross function, most generated noise is suppressed.

To know more ….

Motor Starting

An electric motor is an « Inductive Load ». Motor control applications include :

  • Pumps
  • Compressors
  • Conveyor systems
  • Fans
  • Elevators
  • Lifts
  • Hoists

When a motor is started, an inrush current of 5 to 10 times the rated current flows and the inrush current flows for a longer time than for a lamp or transformer. In addition to measuring the startup time of the motor or the inrush current during use, ensure that the peak value of the inrush current is less than half the inrush current resistance when selecting an SSR. The SSR may be damaged by counterelectromotive force from the motor. Be sure to install overcurrent protection for when the SSR is turned OFF.

If you have an inductive load such as an electric motor, this can cause a large transient voltage spike when you turn off the relay, as the magnetic field surrounding the inductive load collapses. Switching a relay during a peak in the mains voltage also causes an electric arc between the relay terminals, wearing them down and contributing to the mechanical failure of the relay.

When using an SSR that supports zero-crossing detection, it will maintain its state until the AC output waveform crosses zero on its own. At that point it turns on or off safely.

To know more …


Lighting applications include :

  • Municipalities
  • Cinemas and Theaters
  • Airport runways
  • Streets and roadways lighting
  • Office spaces

A large inrush current flows through incandescent lamps, halogen lamps, and similar devices (approx. 10 to 15 times higher than the rated current). Select an SSR so that the peak value of inrush current does not exceed half the inrush current resistance of the SSR. Refer to “Repetitive” indicated in our data-sheets. When a repetitive inrush current of greater than half the inrush current resistance is applied, the output element of the SSR may be damaged.

To know more

Other Loads

Solid State Relays are also used to control other loads such as :

  • Power transformers
  • Electromagnets
  • Switching power supplies
  • Regulators
  • Inverters
  • Power converters
  • Uninterruptible power supplies
  • Power factor correction capacitors
  • Solenoid Valves

2- The industries we supply

Solid State Relays are therefore used in various sectors of activity.

Food & Beverage

The number of switching cycles in food and beverage equipment is quite substantial and a reliable switching solution that guarantees a long, maintenance-free lifetime can be provided only with solid state relays. Further more Food & Beverage processes demand components capable of working in harsh environments and conditions.

Celduc’s SSRs are used in Coffee and Vending machines, Heating and cooking equipments, cooling and refrigeration systems, culinary preparation equipment …

To know more …

railway-industry-celducRailway Industry

Celduc’s solid state relays offer long-term reliability and safe signal transfer even in the most demanding industrial conditions, such as railway applications. Celduc has been a reliable and experienced partner in the rail industry for many years.

In this market segment, our Solid State Relays are used for:

  • HVAC (Heating Ventilation Air Conditioning)
  • High voltage floor heating
  • Compressors for hydraulic or pneumatic braking
  • Wheel greasing compressor
  • Switch point heating
  • Railway signalling

To know more …

Plastic Industry

Plastics and its transformation processes have always been one of our primary sectors. New products development, as well as an innate approach to serving customers, have made celduc the leader on a global and constantly more competitive market.

In plastic processing, accurate temperature control is essential in order to determine the quality of the final product. With our integrated back to back connected thyristors and TMS² technology (direct bonded copper substrate), celduc relais’ SSRs provide an extremely robust switching solution for plastic processing equipment manufacturers.

Our solid state relays are installed in Extruders, Injection Moulding Machines, Blow Moulding Machines, Recycling Machines, 3D printers, granulate dryers as well as dehumidifying dryers…

To know more …

Packaging Industry

Packaging optimization is central in the supply chain. Many sectors like medical and food industries are very dependent to the packaging industry which has a very important role to play, and many challenges to face.

celduc® relais is a well-established partner to the pakaging industry, we offer a wide range of Solid State Relays to meet the requirements of this strictly regulated market. Major actors of the industry trust us.

To know more …

Medical & Healthcare

celduc Solid State Relays (SSRs) are utilized in numerous medical applications. They are used, for example, to control motors in hospital beds, examination tables, and rehabilitation equipment. SSR’s are also widely used for heating controls in sterilization equipment, blood warming units, and incubators.

To know more …

Electronics Industry

The electronics industry is today one of the largest global industries. celduc® relais supplies equipment to manufacture photovoltaic cells, for the semiconductors manufacturing process and components manufacturing process requires Solid State Relays for controlling the required temperature.

To sum up, for all the equipment used for the manufacturing processes in the electronics industry, Solid State Relays are the perfect solution because they can operate in harsh environments and are extremely reliable.

To know more …

HVAC in Buildings

HVAC means Heating, Ventilation, and Air Conditioning. HVAC units are systems to regulate the flow of air, heat, and ventilation in a building.
HVAC applications demand high efficiency. They require system architectures and specific products that offer advanced controls and also guarantee energy efficiency.
celduc offers a wide range of Solid State Relays and customized solutions that satisfy the demands of all types of customers for heating, ventilation, and air conditioning. As for example celduc is offering three-phase power controllers SWG8 to be used for temperature controller in buildings.

If you need any assistance for selecting the right product for your application, contact our technical team.