Solid State Relays

What is a Solid-State Relay?

A solid-state relay is a special type of relay that utilize semiconductors. They provide the same basic function and use a small control signal in order to handle and control a larger current or voltage. They have a sensor that responds to the control signal and then switches power to the load circuitry.

Solid-state relays have a number of advantages and benefits. They have a very long life when used properly, since they have no moving parts. They work for millions of turn on and turn off cycles without wearing out. SSRs also do not have contract arcing. The SSRs are highly resistant to issues with shock and vibration as well. Since they have no mechanical movement inside, there is virtually no acoustical noise. This proves to be a great advantage for power cabinets that have several dozen relays in them.

Most of the SSRs require less power than a standard relay, and it is possible to control the voltages in AC or DC. AC output SSRs will allow for two different types of turn on responses – instantaneous and zero cross. The SSRs have a very fast switching capability too, and the fast response time has no appreciable contact bounce. Thanks to the speedy response time, yet another advantage is that the power to load can be applied and removed with great precision. This is something that the traditional standard relays with electromechanical switching simply cannot match.

These things, along with the fact that they integrate with Boolean logic for programmable controllers, computers, and digital circuits help to make them very popular as a form of relay. The SSRs are a reliable option.


How Does a Solid-State Relay Function?

The solid-state relay will require several different components. They need to have the input circuit. Each of the circuits works with a specific voltage range. They also need to have an optocoupler chip, which can provide voltage isolation and switching capacity between low and high frequencies. This works similarly to the armature in other types of relays. The solid-state relay also needs an output circuit, which will switch to either AC or DC voltage.

When choosing to use SSRs, it is important for people to identify the voltage they will be using and to know they need to switch AC or DC voltage. Determine the number of volts needed, as well as current. Always know what you need and what you are switching, otherwise the relay will not work properly, or not at all. It could cause safety issues as well.


What Are Solid-State Relays Used For?

Today, solid-state drives are a part of many different sorts of products and items. They are in transformers, heaters, motors, AC and DC power supplies, fluorescent light fixtures, computers, and many different types of consumer electronics.

Solid-state relays are quite useful in the area of heating control. The field of heating is actually the largest segment that makes use of these types of relays. Some of the most common applications include plastic molding and extrusion machinery, soldering equipment, HVAC, and professional food equipment. The SSRs are popular in this industry because of their long life and the fact that they do not require maintenance. They also have precise temperature control. These are common in blowers, fans, heaters, and with valve control.

SSRs are helpful for many types of lighting control as well, including commercial, warehouse, and theatrical. The control the SSRs offer is helpful for dimming and for fast switching. They operate silently, and again, the long life and no maintenance are quite beneficial.

Some of the other applications for SSRs are in motion control devices, such as elevators, fans, hoists, and even exercise equipment. The durability and shock resistance makes them ideal for these applications.


What Are the Various Parameters of Solid-State Relays and What Do They Mean?

·         Mounting Type – SSRs have various mounting types based on their usage. It is possible to mount them directly to a PCB, or to mount them to rails and even flat surfaces. Adapters are available to make mounting to different surfaces easier.

·         Terminal Type – this refers to the different types of terminals used with SSRs. They include modular terminal enclosures as well as plug-in bases for rail mounts, and more.

·         Maximum Load Current – the maximum load current refers to the maximum amount of current able to flow through a sensor and not cause it to fail or short circuit.

·         Minimum Load Voltage – the minimum load voltage refers to the minimum voltage that can flow through the relay and still cause it to trip and activate.

·         Maximum Load Voltage – the max load voltage refers to the highest amount of voltage that can flow through the SSR.

·         Minimum Control Voltage – the minimum control voltage is the lowest voltage at which a solid-state relay will turn on, and again, this varies depending on the SSR you are using.

·         Maximum Control Voltage – the maximum control voltage is the highest voltage that can go through the SSR.

·         Switching Type – Solid-state relays have a number of different switching types they can use depending on their purpose. Some of the most common include the zero-crossing, random turn on, and proportional control switching types. The zero-crossing type is the most common and refers to the switch from non-conducting to conducting. The random turn on type is asynchronous and they will switch on right after the application of the control signal. The proportional control type will give proportional power to the load.

·         Output Device – the output devices for solid-state relays vary. They can be digital with LED displays, or they could be simple housing with no moving parts. It depends on the nature and the function of the SSR in question.

·         Contact Configuration – the contact configuration varies with different sorts of SSRs. They can have a different number of contacts, and they may have different sorts of connectors, such as lug connectors with some SSRs.

·         Minimum Load Current – the minimum load current refers to the minimum amount of current that the sensor requires in order to continue operating reliably.

·         Maximum Turn On Time – this refers to the max amount of time that it takes for the solid-state array to turn on and work. The time is usually very short, measuring 3mSec or less in some cases.

·         Off State Leakage Current – other names for this include load current and residual current, and it refers to the amount of current required to keep a device in an active state while it is not actually operating. Different SSRs will provide varying off state leakage current.

·         Package Style – the package style refers to the type of enclosure for the SSR. The type and size of the enclosure or housing can vary quite a bit, but they tend to have a similar look to them. The size may change based on the size of the SSR, but most are relatively small.

·         Maximum Operating Temperature – the SSR and the accessories that go into the device have a temperature range in which those products can work. The maximum operating temperature is the highest temperature in which the SSR can work reliably. It is important to know the temperature range for the best results.

·         Minimum Operating Temperature – just as the SSR has a maximum operating temperature, it will also have a minimum operating temperature. If the temperature drops below this number, which could be as low as negative 30 degrees, the SSR or part may fail. It is in your best interest to know the temperature extremes the products used with the SSR can withstand.


What Kinds of Accessories are Available for Solid-State Relays?

·         Solid-State Relay Covers – the covers are available in different sizes and for different voltages, but most will work with AC and DC control. It is important to check the specifications to make sure the cover will work with the SSR you are trying to create. Keep in mind that the solid state relay covers do not generally come with a heat sink, which you will also need when you are dealing with SSRs.

·         Solid-State Relay DIN Rail Adapters – these adapters come in various shapes and styles in order to facilitate easier mounting and installation of SSRs. Many solid-state relay DIN rail adapters have DIN rail mounting options, as well as surface mounting options.

·         Solid-State Relay Filters – filters can help to control the output for heavy industrial loads. The filters are easy to install and use with most SSRs, but they do need to be compatible. Some of the solid-state relay filters allow for filtering of resistive loads and inductive loads. They primarily help with the suppression of noise.

·         Solid-State Relay Heat Sinks – a heat sink is a necessity for SSRs. The heat sink helps the device to cool down and continue working. The heat sink ensures that the temperature never exceeds the maximum operating temperature for the SSR as well as the device in which it resides. Solid-state heat sinks are available in different sizes so it is possible to find them to fit nearly any device and SSR. It is important to make sure the heat sink is large enough for the device.


·         Solid-State Relay Lug Terminals – the lug terminal is an electrical connector. With this sort of connector, the wire is held in place by tightening a screw. Solid-state relay lug terminals are a very simply type of connector.

·         Solid-State Relay Mounting Kits – the mounting kits for SSRs should come with all of the required parts and pieces necessary for installation. Different kits will work for different types and sizes of devices, so it is important to make sure you are working with the correct type of mounting kit. Solid-state relay mounting kits will generally include the resistor, input terminal block, housing, circuit board, profile extrusion, and screws.


·         Solid-State Relay Screws – the screws, which come with the mounting kits are also available separately. Solid-state relay screws affix to the mounting and housing pieces in order to install and keep the SSR in place.


·         Solid-State Relay Semiconductor Fuses – a semiconductor fuse is important to have in order to protect against overcurrent conditions in semiconductor devices such as SSRs. Solid-state relay semiconductor fuses have a fast action, which helps limit the possibility of short-circuiting. Remember that these are for helping stave of short circuits, but they are not a traditional type of current limiting fuse.


·         Thermal Transfer Pads – because SSRs have a tendency to heat up, even with the addition of a heat sink, using thermal transfer pads can be a good idea. These pads are great for dissipating heat. They can also minimize the heat resistance and will work with many temperature ranges. Thermal transfer pads are helpful for many different applications.