The evolution of the SSR: From the hockey puck to the 22.5mm relayFollow article
Since their appearance in the early 1970s, solid state relays (SSRs) have been steadily evolving, covering an ever wider range of applications, from the industrial and commercial sectors, up to highly demanding applications in the transportation, aerospace and defense markets. There are several well known benefits of solid state switching technology that make SSRs better suited than electromechanical devices on certain type of applications, the following being just a few of them: no mechanical wear (which translates into a longer life expectancy), no electrical arcing, quiet operation, low power consumption, high resistance to shock and vibration and fast switching (for better process control).
Even though there are no actual standards that specify the mechanical layout and dimensions of solid state relays, there are several housing styles that have become industry standard, and most SSR manufacturers today produce relays in at least one of these housing styles. These different package styles allow the SSRs to be mounted in several different ways, depending on the preferences and the space availability of the user, such as: panel mount, DIN Rail mount, PCB mount and plug-in mount.
SSR package styles
The “hockey puck” package
The most common package style of SSR, introduced by Crydom in the early 1970s, is the panel mount type popularly known as “hockey puck”, being a rectangular block of roughly 1.8”x 2.3” that is mounted on a flat panel by using a couple of screws. This package has been extremely popular because it can be easily mounted and it can handle currents ranging from less than an Amp up to 125 Amps (when mounted on a suitable heatsink).
Typical “hockey puck” SSR
As control panels continue evolving there is an increasing need for a higher density of components, which means to have more devices in a smaller space. This has translated into a growing popularity of 22.5mm wide switching devices, in both DIN rail mount and panel mount package styles, allowing a higher number of relays, when compared to standard hockey puck SSRs, to be mounted in a panel or on a heatsink. This is very practical when the current to be switched is not very high or when not all the SSRs are switched on at the same time.
The new 22.5mm relay from the market leader
Crydom, being the global expert in solid state switching technology, is constantly looking to improve upon the performance of their products in order to offer the best switching solutions to an ever demanding market and recently launched the NOVA22 family of Solid State Relays, a brand new line of 22.5mm wide relays. Due to the improved features and capabilities we can consider the NOVA22 to be the state of the art 22.5mm Solid state relay in the market. We will refer to this SSR family in order to show the possible types of connections as well as the benefits that this type of package can offer.
Available in AC and DC output versions, these Solid State Relays offer versatility and enhanced power capability in 2 mounting package styles, DIN rail and Panel mount.
DIN Rail Mount. DR22 Series SSRs are available with AC or DC output and current ratings up to 35 Amps at 40°C, which make them the only 22.5mm DIN rail mount SSRs in the market today with such current capability.
DIN rail mount
Even though there is a great demand for DIN Rail mount relays, panel mounting is still the most popular mounting type for SSRs, especially for higher current ratings. NOVA22 panel mount aka PM22 SSRs are available with AC output and current ratings up to 95 Amps, which make them the 22.5mm panel mount SSRs with the highest power density in the market.
Terminal Layout Configurations
In order to allow for greater flexibility when wiring into the relay, the NOVA22 family offers two different layouts for the input and output terminals.
Relay configuration. This is the configuration most typically found on solid state relays, where you have the control terminals on one side of the relay and the output terminals on the other side of the relay. This configuration allows the separation of the control and power wires, one on each side of the relay.
Contactor configuration. This type of configuration has become increasingly popular in the case of power relays. In this configuration you have one output terminal on one side of the relay and the other output terminal on the other side, with the control terminals commonly placed one next to the other in the middle of the relay. The main advantage on this configuration is that it allows to have greater wire size capability on the same package, This allows, in most cases, the direct attachment of the wire to the relay, without the need of an additional accessory (lug terminal, pin terminal, etc.). The Contactor configuration also allows greater flexibility on the wiring of the control terminals due to the use of a plug-in connector.
NOVA22 solid state relays, depending on the terminal layout, offer several types of connecting terminals. In the case of SSRs with the Relay configuration, the terminals are standard screw type with v-shaped clamp, with capacity to connect 1 or 2 wires from 18 AWG up to 12 AWG sizes, either solid or stranded.
Input terminals, Relay configuration
In the case of SSRs with Contactor configuration, there is much more flexibility when it comes to terminal styles available. These relays come with a plug-in connector, available with 2 different styles of terminals:
Standard screw terminals with box clamp, with capacity to connect wires from 30 AWG up to 12 AWG sizes.
Plug-in input connector with screw terminals
Spring cage terminals, with capacity to connect wires from 26 AWG up to 12 AWG sizes.
Plug-in input connector with spring terminals
Having a removable connector for the control terminals allows for a quick and easy installation and replacement. It also allows the end user to use other connectors, with different configurations from the 2 offered by Crydom, should he desire to do so.
SSRs with Relay configuration come with standard screw terminals with v-shaped clamp, with capacity to connect 1 or 2 wires from 18 AWG up to 10 AWG sizes, either solid or stranded.
Output terminals, Relay configuration
SSRs with Contactor configuration have the same flexibility with regard to the input terminals, they also though provide additional flexibility for the output terminal connections. NOVA22 relays with Contactor configuration are available with 2 different styles of output terminals:
Standard screw terminals, similar to the output terminals on the Relay configuration but with capacity to connect 1 or 2 wires from 20 AWG up to 8 AWG sizes, either solid or stranded.
Standard screw terminal, Contactor configuration
“Elevator” screw terminals, with capacity to connect 1 or 2 wires from 20 AWG up to 8 AWG sizes, either solid or stranded.
“Elevator” screw terminal, Contactor configuration
The “elevator” screw is a proprietary patented design that allows the screw and clamp to be raised out of the mating threads completely. This provides for the insertion of a ring or lug type terminal. This innovative feature makes a true IP20 (finger-touch safe) termination possible when using such rings or lugs as the cover does not have to be removed.
Internal view of “elevator” screw terminal
More about NOVA22
The advanced design and technology used in NOVA22 products, as seen above, along with their innovative features and wide range of options and configurations make it the most versatile and the highest performing 22.5mm SSR in the market today:
- Ratings of 20, 30 and 35 Amps on DIN Rail mount models, and 25, 50 and 95 Amps on Panel Mount models.
- Current regulated inputs with 3 available control ranges in order to cover most control voltages used: 4-32 VDC, 90-280 VAC/DC and 18-52 VAC/DC.
- Relay or Contactor terminal configurations, to allow for greater flexibility when wiring inside a panel.
- Innovative “Elevator” screw for easy connection of ring or lug terminals (patented design).
- Internal overvoltage protection on AC output models
- Zero voltage or instantaneous turn-on output options, to cover applications with resistive or inductive loads.
- Fast switching circuit on DC output models which allows them to handle a PWM frequency of up to 1 kHz.
- 100 kA Short Circuit Current Rating, when coordinated with suitable semiconductor fuses.
- Maximum I²t rating of 8320 A²s, which provides greater flexibility when selecting an overcurrent protective device and allows the use of circuit breakers instead of semiconductor fuses for the protection of the SSR itself.
- High resistance to surge current: up to 1350 Amps peak for 1 AC cycle.
- Broad operating temperature range: -40°C to +80°C.
- High resistance to shock and vibration: tested up to 50g and 500 Hz, per standard IEC 60068-2.
- Plug-in input connector on Contactor configuration models, available in 2 options: standard “screw” or “spring” terminals.
- All the models are C-UL-US Recognized according to UL508 standard, while the Contactor configuration models are C-UL-US Listed, which makes them ready-to use devices.
- AC output models are also TUV certified according to EN 62314.
All these features make the NOVA22 a unique product in the market, suitable for a wide range of applications.
Co-Authors: Alessandro Bosio & Jesus Miranda.
Last Reviewed on 06/27/16
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