The SSRL series of solid state relays are used to control large
resistance heaters in conjunction with temperature controllers. Solid
state relays are SPST, normally open switching devices with
no moving parts, capable of millions of cycles of operation. By applying a
control signal, an SSR switches ON the ac load current, just as the
moving contacts do on a mechanical contactor. Three-phase
loads can be controlled using 2 or 3 SSR’s. Use 3 SSR’s for Y or star
3-phase loads using a neutral line. Two SSR’s will control “delta” loads
with no neutral line. Three solid state relays are also used when
there is no neutral load to provide redundancy and extra assurance of
control.
"Switching" takes place at the zero voltage crossover point of the
alternating current cycle. Because of this, no appreciable electrical
noise is generated, making SSR’s ideal for environments where there
are apparatuses susceptible to RFI.
Common Specifications Operating Temperature: -20 to 80°C (-5 to 175°F) Storage Temperature:-40 to 80°C (-40 to 175°F) Isolation: 4000 Vrms, input to output; 2500 Vrms input/output to ground Capacitance: 8 pF, input to output (max) Line Frequency Range: 47 to 63 Hz Turn-On Time: 20 ms, ac; 05 cycle, dc Turn-Off Time: 30 ms, ac; 05 cycle, dc
These SSR’s are of the twin SCR type, inherently more
reliable and capable of higher overloads before failure than
triacs. Heat is developed in a solid state relay due to the
nominal voltage drop across the switching device. To
dissipate the heat, an SSR must be mounted on a finned
heat sink or aluminum plate. An SSR should be located
where the ambient temperature is relatively low, since the
current switching rating is lowered as the temperature
increases. Another SSR characteristic is a small leakage
current across the output when the relay is open. Because
of this, a voltage will always exist on the load side
of the device.
In comparing SSR’s with mechanical contactors, the SSR
has a cycle life many times that of a comparably priced
contactor. However, SSR’s are more prone to failure due to
overload and improper initial wiring. Solid state relays can
fail, contact closed, on overload circuits. It is essential that a
properly rated, fast blowing I2T fuse be installed to protect
the load circuit.
Finned heat sinks are anodized fabrications that come
complete with tapped mounting holes and screws. See
thermal rating curves and ordering instructions for proper
selection.
All SSRL series relays come with a thermally conductive
pad mounted on the baseplate. This will significantly
improve the thermal conductivity between the heat sink and
SSR baseplate. It is also suggested that 10-inch-pounds of
torque be used on the SSR mounting screws.
Output Specifications for Vac and Vdc Input Models
† All dollar amounts on this site are shown in US currency.
Note: All SSRL Series come with thermally conducting pad. Reference SSR330 Series for additional heat sinks. Ordering Example: (1) SSRL240DC25 Solid state relay, $26.00
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