Opto 22's Product Support Group (PSG) develops some helpful tips as they work with customers who contact them for free product support.
Back in 1974, Opto 22's first products were solid state relays (SSRs). Over 30 years later, we still make the most reliable SSRs in the world, and they still sell like hockey pucks. Here are some tips about SSRs from Product Support engineers.
For SSR Outputs Whenever you're using a solid-state relay output to control a solenoid or a relay, always use a commutating diode on the coil. The diode protects the solid-state output from inductive "kick" when the load is turned off.
Choose a silicon diode, such as a 1N4005. Locate the commutating diode as close to the coil as possible, and install the diode's cathode on the side of the coil with positive excitation voltage.
Handling the Heat
Did you know that SSR's dissipate power—in other words, they heat up? And the relay's current rating is substantially degraded the hotter it gets.
When using the Power Series solid-state relays, make sure to design adequate cooling systems to dissipate the heat emitted by the relay. Use items like heatsinks (with thermally conductive grease), fans, and air vents to ensure that the relay operates at an appropriate temperature.
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