Solid state relays have no moving parts so there is no mechanical reason why they should fail. However, traditional solid state relays (and other modern electronics) may be damaged by three local installation reasons -- over voltage power surges, over current due to inrush or improper fusing, and over temperature due to poor thermal dissipation. If you plan for these three situations, you will remove the vast majority of solid state relay failures.

Over voltage power surges

In ALL industrial applications, the local factory power is fluctuating in voltage due to starting and stopping of nearby drives (inductive fly back surges), inductive loads, noisy mechanical or mercury contactors (non-zero cross switching of medium amperage loads), e-stop and other machine stop conditions without proper filters, local phase angle control, and more. This creates a variety of voltage surges on the same (normally unfiltered) power line that directly feeds to the solid state relays and the loads. The Power-IO families of SSRs set the new standard for solid state switching due to the Maximum Surge Survival™ technology. This results in a SSR or solid state contactor that is 10-12 times more bullet-proof to over voltage power surges than other units in the market place. This is a triple-layer approach to surge survival based upon the cumulative effect of attenuate + block + control the activation. The Maximum Surge Survival feature adds: 1) a strong internal attenuator to reduce the peak voltage surge from a short duration, extremely high spike to a longer duration, less destructive, voltage bump; 2) then it adds a strong blocking voltage barrier at 800 volts (for 330 volt rated products) or 1200-1400 volts (for 660 volt rated products); 3) then it adds a pass through circuit that protects the SSR die from the destructive "punch through" that happens during a momentary voltage surge. With-in a sinewave or two, the SSR recovers from the pass-through and then continues to operate. These three layers supply a triple-layer barrier to avoiding voltage surge related product failure. These three layers represent: soften the surge; block what remains; and if is still is a massive surge, then control the turn-on so the SSR will return to normal operation at the next zero crossing mark. If the application is subjected to constant repetition of voltage surges, you can also add a MOV across the power terminals of the POWER-IO SSR. This will act as a fourth layer of surge protection, if you wish, and it is highly recommended for motor starting applications. Voltage surges are always one of the hardest problems to locate in an installation, whether it is industrial or residential, so it is to your advantage to anticipate them in advance.

Over current

The Power-io products (H, C, and D families) uses over-sized internal components so it can absorb short term amperage inrush fluctuations such as when used with tungsten loads or similar high inrush loads. For example: both the 25 amp and the 40 amp D units can be properly protected by a 50 amp I²T fuse, due to the over-sized internal design. The new CE testing (the new CE EN60947-4-3, effective 2002 for new products) requires solid state relay survival testing under a variety of 20% over-amperage switching into a 0.8 power factor inductive load. Power-IO's D families din rail relays and the H family of hockey puck relays meet all of the requirements of CE EN60947-4-3 without any filters or other external, add-on devices. Please be aware, even though we test the product at 20% over the rated amperage (such as 60 amp loads on a 50 amp SSR), you should ALWAYS design your installation so that you do NOT exceed 80% of a SSR's ampacity during normal operation, at 40ºC. Many local electrical codes, circuit breaker companies, wire suppliers, and fuse companies also recommend that the installations always be designed to run at no greater than 80% of any component's rating, and additionally derated based upon local installation temperatures. This 80% rule helps to anticipate resistance changes, amperage fluctuations, and it is an excellent recommendation to ensure long life of all of the components in an installation.

Over temperature

POWER-IO's C and D families are available as manufactured on an optimized heat sink. First, POWER-IO uses a customized ceramic direct copper bonding technique resulting in the absolute minimum thermal resistance from the SSR die to the heat sink. The SCR die is bonded to the thinnest ceramic substrate that is mechanically strong enough for the application. This substrate electrically isolates the SCR from the aluminum heat sink while permitting the thermal rise to dissipate and spread to the copper subplate and then the aluminum heat sink. These substrates are x-rayed with an electron microscope to ensure that we have a void free assembly. Then, we use a new heat sink design that is specifically engineered to maximize exposed aluminum surface area, thermal draw down channeling, heat flow patterns, and the chimney effect. This is why the popular POWER-IO products that have an integrated heat sink can be installed with NO space between units on the same horizontal din rail. This means that they stand up better to installations where the ambient temperature is warm. Please note -- all POWER-IO units are rated to operate in an environment of 40°C without any derating compared to competitive units that may be rated only at 20 or 25°C and need to be de-rated at 40°C. In addition, most other brands of solid state relays require AT LEAST one inch between horizontal units on the same din rail or else they need additional temperature derating up to another 50% reduction in ampacity. The POWER-IO products use a highly efficient design so they typically generate less than 1 watt (25 amp units) or 1.2 watts (40-100 amp units) per amp switched. This compares to other units that might generate 50% - 75% more heat. The POWER-IO product line works harder -- runs cooler -- needs less installation space. The more information on the POWER-IO products, click on solid state relay products.

In addition to avoiding over-voltage, over-current, and over-temperature situations; it is expected that the POWER-IO product should be installed only by qualified personnel, in accordance with all electrical and safety regulations. Naturally, any electrical product can stop functioning at any time, so all installations must be designed in such a way that they use all external fail-safe methods to ensure a safe shut down capability.

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