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Main Causes and Solutions of SSR Failures

FAQ No. FAQ02150

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Question

What are the main causes and solutions of the Solid-state Relays (SSR)'s failures?

Answer

If an inrush current exceeds the rated making current of the SSR due to the high inrush current of loads such as motors and lamps, SSR output elements are damaged.

Consider using an SSR with a higher capacity.

1. Reverse voltage of the load

High reverse voltage caused by inductive loads such as valves and solenoids may have the SSR output elements damaged.
Use the SSR with an element absorbing reverse voltage generated.

2. Malfunction caused by external surge

An external surge may suddenly damage input or output elements. A load short circuit may also cause malfunction. Design a safety circuit which will turn off the load by a contactor or a circuit breaker on the load power supply side when the SSR causes an error. It is also recommended to connect a quick-break fuse in series with the load as an over-current protection measure.

3. Installation environments

If an ambient temperature exceeds the rated value, the SSR output elements may be damaged. Install the SSR considering its heat radiation conditions such as air convection around the heat radiator.

If the SSR is used with loose screws of its output terminals or imperfect solder, abnormal heat generation while current flowing causes the SSR to burn out. Perform the proper wiring and soldering.