What Causes a Solid State Relay Burnout?

Solid state relay, SSR in short, is the non-contact switch constituted by the microelectronics circuit, discrete electron device and power electronics power device. The isolation device is used to realize the isolation of the control terminal and load terminal. The input terminal of the solid state relay adopts the tiny control signal, thus realizing the direct driving of the high-current load.

Then, we will mainly introduces the faults of the solid state relay burnout. How to test the SSR if it is damaged or not? What is the reason of the solid state relay burnout and how to deal with it?

How to test a solid state relay if it is good or bad?

In general conditions, the multimeter cannot be used to test if the solid state relay is good or bad. The correct method is to test the circuit as the diagram shown below. When the input current is zero, the voltage tested by the voltmeter is the voltage of power grid, and the bulb is not on (the power of the bulb should be over 25W). When the input current reaches a certain value, the bulb is on, and the voltage tested by the voltmeter is the break over voltage drop of solid state relay (below 3V).

What Causes a Solid State Relay Burnout?

During the usage of SSR, it might cause the burning if the working conditions of different relays are not concerned , or improper using of the solid state relay may also result in the sudden immediate burning in just purchasing. The following will introduce what causes the solid state relay burnout.

1. Selection of SSR rated current

This is probably because the rated loading capability of the solid state relay you selected is lower than the practical loading power. In addition, the surge current of the load may also damage the solid state relay if it exceeds the overloading capability of SSR.

For the above issue, the solid state relay should be selected properly based on the different types of loads. For the resistive load, the actual load current is not recommended to be higher than two-thirds rated current of the solid state relay. For the inductive load, the load current should be no higher than one-half rated current of SSR. It is required to equip the SSR with the overload protective device. When selecting a solid state relay, the SSR with higher rated current should be selected if possible, so as to guarantee the enough current margin.

2. SSR DC or AC type

Please note that solid state relay is divided into DC mode and AC mode. DC SSR is only used to control DC power and DC load while AC SSR is just for controling AC power and AC load. When selecting a solid state relay, please pay attention if it is selected correctly based on the working condiitons.

3. Installation environment

The ambient temperature also really matters. So, the heat radiator should be equipped with if the load current is higher than or equivalent to 10A. Besides,  it is also recommended to connect a varistor in series at output side as an over-current protection measure.