Q: What is a solid state relay (SSR)?
A: An SSR is a relay with no moving contacts, and employs semiconductor switching elements like triacs, thyristors, and diodes. Input and output sides are isolated using photocouplers.
Q: How are SSRs different from electromechanical relays?
A: Both perform the same switching function, but their constructions are different. SSRs do not have any moving parts such as an armature or metal contacts, making them free of noise and arcs.
Q: Are SSRs expensive compared to electromechanical relays?
A: Initial cost of purchase is high for SSRs. But due to their long life capactiy and ability to handle heavy loads, SSR cost works out economically in the long run.
Q: Why should one consider using SSRs?
A: SSRs have an unlimited number of switching operations, couples with the ability of high speed switching. There is no concern of possible contact erosion, as SSRs use semiconductor switching elements. SSRs also have zero cross functions.
Q: Are SSRs available with NC configurations?
A: Yes, they are.
Q: Do SSRs have multiple contact forms, similar to EMRs?
A: No. Changeover contact options are not available in SSRs due to technical limitations.
Q: Can we connect the SSR in series/parallel combination/both series & parallel combination?
A: Series and parallel connections are possible, but TE does not recommend this option as the characteristics of the semiconductors differ from one device to another.
Q: What type of loads can be switched using the SSRs?
A: SSRs are capable of switching resistive, inductive, and capacitive loads. Examples are listed below.
Resistive loads: Lamps, heaters, and resistors.
Inductive loads: Motors, solenoid coils, and transformers.
Capactitive loads: Power capacitors and capacitors.
Q: What mounting types are available?
SSRs have PCB, panel mount, and DIN rail mounting options.
Q: What are the "must do" conditions when using an SSR?
A: Make sure to use an external heat sink for load current that is more than 3 Amps. Apply a heat sink compound to the base of the SSR before mounting it on the heat sink.