Questions about Relays

Questions about relay products are posted.

Relays in general

Relays in general


  1. What are “thermoset” and “thermoplastic”?

    Thermoset or thermosetting resin is hardened by heat. Thermoplastic resin, on the other hand, softens and unmolds when exposed to heat and then hardens again when its cooled. Thermosetting resins generally have a higher resistance to heat (i.e. high heat by arc discharge).


  1. What is time constant?

    The L/R time constant is used to determine the time required for current to reach 63.2% of the maximum current once voltage under load is delivered as it takes some time for the current to start flowing. The larger the time constant, the longer it takes for the current to reach its maximum value which ultimately increase inductive loads.

  2. What is power factor?

    Power factor is defined as the difference in phase between voltage and current. Large inductive loads result in low power factor.

Signal Relays

Signal Relays

Contact rating

  1. Can the relays which its contact rating represents only the resistive loads used for other applications?
    ・Can the relay be used under an inductive load?
    ・Can the relay be used under a load drawing inrush current?
    ・What is the maximum inrush current (A) possible to energize?

    The relay is generally rated for switching resistive loads.

    According to the type of relay, the contact ratings only indicate resistive loads because the actual load conditions (values of power, voltage, current etc.) may affect the durability of the relay.

    The guaranteed condition of the inrush current must be within the maximum rated contact current. However, with the load condition where the inrush current is high and the breaking current is low, it may lead to contact transfer (for DC application) or locking phenomenon therefore the relay must be properly tested with the actual load and actual system to confirm its usage and ultimately determined by the customer.

Coil polarity

  1. What happens to the relays when its coil polarity is reversed?

    It will not cause malfunction or damage to the relay itself but the coil will be affected leading to the following conditions.

    Single-side stable relays : no move.
    Single-winding latching relays: SET and RESET actions reversed
    Double-winding latching relays: It may lead to malfunction or may stop operating depending on the type of relay used.

    With latching relays, some are configured in a way when the reverse-polarity voltage is applied to the set coil, the contact is in the reset state; and when the reverse-polarity voltage is applied to the reset coil, the contact is in the set state, however, regardless of the design, the relay must NOT be used in this way.


  1. Can ultrasonic cleaning used on the relays?

    Only for relays specifically manufactured for ultrasonic cleaning.
    Standard type relays are not designed for ultrasonic cleaning; it can cause disconnection to coils, sticking of contacts and eventually leading to malfunction.


  1. Is there a socket exclusively designed for the relay? Can we use commercial sockets?

    There is no dedicated socket. The standard terminal size is 2.54mm pitch so any socket that fits the size can be used.

    We do not make recommendations or give conformity guidelines in terms of connectivity or reliability as specification of each socket differs.

MOS FET Relays

MOS FET Relays

Failure rate

  1. What is the failure rate of MOS FET relays?

    The estimated failure rate of MOS FET relays is calculated in units of FITs. According to the experience, the failure rate of the relay under normal operating conditions (without surge) at ambient temperature of 40degC is 30 Fit and below.

Life cycle

  1. What is the life span of MOS FET relays?

    Longer life can be expected (semi-permanent) in MOS FET relay (on the output side) as long as it is used within the rated conditions. The life span is reduced if the input side (internal LED) degrades caused by long-term usage.

    In particular, When the inner LED degrades, the luminous amount of the LED falls. And more, MOSFET doesn't normally move any more.

Failure caused by Surge Voltage

  1. What are the causes and countermeasures for MOS FET relay failure caused by Surge Voltage?

    Please refer to the link below.


PCB Power Relays

PCB Power Relays


  1. Are there any differences between the ultrasonic cleaning type and the standard type relays?

    With ultrasonic cleaning type relays, the number of turns in the winding is increased to prevent coil disconnection. The relay delivers the same performance as the standard types.

Polarized relay

  1. Permanent magnets are added to some of the small size relays. What is the purpose?

    Space for coils and number of winding turns are usually limited in small size relays. The permanent magnet is added to help the coil increase sufficient force and maintain stable operation by the combined magnetic force of “electromagnet + permanent magnet”. The coil output voltage will have negative or positive according to the north or south magnetic poles of the permanent magnet.

    Permanent magnets are used in many of the latching type relays.

Contact material

  1. What does “-ASI” indicated in some of the type descriptions mean?

    The acronym ASI stands for AgSnIn, which is a type of contact material known as Silver-Indium-Tin contact. ASI (AgSnIn contact) can tolerate large inrush currents.

    There are also relays that have “-FD” indicated in the type description which stands for the same meaning.