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relay rating question

Discussion in 'Beginner Electronics' started by krem, Dec 3, 2003.

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  1. krem

    krem Guest

    I have a relay which is labed to be able to switch 120vac @ 1A. Will i
    still be limited to 1 amp if i'm only switching 30vac?
  2. Maybe yes, maybe no. It depends on whether the current rating is
    based on the continuous rating of the contacts (current) or on the
    ability of the contacts to handle the flash when the current is
    interrupted. I have seen both cases.
  3. Jerry G.

    Jerry G. Guest

    The ratings of the contacts can be fairly complex, and involve a number of
    factors. Basically the contacts should be able to support 1 Amp of
    continuous current, not including any peaks upon closure (latching) of the

    I would normally rate the relay contacts to at least double or more of the
    amount of current I want it to handle. This way, a high reliability factor
    will be introduced.



    Jerry Greenberg GLG Technologies GLG

    I have a relay which is labed to be able to switch 120vac @ 1A. Will i
    still be limited to 1 amp if i'm only switching 30vac?
  4. Guest

    A couple of points:
    1) If your relay is really rated to *SWITCH* 1A at 120 vac,
    then it can handle more at 30 vac, all other conditions being
    2) A rating to switch 1A *should* limit your design to
    switching less than that. It is not a good practice to
    run components at their rated maximum.

    Essentially, if a hobbyist has a question about a relay's
    ability to handle the current in the circuit, he should use
    a bigger (higher rated) relay - one *well* in excess of the
    maximum expected current.
  5. krem

    krem Guest

    Thanks, the only reason i'm not just going out an buying the higer rated
    relays is that i already have 100 of the 1A 120vac around the house and need
    to use about 28 for the project i'm working on so its an expensive
    proposition. Unless some one knows of a cheep source
  6. You might improve the contact life of the ones you have with well
    designed contact snubbers, but that might cost a significant fraction
    of what better relays cost.

    Do all the contacts need to carry more than 1 amp, or just a few of
    How much current must the contacts carry (worst case) and what sort of
    load is being driven?
  7. Michael

    Michael Guest

    Simple, Try one, see how hot it gets.
    Relays can dissappate heat through the pins, so if you are making
    your own pcb for them , try to have a lot of copper around the contact
  8. Spudley

    Spudley Guest

    If your relay has multiple contacts then I would advise running them
    in parallel to double their contact rating.
    Else get relays with higher contact current rating.
    Perhaps you could divide the loads across multiple relays to reduce
    the current imposed on each relay.
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