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Relay or contactor for 50KHz, 1.9Arms?

Discussion in 'General Electronics Discussion' started by eem2am, Jul 8, 2013.

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  1. eem2am


    Aug 3, 2009
    I wish to have a relay or contactor which will switch ON/OFF a current that is 1.9A RMS. This current is also sinusoidal and at a frequency of 50 KiloHertz (50000 Hertz).
    The peak voltage of this is 483Volts.
    That is, the voltage is sinusoidal and 342Vrms.

    Do you agree that “normal” relays , that have AC ratings, do not apply here, because their AC ratings always refer to 50Hz rather than 50KHz?

    Do you agree that at 50KHz we must look at the DC rating, because at 50KHz, the contact arc is not extinguished when the sine wave goes through zero, because it is reignited as the waveform moves above zero within a few microseconds.

    I have found this contactor, and believe it is suitable to switch this waveform, do you agree?

    (Farnell 3621819)
    Schneider CAD50BD contactor…
  2. duke37


    Jan 9, 2011
    You still do not mean 50KHz, you mean 50kHz.

    The contactor referred to is 5 pole. Putting all 5 contacts in series will enhance the voltage capability.
  3. eem2am


    Aug 3, 2009
    Thanks...i'm just glad i put "H" as its Professor Hertz's name. I cringe when i see Henrys or Farads not capitalised. Though feel sorry for Mr Oliver Heavyside, as he deserves a unit named after him.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Back when it was Kilocycles I used KC. Since then I've used KHz. This is because anything less than units (milli, ucro, nano, pico) is always represented in lower case and everything above units (Kilo, Mega, Giga, Tera) is represented in upper case.

    Admittedly my Tina wants to see lower case for Kilo but it's contrary to the above convention. In short the only reason that 'k' is acceptable is because it can't be confused with anything else. Either way I'm not changing at this late date. ;)

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Lord Kelvin would be proud to see such double use.

  6. Solidus


    Jun 19, 2011
    Whether or not to use AC or DC conditions for judging a relay depends on where the high-frequency components are used. If it's used at the will be limited by the minimum switching time of the armature itself. That is the only time you would get a sustained arc - if you are operating at high voltage, high current and at a high switching frequency so the state of the relay is never "sitting" at closed or open for long.

    If you plan on switching the coil with DC or routine LF AC and running 50kHz ~400V/1.9A through it, then you need only find a relay capable of putting up with that level of power. There are fairly robust relays that are still sub-contactor-grade that can do that.

    Obviously, in that case, there are HF considerations, although at 50kHz they can mostly be ignored in the case of the relay.

    You haven't said anything about the source of this power, so it bears mentioning that it would be easier to low-level-switch the power stage then trying to high-level-switch the output of that power stage. You will incur a lot more expense trying to buy power relays then a small- or medium- relay (or SSRs, which are much faster than electromechanical relays) and the power handling will be much more simple.
  7. Solidus


    Jun 19, 2011
    What you put below is being crowned as my signature.
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