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Solid State relay question

Discussion in 'Electronic Basics' started by Bart, Nov 21, 2007.

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  1. Bart

    Bart Guest

    I have a solid state relay that has 5 to 24Vdc input
    requirements, and 24 to 240Vac~10amps load limitations. Can I
    hook up a DC load to the load side of this? I don't understand
    why I could not, and how to determine the limitations of the DC
    load given the AC specs.
    The relay is an OMRON "G3NA-210B" and the documentation mentions
  2. Dave22

    Dave22 Guest

    Solid state relays are typically thyristor ot Triac based internally.

    While you would be able to use a DC supply with one the problem is
    that the relay will not turn off until the voltage applied across it
    reaches 0 volts. This zero crossing detection is also used by the
    internal control signals to re-fire the triac each time the AC voltage
    starts up again (120 times a second for 60 cycle power) as long as the
    control signal is present.

    This is typical of all general purpose solid state relays.
  3. Bart

    Bart Guest

    Thanks Dave22,
    I understand now. I may run across an application someday where
    this info will be useful in a DC circuit. Any thoughts on what
    the DC amperage limitations would be?
  4. Phil Allison

    Phil Allison Guest

    ** Very doubtful.

    ** DC load switching means using a mechanical relay, MOSFET or transistor.

    ** Irrelevant.

    ......... Phil
  5. Dave22

    Dave22 Guest

    The current limitation should be the same for both AC or DC. Since
    the device you mention is fro a 10 amp load that is the maximum
    current I would expect it to be able to handle. Be aware though solid
    state relays generally need to be mounted on a heat sink since they
    typically drop a volt or two even when turned on. That would mean at
    10 amps that you would need to be able to dissipate 20 watts. Most of
    the cases will not be able to handle more than 1 watt continuously
    without a heat sink.
  6. Jamie

    Jamie Guest

    Assuming I know exactly what you're looking for with the way you
    asked it.

    You can connect a DC load on one side of the SSR how ever,
    since the SSR operates on AC, you would need to rectify it first
    before it goes to the DC load.

    If your idea is to control a DC source to this DC load, then you
    have a problem. These devices will latch on. The only way to
    turn them off is to remove the DC source from the input side
    of the SSR, disconnect the load or lower the load or source enough below
    the holding current.

    You could use a unfiltered AC to DC bridge source for
    example where the valleys will drop low enough for the SSR to unlatch.

    On the load side of the SSR, I guess one could simply filter it if
    one wish to :).
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