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    Solid State Relay Off Voltage

    I have a Solid State relay that is controlled by a digital output which turns on and off 120Vac supply to load.

    When I enable the relay with digital output (SSR = ON), the measured AC voltage on the load = 120Vac.
    When I disable the relay with digital output (SSR = OFF), the measured AC voltage on the load = 12Vac.
    I know that an SSR has leakage current when = OFF.

    The off case is still turning the load on lightly.

    When the SSR = OFF, how do I make the AC voltage on the load = 0Vac so that the load does not turn on at all?

    Thanks!

    •   Alt14th November 2017, 05:14

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    Re: Solid State Relay Off Voltage

    Hi,

    Find out at what maximum voltage the load is safely OFF.
    Then find out leakage current of relay.

    Then use Ohm's law to calculate a what (maximum) load is neede to make the load stay OFF.
    Calculate the power dissipation of this resistor with full voltage (120V).
    Connect this resistor in parallel to the load.

    If the power dissipation of the resistor is too high, then you may replace the resistor with a series RC combination.
    Calculate the C to meet the impedance value.
    Use a resistor with about 1/10 of the impedance.

    Klaus
    Please don´t contact me via PM, because there is no time to response to them. Thank you.


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    •   Alt14th November 2017, 07:39

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  3. #3
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    Re: Solid State Relay Off Voltage

    Quote Originally Posted by KlausST View Post
    Hi,

    Then use Ohm's law to calculate a what (maximum) load is needed to make the load stay OFF.
    Calculate the power dissipation of this resistor with full voltage (120V).

    Klaus
    KlausST,

    Just to be certain, the equation to calculate the resistor value would then be:

    R = (Vmax load off)/ (I leak)

    where Vmax load off = the max load needed to make the load stay off
    I leak = leakage current of relay

    Is this equation correct?

    Thanks for you help.



    •   Alt14th November 2017, 16:40

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  4. #4
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    Re: Solid State Relay Off Voltage

    Hi,

    Yes, I think it is correct.

    where Vmax load off = the max load needed to make the load stay off
    in other words: The max voltage where the load safely is OFF.

    Klaus
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    Re: Solid State Relay Off Voltage

    Mind you if I ask two questions??

    -What exactly is the load?
    -With the 12 volt at its input when the SSR is "off", what is the behavior of the load?
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post



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