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Solid State Relays What do I need to know

Discussion in 'Electronic Basics' started by Jan Wagner, Jul 19, 2004.

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  1. Jan Wagner

    Jan Wagner Guest

    These can leak a few mA, IIRC depending on which type of snubber network
    they have inside. So it isn't necessarily broken. Other SSRs leak only
    microamps or less, though. Maybe you should google for the datasheet, it
    should state the off-state leakage current.

    - Jan
  2. Starbase

    Starbase Guest

    I have a solid state relay but I can't get it to work.

    It is a 25 amp 240v a.c. with 3 - 32v d.c. control. The problem is when I
    connect the mains to post 1 it always delivers current to post 2 even with
    pin 4 and 3 shorted. The load I am driving is only in the order of 0.04 amps
    (7k Ohm soenoid plus a neon indicator lamp), the relay is not earthed but
    before I write it off as broken I am wondering, is there a minimum load
    current? does the SSR need a minimum (1-3v d.c.) off voltage, does it need
    to be earthed or is there something else I should know. I will experiment
    further but in the intrests of saving myself some time and possibly gain
    some knowledge I though I would post here also.

    Many thanks

  3. A 25 amp relay includes some sort of snubber across the output that
    carries a bit of current, even when the relay is off. You can prove
    that this is the cause of your trouble by paralleling the relay with a
    light bulb to suck up this leakage current. For this small a load,
    you should probably be using a smaller relay.
  4. Starbase

    Starbase Guest

    Many thanks John and Jan for your input on this problem, it would seem that
    you are correct and I will therefore be using a small low power mechanical
    relay in place of the SSR for the time being, (as the whole affair is Solar
    power driven through an inverter so the aim is to save power, and I need to
    learn a bit more as the system must be bullet proof as it controls the
    frige/freezer and I will be in serious trouble if I accidently defrost it).
    The sharing of your knowledge on the newsgroup is very much appreciated.

    Best regards

  5. Starbase

    Starbase Guest

    Thanks again, as a temporary measure I have sunk the excess current using a
    15 k ohm (7 watt) resistor and the circuit now works as anticipated (less
    the extra un-anticipated 4 watts power drain) but for now it will do the job
    it is inteded to do until I can find a suitable replacement. Forever

    Best Regards

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