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Solid State 110 Volt timer delay circuit help

Discussion in 'General Electronics Discussion' started by MalcolmV8, Sep 2, 2011.

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  1. MalcolmV8


    Sep 2, 2011
    Hi Guys,

    I've been trying to build a simple power up delay circuit for 110 volt skimmer/pump on my salt water fish tank. My issue is that in a power failure water levels change. The sump water level rises a few inches. When power comes back on my auto top off pump is confused and pumps extra water in and my skimmer kicks on with the wrong water level and dumps nasty collected crud back into the tank.

    However if both of those items could be on their own delayed power up it would cure those issues. So when power returned if there was a 3 ~ 5 minute delay for the water levels to stabilize and go back to normal, then my skimmer and auto top off get powered back on they'd work as expected.

    I did some googling and found this circuit in particular

    It's for 230 volts instead of 115 which we have in the US but not a big deal. I'm sure I could make that work. However I don't fully understand that circuit and would like someone to explain it to me or show me a better circuit (or design a better one).

    I was going to just order the parts for that one and try and build it and play around with it but I can't find the SCR 2P4M so that's when I figured I better understand what I need exactly before randomly substituting parts in.

    Thanks for any pointers or advice.

  2. shrtrnd


    Jan 15, 2010
    It's up to you. When I consider the time and effort to build something that is already
    in existance. I decide how made-to-order the circuit needs to be for my application.
    They make 'Time Delay Relays' (TDR's) already. Which is what I would use in your
    case, rather than taking the time and effort to build my own circuit.
    Google them, and find what you need.
    If you're a serious do-it-yourselfer, and want to design your own circuit, more power
    to you. Just thought I'd give you an alternative.
  3. daddles


    Jun 10, 2011
    I agree completely with shrtrnd -- there are lots of types of time delay relays and you're sure to find something that fits your needs. Once you have the right relay, then it's a matter of 15-30 minutes to wire everything up and have it working.

    The problem is people often then find out that these relays can cost 20-75 USD. They then conclude this is too expensive and pursue some custom-made circuit where the parts cost a lot less. Frankly, this is often false economy in that they don't account for their time in designing, building, and troubleshooting the circuit -- not to mention that their solution may not be as robust as a well-engineered time delay relay. Note there are solid state time delay relays that can get costs down into the $10-$20 range. You'd be making a mistake if you thought you could build something yourself for that cheap, at least if you set the value of your time at the minimum wage rate.

    Google "time delay relay" and you'll find lots of stuff.
  4. MalcolmV8


    Sep 2, 2011
    Thanks guys. I googled around and found these

    Had no idea such items existed. Perfect. I ordered a couple of them. One will work perfectly for the skimmer. For the top off pump I'll need an additional relay that it activates but I can just pick one up at my local radio shack. Thanks again.
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