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Low voltage switching of a pump, on a countdown

  1. Dec 18, 2014 #1
    New member here. This might be the coolest subject for a forum I've seen in awhile (that probably sounds like robot spam). On to business...

    I have been scr*wed by a succession of people over our home's improperly plumbed hot water. It takes forever to get hot water to the faucets. I bought a product to fix that. It uses a valve plumbed into the water heater outgoing line to detect movement of hot water, and it then switches on a recirculating pump to push water around the circuit (so turn water on/off, wait a minute, poof, hot water is there). The pump shuts off after 2 minutes. Of course, the electronics soon failed. The company owner is a nightmare, so I am on my own.

    The valve mentioned above has two low voltage wires that complete a circuit when the hot water moves. I want to replicate what the product did, by taking those two wires and connecting them to.... something... that will switch power to the pump on (it's 110v) when the circuit is complete, and keep it on for 2 minutes.

    Thanks in advance for any ideas!
     
  2. jcsd
  3. Dec 18, 2014 #2

    billy_joule

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    Science Advisor

    110Volts can kill. You need a licensed electrician to install it.

    What you need is a timer relay:
    http://en.wikipedia.org/wiki/Relay
    http://www.allaboutcircuits.com/vol_4/chpt_5/3.html
    Presumably of the NOTO type

    Your local electrical store will probably have some in stock. They are used to delay bathroom extractor fans to stay on after the light is switched off among other things. If you shop around on the internet you could find cheaper ones. There are over 1300 timer relays ranging from $16 to $2.5k USD here:

    http://www.digikey.com/product-search/en/relays/time-delay-relays/1049305 [Broken]
     
    Last edited by a moderator: May 7, 2017
  4. Dec 19, 2014 #3
    Thanks. I've done a lot of electrical work, just none of this type -- I get the dangers for sure.

    The NOTO makes sense. I'm not even sure there's an electrical store around. Everyone seems to source at Home Depot now. :-(
     
    Last edited by a moderator: May 7, 2017
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