Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

New problem for you: household thermocouples, Etc.

  1. Jul 11, 2008 #1
    Household water heater thermocouple and power-open gas valve:
    Here's the riddle:
    (this is not a homework problem, it's a DIY thing)
    how can I use a small amount of electrical power to operate a natural gas valve?
    Background:
    Household gas water heaters have a built-in safety valve that needs a small current of DC to keep the valve open. They have a suspiciously large pilot, which heats a small thermocouple. The thermocouple provides electricity to keep the safety valvle open. If gas supply is interuppted, or the pilot goes out, then no more power from the thermocouple, and the gas valve closes. No gas build-up, and your home doesn't blow up. Nice, eh?
    How much power does a household gas waterheater produce? How can I generate the same amount of power by induction? If I have a hefty load (220V, 50A AC) nearby, can I wrap a coil of wire around this (very insulated) power cable to collect enough power to replace the thermocouple? (BTW-not using it to keep a gas line open anymore)

    Any other easy ways around this, or another solution? I thought of using yard irigation valves, which use 12V DV to operate, but I *think* they open OR close whenever they get power... I need a simple system, no ICs involved, as it will be outdoors with little protection from the weather. I want to gate to be open when power flows through large power cable nearby.

    Any suggestions of help appreciated. Thank you for your time.
     
  2. jcsd
  3. Jul 12, 2008 #2

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    It might help if you would say how you intende to use your valve. Solenoid valves is the way to go. There are all kinds of solenoid valves.
     
  4. Jul 12, 2008 #3
    That is exactly what a thermocouple valve is. A solenoid valve that is designed to run on the very low voltage and high (relative) current from the thermocouple.
     
  5. Jul 12, 2008 #4

    berkeman

    User Avatar

    Staff: Mentor

    If the power conductors are in the same sheath, then you will not be able to tap much powe off of them. You need to separate them so you can capture the magnetic flux from just one conductor, instead of having the multiple fluxes cancel each other out. Is there a practical way to separate the conductors? One way is to make an adapter that takes the cable in, separates the conductors, then recombines them, and has the cable continue out of it. You can put (safe) male/female connectors on the cable, for example, and plug those into your tap box...
     
  6. Jul 12, 2008 #5

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    Averagesupernova,

    I really didn't want to get into how to keep your furnance valve open when you loose flame.
     
  7. Jul 12, 2008 #6

    berkeman

    User Avatar

    Staff: Mentor

    But I get the impression the OP has some other function in mind, not a dangerous thing like bypassing the pilot flame safety valve:

     
  8. Jul 13, 2008 #7

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    Yes, but I want to bring it to the attention of others that might want to try to bypass the saftey.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: New problem for you: household thermocouples, Etc.
  1. Household Amperage (Replies: 18)

  2. Household wiring (Replies: 6)

Loading...