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Auto A-B Switch

Discussion in 'General Electronics Discussion' started by lagman, Feb 28, 2012.

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  1. lagman

    lagman

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    Feb 25, 2012
    I'm looking for an A-B power switch that automatically cuts off power to B if a load is present on A and vice versa. Does such a switch exist? I have 2 sump pumps connected to 1 inverter and I want to make sure they never run at the same time.

    Thanks,
    Dan
     
  2. KMoffett

    KMoffett

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    73
    Jan 21, 2009
    Use a relay with it's coil in parallel with pump A. Wire the common and normally-closed in series with the power to pump B. If A is running, the relay is activated, the normally-closed contact is open, and no power can be supplied to B. If A is not running, the relay is not activated, the normally-closed contact remains closed, and power is supplied to B. However, if B is running and A's sensor calls for A to run, A will start and B will be shut off.

    Ken
     
  3. lagman

    lagman

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    0
    Feb 25, 2012
    Thanks.. Actually I was hoping something like this could be purchased already assembled.. Not being a professional I don't think I would trust myself with something that could flood my basement if I make a mistake :)
     
  4. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
    You probably can. What are the voltage and current/HP specs on pump motors? Or a link?

    Ken
     
  5. lagman

    lagman

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    Feb 25, 2012
    the sump pump motor is 110v AC 6A.

    Thanks!
    Dan
     
  6. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
  7. lagman

    lagman

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    Feb 25, 2012
    Wow thanks! This makes it much easier.

    To answer your question, there is a float attached to the motortthat flips a switch when the water level is high enough.
     
  8. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
    You need to be able to connect two wires from the relay coil terminals directly across sump pump A's motor terminals. Is that possible?

    Ken
     
  9. lagman

    lagman

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    Feb 25, 2012
    I can try but it will involve taking it apart.. The terminals are not exposed
     
  10. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
    That may make this not so simple a solution.

    Ken
     
  11. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
    OK, another approach. Use this "current sensing" switch around one power wire of pump A. http://electronicaircleaners.com/aprilaire-51.aspx. Replace the outlet in the diagram with the coil of relay that I suggested. Connect the common contact of the relay to 120vac hot and the NC contact to one wire of pump B. The other wire from pump goes to 120vac neutral. It adds one more component, but you don't have to get inside pump A.

    Ken
     
  12. lagman

    lagman

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    0
    Feb 25, 2012
    Hmm.. My inverter has 2 AC outlets and I think it would be able to power both pumps.. It's the initial surge I'm worried about if both turn on at exactly the same time. I assume my inverter would freeze up forever (or at least until I unplug one of the pumps).. Or would it be smart enough to let one of the pumps (i.e. one of the outlets) "win"?
     
  13. lagman

    lagman

    13
    0
    Feb 25, 2012
    Actually, I decided last night just to bite the bullet and order a second inverter for the other pump (I found a good deal on eBay).

    I really do appreciate all the help though!

    Dan
     
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