AC current detection

Discussion in 'The Projects Forum' started by Arkole Blake, Feb 21, 2012.

  1. Arkole Blake

    Thread Starter New Member

    Feb 15, 2012
    4
    1
    o/ All

    I am looking for a way to detect current through one of two power connections feeding the same transformer. (see pic below)

    What I have is a 115v transformer that draws ~11a. (t1). It is hardwired to an gasoline powered generator(j1), It also has a powercord(j2) that is used to draw power from the grid when it is avalible.

    I need a way to detect when current is bieng draw from the powercord(j2) and trip a relay (or other device)(LS1) that will close another circuit which is isolated from this one.

    The second (isolated) circuit has its own power source and will be looking for a closed or open indication from the relay.

    The only power source avalible to run LS1 is the 115v from the transformer power cord (j2).

    I have a working solution using 3 AC relays but was hopeing to find a simpler and more cost effective solution.

    Thanks in advance for any help, and feel free to ask for any relivent info that I have left out.
    (consider it safe to assume that the generator and the powercord will never be providing power at the same time.)

    -Tim D.
     
  2. #12

    Expert

    Nov 30, 2010
    16,314
    6,818
    This seems so much easier to do with voltage but if you must use current, .45 ohms in series with 11 amps will provide a voltage that will drive a 5 volt AC relay coil. The loss of 5 volts on your 115 volt line will probably not hurt anything.

    I'm really not very clear about what you want so I just suggested something I could cobble up from my spare parts bin.
     
  3. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    I am about to build prototypes of a unit that does exactly this function--if interested, email me.
     
  4. Arkole Blake

    Thread Starter New Member

    Feb 15, 2012
    4
    1
    Thanks for the responces so far guys.

    #12 sorry if the title of the thread was misleading, using voltage instead of current is an option. The three relay solution that I mentioned in the op actually does this in a rather crude way. (see below for how this is wired)

    In a nutshell, what I have is two inputs that can power the same transformer and a seperate circuit that needs to know which input the power is comming from. This seperate circuit has a connection avalible that just needs to be closed when one cord is powered. (and open otherwise of course)

    As you will see from the pic below, what I am currently doing simply disconnects j2 when j1 is powered so that LS1 will only activate when j1 is running the system. This system works but is rather crude and bulky, I was hopeing for a few ideas how to do this in a more 'modern' way that would take up less room and (hopefully) be a bit less costly. (these large ac relays are not exactly cheap :p)
     
  5. #12

    Expert

    Nov 30, 2010
    16,314
    6,818
    Here is a way to do this with one DPDT relay.

    I assumed the common points are in the usual places and you know the difference between ground, common, and bond. In other words, I'm lazy. I assume you can fill in the common conections yourself.
     
    Last edited: Feb 23, 2012
    Arkole Blake likes this.
  6. Arkole Blake

    Thread Starter New Member

    Feb 15, 2012
    4
    1
    Thanks #12,

    I am sure I can fill in the blanks, will check it out. :)
     
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