Detecting an open of closed AC circuit with nominal.3A draw

Discussion in 'The Projects Forum' started by StarfleetRP, Mar 23, 2009.

  1. StarfleetRP

    Thread Starter Member

    Mar 23, 2009
    24
    0
    I would like to check if the AC circuit that my Micro Processor is controlling is being short circuited or if there is not draw on the circuit at all. The nominal load on the circuit would be about 300mA. If it is too large (1.5A for example) I would like to know this, because this would mean that there is a short, and would result on the Micro telling the Triad to stop the current.

    I however do not know how I would detect the current being drawn.
    Also would there be a way to protect the Micro from the current detecting, incase there is a large voltage spike from frying the Micro? (the triads are rated for 4kV separation from AC to DC) and I would like to maintain this with the current detection.

    I forgot to add that the Voltage will be 25V AC nominally, with a "max (transformer)" current of 2.0A, unless there is a current spike.

    Your help is greatly appreciated!
     
    Last edited: Mar 23, 2009
  2. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    You seem to know what you're talking about but I'll ask the obvious question anyway: Why can't you just put an ammeter in the circuit?
     
  3. StarfleetRP

    Thread Starter Member

    Mar 23, 2009
    24
    0
    That would work, however the problem is that I would have to be present to take the readings. If it were possible for me to be present there would also be the downside because of the large latency it would take to turn off the power to the circuit (seconds vs milliseconds). I however need my Micro to be able to read the current in the circuit, and I am not sure how I would go about doing this. If you meant why don't I hook up a ammeter to my circuit and have my Micro read that, I am not sure how to do that either. Also I would need the ammeter to be fairly small to fit on a PCB.

    Thanks for your reply, and I hope this clarified my problem a bit more!

    Edit: An idea that I had would be to use a current limiter (and rectifier) to translate the current into a DC voltage that could be read by an ADC. I however have never done this before and am not sure how exactly it would be done (to be connected to the Micro and still be in series). I am also concerned that it would require a very large resistor (way over 4W). Since it would have to drop a potential 2A 25V current down to 2.5Volts and a few mA.
     
    Last edited: Mar 23, 2009
  4. StarfleetRP

    Thread Starter Member

    Mar 23, 2009
    24
    0
    Thanks for your reply, that is a good option.

    I am also wondering if there would be another way of doing this without using a "transformer"?
     
  5. StarfleetRP

    Thread Starter Member

    Mar 23, 2009
    24
    0
    What would you recommend to do, if I did not have to keep a separation of the AC and DC circuit? I am not sure exactly the path that I want to take at the moment for the project, and as such would like to expand my knowledge of any other possibilities, with the "separation of circuits" constraint removed.

    Thanks for all of your help so far!
     
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