AC overload prevention using microcontroller

Discussion in 'Embedded Systems and Microcontrollers' started by robomind, Sep 7, 2009.

  1. robomind

    Thread Starter New Member

    Sep 7, 2009
    can anybody explain me about AC load measuring ckt for the use of overload protection using microcontrollers.

    Thanks inn Advance...
  2. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    A resistive load is required immediately across the secondary of the current transformer terminals or else the voltage after the bridge rectifier will rises to hundred of volts.

    With this loading, The voltage across and hence also the rectified DC voltage will then be proportional to the primary current.
  3. Tahmid

    Active Member

    Jul 2, 2008
    I attached such a circuit. I once saw this implemented in some German inverter. This can act as an overload sense for roughly 800W (200V). At 800W, 200v, 4A will pass, crossing a drop of
    V = I * R = 4 * 0.1 = 0.4V across the sense resistor.
    This voltage at 30v input causes output of
    (0.4 / 30) * 220 = 2.93v after the 220v winding
    When rectified(assuming sine wave input) this becomes
    2.93 * 1.41 = 4.1v
    So the zener will not be active at this power, but slightly more than 800W. You can sense the output with a PIC (ADC or comparator) and if it is more than 4.5v, the PIC can shut off the supply.
    Hope this helps. I didn't try this myself, but found it in another design, but I can't find that circuit right now, so I just drew it.