CT for overload protection

Discussion in 'General Electronics Chat' started by nev, Apr 28, 2011.

  1. nev

    Thread Starter New Member

    Apr 28, 2011
    Hi all,

    I am busy building a CT for overload protection on an inverter(500W, 12V-240V). I am using the CT to trigger an op amp which is intended to trigger a relay to open the circuit.
    Is this a good idea?

    The problem is when the op amp is connected to the relay it seems to 'draw' the output voltage from 12V to 7V. So now the relay is not switching.

    I tried to use a 6V relay, but with no luck. the voltage then dropped to about 1V

    Any feedback would be appreciated.

  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    My guess would be that the relay coil resistance is too low for the output current capability of the op-amp. The 6V relay possibly has an even lower coil resistance, so that it makes matters even worse.

    What type of op-amp are you using? What is the relay coil resistance (or manufacturer and part number)?
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    typically one would trigger a transistor with the op amp and then use the transistor to energize/de-energize the relay. As you have already found you can't get enough current right out of the op amp
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Why not just use a fuse/circuit breaker for overload protection?