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inductive or resistive load

Discussion in 'Electronic Basics' started by Cepowak, Dec 12, 2007.

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  1. Cepowak

    Cepowak Guest

    Hi, all. This is my first post in this group.
    I'm trying to make a board for controlling AC loads. I mean to be
    able of swithing on/off the AC power supply. I have seen a lot of
    examples around the internet, and most of them use the typical I/O pin
    + opto-triac+triac, for example, this one:

    I made a very similar board but it didnt work and i dont know why. I
    used MOC3011, BT16A, and a GPIO from a microprocessor.I would like to
    be able of a remote turning on and off some of the equipments of my
    lab, and most of them are powered by classical AC/DC adaptors, so I
    want to turn on and off the AC input of every adaptor of the
    equipments. The first question is: what kind of load is an AC/DC
    adaptor, assuming that the total consumption of the equipment that it
    feeds is about 50 watts: inductive or resistive? Since they usually
    have a transformer as the first component that sees the AC input, I
    supposed it's inductive... am I right?
    Another question about the triggering. If the led is always lightning
    (feeded by a gpio, for example), the final triac should be at on-state
    so that the adaptor would be powered on? A while after, if I drive low
    the gpio turning off the led, should the adaptor power off??? Is it
    an optimal approach for this problem? What is the real benefit of
    using zero crossing detectors? I read a lot about controlling the
    amount of power given to lamps or other devices, but i dont want
    controlling the amount, but only the on/off state.

    Thanks in advance.
  2. Jamie

    Jamie Guest

    first thing you must do is place a volt meter across the LED diode of
    the isolator.. See if you're getting the required drive voltage.
    Also, I assume you're leaving the trigger signal on at all times until
    you want to turn it off ?
    Putting that aside, you may also want to check a couple of other
    things, and that is the resistor you have going to the coupler that
    drives the gate.. The gate current needed for trigger may be more than
    what your giving it.

    Things to ponder on..
  3. Cepowak

    Cepowak Guest

    I think the LED is well powered. It has 1.15 volts across it. The
    datasheet of the opto-triac shoes that the Vd should be 1.2 so i think
    it's right. I have 2 resistors of 100ohms in series ( i hadnt another
    type when i made the experiment) with the gate of the triac. Maybe I
    should use lower values?

  4. Jamie

    Jamie Guest

    put your ma meter in series with the LED feed and see what current
    readings you're getting..
    You maybe just on the threshold of it.
    Also, If you jump the gate of the Triac to the feed side of the
    isolator, you can determine if the resistors you're using have
    sufficient current for the TRIAC..
    Use this approach to determine the problem. If the TRIAC is comes fully
    on, then, this means you have an Optical coupler issue.
    if it does not turn on, then you have insufficient gate drive..
    You also need a minimum load of course on the output to test this.
    You need to get above the holding current of the TRIAC..
    for now, You could use a incandescent lamp as your test load.
  5. Cepowak

    Cepowak Guest

    Ok i will try that, but, do you know the answer of the question about
    if an AC/DC laptop adaptor is an inductive or a resistive load?

    Thanks in advance.
  6. Phil Allison

    Phil Allison Guest


    ** It is neither.

    The load is " non linear ".

    Current is drawn in pulses at the time of the each sine wave peak.

    Voltage and current are essentially in phase.

    ........ Phil
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