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SSR Power Control

Discussion in 'Power Electronics' started by Danneskjold, Sep 11, 2021.

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  1. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    I am looking for a simple way to control line power to a 10A HVDC inductive load. at present there is a triac-based, zero-cross SSR that is used for on-off power. My thought is to send sub-120Hz pulses to the SSR gate, removing complete cycles, thus limiting input power. so, for 90% power, 9 cycles would conduct and 1 would remain off.

    I have not been able to find a control IC that does that, which suggests that it's kind of not a good idea. my guess would be noise to line (I have a large common mode filter), and inrush (I have a 2.5 ohm NTC).

    more than anything I am just curious about whether this can be done, should it, and if not, why?

    thanks in advance

    ~RD
     
  2. Minder

    Minder

    3,103
    664
    Apr 24, 2015
    What is the exact nature of the load?
    A small (8pin) microchip should be able to do it.
     
  3. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    induction heater, half-bridge
     
  4. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    going a different route now. I am told that one can use the 'enable' pin on a high-side gate driver in conjunction with a pwm signal. hard for me to think of anything easier than that....

    I'm still curious about the triac power control scheme, so if anyone has any answers, I'm all ears.
     
  5. Bluejets

    Bluejets

    4,991
    1,048
    Oct 5, 2014
    Diac and a pot as in ac series speed control should work.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,662
    2,697
    Nov 17, 2011
    This means that once the SSR has turned on, it will automatically turn off at the next zero crossing of the AC mains. It will not be able to be turn this SSR off before. Therefore your PWM scheme is not going to work. At least not with a 120 Hz PWM pulse train.
    A heater is a thermally slow device. There is no need to control it by a rapid on-off sequence. Look for example a the heater soil of a stove. The boilerplate is turned either fully on or fully of. The mean het is controlled by the duty cycle at a very low frequency, less than 1 Hz, more like 1/10 Hz.
    You can use the SSR in the same manner: turn the heater on for 9 seconds, then off for 1 second and you have 90 % mean heating. Or on for 1 s and off for 9 s to achieve 10 % heating.
    Using this kind of timing the absolute phase of your on-off signal with respect to the AC mains phase is not relevant. But if you want to be nice to your components, make the controlling signal in phase with mains (using e.g. a zero crossing detector). Here is an example for such a DIY project.

    Be careful! You are dealing with mains and as such dangerous voltages and currents. Observe your local regulations as applicable.
     
  7. Bluejets

    Bluejets

    4,991
    1,048
    Oct 5, 2014
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