dc circuit breaker

Discussion in 'The Projects Forum' started by ol'trusty, Sep 15, 2009.

  1. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    Hello

    I am trying to find out if it is possible to make a DC circuit breaker based on scr or any thyristor.
    It will be for a solar power system needing to withstand 600v at 25 amp.

    The breakers that are in use now are mechanical very "heavy duty" ones (120$). Since ive been getting into electronics recently it got me thinking....

    Do you guys think it is possible?

    By the way I am starting to get hooked on this forum it is great.

    Thanks in advance

    Trusty
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Trusty,
    Glad you're enjoying the forums. :)

    SCRs and TRIACs work great with AC. However once you turn them on via the gate, they are "stuck" ON until the current through them drops to nearly zero. To get them to turn off, you'd have to do something to get that current to stop flowing first.

    You might look at using an IGBT, but even then you'd wind up having a good bit of power lost in them - and when they fail, they can fail shorted. Not a good thing for a circuit breaker.

    It's not very straightforward to design a breaker. They have to be tolerant of reasonable transients, otherwise any time you turned on a large motor, it would trip the breaker. At the same time, it needs to be able to trip if operated at a current slightly over the ratings if it continues for a period of time.

    Some mechanical breaker designs incorporate both a solenoid to take care of the overly-heavy transients (like near-dead shorts), and a bi-metal strip to take care of the current slightly over the ratings vs time. These have proven to be highly reliable and robust, giving decades of service even under adverse conditions.

    Although your store-bought breakers might seem expensive, they are indeed a bargain compared to what damage might occur if they failed.

    I suggest that as this is a safety item, also dealing with high-voltage high-power circuits, it is not a project for a novice to attempt, or even a very knowledgeable person unless they had full access to a well-equipped high-power laboratory.

    The risks to lives and property is just too high for a casual experiment.
     
  3. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    That makes sense to me..
    Thanks sgt. ;)
     
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