Short Circuit from a DC source

Discussion in 'Homework Help' started by Leoh, Jul 18, 2010.

  1. Leoh

    Thread Starter New Member

    Jul 18, 2010
    2
    0
    Please help me with this question.

    " It has been known that the short-circuit energy from a battery source is higher and therefore more dangerous than a normal AC circuit.What is the reason that a short-circuit from a battery source is more dangerous ? "
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,675
    899
    What are the assumptions? Is this the entire question?

    Surely, you know that one can short a 9V transistor battery with little risk, but doing the same with AC from the mains would create quite a show.

    John
     
  3. Shapath

    New Member

    Jul 10, 2010
    11
    0
    when you short circuit the battery source a huge amount of current will flow through the circuit and it will be catastrophic. Remember always Short circuiting a battery or using the batteries in a way not recommended by its Manufacturer can result in uncontrolled and dangerous failure of the battery. This may include explosion, fire and the emission of very harmful toxic fumes.
    A simple example can be
    a fully charged 3.6 Volt, 1000mAh mobile phone battery has a low internal impedance and contains 12,960 Joules of energy. Short circuiting these cells can cause extremely high currents and temperatures within the cell resulting in the breakdown of the chemical compounds from which it is made. This in turn can cause the rapid build up of pressure within the cell resulting in its catastrophic failure, with unpredictable consequences including the uncontrolled rupture of the cell or even fire.
    By the same token, a single, fully charged 200 Ah, 3.6 Volt Lithium Ion automotive cell contains 2,592,000 Joules of energy. So i hope you can understand the consequences might happen if you short the terminals...:D!!!
     
  4. Ghar

    Active Member

    Mar 8, 2010
    655
    72
    I've seen this claim before as well and I'm not really sure.
    Aside from what Shapath said DC current/voltage doesn't drop which tends to keep an arc going while AC transitions into zero dissipating the arc and you have to start it again.
     
  5. Nik

    Well-Known Member

    May 20, 2006
    55
    3
    My rule of thumb is that a DC arc may weld victim across the lines, while AC tends to throw them clear.

    A second factor is that you can arrange a current-balance safety device for AC easier than for DC.

    The final advantage of AC is that you can convert it with a modest transformer, eg to give the safer 110/110 centre-grounded instead of 220 Volts phase. This is standard practice on UK work-sites.
     
  6. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    The question is really vauge, but if a
    was the output from a lowish power and voltage transformer, then the winding resistance would be higher than the internal resistance of some battery types.
     
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