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Shorted Battery, What happens?

Discussion in 'General Electronics Chat' started by electronicslearner77, Jun 13, 2012.

  1. electronicslearner77

    electronicslearner77 Member

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    Hi All,

    I have this general question if we short a 9V battery or in general any battery does the battery get damaged permanently? Why it happens? (I read that, it is because maximum current flows, is it correct?)

    Thanks in advance,
    Regards,
    Satya
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Very likely, if the short is prolonged. High current through the battery's internal resistance causes heating which can generate gases. If they are vented there is a permanent loss of battery capacity. If they are not vented ......KERBOOM :)
     
    Last edited: Jun 13, 2012
  3. Dean Huster

    Dean Huster Well-Known Member

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    However, you must be careful here. A high-capacity battery such as a car battery will cause all kinds of nasty problems to you, the wiring and the battery if you subject it to a short circuit as hundreds of amperes can flow under such conditions. I knew of a situation when I was in the Navy where a guy dropped a 10-inch "Crescent" wrench and it fell to the bottom of the equipment bay where he was working. In the bottom of this bay were the very large conductors coming in from the adjoining building where the wet-cell nickel-cadmium battery packs were located. We are talking about a room the size of a single-car garage with multiple rows of multiple-tiered shelves containing hundreds and hundreds of these wet cells connected in a series-parallel arrangement. The result was that those bus bars at the bottom of the equipment bay were at around 200-300 volts with a capability of several thousands of amperes of current. That Crescent wrench VAPORIZED when it hit the buss, causing a flash that "sunburned" the technician. He was very lucky to have no worse an injury. After that incident, all techs were required to have all conductive tools with lanyards attached and around the tech's neck when working around high-energy systems.
     
  4. dave

    Dave New Member

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  5. bountyhunter

    bountyhunter Well-Known Member

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    Even a AA NI-CD which is shorted for a few seconds will get very hot.
     
  6. electronicslearner77

    electronicslearner77 Member

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    Thank you all for your replies, So when I short the terminals of a battery, the current that would flow is dependent on the internal resistance of the battery. Am i correct in this? One more small clarification is that, I have to just avoid shorting the battery terminals only and even if I connect a very small resistance is also no problem? Or is there a minimum resistance value from where i have to start?

    Thanks in advance,
    Regards,
    Satya
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I would say there should never be a reason to deliberately 'short out' a battery.

    Depending upon the batteries internal resistance and its voltage, the current flowing in the shorting wire current could melt the wire.

    To do a controlled maximum load test on a battery use Ohms law to calculate the resistance of the load and then calculate the required Wattage of the 'shorting' [load] resistor.

    Measure the off load voltage of the battery and then the on load voltage, from these two voltages you can get a close approximation of the battery's internal resistance.
     
  8. Dean Huster

    Dean Huster Well-Known Member

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    I carried some AA's around in my pocket after work one evening and noticed that my leg kept getting hot. The cells were shorting out against my keys!

    Also while in the Navy, we all had to wear our top secret security badges, may of us on a "bathtub plug" chain around our neck. One such individual was working on his car under the hood trying to get it started before work and one end of the chain was laying on a chassis component while the other dragged onto the positive post of the battery. The result was a "chain" of little red dots around the back of the guy's neck caused by this new-found, unintentional heating element.

    This is also why when working on an automotive electrical system, you ALWAYS remove the ground cable from the battery first, then the positive cable. That way, if the wrench slips and contacts chassis while removing the positive cable, no harm done.
     
    Last edited: Jun 14, 2012
  9. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Lithium Ion batteries also cause a pretty big problem if shorted. They can ignite and explode quite vividly. There are vids on the web.

    I know someone who had a Lead Acid car battery blow up right under their chin just about. Very luckily there was no injury. Battery case pieces all over the back yard though.
     
  10. JimB

    JimB Super Moderator Most Helpful Member

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    Many years ago I worked for a company which made submarines, real ones, BIG ones.

    To test and calibrate the DC circuit breakers to give the correct tripping time under various overload conditions, currents of up to 10,000 amps were run through each circuit breaker and the current and time were recorded using a thing called a UV recorder.

    To produce the high currents required, there was a shore based battery of cells which were connected to the DC switchboard onboard the boat through several large (30mm diameter) cables.

    To set the current for each test was a bit of a guessing game based on previous experience and was done by varying the number of cells in series and the number of cables in parallel. As the tests progressed, it was often necessary to connect the cables to a fresh set of cells to get the required current.

    It was quite entertaining watching the cables as the circuit breaker was closed to start the current, the cables would "jump" due to the large magnetic fields from the currents involved.

    As the guy operating the recording equipment, it was also entertaining being showered with sparks of molten copper if the guy operating the shore based circuit breaker in the test shack made a mess of closing it and "bounced" the contacts rather than getting a nice clean closure.

    So, yes, we did short circuit batteries quite deliberately, but under carefully controlled conditions.

    JimB

    On edit:
    The cells were lead-acid types.
    Each cell was about 1ft square by 3ft tall, I have no idea what the AH capacity was.
     
    Last edited: Jun 14, 2012
  11. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Jim,

    Very interesting story there. I'd hate to be around the test area during those times :)
     
    Last edited: Jun 14, 2012
  12. unclejed613

    unclejed613 Well-Known Member

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    lithium is a highly reactive metal (even more reactive than sodium IIRC), and if a lithium battery has degraded to the point where there's a lot of metallic lithium deposited in it, and the case breaches, the metal bursts into flames when the air hits it.


    i was calibrating a clamp ammeter once, and part of the procedure required testing it at 300A. one method used a 300A power supply and #00 ga wire, but there was an alternate method in the manual using a 75A supply and a loop of 4 turns of #4 wire (75Ax4 turns=300A-turns). i ended up using the alternate method. every time i turned up the current control on the supply, the wire loop moved to be perpendicular to the earth's magnetic field, and would return to it's original position when i turned the current off.
     
  13. JimB

    JimB Super Moderator Most Helpful Member

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    I was not as bad as it sounds but these test were done on nightshift when there were few people around to minimise safety problems with the jumping cables.

    JimB
     
  14. JimB

    JimB Super Moderator Most Helpful Member

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    I have a 12volt 10 amp bench PSU which I built a couple of years ago, it would do a lot more than 10 amps with a quick re-configuration and adjustment, but 10amps is good enough for now.
    For some reason this PSU is prone to mains switching transients (I must investigate why, one day) and trips its overvolt crow-bar and so its output to zero.
    In the few milli-seconds before the current trip takes over and shuts the thing down completely there is a melodic twang from the current sensing "resistor", which in reality is a coil of copper wire.
    The current pulse is plucking the string of a musical instrument in the earths magnetic field orchestra!:D

    I originally bought an expensive 4 terminal resistor for the current sense but failed to calculate how much power it could disipate under fault conditions. I did not last very long, hence the coil of wire!:eek:

    JimB
     
  15. strantor

    strantor Active Member

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    I feel like I'm in the company of friends in this thread. I'm a prior Navy Submariner. Jim, did you work for EB? Dean, did you have to wear those badges because you were in the shipyard? or maybe a-school?
     
  16. JimB

    JimB Super Moderator Most Helpful Member

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    Wrong country!
    Vickers Shipbuilding Ltd in the UK.

    JimB
     
  17. strantor

    strantor Active Member

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    DOH! :eek:
     

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