What exactly happens at short circuit?

Question

I'm new to electronics and I don't fully understand how short circuiting works. For example I have this battery LiMn 3000mAh, it states:

 Nominal Voltage: 3.6V
 Standard Charge: 2A
 Continuous discharge current: 20A

First thing I don't understand is if I connect a wire between the positive and negative terminal, it would create a short circuit, correct? Can the battery blow up?

My goal is to simply make a hot wire, but I don't understand how will the wire 'determinate' how much current it needs or will it draw full 2A or even 20A from the battery?

If I use resistors, what's their purpose? to protect the battery from all the 'unused' electrons or to protect the wire?

What about taser gun? is it 'short circuiting' and what effect does it have on the power source?

Answer 1

1) Yes, connecting a voltage source directly to its return with a wire creates a short circuit. 1b) Yes, discharging a battery at too high a current draw will overheat the battery and can result in a catastrophic failure (blowing up, boiling electrolyte, fire, other bad things).

2) To just heat a wire, ideally, you would connect it to a controlled (regulated) current source. Then you can adjust the available current to control the heating. Most mid-range and up bench power supplies have a current limit mode.

3) Resistors server many purposes, you will need to be a little less broad. Resistors can limit current, but at the cost of heating up. They won't "Protect" the wire actually, just reduce the current available, and make the resistor a heater.

4) A Taser generates very high voltage pulses, at a very very low current. There is a lot of circuitry between the taser contact points and the battery... Again, really too broad to answer here.

Answer 2

Battery specs are often stated assuming a constant average current over the span of decreasing voltage range.

All batteries have an internal resistance that defines what the short circuit current is which is never specified since the internal heat can be dangerous ( explosion) but can be estimated from a load test from say 1A to 20A std discharge 3.6V/20A=R = 180 mOhms

Using AWG calculator or table use AWG 20 to 30 and determine length of wire needed to make 380 mOhms and coil it up and you have a heater or Igniter wire which gets very hot. Better wire is NiChrome or "heater wire" which is high resistance in a shorter length.

Exactly what do you intend to blow up with this wire? ;) everyone is watching you ;)

Answer 3

A short circuit is, generally, just an unwanted connection between two or more points in a circuits, permitting current to take a shorter path than the deisgner intended.

If a short circuit occurs between two signal lines, it probably won't cause a large current to flow, but it will prevent the circuit from operating correctly.

A short circuit between power supply leads will cause a large current to flow. The current will be limited only by the power source's internal resistance, and the resistance of the wires carrying the short-circuit current. If the wires, printed circuit tracks, or other components carry excessive current, they may overheat, melt insulation, burn the PC board, or otherwise cause the circuit to emit the magic smoke that electronics depend on.

Answer 4

LiMn: Li=lithium, Mn=manganese

Continuous discharge current: 20A

This is a type of battery which can supply high current. If your information is correct, during a short circuit this battery may be able to supply upto 20A Max current for a short time. (The amp hour rating is 3000mAh or 3Ah) Which means in normal operation this battery can safely supply 3A for approximately 1 hour continuously.

Short circuit current is usually not specified by the manufacturers as it depends on many factors. If one were to come up in producing 20A out of this battery the internal resistance of the battery must be around 0.18 Ohms and short circuit wire must be of resistance of this value or less. As the internal resistance of battery would be in series with connecting short circuit wire.(Resistances in serious added to produce total resistance)

Finally, short circuit is quite useful in battery cell maintenance. Often Deep cycling Nickel Cadmium battery individual cells on Aircraft batteries require total depletion of voltage. For this particular purpose, after discharge cycle by the charger, low value resister is used across the battery terminals first for a period, then a conductive plate/wire of low value resistance is used to short circuit the battery cell in order to completely drain cell to 0 volt.

So Short circuit in electronics is not all that bad when used within the context and for useful purpose. All the best in learning electronics!