Measure Short Circuit Current

[umery2k75]

how to measure short circuit current

I have a bench power supply DC from 0V-20V, rated at 0.5A.I set that supply to 12V. I used the Digital Multimeter to measure the short circuit current. I got some reading in Ammeter, but the 12 Volts droped to 0V, as indeed that was a short circuit current.
Then I thought about checking up the short circuit current of my Car battery, it was rated at 12V, then I set my Digital Multimeter on 15A Ammeter, when I tried checking it up, that battery just blew up the fuse of my digital multimeter and wires got very hot and was little bit smoking.

I didn't do any more experiment, because one night, my neighbour car wasn't getting started. His car battery was down. I said to him, I'll help you. I connect the battery from one car to another like this:



I was doing correctly, my Dad said to me, be very careful when connecting polarity of two car battery. If you connect them in reverse, like Positive to Negative and Negative terminal to Positive terminal. The battery would explode.
So I didn't reverse the polarity, just to see whether the battery would explode or not, because I didn't have any more battery available at that time.

So this was the reason, I didn't carry on the Short Circuit check of that battery, because my dad told me, it could explode on reverse polarity, so at that time I thought maybe the battery could explode in short circuit test too.

I think short circuit current test is much like a car's top speed. How far you can push it. Now, I want to check up the maximum current my car battery can supply. Also I want to check the maximum current my AC outlet can give, for this I have to disconnect the fuses and main breakers installed right after the 3 phase AC supply.In this way




But still, I'm afraid of burning up home wiring, that's why I am not doing it. I can see this trend, as shown in figure, the more the current a source has, the more destructible they become.

Its like they all are saying to me. I won't let you measure my maximum current, I will self terminate myself, but I don't let you know my secret maximum current. Small batteries like AA,AAA can give us short circuit very easily, without destroying them self up, but heavy sources destroys themself, but they don't let me know their maximum current.
It's like breaking a speed record on Road, I don't remember the car's name, which goes super sonic, I think it touched around 769 Km/hr or something, but it didn't blew up, that car showed it's maximum speed, much like in the same analogy I have battery, my Home electric supply. I want to know how much those sources can push their self up, but before reaching their maximum output, they all are blown up.

How can I measure short circuit current for all these type of things?

 

[endel]

car battery short circuit current

Well, You can measure the maximum currents, but only once. When you remove all protective elements and use thick enough wires, not to have any significant resistance, then the only factor left to limit the short circuit current, happens to be the destruction of the current source.

 

[FvM]

measuring short circuit current

The short-circuit current is mainly a theoretical value, that can be calculated from grid respectively voltage source impedance, assuming current independent impedance. It is extrapolated from voltage drop measurements at nominal load current (for AC voltage sources, a complex impedance should be used in calculations).

Besides grid short-circuit characteristics, the breaking capacity of fuses and circuit breakers can be topic of interest. Obviously, it must be higher than a possible short circuit current. Also the time-current- or cut-off characteristics can be determined. Some of these measurements require the usage of high currents in the kA range. However I don't expect that you have either the equipment to perform these measurements or can provide the safety means to regard them safe at your home, e. g. an independent emergency-out for your power supply. You should take an opportunity to visit an university electrical energy engineering lab and learn about the way such measurements are performed in a safe way.

 

[Siniša]

short circuit car battery

"short circuit" current of the source can be measured indirectly without blowing things up.
Every practical source will have some internal resistance. This is sum of all limiting factors in your power source in regards to output current expressed as imaginary series resistor.

Acording to Ohm's law, I=U/R, so your short circuit current will be voltage of unloaded power source (e.g. car battery) divided by it's internal resistance.

To obtain value of this internal resistance we don't have to apply short circuit to power source, we just have to measure power source voltages when source is not loaded and when it's loaded with known resistance. From those two values and using Ohm's law we can calculate value of internal resistance and would be short circuit current.
Have in mind that load has to produce enough voltage drop to be measured acuratelly, depending on voltmeter accuracy and resolution. So less accurate voltmeter you are using, more current you have to draw from the source to produce sufficent voltage drop.

Do not create short circuit on battery terminals ever! It is dangerous, you can really hurt yourself, never mind battery.