Electronics > Beginners
Power source, internal resistance and Ohm's law?
<< < (3/6) > >>
timelessbeing:

--- Quote from: Mr D on June 05, 2019, 07:30:37 pm ---1 kiloamp is an absolutely enormous current, enough to kill a herd of elephants a 100 times over, right?

--- End quote ---
A couple of car batteries in parallel can produce a kiloAmpere, yet you can safely grab the terminals. You could probably even lick them. Skin resistance is too high. You would have to generate in the order of megavolts to put that much current through a human.

Infinite current would require either infinite voltage, or absolute zero resistance. We have superconductors, but I'm pretty sure the laws of physics don't allow infinite current.
garethw:
1V from a small AA battery is not, at least with technology available today, going to output 1000A. This is because the internal resistance of the battery is far higher than 1mOhm. The internal resistance changes with temperature and is probably not linear with current flow due to the chemical reaction taking place.
Still, a typical NiMH AA battery can output over 20A through a short piece of wire across its terminals, measured with an current clamp.

An ideal voltage source will output as much current as necessary to keep its voltage stable. The simulator is treating the 1V source as if it has infinite current available. Ohm's Law is correct, but real life circuits have lots of hidden gems waiting to screw up your day!

Gareth
Mr D:
Ah wait, i think i'm beginning to get it!

Is it so:

Voltage is the measure of the "push" available.

With ideal, zero resistance the concept of "push" is meaningless?

Therefore with no resistance, the push becomes infinitely strong (if there's no push, there must be infinite flow??!!)

But wait!............. Ohm's law always applies?

But the equation for current with zero resistance is i = V / 0, which is meaningless and not even allowed in algebra?!



garethw:
With regards to the NiMH battery I mentioned just now, Yes I have tried this out of curiosity when I got my current clamp.  :-DMM
As far as I remember the voltage dropped to around 1.25V and drew around 24A during the short circuit. Resistance is Voltage / Current so:
1.25 / 24 = 52mOhm.
This is close to the estimated figure of 50mOhms from Energiser's datasheet.
I definitely wouldn't recommend trying it yourself as it can result in batteries rupturing etc.

Gareth
garethw:
Voltage / 0 = Infinity. That is why the simulator assumes the perfect voltage source has infinite current available.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod