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gbalkam
Post  Post subject: 9 volt battery. 0.05 ohm resistance?  |  Posted: Wed Nov 09, 2016 11:12 pm
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Ok for curiosity sake....
You have a standard, 9v battery.
Then you stick a resistance wire across the +/_ leads.. say 0.05 ohm.....
Ohms law states...
9v / 0.05 resistance = 1620 watts at 180 amps.

Shouldn't this make the battery go boom?


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PhDemon
Post  Post subject: Re: 9 volt battery. 0.05 ohm resistance?  |  Posted: Wed Nov 09, 2016 11:27 pm

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The battery going boom (or at least getting very hot) is a definite possibility, depending on the battery type (if the chemicals in the battery decompose or release gases at high temperature a boom is much more likely). Shorting out batteries can be dangerous... Don't do it!

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janus
Post  Post subject: Re: 9 volt battery. 0.05 ohm resistance?  |  Posted: Thu Nov 10, 2016 1:50 am

Joined: Mon Dec 28, 2015 7:11 pm
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gbalkam wrote:
Ok for curiosity sake....
You have a standard, 9v battery.
Then you stick a resistance wire across the +/_ leads.. say 0.05 ohm.....
Ohms law states...
9v / 0.05 resistance = 1620 watts at 180 amps.

Shouldn't this make the battery go boom?


The battery itself has its own internal resistance which limits the maximum current of the circuit even if were able to directly short it out.


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gbalkam
Post  Post subject: Re: 9 volt battery. 0.05 ohm resistance?  |  Posted: Thu Nov 10, 2016 3:57 am
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Oh, I'm not planning on doing it. Which is why I am posting here.
So just a regular old 9v square battery. (well rectangular).

Now, as I understand a batteries inner resistance, if you draw off power fast enough, the internal resistance is exceeded, which causes a thermal run. In other words, the battery would continue to short, even if you removed the cause of the original short. As the battery heats, the internal resistance decreases until a point where it hits near zero resistance and that is bad juju.

Now, this question wasn't because I was planning on doing this, it is more because of a tv show, MacGyver. Where he, at the intro, uses his famous paperclip on a 9v battery to act as an ignition for some volatile liquid. Gasoline, Kerosene.. Diesel.. can't tell but it burns nicely. With what I do know about batteries, that thing should have popped in seconds. I mean, 180 amp draw from a 9v battery? You could run an electric chair on that.

This is more a theoretical question. For example, what would prevent a simple 9v battery from going boom with that insane draw of current and amps?
I have done a fair bit of research on batteries, since I use them in my e-cig equipment. But I use batteries designed for high drain. 4.2v at 0.08 ohm resistance gives 220 watts at 50 amps in short 3 second firings, with a rest between. So of course, when I saw MacG shorting a 9v transistor radio battery with a 6 inch length of paper clip.. I was like.. Hey.. wait just one cotton picking minute here.....

I suppose it is like those "curving bullets" in the movie Wanted.. looks cool on film, don't try this at home.
And thanks for the answers guys, I should have been a bit more clear on the question in the first post..

So let's rephrase the original question.. what factors would cause that 9v battery NOT to go pop with that much of a load?


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g o r t
Post  Post subject: Re: 9 volt battery. 0.05 ohm resistance?  |  Posted: Thu Nov 10, 2016 11:24 am

Joined: Sat Sep 24, 2016 7:16 am
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A standard alkaline nine volt battery has about 1/4 ohm internal resistance.
As the battery discharge rate increases the internal resistance raises drastically and total battery capacity drops.
So, upon shorting one out, instantaneous current would fall from around 30 amps or higher to around 5 in mere milliseconds and continue to fall in a power curve.

A lithium version would not drop output current as fast and may indeed pop.


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gbalkam
Post  Post subject: Re: 9 volt battery. 0.05 ohm resistance?  |  Posted: Thu Nov 10, 2016 5:10 pm
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g o r t wrote:
A standard alkaline nine volt battery has about 1/4 ohm internal resistance.
As the battery discharge rate increases the internal resistance raises drastically and total battery capacity drops.
So, upon shorting one out, instantaneous current would fall from around 30 amps or higher to around 5 in mere milliseconds and continue to fall in a power curve.

A lithium version would not drop output current as fast and may indeed pop.


Cool. I was watching that show and thinking.. WTH????


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