why does a car battery spark

Ever heard of a monostable multivibrator?

No. THAT is an ARC.

They also do when NOTHING is connected to them. D'oh!

You short across those poles and watch!

Oh goodie, we have an expert here.

Can a AAA battery make a visible spark?

John

Is that your way of making yourself feel superior? Too bad you have such an utter disregard for your own ignorance. There are many great minds of humanity and your not one of them. Maybe next life?

Most of those "sparks" are actually bits of the metal being thrown off. Even low voltage batteries will do it. Especially if they have a high shorted pole current value.

Remember? No arc in a vacuum until... Once it does happen, the voltage required for a repeat arc is much lower. This is due to gasified metals, and other conductive debris filling the vacuum chamber after the first spark occurred. It is almost the same as water NOT being conductive until some salts or other compounds or elements get introduced into it.

When an electron stream (arc talk) leaves a conductor, some of the molecules on the surface of said conductor can be ripped away and "splash" into the other conductor. Also, the electron stream hitting the other conductor can exhibit surface molecules to the air as well, if the current the arc carried was high enough. Also electron that move from a conductor to the air and then back into a conductor will exhibit X-rays. ANY electron stream exhibits X-rays when it strikes its destination conductor. The flux produced is greater for some conductors than others.

Sustain time is also a factor since HV is required, and is not always available at a high current value. So the moment of the arc maximizes the current for a split second until all the stored energy is gone, and then it stabilizes at the value the (power supply)circuit is capable of providing.

So the first milliseconds of the initial arc are going to be at the max current value of the stored energy of the supply system (source). Once that is dumped, the supply gives whatever its max clamped value is, which could be mere milliamps and usually is.

You derived that from what I said? You have a pretty convoluted view.

Depends on its capacity. Brand new, or newly charged... perhaps so.

Where do you see a claim of superiority in that remark, you retarded little piece of shit?

Too bad you have no clue about anyone's ignorance, much less your own.

You wouldn't know. All you are is retarded, pussified speculation.

Sorry, but no, I do not date retards.

That's not a definition of "spark." Dielectric breakdown of air is one of many ways to make a spark. Flint and steel will do it too. Campfires make sparks.

A voltage source plus metal-metal contact makes great sparks with no air dielectric breakdown required. The current density and the temperature can get extreme with even a little 9 volt battery... 1 amp on a 1 mil square area is a million amps per square inch. At that density, the metal turns to plasma, UV is blasting the contact areas, metal vapor is oxidizing, magnetic things are happening... it's literally hell.

John

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"A spark is triggered when the electric field strength exceeds approximately 4 - 30kV/cm[2] ? the dielectric field strength of air."

I can't tell if they mean 4V - 30kV or 4kV - 30kV, if they mean the latter... then batteries are no where near that

so... the difference between the car battery and the table top battery is how much current the thing can source, right? so is that the parameter... can a 2V battery that can source 10A then cause a spark (if you short the leads) while a 10V battery that can source 100mA can't

I'm only talking about visible sparks, and I'm not talkin about static electricity, just shorts... no esd

any thoughts? thanks

John Larkin had it right- with enough energy, you will vaporize metal When you open a contact, the current doesn't want stop and that when the gap is very small, even 12V is sufficient to cause a field of the order of

30kV/cm and breakdown and conduct. If the current is limited as when you use a series of AA batteries, there is little energy involved and the gap stops conducting quickly. The result is that the spark is minimal and of short duration so that you don't see it. Typically when using a car battery, there is far lower circuit resistance and the spark goes to the next stage- an arc which is a hot plasma enhanced by the vaporization of metal from the contacts. It has the nasty characteristic that over a range, the voltage across the arc drops as the current increases (for a given length) so it is doing little to reduce the current. With DC an arc will be sustained until energy can be removed faster than it is being produced and this implies lengthening and cooling of the arc. At 12V with only a few ma this is very quick and the arc stage may not even be reached. At 12 V with a short circuit on an automotive battery, the current could be several hundred amperes and lots of fireworks. AC is much easier to interrupt because AC goes through zero every half cycle, at which time the arc collapses and it is relatively easy to clear out the conductive path. You can see this in the ratings of some switches- 15A, 120V AV and 30V, 5A DC (or they may not be rated for DC at all).

-- Don Kelly snipped-for-privacy@shawcross.ca remove the x to reply

Try again. A fresh 9-volt battery sparks, arcs, and hisses nicely. Just adjust the gap carefully.

I can see sparks while shorting a AAA battery.

John

Just wire a hundred of them in series and bring the two wires together. Don't worry - they are only crappy little batteries that probably won't even deliver 2 amps. Hardly kill you at all.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff

Right, you don't actually need a thousand volts or whatever to get an arc going, because heat from point-of-contact resistance will ionize the air. Then you only need the sustaining voltage of an arc. According to your little experiment, 9 volts will sustain an arc. And without doubt you can sustain an arc with about twice that, because welders operate on voltages in the low double digits. The fact that your tiny RatShack welder worked better with a rusty screwdriver than a shiny one makes me wonder if a sort of continuous ionization of the air caused the effect rather than a truly sustained arc. Not that it matters a whole lot for the purposes of the discussion. I did a welding repair on my truck this summer using two starter batteries in series, for 24 volts nominal, probably less than that on account of the heavy current draw. To get a starting spark, I had to scratch the welding rod against the piece of metal I intended to weld. Once I got a spark that way, I got a nice hissing blue arc and made a nice weld. Jumper cables make ok welding cables.

Yeah that makes sense. You can charge up a cap to a few volts and then make a nice spark.

And yes in my darkened office/lab I can see the spark form a 9V battery.

Now electric field breakdown is cool. As you reduce the pressure the E field strength needed to cause a breakdown first decreases and then increases.... I would guess the minimum is in the 1 Torr to 1 milli Torr range (right where thermocouple gauges work.) but I couldn't find the answer in a quick web search.

George H.

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Hee Hee, I used a cable with alligator clips

early

Yup.... same cable with alligator clips.

George H.

I think the rust particles make the nice sparklers you see at initial contact.

John

So this thread has two experimenters and a zillion theorists.

John

And you're such a coward that you hide behind a pseudonym.

Please go away.

Thanks, Rich