Battery cable came off!

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Hi, was checking my '95 Civic 1.6L today. It was idling, and I heard the idle sound change: it seemed higher. I stepped on the gas a bit, and I heard a soft electrical "pop" near the stereo panel. I hurriedly
shut down the engine, I found that the negative battery cable had come off! (It had a quick-release connection). I connected it, restarted and found everything working fine, even checked all the stereo functions, LEDs, and the ECU.
I've read that the battery acts as a big capacitor to smooth out voltage spikes. The entire episode didn't take more that 10 seconds, but I'm worried... could there be any permanent damage?
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For an event like that, the damage will be clear immediately. The only electrical zaps I've seen delayed failures on were lightning strikes. I've dealt with about two dozen lightning strikes (one on a bizjet, the rest at communication sites) and have come to the conclusion that although the failure rate drops off after 6 months the equipment is often never completely right again.
Sounds like you dodged the bullet. Congratulations!
Mike
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sharx333 wrote:

You read wrong. The battery reacts too slowly to absorb spikes, it lives at 12V versus your alternator's typical 13.5-14.5V, your alternator wouldn't produce a spike unless it failed spectacularly, and having the terminal come off wouldn't cause a spike either.
Ultimately, cars have batteries for one purpose: starting the engine. Once the engine is running, the alternator provides for all the car's power requirements. Yes, batteries are also used to power accessories when the car is off, but the only reason they're there in the first place is to crank the starter.
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It absolutely would. Damage may not always occur, but there will be spikes.
The battery's secondary function IS to provide a buffer for the alternator's pulses. Connecting the cables together without the battery in between is dangerous to the car and should NOT be done. You could to that n 1976, but not now.
http://www.uuhome.de/william.darden/carfaq2.htm

See the above link.
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Tegger

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To clarify;the alternator generates AC voltage which is rectified to pulsating DC,and the ONLY thing that smooths it to reasonably pure DC is the battery. Otherwise,your car radio would be buzzing in tune with the engine RPM.
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Jim Yanik
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Tegger wrote:

Fair enough - a SIGNIFICANT spike.

And pray, how does it do that? It's not a voltage regulator, it's not a capacitor. Internal resistance limits how quickly it can react to voltage changes.

You mean the battery cables? Yeah, that'll fry your alternator in a hurry, since you're basically shorting its output.
> You could to that n 1976, but not now.
I wouldn't even try it in a '76.

See the phrase "IN THE FIRST PLACE" in my above paragraph.
Of the four uses Darden lists for the battery, I've already noted the first and fourth above... for the second ("filter and stabilize") it can only do so much - there's still ripple in the voltage measured even with the battery, as the charging voltage is usually well above the battery's voltage... as for the third, if the battery is really needing to "provide extra power" while running, then the charging system is under-rated to begin with, and the battery is acting as a band-aid.
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Matt Ion wrote:

Uh, the battery is nothing more thann a large capacitor. Capacitors are the main components of voltage "smoothing." You know, like radio noise suppression etc.
JT
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Grumpy AuContraire wrote:

Actually, they're not. Capacitors /store/ electrical energy. Batteries /create/ it via a chemical reaction. Charging a battery is not storing energy; it's (to oversimplify) merely reversing the checmical reaction.
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Matt Ion wrote:

Technically yes, but both smooth voltage..
JT
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Grumpy AuContraire wrote:

Batteries do, to a degree. That's not what they're designed for though.
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But it's one of the things they're *used* for.
Do you want to email Bill Darden and tell him he's wrong?
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Tegger wrote:

I didn't say he was wrong.
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Batteries most definitely do have capacitance, do you have a meter?
Batteries most definitely do store energy when charged. Or are you suggesting that when it is used up that more is created out of nothing?
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Capacitors are electrostatic while batteries are electrochemical. A capacitor capable of storing the energy within a car battery and power capability needed to start a car would be the size of a double long semi.
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True, but nobody is suggesting that you start your car with a capacitor. At issue was the batteries ability to absorb spikes from the alternator. Given that, batteries do have capacitance. I don't know how much it should be to be effective though, but its there.
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jrk wrote:

Sure they do. A pair of wires running side-by-side do too. Not enough to consider them functional "capacitors" though.

Yes, they store energy... but not ELECTRICAL energy. That's generated out of a chemical reaction.
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I've seen such a "pair of wires" literally used in a electronic circuit for a capacitor,by DESIGN.
Engineers modeling components like a battery for computer aided design,the battery model definitely has capacitance. Even the electronic symbol for a battery is two plates,just like a capacitor.

yes,it is electrical energy. What other sort of energy would it be?

differing from electric charges generated by friction;static electricity. They both are ELECTRIC charges,though.Both are electric current,too.
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Jim Yanik wrote:

Sure, usually in RF circuits where very tiny amounts of capacitance are needed. Sometimes a "capacitor" even exists as just a pair of interlaced traces on the circuit board. And in high-frequency designs, particularly network cables, the inherent capacitance of the wires must be taken into account.
That doesn't mean a pair of wires *are* "a capacitor", or that in most cases the inherent capacitance is of any concern or use, any more than the capacitance in a lead-acid battery is of any concern or any real use.

Well, usually a series of stacked plates of alternating lengths. But that's true of the the symbol for ANY battery, including your good old carbon-based flashlight batteries.

They don't STORE electrical energy. When you charge a battery, the electrical (kinetic) energy you feed into it creates a chemical reaction; the electrical energy is converted to chemical (potential) energy. When not charging, the inverse chemical reaction converts chemical energy back to electrical energy.
In a very simpistic sense, sure, a battery is "storing" electricity (as opposed to "electrical energy"). At the physics level, it's merely converting one form of energy to another.
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When you DRAW current from a battery,how does the chemistry knows to start converting chemicals to electric current? Where does that initial current come from?
Simple,the *charge on the plates* decreases and the chemical reaction adds more electrons to fill the depletion of the plates charge.
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Jim Yanik
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Jim Yanik wrote:

Very good, you get a gold star.
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