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Ohms's Law Violation

01/29/2017 8:54 AM

A fully discharged lead acid battery cell has a potential difference of 2 Volt (any one can measure it with voltmeter ). If we connect a 2 ohm resistor across the battery cell, then according to ohm's law , the battery should circulate I=2V/2 ohm =1A current continuously. but in actual, a discharged battery cell cannot circulate any current. is it not violation of ohm's law? any explanation?

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#1

Re: Ohms's law voilation

01/29/2017 9:07 AM

A discharged battery has a high internal resistance which your circuit diagram does not show. That resistance is in series with your load resistor, making a voltage divider.

Replace that 2-ohm resistor with, say, a 1kΩ resistor and measure the voltage. Less than 2 volts but greater than zero, no? Now, using the voltage across the 1kΩ resistor and the fact that the open-circuit voltage of the battery is 2 volts,

1) calculate the battery's internal resistance.

2) what load resistance would you need such that the battery voltage is 1 volt?

3) are they the same?

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#2

Re: Ohms's law voilation

01/29/2017 10:19 AM

Bravo. You have now discovered the difference between an ideal and a real voltage source. A fully charged battery is reasonably close to an ideal source but as the battery becomes further discharged that changes. Follow the steps that Andrew described to identify the state of your battery. (Also, your battery cell is not fully discharged.)

All real components (capacitors, resistors, wires, diodes, fully charged batteries, etc.) differ from their ideal characteristics. The differences from ideal are electrically described by making a more complex model of multiple ideal components. The series resistance described is but one model of the difference between a battery in any state of charge and an ideal voltage source.

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#15
In reply to #2

Re: Ohms's law voilation

01/29/2017 4:23 PM

We're wasting our time. He is impervious to new information.

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#16
In reply to #15

Re: Ohms's law voilation

01/29/2017 4:29 PM

Hey, wait for me!

I've had all of the spoiled pizza boy I can stand.

<exit, stage left>

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#20
In reply to #15

Re: Ohms's law voilation

01/29/2017 7:56 PM

"We're wasting our time. He is impervious to new information."

Yeah, but going by the number of responses he gets to his inane questions, many here find it entertaining, and that - no matter the subject - is the key to a good discussion .

One would hope, albeit rather futilely I fear, that he may actually be learning something from all of this - I certainly am.

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#21
In reply to #20

Re: Ohms's law voilation

01/29/2017 8:20 PM

Haris started here:Parameter Settings of SENTRON 3WL11 10 ACB 6 years ago and has steadily asked more and more questions instead of doing any work himself.

These questions are not those of an educated contemporary.

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#24
In reply to #21

Re: Ohms's law voilation

01/29/2017 8:46 PM

226 posts later he still doesn't know batteries have internal resistance and thinks Ohm's Law is violated instead - and presumably works in a technical capacity somewhere dealing with circuit breakers and MW-scale generators?

Oh boy.

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#36
In reply to #24

Re: Ohms's law voilation

01/30/2017 9:07 AM

Indeed.

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#22
In reply to #20

Re: Ohms's law voilation

01/29/2017 8:21 PM

True. Sort of like watching a techie version of Lost being enacted right before our very eyes.

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#35
In reply to #20

Re: Ohms's law voilation

01/30/2017 8:35 AM

You got it. As soon as I saw who posted it, I immediately opened this discussion. He does try to make us think again about the basics, doesn't he? He is creating a bit of a schooling refresher.

Do you suppose he is actually a genius and he is trying to see if we really have a grasp on basic laws and theorems? Could he be just playing with us?

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#38
In reply to #35

Re: Ohms's law voilation

01/30/2017 10:28 AM

"Do you suppose he is actually a genius?"

No!

To paraphrase Oscar Levant: “There's a fine line between genius and ignorance. Haris has erased this line.”

Haris is a genius at asking ignorant questions!

Ignorance - Wikipedia

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#39
In reply to #38

Re: Ohms's law voilation

01/30/2017 11:41 AM

Ah, but, he is a genius at getting you upset and provoking some extra fine cutting responses from many of us. He even had me going the other day on a lightning post. Perhaps he simply revels in such mischievousness. (new type of troll????)

If one had such a bent in life, one would only need to review the last 5 or so years to see what type of post gets such responses from the populace who frequent CR4. Could be great fun for some.

The cure for that is to ignore the imp.

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#3

Re: Ohms's law voilation

01/29/2017 10:30 AM

The open circuit voltage may read 2 volts, but that only applies when virtually zero current flows. You are measuring the potential difference between the 2 electrodes - one containing only a trace of PbO2 coating (the active material on the cathode in the charged state) and the other just lead (anode). As soon as you try to draw any current the cell voltage will fall to near zero simply because there is insufficient "fuel" (PbO2) to support the electrochemical reaction.

If you were to use an old voltmeter that consumed significant current to produce a reading, then it would read 0v, or nearly so.

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#4

Re: Ohms's law voilation

01/29/2017 10:55 AM

If the battery is fully discharged, there will be no lead ions of the correct charge state to constitute a flow of current. That is, ipso facto, the fully discharged state.

That means a fully discharged battery will have no voltage across it. Should you charge the battery you would build up an inventory of lead ions in the charged state and this would continue until all the lead ions that could be charged, were charged and the battery would no longer accept charge. Incrementing the voltage would dissociate water into H2 and O2. With a platinum catalytic cap this would combine into water and fall into the battery and a steady state would ensue, and the battery would be warmed by all this activity.

A vented battery would lose water until only oleum(100% SO3 + H2O) remained and the electrodes might not be covered.

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#5

Re: Ohms's law voilation

01/29/2017 11:07 AM

Ask your instructor!

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#6
In reply to #5

Re: Ohms's law voilation

01/29/2017 11:32 AM

My instructor said that battery is not a "Voltage source" .It is actually a"Current Source". did you know that ????

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#7
In reply to #6

Re: Ohms's law voilation

01/29/2017 11:46 AM

Does your instructor work at Pizza Hut too?

Without voltage the current won't go anywhere. Google emf.

Make mine a pepperoni with double cheese.

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#8
In reply to #7

Re: Ohms's law voilation

01/29/2017 11:58 AM

without voltage no current ? then lets circulate current from a discharged battery.

why don't u have "voltage BBQ" with "Current sausage" .

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#28
In reply to #8

Re: Ohms's law voilation

01/29/2017 10:49 PM

To circulate current, an energy source is required. By definition, a discharged battery has no energy left, so some other source of energy will be required to cause a current to circulate. What other source are you assuming?

I haven't the slightest idea of the meaning of your second "sentence", assuming there is a meaning...

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#10
In reply to #6

Re: Ohms's law voilation

01/29/2017 12:53 PM

He sounds like one of the number of halfwits that I see on a few electronics forums most days who learned their electrical theory for the village idiots stupid cat.

I know of one that will argue with you all day that a generator or alternator is not a constant voltage source but a constant current source that continuously varies its current output to keep the voltage constant. And he's one of the better half wits to deal with.

As far as professors go, just because they have a job in a teaching position doesn't mean they actually know a damn thing correct about the reality of whatever it is they are trying to teach others.

Personally I could write a book of the stories of the stupid things I have seen so called experts (long term experienced ones at that) say and explain that were dead wrong and easily proven and with many even proven wrong by themselves without their realizing they did it when they explained some other aspect of a subject.

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#13
In reply to #10

Re: Ohms's law voilation

01/29/2017 2:47 PM

At one time our pizza boy claimed to be working on a 25MW 132kV grid-connected coal power station.

He's been coming here for over 5 years and is still asking elementary questions, all easily answered by a simple search.

He's hopelessly lost and dangerous.

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#37
In reply to #10

Re: Ohms's law voilation

01/30/2017 9:33 AM

As far as professors go, just because they have a job in a teaching position doesn't mean they actually know a damn thing correct about the reality of whatever it is they are trying to teach others.

In college, I had 2 EE professors who had been in the real world, or at least close to it. One came from Bell Labs, and the other had worked for several electrical power companies. They were the best teachers I encountered in 6 years in college. The remainder were just there for their ability to do research, and that was the set of their thought train.

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#11
In reply to #6

Re: Ohms's law voilation

01/29/2017 1:38 PM

If your instructor is worth his salt he very likely said that a battery can be

1) modelled as a voltage source in series with a resistor (Thévenin equivalent)

or

2) modelled as a current source in parallel with a resistor (Norton equivalent).

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#14
In reply to #6

Re: Ohms's law voilation

01/29/2017 3:58 PM

Really?! Your instructor say a battery is a current source and not a voltage source. Well either you should listen more carefully or you should find another instructor.

Riddle me this then... Why is a AAA battery identified as 1.5 volts instead of 100 milliamperes?

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#31
In reply to #14

Re: Ohms's law voilation

01/30/2017 7:07 AM

Why is a lead acid battery rated as C20=60AH ?

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#32
In reply to #31

Re: Ohms's law voilation

01/30/2017 7:17 AM

How else would one rate the capacity of the battery (rhetorical question - NNTR)?

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#33
In reply to #31

Re: Ohms's law voilation

01/30/2017 7:55 AM

Because the total number of Coulombs of charge identifies if an AA or an AAA battery is needed. Since the number of Coulombs is an impractically large number the unit of Ampere Hour (AH)

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#9

Re: Ohms's Law Voilation

01/29/2017 12:45 PM

Not all electrical phenomena follow Ohms law. Battery are largely driven by a chemical reaction that just happens to be controlled by electron flow. (over simplified I know.)

Same concept with semi conductors. Very few attributes of an semiconductors operation can be defined by Ohms law as well.

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#12
In reply to #9

Re: Ohms's Law Voilation

01/29/2017 2:10 PM

Both, however, can be and are modelled by equivalent circuits that use Ohm's law (often in addition to other laws as well); the circuit complexity typically in proportion to the accuracy of the model. A bipolar transistor for example

At high frequencies, even a simple resistor behaves like this circuit

Here, however, in the case of the OP's problem, the battery can be simply modelled as an ideal voltage source in series with a resistor, as a first approximation. The OP seems to be completely unaware that batteries have an internal resistance.

If this bloke is in college, he is not paying attention. If his instructor is actually telling him what he is repeating here, he needs to find a better school. If his instructor is indeed a college professor, it is highly, HIGHLY doubtful he is telling the OP what the OP remembers of the lesson. I suspect that either this is the case, or his fired 'professor' now works alongside him at Pizza Hut and is telling him this tripe.

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#17
In reply to #12

Re: Ohms's Law Voilation

01/29/2017 5:06 PM

Yes exactly.

Under very specific sets of conditions certain aspects of a active semiconductor device can be made to fit into an Ohm's law equation and give a valid answer but that itself does not make it a unifying and all encompassing realistic or accurate method of representing the device/component, or any devices/components, full characteristics and function.

If it did there wouldn't be dozens of other fundamental electrical physics laws and their formula's to mathematically represent and describe other aspects and function of electrically related phenomenon both in theoretical and real live operation.

'Sort of fits some times' doesn't mean it's the correct process all the time.

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#19
In reply to #17

Re: Ohms's Law Voilation

01/29/2017 5:32 PM

Of course it doesn't fit all the time and this is understood. The large-signal model of a bipolar transistor is different than the small-signal model, for example, yet it's the same part. They're all tools and, like tools, you pick the right tool for the job, whatever it is - or build your own if no tool yet exists. But you're right, they're all approximations and, as approximations, go only so far. Most times first approximations work just fine. In the OP's case, he's not even familiar with that much. Baby steps.

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#18

Re: Ohms's Law Voilation

01/29/2017 5:11 PM
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#23

Re: Ohms's Law Voilation

01/29/2017 8:42 PM

For someone who can measure Voltage it seems it did not appear to you that you could measure the Amperage for a quick check.

Or did you?

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#25

Re: Ohms's Law Voilation

01/29/2017 9:13 PM

In the interest of fair play, India has many very intelligent EE's, other engineers, scientists, and other professionals and workers.

We have members who are respected educators, scientists, technicians and professionals.

Haris is not representative of the vast majority of Indian professionals.

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#26
In reply to #25

Re: Ohms's Law Voilation

01/29/2017 9:17 PM

I know that I'm bending backwards to say this but I hope some of these questions are from their child using their CR4 account.

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#27
In reply to #25

Re: Ohms's Law Voilation

01/29/2017 10:04 PM

Sorry, just reminded that Haris is from Pakistan, not India. No offense meant to either nation's engineers, scientists, professionals and residents.

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#29

Re: Ohms's Law Voilation

01/30/2017 1:19 AM

Go to the EEVblog in YouTUBE and learn how batteries actually work.

This reminds me of the Batteriser BS.

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#30

Re: Ohms's Law Voilation

01/30/2017 4:03 AM

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#34

Re: Ohms's Law Voilation

01/30/2017 8:32 AM

I don't know whether to stay here and laugh at the stupid/idiotic "coolya" posts, or go elsewhere and do some serious REAL work!!!

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#40

Re: Ohms's Law Violation

01/30/2017 12:33 PM

I think it must be a social point he is trying to make. For instance, when in need of some temporary labor, one might drive by the employment office to find all kinds of potential workers for a particular task. The problem is that they represent fully discharged batteries. Consequently, that which may appear to be a good source of usable energy (upon initial investigation) may actually be nothing more than an empty vessel, or fully discharged battery.

Digital voltmeters are like eyeballs. They see lots of potential, even when it isn't real...

No laws violated here. Only minds.

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#41
In reply to #40

Re: Ohms's Law Violation

01/30/2017 12:40 PM

So, he's just lonely?

I'd ignore him, but it is mildly interesting to see what's next.

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#42

Re: Ohms's Law Violation

01/30/2017 4:54 PM

You have no understanding of Ohm's Law! ...... Measure the terminal voltage WITH the 2 Ohm resistor connected NOT open circuit!!!!

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#43

Re: Ohms's Law Violation

01/30/2017 5:04 PM

This is getting very disturbing given what you have implied you do for a living.

This is basic stuff, more so the answers are easily found with a simple online search.

Stop being lazy and do some basic research online yourself before asking us basic electrical questions an average college student (or younger) could answer. Your not some ten year old kid asking homework questions in school, take your very dangerous job seriously.

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