Earthing negative pole of battery

[Jr.Maxwell]

I have a question where I cannot find a good answer for,

What are the risks of earthing the negative pole of a 12V battery? I think what will happen is that the battery keeps on discharging. Am I right? and Im I missing something?
Thank you for your time.

[Gyro]

You're kidding, right? [EDIT: Too harsh, sorry.]

Where is the circuit path between the positive to the negative poles of the battery? If there's is no current path then there's nothing to discharge the battery.

[Brumby]

Using the words you have, your question does not make much sense at all.

Draw a picture and show us the situation you have in mind.

[SoundTech-LG]

So, try disconnecting earth, and connect a huge mast antenna to the + terminal. It could eventually get a huge charge, at no charge. Just be at least 100 feet away at all times.

[Ysjoelfir]

Using the words you have, your question does not make much sense at all.

Draw a picture and show us the situation you have in mind.

I agree. To be precise: The way you describe it, you want to connect the negative pole of a battery to earth, while nothing is connected to the plus pole. If that is what you are asking - go on, nothing will happen, since you have no path for the current to flow between the pos and neg battery terminal. It all depends on what your intention in doing so is.

[gbaddeley]

Can you provide more context? What else is connect to neg and pos terminals of the battery? To discharge via earth, there would need to be a DC circuit path from neg to earth to pos.

[paulca]

I expect he just wants to ground reference his DC supply.  This would be akin to the ground referenced DC systems in solar setups.  So he gets 0-12V DC with 0V being Earth referenced rather than floating.

But I suppose we are right to confirm this.

[Nerull]

I expect he just wants to ground reference his DC supply.  This would be akin to the ground referenced DC systems in solar setups.  So he gets 0-12V DC with 0V being Earth referenced rather than floating.

But I suppose we are right to confirm this.

I have encountered people who have been told that the ground is an infinite electron sink in physics classes and think that this means that if you connect something to ground all the electrons flow out of it.

[Brumby]

I have encountered people who have been told that the ground is an infinite electron sink in physics classes and think that this means that if you connect something to ground all the electrons flow out of it.

Hmmm...  That would explain the question.

That's not unreasonable for static electricity and lightning, but it is really negligent for such a statement to be made without clear qualification.

[Zero999]

You're kidding, right?

Come on, this is the beginners section!

I have encountered people who have been told that the ground is an infinite electron sink in physics classes and think that this means that if you connect something to ground all the electrons flow out of it.

Hmmm...  That would explain the question.

That's not unreasonable for static electricity and lightning, but it is really negligent for such a statement to be made without clear qualification.

I think that's sensible. The self-capacitance of the earth is 710µF, which is massive, compared to everyday objects which will be in the hundreds of pF, so it can indeed be seen as an infinite source/sink of electrons.

What's missing from this explanation is the conservation of charge and that it's relative. You can connect a battery's negative terminal to an object with a limitless supply of electrons, but the current will not flow continuously. A current will flow, but only until the battery and earth have equal charge. Now I'm aware that statement is probably confusing, since the battery might have several Ah of charge, but that refers to the charge between the terminals.

Forget the battery for now and consider a capacitor, say 1000µF or 1mF. Charge it to 10V. Connect the negative place to earth and only a current will flow for a short period of time. Now disconnect the negative plate from earth and connect the positive plate to earth, again a current will flow for an instant. Disconnect the positive plate and reconnect the negative plate and a short current pulse will flow again. If the previous steps are repeated indefinitely, the voltage on the capacitor will fall to 0V. The reason for this is the capacitor has a self-capacitance, which is not normally specified on the component, or data sheet. The value marked on the can is the mutual capacitance, between the two plates of the capacitor. The self-capacitance depends on the physical dimensions of the capacitor.

Now let's go back to the battery, if we leave it floating, with neither the anode nor cathode, earthed and connected an oscillator circuit up to it. If we connected the output of the oscillator to earth, a current will flow, depending on the specific capacitance of the battery, the voltage and frequency of the oscillator.

[Jr.Maxwell]

Hello again,

Thank you all for taking the time to answer my question, I realise now that I need to work on how I present my questions haha. This question is a pure hypothetical question meant to further enlarge my understanding of the earthing concept. I feel asif I'm having problems understanding the earthing concept.

I understand that one needs to reference metal enclosures of equipents to earth to prevent dangerous situations from happening, but batteries? Should one reference them to earth as well? I can see the point of earthing the metal enclosure of a circuit , but what hapens if I ALSO earth the battery in the same circuit?

What I meant to say in a more practical way was: Say I have a 12V DC circuit powered by a battery. If I reference the 0V of the battery to earth instead of keeping it flooting, what would happen? will current flow from plus to earth discharing the battery? Is it even wise to reference the 0V of a battery to earth? In this same circuit I have earthed the metal enclousure of the circuit.

Sorry for not being clear the last time, I do wish to understand this concenpt.   If There is any selfstudy I can do to understand this concept, point me to it haha:)

[Zero999]

Hello again,

Thank you all for taking the time to answer my question, I realise now that I need to work on how I present my questions haha. This question is a pure hypothetical question meant to further enlarge my understanding of the earthing concept. I feel asif I'm having problems understanding the earthing concept.

I understand that one needs to reference metal enclosures of equipents to earth to prevent dangerous situations from happening, but batteries? Should one reference them to earth as well? I can see the point of earthing the metal enclosure of a circuit , but what hapens if I ALSO earth the battery in the same circuit?

In the case of mains powered equipment, the mains power supply is already referenced to earth, to prevent it from floating, at much higher voltages, relative to earth, due to something like a lightning strike. If a piece of equipment has a conductive case, it needs to be earthed, so the user doesn't receive a shock, if a fault develops, which causes the case to become connected to the mains. There are of course exceptions, such as when all the electrical circuits inside the case are enclosed in an insulating shield, which makes it impossible for the case to become live, if a wire breaks off.

In the case of a battery operated device, there is no requirement for the case to be connected to earth or the battery. Quite often the battery's negative terminal is connected to the case, because it improves screening and reduces interference.

What I meant to say in a more practical way was: Say I have a 12V DC circuit powered by a battery. If I reference the 0V of the battery to earth instead of keeping it flooting, what would happen? will current flow from plus to earth discharing the battery? Is it even wise to reference the 0V of a battery to earth? In this same circuit I have earthed the metal enclousure of the circuit.

Sorry for not being clear the last time, I do wish to understand this concenpt.   If There is any selfstudy I can do to understand this concept, point me to it haha:)

The short answer to this question is no current will flow, without a return path to the battery. There needs to be a conductive path, between the anode and cathode of the battery, in order for a current to flow and simply connecting one battery terminal to earth, will not cause this to happen.

The long answer is, the total charge on the whole battery never actually changes, as it's "discharged". The entire battery contains the same number of electrons, irrespective of its state of charge. When the battery is discharged, electrons flow from the cathode, to the anode of the battery. When the battery is charged, an external voltage source is applied which moves the electrons back from the anode, to the cathode of the battery.^{*SEE EDIT BELOW}

Charge is relative. If we add or remove electrons to the entire battery, then it will become electrostatically charged, with respect to the surrounding environment, but this would not affect the difference in charge between the anode and cathode of the battery. A 1Ah battery would power a circuit for the same length of time, if we removed or added electrons from the entire battery.

EDIT:
When the battery is charged, the same electron doesn't travel from the cathode, through the circuit and back tot the anode. The electric field pushes electrons out of the cathode, repelling other electrons in the conductor. Eventually an electron pushes out of the other end into the anode of the battery. The electrons themselves move very slowly, yet the time between the switched closing and the the current flowing through the circuit is extremely short.

A good analogy for this is, imagine a straight line of snooker balls, each touching one another. Gently tap the first one and the balls themselves will only move slowly, yet the time between the first ball and last ball moving will be almost instant.

[Jr.Maxwell]

 :)Thanks, that made things clear

[Brumby]

Excluding static electricity....

The short answer to this question is no current will flow, without a return path to the battery. There needs to be a conductive path...

This requirement applies to all electrical circuits - AC, DC, battery or otherwise - the word 'circuit' being a big clue!

In the case of mains powered equipment, the mains power supply is already referenced to earth

... which is done by having one side of the electricity supply connected to the dirt under your feet (aka Earth or Ground) usually by a long metal rod driven into it.  It is this act which defines that side as the "Neutral".

These are some key reasons why this is done:

to prevent it from floating, at much higher voltages, relative to earth, due to something like a lightning strike. If a piece of equipment has a conductive case, it needs to be earthed, so the user doesn't receive a shock, if a fault develops, which causes the case to become connected to the mains.

Where many people get confused is the "mystery" of the Earth connection.  There is nothing special about this - just that it is not as obvious as a wire.  The simple fact is that an Earth connection is nothing magic, but a simple, real and deliberate human thing.

[Gyro]

@Jr.Maxwell, thanks for clarifying your question, and sorry that my first reply was sharp.

I find it useful to consider a battery as a simple chemical reaction (that's what it is internally) rather than a holder of electrons or whatever. The only important thing is that the reaction is 'suspended' and cannot proceed while there is no external connection between the Anode and Cathode, it needs electrons to move from one to the other. Once that connection is made, current flows and the reaction can continue. The speed of the reaction depends on the amount of current that the circuit allows to flow. In the case of a direct short circuit, the reaction will complete very quickly and the battery is quickly dead. Thinking about it like this avoids awkward thoughts about electrons leaking to earth or whatever, the only thing that matters is that connection allowing the reaction to continue.

Just one side point, not relevant to understanding but for reference:

I understand that one needs to reference metal enclosures of equipents to earth to prevent dangerous situations from happening,

Mains equipment, especially consumer items, quite often have metal enclosures that are not referenced to earth. This is done by very careful design and testing to ensure that there is tightly specified double 'layer' insulation between the mains and the enclosure, that cannot be accidentally breached by accident, wires coming loose etc. I only mention it because you may come across such items in the future.

[Jr.Maxwell]

Thanks for the insight !

[Gregg]

As Brumby pointed out, you should always consider the complete circuit and what the ramifications of each part of the circuit may be.  It really helps to understand anything electrical.
Next consider what is the source of power; things like a battery, a transformer, mains, generators etc.  Then consider the possible results of grounding one or more parts of the power source and how that may be helpful or even disastrous.
When considering power sources, consider how isolated they really may be.  For instance, your battery is isolated until you connect a charger that may have a ground reference to one of the battery connections.  A transformer can have isolated secondary windings that can be ground referenced is several ways, such as a center tap or one leg; but an autotransformer has one leg  of the output referenced to the primary.
I’ve known power focused electrical engineers that specialized in grounding; there is a lot more to it than meets the eye.
Telco 48 VDC systems are generally positive ground.  I’ve been told it had something to do with minimizing battery terminal corrosion, but I doubt it matters much with modern batteries that are sealed much better than the old fashioned glass jar flooded lead acid ones. The positive ground system did mess with the heads of a number of telco techs.

[paulca]

The long answer is, the total charge on the whole battery never actually changes, as it's "discharged". The entire battery contains the same number of electrons, irrespective of its state of charge. When the battery is discharged, electrons flow from the cathode, to the anode of the battery. When the battery is charged, an external voltage source is applied which moves the electrons back from the anode, to the cathode of the battery.

Not pretending to understand what I'm talking about here, but what you wrote is what I thought actually happened, until someone pointed out to me that the propagation rate of electrons in a conductor like copper is extremely slow.  Like 3cm/minute or something.  Instead it is the electric field moving through the electrons that carries the current, sort of like a wave.  It also relates to the whole skin effect thing and why sharp bends/traces lead to EMF/RF emission and so on.

So this left me wondering how that applies to batteries which are effectively just ion pumps.

[frogg]

Please define "Earth".

Are you talking about literally sticking a pole into the ground (RF or building electrical wiring) or are you using "Earth" to mean "common ground"?

[Zero999]

The long answer is, the total charge on the whole battery never actually changes, as it's "discharged". The entire battery contains the same number of electrons, irrespective of its state of charge. When the battery is discharged, electrons flow from the cathode, to the anode of the battery. When the battery is charged, an external voltage source is applied which moves the electrons back from the anode, to the cathode of the battery.

Not pretending to understand what I'm talking about here, but what you wrote is what I thought actually happened, until someone pointed out to me that the propagation rate of electrons in a conductor like copper is extremely slow.  Like 3cm/minute or something.  Instead it is the electric field moving through the electrons that carries the current, sort of like a wave.  It also relates to the whole skin effect thing and why sharp bends/traces lead to EMF/RF emission and so on.

So this left me wondering how that applies to batteries which are effectively just ion pumps.

You're right, as the battery discharges, the same electron going out of the cathode, doesn't flow through the circuit and back to the anode. I apologise for implying that was the case.

Linking and explaining microscopic/quantum phenomena to the macroscopic world is difficult. I won't pretend to fully understand QED, because it's not something I've studied formally.

The simplest way I can think of describing it is, the electric field created by the electrochemical reaction in the battery, pushes an electron out of the cathode, respelling electrons in the conductor connected to it, until an electron at the other end is pushed into the anode. Think of a tube filled with marbles. Push a marble in one end and the marbles inside it will move along, pushing another marble out of the other end.

[Brumby]

Please define "Earth".

Are you talking about literally sticking a pole into the ground (RF or building electrical wiring) or are you using "Earth" to mean "common ground"?

This is a good question - and it is something worth asking by anyone who isn't sure in any given situation.  It could even be argued that the term "common ground" might be better phrased differently - eg "common" or "common connection" as the word 'ground' can be synonymous to 'earth'.

This confusion will settle down as you become more experienced in dealing with such circuit topology.  Keep paying attention and you will 'get it'.

[paulca]

Linking and explaining microscopic/quantum phenomena to the macroscopic world is difficult. I won't pretend to fully understand QED, because it's not something I've studied formally.

The simplest way I can think of describing it is, the electric field created by the electrochemical reaction in the battery, pushes an electron out of the cathode, respelling electrons in the conductor connected to it, until an electron at the other end is pushed into the anode. Think of a tube filled with marbles. Push a marble in one end and the marbles inside it will move along, pushing another marble out of the other end.

I've been watching hours and hours of physics videos and lectures recently and I get the feeling that they don't really understand how their different models of things actually interact.  Certainly between the "classical" physics and the "quantum" paradigms there are issues where they collide.

In your example - marbles - the electrons still have to move at the speed of light.  It's like the thought experiment if you had a steel bar 1 light year long and hit it with a hammer would the motion travel instantaneously and thus breach the speed of light, but ... no.  the shock travels through the atoms in the electric field at the speed of light.

So in the case of charge travelling in a conductor, it can't be the "particle" electrons moving.  I has to be the charge moving as eletromagnetic waves via the wave like electrons.  More free electrons means easier transfer of those fields between them.  But that leaves the question of what state of an electron records the fact it has interacted this way or not?  Is it just a "virtual" particle exchange in that each electron receives photons of electric field which it immediately releases again and they exchange them down the line.

ElectroBOOM on YouTube (not exactly academic) mentioned something though.  Similar to the steel bar thought experiment, if you consider the electrons as a line (similar to your marbles) and you thump one end with a charge the shockwave travels rapidly though them while the individual electrons do not move much at all.

It still begs the question... In classical physics we say a battery moves electrons from - ions to the + ions on the other side of the electrolyte via the circuit.  If this is the case, and electrons travel so slowly, how is it possible to balance those ions (discharge the battery) so quickly. The slow propagation rate of particle electrons in a conductor makes it impossible to move all the electrons from one side to the other quick enough.  So maybe they don't actually move along the conductor at all.  Do they even propagate through the electrolyte when you charge the battery?

Maybe we should move this to a more general forum.

I want to say, that, no, I don't really understand what I'm talking about.  I also get that physics uses equations which explain things reliably so we can make the predictions of how the world works, but they are analogous models of reality and reality might be very different.  We still use Newtonian gravity because it works and particle physicists still refer to gravity as a "force" when the apex theory of relativity says it's not.  It's only when you try and use multiple sets of these models together that the "WTF!?" moments emerge. 

[Zero999]

Linking and explaining microscopic/quantum phenomena to the macroscopic world is difficult. I won't pretend to fully understand QED, because it's not something I've studied formally.

The simplest way I can think of describing it is, the electric field created by the electrochemical reaction in the battery, pushes an electron out of the cathode, respelling electrons in the conductor connected to it, until an electron at the other end is pushed into the anode. Think of a tube filled with marbles. Push a marble in one end and the marbles inside it will move along, pushing another marble out of the other end.

I've been watching hours and hours of physics videos and lectures recently and I get the feeling that they don't really understand how their different models of things actually interact.  Certainly between the "classical" physics and the "quantum" paradigms there are issues where they collide.

In your example - marbles - the electrons still have to move at the speed of light.

No they don't. The marbles themselves move very slowly, yet the marble pops out of the other end almost instantaneously.

It's like the thought experiment if you had a steel bar 1 light year long and hit it with a hammer would the motion travel instantaneously and thus breach the speed of light, but ... no.  the shock travels through the atoms in the electric field at the speed of light.

All analogies have their limits. In the case of a steel bar, struck by a hammer, the shock travels at the speed of sound. The same also applies to the marbles, assuming they're in physical contact with one another, although I think it will be slightly slower because there will be tiny gaps between them. In both cases the shock or motion propagates in a wave like manner.

So in the case of charge travelling in a conductor, it can't be the "particle" electrons moving.  I has to be the charge moving as eletromagnetic waves via the wave like electrons.  More free electrons means easier transfer of those fields between them.  But that leaves the question of what state of an electron records the fact it has interacted this way or not?  Is it just a "virtual" particle exchange in that each electron receives photons of electric field which it immediately releases again and they exchange them down the line.

ElectroBOOM on YouTube (not exactly academic) mentioned something though.  Similar to the steel bar thought experiment, if you consider the electrons as a line (similar to your marbles) and you thump one end with a charge the shockwave travels rapidly though them while the individual electrons do not move much at all.

It still begs the question... In classical physics we say a battery moves electrons from - ions to the + ions on the other side of the electrolyte via the circuit.  If this is the case, and electrons travel so slowly, how is it possible to balance those ions (discharge the battery) so quickly. The slow propagation rate of particle electrons in a conductor makes it impossible to move all the electrons from one side to the other quick enough.  So maybe they don't actually move along the conductor at all.  Do they even propagate through the electrolyte when you charge the battery?

The conductor is a transmission line and the same is true for a long steel bar, being struck at one end. The steel bar will only move a tiny amount, relatively slowly, compared to the speed at which the shock will travel from one end to the other.

[IanB]

I find it useful to consider a battery as a simple chemical reaction (that's what it is internally) rather than a holder of electrons or whatever.

This is a very important insight. Actually all chemical reactions involve the movement of electrons. A battery (an electro-chemical cell) is just a special device for capturing the moving electrons from a reaction and diverting them out through the electrodes and wiring. An interesting feature of a battery is that if you don't let the current flow then the chemical reaction is stuck in "suspended animation" and cannot move forwards. (Except for self-discharge and shelf life--the reaction still tends to proceed slowly even if the external current isn't flowing.)

[paulca]

I've been up and down the Internet trying to get a satisfactory answer for this and the concensous answer seems to be ...

Charge (or current depending on your pedantry) does not flow as electrons, it's flows as EM fields between electrons.

However this means the classic text book battery being a chemical reaction that moves electrons through a membrane creating positive and negative ions and then returns them via the circuit has to be wrong as the electrons cannot traverse the circuit fast enough.

The marble idea does not cut it.  It's basically saying in "Newtons balls" the middle balls do not move, but the mommentum transfers instantly (at the speed of sound in the balls).  However, that works for 1 marble/swing.  If you want to put 1,000,000 balls _through_ the device then the middle balls must move at the speed of the overall flow. 

It also opens questions about charge and the relationship to electrons.  If Electrons are a "carrier of charge", that suggests an electron can be low charge or high charge, but ... asides not making any sense.  I have never seen anything describing an electron this way.  I have seen electrons having state in that they can be excited into a higher orbital or a lower one by quantum jumps, but not charge.

What I mean is... if you have one of the electrons sitting in the conductor minding it's own business and it gets hit by a photon of EM as the current is "flowing",  at that instant in time, how would you then describe it's state to denote it has received such a photon and is likely to emit one?  Feynman diagrams and virtual particles?

It sounds easier to describe it as an EM wave flowing through the combined electron field of the conductor.... still leave me stuck on the battery though.