batteries, capcitors, energy and charge

[e44-72]

Hello

I maybe should have put this in the physics section of this forum. I have some questions I wondered if people could help me with.

I understand that charge in coulombs, Q can be descrbed as the amount of charge tansported by 1 ampere of current in 1 second. Or the amount of charge of 1 farad charged to a potiential difference of 1 volt.

I understand current tranports charges around the circuit and that the power supply (voltage) supplies these charges with energy to deliever to components to be converted into other forms of energy such as heat, sound, light etc.

Here are some questions:

Do batteries store charge and/or energy? Does the amount of energy from a battery in joules get used up or the amount of charge and when its dead has it released all energy and/or charge?

Do capcitors store energy and/or charge and does it release its charge and/or its energy.

Thank you for reading and any help you can give, I confused between whether charge or energy or both is stored or used.

 

[Sceadwian]

Generally speaking capacitors store energy directly in the form of an electric field created between two conductive objects separated by a non-conductive material. Charge does flow into and out of a capacitor's plates but outside of leakage current charge does not flow from one plate to another, only the energy is transferred via the electric field interaction between the two plates.

Batteries are electrochemical devices and vastly different from capacitors. The energy in a battery is stored in the potential difference between two different chemical substances, generally metals. Nothing in a battery is every really 'used up' it's just energy converted from one form to another and moved between the two plates, once it's done if the chemistry allows for it the charge flow direction can be reversed and the chemical's required for the release of energy will reform, this however is vastly complex and there are many issues involved with electro-chemistry that are FAR outside the realm of electronics in general.

Understanding batteries exact functioning is a field best dedicated to chemists. Electrical equivalents can be made for most battery types allowing people in electronics to understand the behavior if not the details of what's going inside a cell.

 

[e44-72]

Thank you sceadwian for your answer,
If nothing is ever used up in a battery why is it over time the batteries potential difference drops?.
Does this mean batteries do store charge or is it just energy?
Thank you for your help and replies

 

[Sceadwian]

The potential difference drops over time because the chemistry has had electron or ion flow between molecules and atoms which have reduced the number of charge carriers available, generally through oxidation or other impurities causing the atoms to be no longer usable for charge carrier transfer.. Nothing is actually 'used' up, outside of radiation and true electron transfer (which isn't much) the exact same amount of totally energy is available in the cells, outside of the tiny fraction of a percent of chemical energy which is what we can actually use.

Over a finite period of time the chemical impurities of inefficient charge transfer build up and impurities take their tolls, rendering the cell unable to store energy. The charge carriers are there, they're just unavailable for electron transfer. Capacitors store their energy in the electric field, this is a fundamental function of space itself nothing so crude as the chemistry of a battery.

 

[e44-72]

Thank you again for your help, I also just wanted to ask if I have a battery not connected too anything so no current flows would charges build up on the terminals of the battery when not being used?

 

[harold777]

e44-72 you have to be careful to know if the "Battery" (strictly a cell, a battery is several cells joined to increase the voltage), is primary, ie a 1-use like most cheap domestic "batteries". and secondary batteries as used in a car, for example which are charged as you drive along, ready for the next day's start (etc).

A worn-out primary battery can recover . . . there is a limited space for the chamicals and once the cell is discharged the voltage drops to zero (well nearly so). ...then after a while the cell can recover (esp. if heated - but Never do this without precautions/supervision).
So, yes a battery can "recover"

There is a "similar" action in capacitors - If you discharge a large electrolytic capacitor (through a low-ohms resistor - NEVER with a dead-short), the voltage goes to zero. But leave it with the terminals open and a voltage will appear . . . I think this is due to ion drift, but it can give inexperienced folk a nasty jolt if the capacitor was in a high-voltage circuit. Old TV's ( when valves/tubes were the norm) were particularly difficult as the charge could reappear as if by magic.

Why are you asking?
It's not a usual subject-line?

 

[ChrisP58]

There is a "similar" action in capacitors - If you discharge a large electrolytic capacitor (through a low-ohms resistor - NEVER with a dead-short), the voltage goes to zero. But leave it with the terminals open and a voltage will appear . . . I think this is due to ion drift, but it can give inexperienced folk a nasty jolt if the capacitor was in a high-voltage circuit. Old TV's ( when valves/tubes were the norm) were particularly difficult as the charge could reappear as if by magic.

This behavior is know as Dielectric absorption, and varies with different dielectric materials. There is a good explanation in Wikipedia at https://en.wikipedia.org/wiki/Dielectric_absorption.

When capacitors are used as power supply filters and decoupling components, it can usually be ignored other than as a potential safety hazard. But when a capacitor is used in a signal path, such as an audio circuit, it can be a source of distortion. As a sampling component in an A2D converter, it can cause measurement errors.

 

[Ratchit]

e44-72,

I maybe should have put this in the physics section of this forum. I have some questions I wondered if people could help me with.

I can help you with this.

Or the amount of charge of 1 farad charged to a potiential difference of 1 volt.

Charge is not measured in farads, it is measured in coulombs. Capacitors are not charged, they are energized.

I understand current tranports charges around the circuit and that the power supply (voltage) supplies these charges with energy ...

Voltage is the energy density of the charge. Current does not transport charges, current is the transport of charges.

Do batteries store charge and/or energy?

They only store energy. When a battery pumps charges around in a circuit, it receives as many charge carriers from one terminal as it sends out from the opposite terminal. Therefore, it has the same amount of charge after being de-energized and it did when it was energized.

Does the amount of energy from a battery in joules get used up or the amount of charge and when its dead has it released all energy and/or charge

A battery gains or loses energy, never charge.

Do capcitors store energy and/or charge and does it release its charge and/or its energy.

Same thing. A fully energized cap has the same charge as a de-energized cap. The amount of charge added to one plate is balanced by the subtraction of charge from the opposite plate for a net charge of zero. The two plates of an energized cap have a separation of charge. It takes energy to separate the charges, and that energy is stored in the electric field between the plates where the dielectric is located.

Does the amount of energy from a battery in joules get used up or the amount of charge and when its dead has it released all energy and/or charge?

Batteries and caps supply energy to the circuit. They can also receive energy from a circuit if the current is reversed. In all cases, the amount of charge within the batteries and cap is invariant.

If nothing is ever used up in a battery why is it over time the batteries potential difference drops?.

The chemical energy of the battery is being used up. That explains why its voltage drops during use. Remember, voltage is the energy density of the charge.

I also just wanted to ask if I have a battery not connected too anything so no current flows would charges build up on the terminals of the battery when not being used?

Current does not flow twice, charge flows once. Current flow means charge flow flow. Current has existence and direction, but not a double flow. The separation distance between the battery terminals is too far for there to be any energy involved is separating the charges and causing a charge buildup. The metal terminals already contain a sea of mobile electrons that will readily move from one terminal to the other if there is a conduction path.

harold777,

..But leave it with the terminals open and a voltage will appear . . . I think this is due to ion drift,..

No, it is due to dielectric absorption. When a cap is energized, magnetic dipoles form from the molecules of the dielectric. They are aligned in the direction of the electric field. After a cap than has been energized for a long time is de-energized, the dipoles point in random directions for as long as the cap plates are shorted. When the short is removed, the dipoles "remember" where they pointed to previously, and begin to align themselves in the same direction as before. They are able to do this from the residual dipole energy within the dielectric that does not get drained immediately. This dipole alignment causes a voltage to form spontanerously.

Ratch

 

[e44-72]

Thank you all for your help and time. The reason I wanted to know is just beacuaes I wanted to get a better understanding of how electricity works. Thank you for the useful information.

 

[e44-72]

I was just thinking about electrons and protons, If you where to put two protons close to eachother they would repel and the same for two electrons as they are like charges and repel. If a proton and electron where placed next to eachother they would attract as opposite charges attract. Where do these particles get there energy from to do this?

 

[Ratchit]

e44-72,

I was just thinking about electrons and protons, If you where to put two protons close to eachother they would repel and the same for two electrons as they are like charges and repel. If a proton and electron where placed next to eachother they would attract as opposite charges attract. Where do these particles get there energy from to do this

Electrons, protons, neturons, and other subatomic particles are relatively close together in atoms. Whatever or whoever created those atoms and placed those particles in proximity to each other supplied the energy to do so.

Ratch

 

[e44-72]

Thanks everyone for the answers and help

e44-72

 

[Sceadwian]

Thank you again for your help, I also just wanted to ask if I have a battery not connected too anything so no current flows would charges build up on the terminals of the battery when not being used?

It will build up to the potential difference of the chemicals used in the battery, which chemistry dependent, more can't build up than this physically derived voltage.

Keep in mind no matter what battery type you use even if it's not connected to anything there WILL be some current flow within the cell itself. The materials in a cell are not perfectly homogeneous (and can't be) so there will always be some potential difference somewhere which will allow charge carriers to flow. This is called self discharge. Chemistry and anode/cathode construction and materials can create a WIDE range of self discharge of cells.

Modern Lithium rechargeable cells are very good, lasting a year or more on a storage charge. Lithium primary cells can last 10 years or more.

One special consideration is something like a zinc air battery (or similar air batteries) which if properly vacuum packed will have an unlimited shelf life (only as good as the leakage of the packing material)