make your own (diy) batteries

8/8/2019 MAKE YOUR OWN (DIY) BATTERIES

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Build Your Own BatteriesCopyright 2008

www.DIYPowerSystem.com


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Legal Disclaimer

The author and the publisher disclaim any liability, loss or risk, personal or

otherwise, which is incurred as a direct or indirect consequence of the useand application of any of the contents of this book.

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Copyright 2008 www,DIYPowerSystem.com


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Table of Contents

Table of Contents ......................................................................................... 3Storing Electricity ........................................................................................ 4

Types of Batteries ........................................................................................ 7

Battery Parameters ..................................................................................... 13

Safety and Maintenance ............................................................................. 19

Building a Battery ...................................................................................... 20


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Storing Electricity

The simplest definition of energy is the one according to which energy is a

particular property of objects and systems that is described as conservable

scalar physical quantity. That means that energy is a simple physical

property of objects, which can be quantified. Energy is widely found in

nature in a variety of forms. Thus, according to several criteria, we deal with

potential and kinetic energy, thermal and magnetic energy, nuclear and

chemical energy, magnetic and mass energy and, most importantly for

people as consumers of energy, we also talk about electric energy.

This list of forms of energy is far from being complete. However, the point

is that electricity is a form of energy and, as any other form of energy, it can

be converted into a different form, and it can be obtained, as a result of

transformation, from a different form of energy, virtually without loss of

energy, according to the law of conservation of energy.

However, in order to transform one form of energy into another, certain

devices are necessary. For instance, in order to produce energy from water, a

dam is needed. Dams turn gravitational potential energy of moving water

into kinetic energy, and by means of an electric generator, this kinetic

energy is turned into electric energy. A similar process is implied by the

generation of electricity from wind power, except that in this case water is

replaced by wind, and instead of dams we deal with wind turbines.

Batteries, at their turn, are able to turn chemical energy into electricity. But

unlike dams or wind turbines, batteries have the advantage of being designed

also to store energy in the form of electrochemical energy. Storing electricity

is, indeed, an issue, particularly with respect to renewable power systems

that rely on somewhat elusive sources of energy, such as the sun or the wind.

These intermittent sources of energy are subject to weather conditions and,


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as a consequence, people, as consumers of electricity, are also subject to

such an environmental aspect.

The thing is that when it comes to renewable power systems, we can benefit

from peak periods, when the amount of electricity produced is higher than

the amount we actually need in order to be able to use the appliances

commonly found in any home. The rest of the energy generated by such

systems is to be lost, unless devices for storing that excess of electricity are

available.

Batteries are excellent for storing additional electricity that can not be

consumed as it is produced. This is why batteries should be comprised in

renewable power systems, in order to increase the load availability. If we

decide to employ batteries in order to store energy within a large range of

applications, we may either choose a primary battery or a rechargeable

battery, also referred to as secondary battery.

The difference between these types of battery is that with primary batteries,

which are able to turn chemical energy into electricity by means of an

electrochemical reaction, this electrochemical reaction is not reversible,

meaning that after the battery is discharged, it can no longer be used.

With rechargeable batteries, the electrochemical reaction by which chemical

energy is converted into electricity is reversible, meaning that at its turn,

electrical energy direct current from an exterior source can be converted

into chemical energy within the battery. At this moment, the battery is in the

charge mode.


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Storage of electrochemical energy within the battery


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Types of Batteries

According to the electrochemical process inside the battery, we distinguish

between lead-acid batteries, nickel-cadmium and nickel-metal hydride

batteries, lithium-ion and lithium-polymer batteries, and zinc-air batteries.

Each type of battery has its own advantages. For instance, lithium-ion

batteries have the highest level of cell voltage 3.4 but despite this level

of efficiency, they are not the most widely used.

On the contrary, lead-acid batteries are the most popular due to a particular

feature, that is, they are less expensive than any other type, but for that price

they prove a high performance all the same. The main drawback lead-acid

batteries have the lowest level of energy density as compared to weight and

volume.

While the battery releases electric energy that is, when it is in the

discharge mode the water produced reacts with the sulfuric acid

electrolyte, generating its dilution. As a consequence of this reaction, a

decrease of the specific gravity of the electrolyte is triggered along with a

decrease of the state of charge. While charging the lead-acid battery, the

reaction is completely reversed.


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Specific energy and energy density of lead-acid batteries

Vertical axis: energy density Wh/liter

Horizontal axis: specific energy Wh/kg

Among lead-acid batteries, deep-cycle batteries are the most recommended

for applications that require full discharge and charge cycles that must be

repeated. Yet, motor vehicles, for instance, can run perfectly on shallow-

cycle batteries, since they only need a small and rapid amount of energy in

order to start to work.

But should we be interested in deep-cycle batteries with a longer life span,

or in batteries that tolerate better certain temperature conditions, nickel-

cadmium batteries might be what we are looking for. However, the main

drawback of nickel-cadmium batteries is that they have what is generally

referred to as memory effect.

This memory effect describes the propensity of the battery to remember and

to repeat its behaviors in the past, meaning that if the battery has been

charged and discharged at a certain level of its capacity for a longer period


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of time and repeatedly, than the battery will only charge and discharge until

that level is attained, even if the respective level does not overlap the full

capacity of the battery.

Specific energy and energy density of nickel-cadmium batteries

Vertical axis: energy density Wh/literHorizontal axis: specific energy Wh/kg

The long term effect is that the nickel-cadmium battery will lose its capacity

after being subjected to incomplete charging and discharging processes.

Nickel-cadmium batteries are the only ones that experience the memory

effect. But besides this matter, another aspect is that nickel-cadmium

batteries are debated with respect to their impact on environment, the main

reason for which other types of electrochemistry are internationally

recommended for use.

In nickel-metal hydrate batteries, the concerns linked to the impact of

cadmium on the environment are removed along with the removal of

cadmium from the anode. In this new electrochemistry, besides such

concerns, the memory effect is also eliminated. But despite these two


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advantages nickel-metal hydrate has on nickel-cadmium, its downsides must

be mentioned. For instance, constantly overcharging a nickel-metal hydrate

battery can lead in time to damage. More over, the discharge rate of self-

discharge of a nickel-metal hydrate battery is fairly high.

Specific energy and energy density of nickel-metal hydrate batteries



Batteries relied on lithium-based technologies can provide an energy density

which is three times higher than the one proved by lead-acid batteries, due to

the particular features lithium has, that is, due to an atomic weight of 6.9, as

compared to 207, as it is the case with lead.

Another feature that makes lithium-ion electrochemistry much more

efficient is the cell voltage, which, a 3.5, is higher than the cell voltage level

of lead-acid. Lithium-based technologies refer to lithium-ion and lithium-

polymer.


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Specific energy and energy density of lithium-ion batteries



Specific energy and energy density of lithium-polymer batteries




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Another type of battery is the one based on zinc-air. This battery charges and

discharges due to the fact that the positive electrode, made of carbon, is

exposed to the air. While charging, the zinc electrode is oxidized, since the

oxygen in the air is reduced at the cathode, whereas during charging, the

reaction is reversed.

Specific energy and energy density of zinc-air batteries




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Battery Parameters

While choosing or building a battery for a certain application, in order to

make sure the application will run smoothly on the battery we choose or

build, some features must be taken into consideration.

Since it is the efficiency of the entire system that we are looking for, we

should pay a special attention to features like: charge and discharge rate,

charge and discharge duration, voltage and current, temperatures releasedwhile the battery charges and discharges, and, the number of cycles of

charge and discharge expected during the life span of the battery.

The pictures below illustrate the performance of a battery in different

circumstances.

Charge rate and discharge rates affecting cell voltage

Vertical axis: battery cell voltage


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Horizontal axis: cycle time in minutes

Left side: discharge rate

Right side: charge rate

The internal resistance of a 25 Ah nickel-cadmium cell affected by

temperature

Vertical axis: milliohms

Horizontal axis: temperature in C

Curves (percent): First upper curve (the continuous curve) 40

Second upper curve 60

Third upper curve 80

Fourth curve 100

However, other parameters must also be considered in order to make sure

the battery matches perfectly the requirements of the entire system in which

it is comprised because, indeed, different systems impose constraints on

batteries. Thus, for a renewable energy system, we should mind a large


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range of basic parameters, other than the ones presented above. For instance,

the type of battery is essential for a proper functionality of the system. Deep

cycle batteries are definitely much more recommendable and must be chosen

of shallow cycle batteries.

Moreover, the electrochemistry on which the battery relies is yet another

parameter one should take into consideration. A particular case refers to the

above mentioned memory effect in nickel-cadmium batteries. The picture

below shows how this impact of this effect on the discharge voltage.

Vertical axis: voltage volts per cell

Horizontal axis: depth of discharge percent

Upper curve: complete discharge before the memory effectLower curve: depth of discharge lower with 25% after the memory

effect

Also, various systems have various requirements with respect to voltage.

The load conditions are also to be born in mind, and this is why one should

always be aware of the Ah discharge. If the Ah discharge is determined, then


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we can easily calculate the Ah capacity that we obtain by dividing the Ah

discharge by the maxim acceptable depth of discharge. In order to meet the

total Ah capacity, one should calculate the number of battery packs

necessary to attain that capacity.

Finally, a due attention must be paid to thermal and charge and discharge

rate controls, since we dont want to shorten the life span of the battery by

neglecting these aspects, knowing that all batteries have a particular

tolerance to such aspects.

Temperature is a very important aspect, since it can seriously affect the

particular electrochemistry on which the battery relies. For instance, lead-

acid batteries are functional between -10 C and 50 C. On the other hand,

nickel-cadmium seems to have a wider range of operating temperature,

being able to work properly between -20 C and 50 C.

Nickel-metal hydrate batteries have the same operating temperature range aslead-acid batteries, and lithium-based electrochemistry seem to have a rather

narrow scale of temperatures. Thus, lithium-ion batteries work best between

10 C and 45 C, whereas lithium-polymer batteries are functional between

50 C and 70 C.


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Operating temperature range according to electrochemistry

Vertical axis: range of temperatures in C

If we look for a battery able to work properly within the largest range oftemperatures, we should definitely opt for nickel-cadmium electrochemistry.

However, we should not rush into making a decision, since there are other

parameters we must consider.

If we think about overcharge tolerance, we should know that nickel-

cadmium has only a medium tolerance, whereas lead-acid batteries have the

highest tolerance. Nickel-metal hydrate and lithium-based technologies have

either a low or a very low overcharge tolerance.

The point is there are many features we have to consider before deciding

what battery is best suited for our renewable power systems, and even if a

certain type o battery excels from a certain point of view, it might just as

well have serious drawbacks with respect to other parameters. But this is


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precisely why we must accurately acknowledge the requirements the system

we intend to build impose to the battery.

And since the life span of batteries was mentioned above, it must be said that

it depends on the charge and discharge cycles and on how properly these

cycles evolve. Thus, lead-acid batteries are functional between 500 and 1000

cycles, and so do lithium-ion and lithium-polymer batteries, whereas we can

only rely on a life span of 200 to 300 cycles when it comes to zinc-air.

The best batteries from this particular point of view are the ones working onnickel. Both nickel-cadmium and nickel-metal hydrate can undergo between

1000 and 2000 cycles before wearing out.


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Safety and Maintenance

If we have already decided what battery we are to employ within the

homebuilt renewable power system, some other issues are to be handled

with.

For instance, we always have to supervise the charging process, due to the

fact that overcharging determines loss of water at it is the case with lead-

acid batteries on short term, and the shortening of the life span, on longterm. Since it is extremely inefficient and almost impossible to supervise the

battery in person, charge regulators or controllers must be employed.

Charge regulators don not only prevent the shortening of the life span, but

they also represent a guarantee that the battery performance will not be

affected. However, its not just the charge and discharge cycles that must be

monitored.

Other performance parameters should be observed all the same. Modern

control devices supervise, for instance, depth of charge, or rate and sate of

charge and discharge. Voltage and current, as well as Ah released or

consumed by the battery must also be monitored.

As a safety issue, preventing overcharge remains, however, the most

important, mostly if wee talk about employing a battery within a solar power

system, and particularly if no charge controller is used and if the battery is

supplied directly from the PV module.

Due to the fact that overcharging causes overheat, we deal with the risk of

explosion.


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Building a Battery

As an experiment or, at least as a curiosity, on should try to build a battery at

home. Even if this battery will not be powerful enough to sustain a wind or

solar power system, the building process itself will prove that virtually all

important elements of such systems can be made at home and o a low

budget, since almost every component of the battery can be improvised or, at

least, obtained for free or for a low price.

The basic elements of a homemade battery are: a container, some aluminum

and copper pipes and bars, water, bleacher, some silicon and tape for

insulation, and a connector that ensures the link between the two electrodes.

In addition, a D.C. voltmeter may prove to be of help if we want to see how

efficient our homemade batteries are.

Water and bleacher are used to create the electrolyte solution that facilitates

the chemical reaction between the two electrodes, that is, between the

positive electrode represented in this case by the copper pipe, and the

negative electrode for which the aluminum bar stands.

By if we want to simply the battery and the building process even more, we

may just as well use an aluminum can as container, and at the same time as

negative electrode. In order prevent the copper pipe from touching the

aluminum can, silicon is used to seal these components from each other.

With respect to electrolyte, that is, the solution that facilitates the chemical

reaction between the two electrodes, we may be tempted to use more

bleacher in order to obtain a higher level of amperage from the cell.

Because, indeed, the more bleacher we use, the higher the amperage will be.

However, we have to consider the fact that bleacher has a corrosive effect


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both on aluminum and copper, and this is why we have to mind how

concentrate the electrolyte solution will be.

Aluminum cells connected in series in order to prevent corrosion and to

deliver a satisfactory amperage level

In order to prevent corrosion and to have a satisfactory amperage level, we

can build more cells and connect them in series, as it is shown in the picture

above. This way, even if we use more aluminum cans and more copper pipes

which would lead to higher expenses, but not as high as to exceed a fairly

low budget we get both a satisfactory result with respect to amperage and a

longer life span for the cells.

Along with a proper maintenance regular cleaning the copper and

aluminum components are expected to last between 4 and 5 years.

As rudimentary as they may be, such batteries prove to be surprisingly

efficient for emergency cases when power supplies shut down for relatively

short periods of time, or when, given some particular circumstances, we

need lighting, for instance, but no grid or other supplies are at hand.


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This experiment should be interpreted rather like an attempt to demonstrate

that our reliance on fossil fuel can be overcome, and that premises for an

enhanced autonomy are already set.

make your own (diy) batteries

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