Uninterruptible Power Supply - UPS

Uninterruptible Power Supply (UPS) Systems Operation and Maintenance

Prepared By :

Tarek Hussien Mohamed

Consult Electrical Engineer

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Uninterruptible Power Supply (UPS) Systems

Welcome to the Uninterruptible Power Supply (UPS) Systems training module

This course is designed to give awareness knowledge and general understanding of :

Battery Fundamentals

Type of Batteries

Basic principle and major components of UPS system

applications of UPS used in the process industry

safety measures when dealing with cell and batteries

Installation and testing of UPS system

Preventive Maintenance Procedure

Descriptions about DC and AC UPS systems etc.

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After finish this course the trainees will be able to understand the following:

The basic operation of cells and batteries

Classifications of cells and batteries

Understanding the basic need for UPS system

Understanding the Types of UPS system

Compare and contrast the benefits of the type of UPS system

How to maintain the UPS

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Course Contents : What is a UPS System?

Why UPS system is a critical Components ?

Whats the aim of using UPS system?

Whats the alternate names of UPS?

Application of UPS system

Major Components of UPS system

Battery fundamentals

Battery Cells classification

Lead-Acid Batteries

Nickel-Cadmium Batteries

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1- What is a UPS?

UPS (uninterruptible power supply) systems are a critical device in our daily Life (In home , Companies , Factories and sites) and (UPS) are designed to automatically provide emergency power, without delay or transients, to critical applications in case of an interruption to, or unacceptable condition of the mains/utility supply. Some UPSs also filter and/or regulate mains/utility power.

An Uninterruptible power supply (UPS) is a device that has an alternate source of energy that can provide power when the prime power source is temporarily disabled (Power is not available)

is primarily used to provide a backup power source to the load and any other device plugged in to the battery backup

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1- What is a UPS? Cont.

In addition to acting as a backup when the power goes out, most battery backup devices also act as power "conditioners" by ensuring that the electricity flowing to your loads is free from drops or surges. If a load is not receiving a consistent flow of electricity, damage can and often does occur.

When selecting a UPS System , youll have to choose among a number of options, but if you can differentiate between the various available configurations, youll be better able to choose the right system to meet your needs.

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2-Why UPS system is critical components?

Imagine if your heart decided to quit beating for a while, of if it all of the sudden slowed way down or sped up in a sharp burst.

Not a very appealing scenario, is it? Now, imagine that the power supply to your companys IT equipment failed, or if it sent large spikes to your equipment.

Although this situation isnt as macabre as the metaphor of a heart, it nonetheless spells trouble for your business.

Power is the lifeblood of your data center, and your IT equipment is designed to be supplied with a steady flow.

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2-Why UPS system is critical components? cont.

Unfortunately, the power delivered from your utility isnt as steady as youd like it to be. Brief power outages, power sags and power surges/spikes can cause more than just a hasslethey can cause damage to your IT equipment. Although backup power generators can supply your data center in the case of an extended outage (hours or even days), they are no help when youre faced with transient power fluctuations. For example, if another utility customer starts a large inductive load, you may feel the effects down the line in the form of a short lived, but potentially harmful, power event. In such a case, you wouldnt have any warninglet alone time to switch to a backup generator.

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2- Why UPS system is critical components? Cont.

To deal with these short-lived power events, a UPS is critical. These systems not only provide temporary backup power for brief outages, but many also provide protection against transient power events like spikes and sags, thereby supplying your equipment with clean, high-quality power. Essentially, a UPS is a power storage device that cleans your power supply or takes over in the event of a power failure, giving you time to switch to your backup generators if the outage is expected to last more than some short period of time (like a minute or two, depending on your UPSs capacity).

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3- What the aims of using UPS ?

So we can conclusion the important for using UPS as the following :

Protects against multiple types of power disturbances

Only device that protects against an outage (Power Goes out)

Offers protection against

Equipment not operation Properly

Damage

Data losses

Time and expense to recover back to where you were , if even possible (Downtime)

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3- What the aims of using UPS ? Cont.

Downtime: blackouts and brownouts (low voltage) shut down equipment. UPS Systems supply battery backup power to support equipment through blackouts. Select models feature automatic voltage regulation to correct incoming power without relying on UPS batteries.

Damage: surges and line noise can damage internal components in a single devastating event or slowly over time. UPS Systems feature surge suppression and line noise filtering to guard equipment against potential damage.

Data Loss: when power problems shut down equipment, valuable data is often lost. UPS Systems feature battery backup power to allow enough time for data to be saved manually or automatically

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4- What the alternate names of UPS ?

UPS System

uninterruptible power supply System

uninterruptible power source System

battery backup System

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5- Application of UPS System

There many application of usage of UPS system in our life (Homes ,Companies ,Factories and Sites) some of these application :

Emergency lighting

Indoor escape lights

Ladder/ stair area

Walk-ways

Fire and Gas alarm system

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5- Application of UPS System. cont.

Operation of electrical switchgear

For Electrical protection system, control systems, Indications .etc.

Communications and Telecommunication Equipments

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6- Whats the Major Components of UPS system?

Let us imagine we need to keep some of liquid like water, juice or drinks, how we can keep it?

Sure we will bring plastic cups, glass cups or bottles and fill it with juice or water so now we keep it and we can use it when we need

so we need means and ways to keep the electrical energy and in fact we can't store the electrical energy easily and the only means till now are batteries

So the batteries is the major components to store the electrical energy but the consummation electrical energy from batteries depend on rated voltage and current hour of batteries (V Ah)

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6- Whats the Major Components of UPS system? Cont.

So now , we need to fill the batteries with electrical energy and how charging the batteries , the only means to fill it is known as charging unit

There are many application and we already using it in our life like as

Dynamo : Dynamo is famous machine we using it in our daily life which using to charge the car , bus or diesel engine batteries which convert the mechanical energy to electrical energy

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Battery Charger : another type we using it in daily our life which have three famous types one of it using it to charge the cell phone batteries and lap top batteries and second type using to charge car or track batteries and third using to charge the Batteries (AA or AAA) which convert electrical energy (AC Home power source) to electrical energy (DC)

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Now we can imagine the major components for UPS system will be as the following :

Batteries (Rechargeable)

Charging unit

Batteries Charging Unit

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7- Battery Fundamentals

Batteries operate by converting chemical energy into electrical energy through electrochemical discharge reactions.

Batteries are composed of one or more cells, each containing a positive electrode, negative electrode, separator, and electrolyte.

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7- Battery Fundamentals . Cont. Batteries are rated in terms of their

nominal voltage and ampere-hour capacity , The maximum power available from a battery depends on its internal construction.

Example

12V 50AH

18V 5AH

High rate cells, for example, are designed specifically to have very low internal impedance as required for starting turbine engines and auxiliary power units (APUs).

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7- Battery Fundamentals. cont.

The state-of-charge of a battery is the percentage of its capacity available

relative to the capacity when

it is fully charged. By this definition, a fully charged battery has a state-of-charge of 100% and a battery with 20% of its capacity removed has a state-of-charge of 80%.

The state-of-health of a battery is the percentage of its capacity available when fully charged relative to its rated capacity.

Example a battery rated at 30 Ah, but only capable of delivering 24 Ah when fully charged,

will have a state-of-health of 24/30 X 100 = 80%. Thus, the state-of-health takes into account the loss of capacity as the battery ages.

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8- Battery Cells Classification

Cells can be divided into two major classes: primary and secondary.

Primary cells are not rechargeable and must be replaced once the reactants are depleted

sometimes also called single-use, or throw-away batteries because they have to be discarded after they run empty as they cannot be recharged for reuse

Secondary cells are rechargeable and require a DC charging source to restore reactants to their fully charged state

mostly called rechargeable batteries because they can be recharged for reuse.

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8- Battery Cells Classification. Cont.

1- Primary Batteries types :

Carbon Zinc (aka. Heavy Duty) -- The lowest cost primary cell (household) is the zinc-acidic manganese dioxide battery. They provide only very low power, but have a good shelf life and are well suited for clocks and remote controls.

Alkaline -- The most commonly used primary cell (household) is the zinc-alkaline manganese dioxide battery. They provide more power-per-use than Carbon-zinc and secondary batteries and have an excellent shelf life.

Lithium Cells -- Lithium batteries offer performance advantages well beyond the capabilities of conventional aqueous electrolyte battery systems. Their shelf-life can be well above 10-years and they will work at very low temperatures. Lithium batteries are mainly used in small formats (coins cells up to about AA size) because bigger sizes of lithium batteries are a safety concern in consumer applications. Bigger (i.e. D) sizes are only used in military applications.

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Uninterruptible Power Supply (UPS) Systems 8- Battery Cells Classification. cont.

1- Primary Batteries: cont.

Silver Oxide Cells These batteries have a very high energy density, but are very expensive due to the high cost of silver. Therefore, silver oxide cells are mainly used in button cell format for watches and calculators and also known as Lithium coin or Coin cell

Zinc Air Cells These batteries have become the standard for hearing aid batteries. They have a very long run time, because they store only the anode material inside the cell and use the oxygen from the ambient air as cathode.

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2- Secondary Batteries (Rechargeable ):

Nickel-Metal Hydride -- Secondary NiMH batteries are an extension of the old fashioned NiCd batteries.

NiMH batteries provide the same voltage as NiCd batteries, but offer at least 30% more capacity. They exhibit good high current capability, and have a long cycle life.

The self-discharge rate is higher than NiCd at approximately 40% per month.

NiMH cells contain no toxic cadmium, but they still contain a large amount of nickel oxides and also some cobalt, which are known human carcinogens and should be recycled.

Lithium Ion -- Secondary Li-Ion batteries are the latest breakthrough in rechargeable batteries.

They are at least 30% lighter in weight than NiMH batteries and provide at least 30% more capacity. They exhibit good high current capability, and have a long cycle life.

The self-discharge rate is better than NiMH at approximately 20% per month.

Overheating will damage the batteries and could cause a fire. Li-Ion cells contain no toxic cadmium, but they still contain either cobalt oxides or nickel oxides, which are known human carcinogens and should be recycled.

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Uninterruptible Power Supply (UPS) Systems 8- Battery Cells Classification. Cont. 2- Secondary Batteries (Rechargeable ):

Nickel-Cadmium -- Secondary Ni-Cd batteries are rugged and reliable. They exhibit a high power capability, a wide operating temperature range, and a long cycle life, but have a low run time per charge.

They have a self-discharge rate of approximately 30% per month. They contain about 15% toxic, carcinogenic cadmium and have to be recycled.

Lead-Acid -- Secondary lead-acid batteries are the most popular rechargeable batteries worldwide.

Both the battery product and the manufacturing process are proven, economical, and reliable.

However, because they are heavy, Lead-Acid batteries are not being used in portable, consumer applications. Lead is a toxic, carcinogenic compound and should not enter the regular waste stream.

Recycling of Lead-Acid batteries is the environmental success story of our time, approx. 93% of all battery lead is being recycled today in reused in the production of new Lead-Acid batteries

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2- Secondary Batteries (Rechargeable ):

Rechargeable Alkaline -- Secondary alkaline batteries, the lowest cost rechargeable cells, have a long shelf life and are useful for moderate-power applications.

Their cycle life is less than most other secondary batteries, but they are a great consumers choice as they combine the benefits of the popular alkaline cells with the added benefit of re-use after recharging.

They have no toxic ingredients and can be disposed in regular landfills (local regulations permitting).

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8- Battery Cells Classification . Cont. So What Batteries Work Best in Different Devices Today? HEAVY DUTY BATTERIES are still very popular and have been around for many

years because they are so cheap to purchase. Heavy Duty batteries work best in low drain devices such as AM/FM radios, flashlights, smoke alarms and remote controls. Over the lifetime of the device, rechargeable alkaline batteries will provide the better value and result actual in cost savings although the initial cost is higher.

ALKALINE BATTERIES are the most popular battery used today. Alkaline will last 5

to 10 times longer than heavy duty batteries on higher current drains, making them more economical. They get their long life from unique construction and the purity of the materials used. Alkaline batteries are best suited for moderate to high drain devices such as portable CD players, electronic games, motorized toys, tape recorders and cassette players. Again, over the lifetime of the device, rechargeable alkaline batteries will provide the better value and result actual in cost savings although the initial cost is slightly higher.

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8- Battery Cells Classification . Cont. So What Batteries Work Best in Different Devices Today? RECHARGEABLE ALKALINE BATTERIES are specially designed for use 25 times or

more when charged properly in a dedicated charger for rechargeable alkaline batteries. Rechargeable alkaline batteries come fully charged, have no memory problems, up to a seven-year shelf life and will last up to three times longer than a fully charged nickel cadmium rechargeable battery. They do not require to be fully drained before recharge and will actually last longer if frequently recharged. They will work in all applications where Heavy Duty Primary Batteries are being used and in all applications for Alkaline Primary Batteries with not too high drain rates.

RECHARGEABLE NiMH BATTERIES are an extension of the old fashioned NiCd batteries. These batteries offer capacities at least 30% higher per charge than NiCd batteries of the same size. NiMH batteries can be recharged without having to be fully drained and can be charged several hundred times. NiMH work best in high drain devices that chew through alkaline batteries quickly such as digital cameras, hand held TVs and remote controlled racing toy cars.

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8- Battery Cells Classification. Cont. So What Batteries Work Best in Different Devices Today? RECHARGEABLE Li-Ion BATTERIES are mainly used in Laptop

computers and cellphones. They have a 3 times higher voltage on a per cell basis than NiMH batteries and are usually only sold as a system (device w/ built-in charger), as they require a special type of charger. More recently, single Li- Ion cells with dedicated chargers are being offered for cameras that take Lithium cells.

RECHARGEABLE NiCd BATTERIES should not be used due to the toxic cadmium, but are still in high demand for power tools due to their rugged design and performance. However, NiCd batteries have to be recycled to prevent toxic, carcinogenic cadmium entering the waste stream.

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So What Batteries Work Best in Different Devices Today?

PRIMARY LITHIUM BATTERIES offer an outstanding shelf-life of above 10-years and they will work at very low temperatures. They are mainly used in imaging applications, i.e cameras.

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Sr. Battery Type Voltage (V) Common Usage

1

Prim

ary Ce

ll

Alkaline 1.5 V CD/MD/MP3 players, toys, electronic games,

cameras, flash lights, remote controls

2 Carbon zinc 1.5 V Clocks, radios, smoke alarm

3 Lithium coin 3.0 V Calculators, electronic organizers

4 Lithium photo 3.0/6.1 V Cameras

5 Silver oxide

(button cells) 1.55 V Watches

6 Zinc air 1.4 V Hearing aids

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Seco

nd

ary Ce

ll

(Re

charge

able

)

Rechargeable

Alkaline 1.5 V

CD/MD/MP3 players, toys, electronic games,

cameras, flash lights, remote controls

8 NiMH 1.2 V Digital cameras, remote controlled racing toy cars

9 NIiCd 1.2 V Power Tools

10 Li-ion 3.6-3.7 V Notebook computers, PDAs, mobile phones,

camcorders, digital cameras

11 Lead Acid 12 V Car starter battery, lift trucks, golf charts, marine,

standby power, UPS, solar lighting

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8- Battery Cells Classification. Cont. Are Primary and Rechargeable Batteries interchangeable amongst

each other? However, NiMH batteries make only practical sense in very high

drain devices such as digital cameras as their self-discharge rate is too high for applications that require power of long periods of time.

For those slow discharges, a battery type with a very low self-discharge rate is required. Rechargeable Alkaline will fit the bill there.

Remember, whatever battery type you use, NEVER mix battery types for use at the same time and never mix old and new batteries. Keep batteries in sets for best performance.

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8- Battery Cells Classification. Cont. Are Primary and Rechargeable Batteries interchangeable amongst each other? Not all battery types are interchangeable. However, in the consumer, household

small format battery category, the following types of the same format can in most cases be interchanged: Heavy Duty, Alkaline, and Rechargeable Alkaline and NiMH batteries.

Although primary and rechargeable alkaline batteries are rated at a nominal voltage of 1.5 volts, as they begin discharging, their voltage continuously drops.

Over the course of discharge, the average voltage of alkaline batteries is in fact about 1.2 volts, very close to NiMH batteries.

The main difference is that alkaline batteries start at 1.5 volts and gradually drop to less than 1.0 volt, while NiMH batteries stay at about 1.2 volts for most of the service time.

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What are the advantages of using Rechargeable Batteries?

Performance Since rechargeable batteries can be recharged many times over, the cumulative total service life exceeds that of primary batteries by a wide margin.

Savings Recharging rechargeable batteries many hundred times is giving the consumer tremendous savings in the long run.

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So now we can consider there are two classifications of cells and in the UPS system we need to use the rechargeable cells

So we will discuss in brief most famous using batteries in the UPS system

Lead-Acid Batteries

Nickel-Cadmium (NiCd)Batteries

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9- Lead Acid Batteries 9-1 Introduction : The leadacid battery was invented in 1859 by French physicist

Gaston Plant and is the oldest type of rechargeable battery.

Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio.

These features, along with their low cost, makes it attractive for use in motor vehicles to provide the high current required by automobile starter motors.

As they are inexpensive compared to newer technologies, lead-acid batteries are widely used even when surge current is not important and other designs could provide higher energy densities.

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9- Lead Acid Batteries

9-1 Introduction : cont.

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Large-format lead-acid designs are widely used for storage in backup power supplies in cell phone towers, high-availability settings like hospitals, and stand-alone power systems.

For these roles, modified versions of the standard cell may be used to improve storage times and reduce maintenance requirements.

Gel-cells and absorbed glass-mat batteries are common in these roles, collectively known as VRLA (valve-regulated lead-acid) batteries.

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9- Lead Acid Batteries 9-1 Introduction : cont. A VRLA battery (valve-regulated lead-acid battery), more commonly known as a

sealed battery or maintenance free battery, is a type of lead-acid rechargeable battery

Due to their construction, they can be mounted in any orientation, and do not require constant maintenance.

The term "maintenance free" is a misnomer as VRLA batteries still require cleaning and regular functional testing

There are two primary types of VRLA batteries, gel cells and AGM. Gel cells add silica dust to the electrolyte, forming a thick putty-like gel.

These are sometimes referred to as "silicone batteries". AGM, short for "absorbed glass mat", batteries feature fiberglass mesh between the battery plates which serves to contain the electrolyte.

Both designs offer advantages and disadvantages compared to conventional batteries, as well as each other.

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9-1 Introduction :

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An electrochemical battery that uses lead and lead oxide for electrodes and sulfuric acid for the electrolyte

Lead-acid batteries are the most commonly used in photovoltaic (PV) and other alternative energy systems because their initial cost is lower and because they are readily available nearly everywhere in the world.

There are many different sizes and designs of lead-acid batteries, but the most important designation is whether they are deep cycle batteries or shallow cycle batteries

Shallow cycle batteries

Deep cycle batteries

Sealed deep-cycle lead-acid batteries

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9- Lead Acid Batteries 9-1 Introduction : cont. Shallow cycle batteries

Shallow cycle batteries is also called Starting Batteries

like the type used as starting batteries in automobiles, are designed to

supply a large amount of current for a short time and stand mild overcharge without losing electrolyte.

They have a large number of thin plates designed for maximum surface area, and therefore maximum current output, but which can easily be damaged by deep discharge

Starting batteries kept on continuous float charge will have corrosion in the electrodes which will result in premature failure. Starting batteries should be kept open circuit but charged regularly (at least once every two weeks) to prevent sulfation

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9- Lead Acid Batteries 9-1 Introduction : cont. Shallow cycle batteries

Repeated deep discharges will result in

capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling so unfortunately, they cannot tolerate being deeply discharged.

If they are repeatedly discharged more than 20 percent, their life will be very short.

These batteries are not a good choice for a PV (Photovoltaic solar) system.

Starting batteries are lighter weight than deep cycle batteries of the same battery dimensions, because the cell plates do not extend all the way to the bottom of the battery case.

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9- Lead Acid Batteries 9-1 Introduction : cont. Deep cycle batteries are designed to be repeatedly discharged by as much as 80 percent of their

capacity so they are a good choice for power systems.

Even though they are designed to withstand deep cycling, these batteries will have a longer life if the cycles are shallower.

All lead-acid batteries will fail prematurely if they are not recharged completely after each cycle.

Letting a lead-acid battery stay in a discharged condition for many days at a time will cause sulfation of the positive plate and a permanent loss of capacity.

In the world of batteries, Deep Cycle Batteries are classed as "secondary batteries" because they can be continuously charged-up and discharged producing what is know as the batteries charging cycle.

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9- Lead Acid Batteries 9-1 Introduction : cont. Deep cycle batteries

Deep cycle batteries are called secondary batteries because the chemical

reaction that produces and stores the electrical energy on its lead plates is fully reversible, as opposed to standard "primary batteries" that can only be used once and then thrown away once they are fully discharged.

A deep-cycle battery is designed to discharge between 45% and 75% of its capacity, depending on the manufacturer and the construction of the battery.

Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 45% discharge.

There is a direct correlation between the depth of discharge of the battery, and the number of charge and discharge cycles it can perform

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Applications

Cathodic protection, which might include marine use

Other marine use, especially on a sailboat lacking power generation capability, generally smaller vessels

Trolling motors for recreational fishing boats

Industrial electrically-propelled forklifts and floor sweepers

Off-grid energy storage systems for solar power or wind power, especially in small installations for a single building

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Applications

Power for instruments or equipment at

remote sites

Traffic signals

Uninterruptible power supply ('UPS'), usually for computers and associated equipment, but also sump pumps

Audio equipment, similarly to a UPS but also in certain 'clean power' devices to supply clean D.C. power isolated from the public electric supply for inversion to A.C. to maximize audio signal reproduction

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9- Lead Acid Batteries 9-1 Introduction : cont. Sealed deep-cycle lead-acid batteries

These type of batteries are maintenance free.

They never need watering or an equalization

charge.

They cannot freeze or spill, so they can be mounted in any position. Sealed batteries require very accurate regulation to prevent overcharge and over discharge.

Either of these conditions will drastically shorten their lives. Sealed batteries are well-suited for remote, unattended power systems.

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9- Lead Acid Batteries 9-2 Basic Construction . 1. CASE: Container which holds

and protects all battery components and electrolyte, separates cells, and provides space at the bottom for sediment (active materials washed off plates). Translucent plastic cases allow checking electrolyte level without removing vent caps.

2. COVER: Permanently sealed to the top of the case; provides outlets for terminal posts, vent holes for venting of gases and for battery maintenance (checking electrolyte, adding water).

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9- Lead Acid Batteries 9-2 Basic Construction . Cont.

3. PLATES: Positive and negative plates have a grid framework of antimony and

lead alloy. Active material is pasted to the grid ... brown-colored lead dioxide (Pb02) on

positive plates, gray-colored sponge lead (Pb) on negative plates. The number and size of the plates determine current capability ... batteries with

large plates or many plates produce more current than batteries with small plates or few plates.

4. SEPARATORS: Thin, porous insulators (woven glass or plastic envelopes) are placed between positive and negative plates. They allow passage of electrolyte, yet prevent the plates from touching and shorting out.

5. CELLS: An assembly of connected positive and negative plates with separators in between is called a cell or element. When immersed in electrolyte, a cell produces about 2.1 volts (regardless of the number or size of plates). Battery cells are connected in series, so the number of cells determines the battery voltage. A "1 2 - volt" battery has six cells.

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9- Lead Acid Batteries 9-2 Basic Construction . Cont.

6. CELL CONNECTORS: Heavy, cast alloy metal straps are welded to the negative

terminal of one cell and the positive terminal of the adjoining cell until all six cells are connected in series.

7. CELL PARTITIONS: Part of the case, the partitions separate each cell.

8. TERMINAL POSTS: Positive and negative posts (terminals) on the case top have thick, heavy cables connected to them. These cables connect the battery to the vehicle's electrical system (positive) and to ground (negative).

9. VENT CAPS: Types include individual filler plugs, strip-type, or box-type. They allow controlled release of hydrogen gas during charging (vehicle operation). Removed, they permit checking electrolyte and, if necessary, adding water.

10. ELECTROLYTE: A mixture of sulfuric acid (H2SO4) and water (H2O). It reacts chemically with the active materials in the plates to create an electrical pressure (voltage). And, it conducts the electrical current produced by that pressure from plate to plate. A fully charged battery will have about 36% acid and 64% water.

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9- Lead Acid Batteries 9-3 Theory of Operation.

A lead-acid cell works by a simple principle: when two different metals are immersed

in an acid solution, a chemical reaction creates an electrical pressure.

One metal is brown-colored lead dioxide (Pb02). It has a positive electrical charge. The other metal is gray colored sponge lead (Pb). It has a negative electrical charge.

The acid solution is a mixture of sulfuric acid (H2SO4) and water (H20). It is called

electrolyte.

If a conductor and a load are connected between the two metals, current will flow.

This discharging will continue until the metals become alike and the acid is used up.

The action can be reversed by sending current into the cell in the opposite direction. This charging will continue until the cell materials are restored to their original condition.

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9-3 Theory of Operation.

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9-3 Theory of Operation. Cont.

Electromechanical Reaction

A lead-acid storage battery can be partially discharged and recharged many times.

There are four stages in this discharging/charging cycle.

1. CHARGED: A fully charged battery contains a negative plate of sponge lead (Pb), a positive plate of lead dioxide (Pb02), and electrolyte of sulfuric acid (H2SO4) and water (H20

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2. DISCHARGING: As the battery is discharging, the electrolyte becomes diluted and the plates become sulfated.

The electrolyte divides into hydrogen (H2) and sulfate(S04) .

The hydrogen (H2) combines with oxygen (0) from the positive plate to form more water (H20).

The sulfate combines with the lead (Pb) in both plates to form lead sulfate (PbS04)

3. DISCHARGED: In a fully discharged battery, both plates are covered with lead sulfate (PbSO4) and the electrolyte is diluted to mostly water (H2O).

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9- Lead Acid Batteries 9-3 Theory of Operation. Cont. Electromechanical Reaction 4. CHARGING: During charging, the

chemical action is reversed.

Sulfate (S04) leaves the plates and combines with hydrogen (H2) to become sulfuric acid (H2SO4).

Free oxygen (02) combines with lead (Pb) on the positive plate to form lead dioxide (Pb02).

Gassing occurs as the battery nears full charge, and hydrogen bubbles out at the negative plates, oxygen at the positive.

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Electromechanical Reaction The Chemical reaction that occur in a lead-acid battery are represented

by the following equation :

Negative plate reaction:

Pb + HSO PbSO4 + 2H+ + 2e

Positive plate reaction:

PbO + HSO + 2H + + 2e PbSO + 2HO

Discharge

Charge

Discharge

Charge

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The Chemical reaction that occur in a lead-acid battery are represented by the following equation :

The total reaction can be written as

Pb + PbO+ 2HSO 2PbSO + 2HO

Discharge

Charge

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9-4 Maintenance Requirements

Routine maintenance of lead-acid aircraft batteries is required to assure airworthiness and to maximize service life.

For vented-cell batteries, electrolyte topping must be performed on a regular basis to replenish the water loss that occurs during charging.

Maintenance intervals are typically 2 to 4 months.

A capacity test or load test usually is included as part of the servicing procedure.

For sealed-cell batteries, water replenishment obviously is unnecessary, but periodic capacity measurements generally are recommended.

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9-4 Maintenance Requirements

Capacity check intervals can be based either on calendar time (e.g., every 3 to 6 months after the first year) or operating hours (e.g., every 100 hours after the first 600 hours).

Refer to the manufacturers maintenance instructions for specific batteries of interest.

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9- Lead Acid Batteries 9-5 Failure Modes and Fault Detection

The predominant failure modes of lead-acid cells are summarized as

follows:

i. Shorts caused by growth on the positive grid, shedding or mossing of active material, or mechanical defects protruding from the grid, manifested by inability of the battery to hold a charge (rapid decline in open circuit voltage).

ii. Loss of electrode capacity due to active material shedding, excessive grid corrosion, sulfation, or passivation, manifested by low capacity and/or inability to hold voltage under load.

iii. Water loss and resulting cell dry-out due to leaking seal, repeated cell reversals, or excessive overcharge (this mode applies to sealed cells or to vented cells that are improperly maintained), manifested by low capacity and/or inability to hold voltage under load.

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10- Nickel-Cadmium (NiCd)Batteries

10-1 Introduction

The nickelcadmium battery (NiCd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.

The abbreviation Ni-Cd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all NiCd batteries.

Wet-cell nickel-cadmium batteries were invented in 1898. Among rechargeable battery technologies, NiCd rapidly lost market share in the 1990s, to NiMH and Li-ion batteries; market share dropped by 80%.

A Ni-Cd battery has a terminal voltage during discharge of around 1.2 volts which decreases little until nearly the end of discharge.

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10-1 Introduction. Cont.

Ni-Cd batteries are made in a wide range of sizes and capacities, from portable

sealed types interchangeable with carbon-zinc dry cells, to large ventilated cells used for standby power and motive power.

Compared with other types of rechargeable cells they offer good cycle life and performance at low temperatures with a fair capacity but its significant advantage is the ability to deliver practically its full rated capacity at high discharge rates (discharging in one hour or less).

However, the materials are more costly than that of the lead acid battery, and the cells have high self-discharge rates.

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10-1 Introduction. Cont. Advantages: Low internal resistance (less than half the equivalent NiMH cells) High rate charge and discharge rates possible Up to 10C discharge rates for short periods typical Flat discharge characteristic (but falls off rapidly at the end of the cycle) Tolerates deep discharges - can be deep cycled. Wide temperature range (Up to 70C) Typical cycle life is over 500 cycles. Charging process is strongly endothermic-the battery cools during charging. This

makes it possible to charge very quickly, as the I2R heating and endothermic chemical reaction counteract each other.

Rapid charge typically 2 hours, but can be as low as 10 to 15 minutes. The coulombic efficiency of nickel cadmium is over 80% for a fast charge but can

drop to below 50% for slow charging. The sealed nickel-cadmium cell can be stored in the charged or discharged state

without damage. It can be restored for service by recharging several charge/discharge cycles.

Available in a large variety of sizes and capacities.

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10- Nickel-Cadmium (NiCd)Batteries 10-1 Introduction. Cont. Disadvantages:

The primary trade-off with NiCd batteries is their higher cost and the use of cadmium.

This heavy metal is an environmental hazard, and is highly toxic to all higher forms of life.

NiCd batteries are also more costly than lead-acid batteries because nickel and cadmium are

more costly materials.

One of the NiCd's biggest disadvantages is that the battery exhibits a very marked negative temperature coefficient. This means that as the cell temperature rises, the internal resistance falls. This can pose considerable charging problems, particularly with the relatively simple charging systems employed for lead-acid type batteries.

Whilst lead-acid batteries can be charged by simply connecting a dynamo to them, with a simple electromagnetic cut-out system for when the dynamo is stationary or an over-current occurs, the NiCd under a similar charging scheme would exhibit thermal runaway, where the charging current would continue to rise until the over-current cut-out operated or the battery destroyed itself.

This is the principal factor that prevents its use as engine-starting batteries. Today with alternator-based charging systems with solid-state regulators, the construction of a suitable charging system would be relatively simple, but the car manufacturers are reluctant to abandon tried-and-tested technology

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10-1 Introduction. Cont.

Applications

Motorised equipment

Power tools

Two way radios

Electric razors

Commercial and industrial portable products

Medical instrumentation

Emergency lighting

Toys

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10- Nickel-Cadmium (NiCd)Batteries 10-2 Basic Construction . The nickel-cadmium battery is similar in construction to the lead-acid battery with the exception

that it has individual cells which can be replaced As in the lead-acid type, the cell is the basic unit of the nickel-cadmium battery, It consists of

positive Plates negative plates Separators Electrolyte cell vent cell container

The positive plates are made from a porous plaque on which nickel-hydroxide has been deposited. The negative plates are made from similar plaques on which cadmium-hydroxide is deposited. In both cases the porous plaque is obtained by sintering nickel powder to a fine mesh wire screen.

Sintering is a process which fuses together extremely small granules of powder at a high temperature. After the active positive and negative materials are deposited on the plaque, it is formed and cut into the proper plate size. A nickel tab is then welded to a corner of each plate and the plates are assembled with the tabs welded to the proper terminals. The plates are separated from each other by a continuous strip of porous plastic.

The electrolyte used in the nickel-cadmium battery is a 30 percent solution (by weight) of potassium hydroxide (KOH) in distilled water. The specific gravity of the electrolyte remains between 1.240 and 1.300 at room temperature.

No appreciable changes occur in the electrolyte during charge or discharge. As a result, the battery charge cannot be determined by a specific gravity check of the electrolyte. The electrolyte level should be maintained just above the tops of the plates

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Documents

Uninterruptible Power Supply - UPS