low volatge and battery

8/14/2019 Low Volatge and Battery

1/74

ELECTROTECHNOLOGY I

By

Sulaiman Olanrewaju, Oladokun


2/74

Objectives

Differentiate between primary & secondary

cell

Operation (with aid of sketches):Lead-acid battery

Alkaline battery

Battery charging system


3/74

Sources of Power: Batteries


4/74

WHAT IS A BATTERY?WHAT IS A BATTERY?

A battery is a device consisting of one or more galvanic cells, which

store chemical energy and make it available in an electrical form.A battery has a voltage, measured in volts, an internal resistance

measured in ohms, and a capacity, measured in ampere-hours, which

may vary due to many factors including internal chemistry, currentdrain, and temperature.There are two types of batteries,primary and secondary, both of

which convert chemical energy to electrical energy.

Aprimary batteries can only be used once, as they use up theirchemicals in an irreversible reaction. Secondary batteries can berecharged because the chemical reactions they use are reversible;

they are recharged by running a charging current through the battery,

but in the opposite direction of the discharge current.
http://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Volthttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Ohmshttp://en.wikipedia.org/wiki/Ampere-hourhttp://en.wikipedia.org/wiki/Primary_batteryhttp://en.wikipedia.org/wiki/Secondary_batteryhttp://en.wikipedia.org/wiki/Reversible_reactionhttp://en.wikipedia.org/wiki/Reversible_reactionhttp://en.wikipedia.org/wiki/Secondary_batteryhttp://en.wikipedia.org/wiki/Primary_batteryhttp://en.wikipedia.org/wiki/Ampere-hourhttp://en.wikipedia.org/wiki/Ohmshttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Volthttp://en.wikipedia.org/wiki/Voltage


5/74

BATTERY HISTORYBATTERY HISTORY

The story of the modern battery begins in the 1780s with thediscovery of "animal electricity" by Luigi Galvani, which hepublished in 1791. He created an electric circuit consisting oftwo different metals, with one touching a frog's leg and the othertouching both the leg and the first metal, thus closing the circuit.He noticed that even though the frog was dead, its legs wouldtwitch when he touched them with the metals.

By 1791, Alessandro Volta realized that the frog could be

replaced by cardboard soaked in salt water, employing anotherform of detection. Volta was able to quantitatively measure theelectromotive force (emf) associated with each electrode-electrolyte interface (voltage) in volts, which were named after

him. In 1799, Volta invented the modern battery by placingmany galvanic cells in series, literally piling them one above the
http://en.wikipedia.org/wiki/1780shttp://en.wikipedia.org/wiki/Luigi_Galvanihttp://en.wikipedia.org/wiki/1791http://en.wikipedia.org/wiki/Electric_circuithttp://en.wikipedia.org/wiki/1791http://en.wikipedia.org/wiki/Alessandro_Voltahttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Volthttp://en.wikipedia.org/wiki/1799http://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/Series_and_parallel_circuitshttp://en.wikipedia.org/wiki/1799http://en.wikipedia.org/wiki/Volthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Alessandro_Voltahttp://en.wikipedia.org/wiki/1791http://en.wikipedia.org/wiki/Electric_circuithttp://en.wikipedia.org/wiki/1791http://en.wikipedia.org/wiki/Luigi_Galvanihttp://en.wikipedia.org/wiki/1780s


6/74

In 1836, Daniell cell provided more reliable currents andwere adopted by industry for use in stationary devices,particularly in telegraph networks where they were the onlypractical source of electricity. These wet cells used liquidelectrolytes, which were prone to leaks and spillage if nothandled correctly. Many used glass jars to hold theircomponents, which made them fragile.

Near the end of the 19th century, the invention of dry cellbatteries, which replaced liquid electrolyte with a pastemade portable electrical devices practical.

The battery has since become a common power source formany household and industrial applications. According to a2005 estimate, the worldwide battery industry generatesUS$48 billion in sales annually.
http://en.wikipedia.org/wiki/1836http://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/1000000000_(number)http://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/1836


7/74

HOW A BATTERY WORKS

A battery is a device that converts chemical energy directly toelectrical energy It consists of one or more voltaic cells.

Each voltaic cell consists of two half cells connected in series

by a conductive electrolyte. Each cell has a positive electrode(cathode), and a negative electrode (anode). These do nottouch each other but are immersed in a solid or liquidelectrolyte. In a practical cell the materials are enclosed in acontainer, and a separator between the electrodes prevents the

electrodes from coming into contact.
http://en.wikipedia.org/wiki/Half_cellhttp://en.wikipedia.org/wiki/Half_cell


8/74

The electrical potential difference across the terminals of a

battery is known as its terminalvoltage, measured in volts. Theterminal voltage of a battery that is neither charging nordischarging is called the open-circuit voltage, and gives theemf of the battery.

The voltage developed across a cell's terminals depends onthe chemicals used in it and their concentrations. For example,alkaline and carbon-zinc cells both measure about 1.5 volts,due to the energy release of the associated chemical

reactions.
http://en.wikipedia.org/wiki/Volthttp://en.wikipedia.org/wiki/Open-circuit_voltagehttp://en.wikipedia.org/wiki/Open-circuit_voltagehttp://en.wikipedia.org/wiki/Volt


9/74

TYPES OF BATTERIES.

There are various types of batteries depends on its sizes and

chemical properties. Generally there are two main types ofbatteries:

1. non-rechargeable (disposable)

2. rechargeable

Non-rechargeable (disposable)Disposable batteries, also called primary cells, are intended to

be used once and discarded. They are not designed to be

rechargeable. These are most commonly used in portable

devices with either low current drain, only used intermittently,

or used well away from an alternative power source.


10/74

Rechargeable BatteriesRechargeable batteries are also known as secondary

batteries or accumulators .They can be re-charged by

applying electrical current, which reverses the

chemical reactions that occur in use. Devices to supply the

appropriate current are called chargers or rechargers.

The oldest form of rechargeable battery still in modernusage is the "wet cell" lead-acid battery. This battery is

notable in that it contains a liquid in an unsealed

container, requiring that the battery be kept upright and

the area be well ventilated to ensure safe dispersal of thehydrogen gas produced by these batteries during

overcharging. A common form of lead-acid battery is the

modern wet-cell car battery.
http://en.wikipedia.org/wiki/Chemical_reactionshttp://en.wikipedia.org/wiki/Wet_cellhttp://en.wikipedia.org/wiki/Lead-acid_batteryhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Car_batteryhttp://en.wikipedia.org/wiki/Car_batteryhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Lead-acid_batteryhttp://en.wikipedia.org/wiki/Wet_cellhttp://en.wikipedia.org/wiki/Chemical_reactions


11/74

Battery Capacity and Discharging

The more electrolyte and electrode material there is inthe cell, the greater the capacity of the cell. Thus asmall cell has less capacity than a larger cell, given thesame chemistry though they develop the same open-

circuit voltage.

The capacity of a battery depends on the dischargeconditions such as the magnitude of the current, the

duration of the current, the allowable terminal voltageof the battery, temperature, and other factors.


12/74

The available capacity of a battery depends upon therate at which it is discharged. If a battery is discharged

at a relatively high rate, the available capacity will belower than expected. Therefore, a battery rated at 100Ah will deliver 5 A over a 20 hour period, but if it isinstead discharged at 50 A, it will run out of charge

before the theoretically expected 2 hours.

The relationship between current, discharge time,and capacity for a lead acid battery is expressed by

Peukert's law. The efficiency of a battery is different atdifferent discharge rates. When discharging at lowrate, the battery's energy is delivered more efficientlythan at higher discharge rates.
http://en.wikipedia.org/wiki/Peukert's_lawhttp://en.wikipedia.org/wiki/Efficiencyhttp://en.wikipedia.org/wiki/Efficiencyhttp://en.wikipedia.org/wiki/Peukert's_lawhttp://en.wikipedia.org/wiki/Peukert's_law


13/74

Environmental Considerations

Since their development over 250 years ago,batteries have remained among the most expensiveenergy sources, and their manufacturing consumesmany valuable resources and often involves

hazardous chemicals. For this reason many areasnow have battery recycling services available torecover some of the more toxic and sometimesvaluable materials from used batteries. Batteries may

be harmful or fatal ifswallowed. It is also important toprevent dangerous elements found in some batteries,such as lead, mercury, cadmium, from entering theenvironment.
http://en.wikipedia.org/wiki/Recyclinghttp://en.wikipedia.org/wiki/Swallowinghttp://en.wikipedia.org/wiki/Leadhttp://en.wikipedia.org/wiki/Mercury_(element)http://en.wikipedia.org/wiki/Cadmiumhttp://en.wikipedia.org/wiki/Cadmiumhttp://en.wikipedia.org/wiki/Mercury_(element)http://en.wikipedia.org/wiki/Leadhttp://en.wikipedia.org/wiki/Swallowinghttp://en.wikipedia.org/wiki/Recycling


14/74

The Electric Battery

A BATTERY is a source of

electric energy.

A simple battery contains

two dissimilar metals,

called ELECTRODES, and

a solution called the

ELECTROLYTE, in which

the electrodes are

partially immersed.


15/74

The Electric Battery An example of a simple battery would

be one in which zinc and carbon areused as the electrodes, while a diluteacid, such as sulfuric acid (dilute),acts as the electrolyte.

The acid dissolves the zinc and causeszinc ions to leave the electrode.

Each zinc ion which enters theelectrolyte leaves two electrons on thezinc plate.

The carbon electrode also dissolvesbut at a slower rate.

The result is a difference in potentialbetween the two electrodes.


16/74

The Dry CellThe Dry cell is relatively inexpensive

and quite portable.

It has many uses such as in flashlights

and radios.

The anode consists of a Zinc can in

contact with a moist paste of ZnCl2 andNH4Cl.

A carbon rod surrounded by MnO2 and

filler is the cathode.

The cell reaction appears to vary with

the rate of discharge, but at low power

the probable reactions are as follows:


17/74

Lead Storage Cell

The basic features of the lead

storage cell are electrodes of

lead and lead dioxide, dipping

into concentrated sulfuric acid

Both electrode reactionsproduce lead sulfate, which adheres to the electrode.

When the cell discharges, sulfuric acid is used up and water is produced.

The state of the cell can be determined by measuring the density of the

electrolyte solution (the density of water is about 70% that of the sulfuric acid

solution).


18/74

Primary cell

Chemical action eats away one of the

electrodes (usually -ve side)

When happened, electrode must replaced or

cell discarded

In galvanic-type cell, zinc electrode &

electrolyte must replaced

Dry cell - cheaper to buy a new one


19/74

Secondary cell

Electrodes & electrolyte altered by chemical action when celldelivers current

Cells may restored to original condition by feeding current inopposite direction

Metal plates & acid mixture change as battery supplies voltage Metal plate become similar & acid strength weakens

discharging

Recharging - applying current to battery in reverse direction,

restored battery materials Example - automotive lead acid batteries


20/74

Battery capacity

Capacity of battery to store charge - ampere hours (1Ah = 3600

coulombs) 1 Ah - battery can provide 1A) of current (flow) for one hour Factors affecting battery performance:

Chemical reactions within cells

Discharge conditions current magnitude, duration, battery terminal

voltage, temperature etc Battery is discharged at constant current rate over fixed period of

time such as 10 or 20 hours, down to set terminal voltage per cell So, 100Ah battery is rated to provide 5A for 20hours at room

temperature

Battery efficiency - different at different discharge rates When discharging at low rate, battery's energy is delivered more

efficiently than at higher discharge rates - Peukert's Law


21/74

General description

Rated at 24V DC - some cases use 110V or

220V DC large emergency lighting, vital &

battery is the only single source

2 main types of rechargeable battery:

Lead-acid

Alkaline


22/74

Lead acid battery

Nominal cell voltages - 2V

Thus, 12 lead-acid cells must connected in series - 24 V

More cells connected in parallel - increase battery capacity

Battery capacity rated at 10 hrs discharge

350 Ah will provide 35 A for 10 hours

Will have lower capacity at shorter discharge rate checkedmanufacturer's discharge curves

After 10 hour discharge, cell voltage will fallen to approx 1.73V

State of charge indicated by its electrolyte SG usinghydrometer


23/74

Lead acid

battery


24/74

Hygrometer tester


25/74

Lead acid battery (cont/) Fully charged lead-acid cell SG about 1.27-1.285 (1270-1285) Falls to about 1.1 (1100) when fully discharged Cell voltage also falls during discharge can also state of charge

indication Safely discharged until cell voltage drops to approx 1.73V Open-circuit (no-load) voltage readings cant interpret that cells are in

healthy charged state (due to high voltage) SG values quoted at 15C ambient temperature SG corrections at any other ambient temperature:

Add 0.007 to reading for each 10C above 15C Subtract 0.007 from reading for each 10C below 15C

e.g. hydrometer reading at an ambient temperature 25C is 1.27 Thus, equivalent SG value at 15C is 1.27 + 0.007 = 1.277


26/74

Alkaline battery


27/74

Alkaline battery (cont/)

Nominal cell voltages - 1.2V

Thus, 20 alkaline cells must connected in series to produce 24V

After 10 hour discharge, voltage fallen to approx 1.14 V SG value cannot determine state i.e. electrolyte density

doesnt change during charge/discharge cycles but graduallyfalls during battery lifetime

New cells have SG around 1190, reduces down to 1145 takeup to 5~10 years depending on duty cycle)

Electrolyte must completely renewed or battery replacedthereafter

Discharge of cells should discontinued when voltage fallen to1.1 V


28/74

Battery Characteristics

Important characteristics: energy density (Wh/liter) and specific energy (Wh/kg)

power density (W/liter) and specific power (W/kg) open-circuit voltage, operating voltage cut-off voltage (at which considered discharged) shelf life (leakage) cycle life

The above are decided by system chemistry advances in materials and packaging have resulted in

significant changes in older systems carbon-zinc, alkaline manganese, NiCd, lead-acid

new systems primary and secondary (rechargeable) Li


29/74

Modeling the Battery Behavior

Theoretical capacity of battery is decided by theamount of the active material in the cell

batteries often modeled as buckets of constant energy

e.g. halving the power by halving the clock frequency isassumed to double the computation time while maintainingconstant computation per battery life

In reality, delivered or nominal capacity depends

on how the battery is discharged discharge rate (load current) discharge profile and duty cycle

operating voltage and power level drained


30/74

Battery Capacity

Current in C rating: load current nomralized

to batterys capacity e.g. a discharge current of 1C for a capacity of 500 mA-

hrs is 500 mA

from [Powers95]


31/74

Battery Capacity vs. Discharge

Current Amount of energy delivered is decreased as the

current (rate at which power is drawn) isincreased

rated as ampere hours or watt hours when discharged at aspecific rate to a specific cut-off voltage

primary cells rated at a current which is 1/100th of the capacity

in ampere hours (C/100) secondary cells are rated at C/20 or C/10

At high currents, the diffusion process that movesnew active material from electrolytes to the

electrode cannot keep up


32/74

Battery Capacity vs. Discharge

Current: Peukerts Formula Energy capacity: C = k/I

k = constant dependent on chemistry & design

= 0 for ideal battery (constant capacity), up to 0.7 for

most loads in real batteries

also depends on chemistry and design

Good first order approximation does not capture effects of discharge profile

Battery life at constant voltage and current

L = C/P = C/(V.I) = (k/V).I-(1+)


33/74

Ragone Plots (log-log plot)

Specific Power

W/kg

Specific Energy

Wh/kg


34/74

Amount of Computation during

Battery Lifetime Consider a system modification that changes

performance by factor n and power by factor x total work (= speed x lifetime) will change by n.x -(1+)

e.g. reducing the clock frequency by xN reducespower by xN (N>1) & reduces performance by

xN, work done changes by (1/N)x(1/N) -(1+) = N > 1 for>0

however, cant just go on reducing frequency static power dissipated even at zero frequency

P = V.I = V.(S+Df) optimum frequency to maximize computation


35/74

Alternate Equivalent View of the

Battery

Manufacturers often give battery efficiency (%) vs.discharge rate (or discharge current ratio)

discharge rate = Iave/Irated

Battery cannot respond to instantaneous changes incurrent

so, a time constant used to calculate Iave

Given actual energy drawn by the circuit, one can use thebattery efficiency to calculate the actual depletion in thestored energy in the battery

Example: battery efficiency is 60% and its rated capacity


36/74

Modeling Battery Efficiency

rated

aveI

I

IR =

cycle

batT

N

=

=

=batN

cycle

system

bat

ave cycleIN

I0

)(1

cyclebatavebatbat TVIE )1( =

from [Simunic01]


37/74

Digression:Metrics to Relate Power

and Performance

MIPS/Watt: millions of instructions per Jouleproblem: running faster gives better MIPS/Watt

increasing frequency by N MIPS go up by xN

power goes up < xN due to static power

MIPS/Watt will increase! W/Spec2 has similar problem

Total computation during battery lifetime isbettershows diminishin returns of increasin fre uenc


38/74

Capacity & Variable Discharge

Current: Constant vs. Pulsed Capacity can be extended by draining power in

short discharge periods separated by restperiods

also works with constant background current

Battery relaxes and partially recovers the

active material lost during the current impulse

longer the rest period, the better is the recovery longer rest period needed as the discharge depth

becomes greater

battery voltage also goes back up


39/74

Benefits of Pulsed Discharge

Higher specific power for a given specific

energy impulses of several times the limiting current value can

be obtained by choosing short pulses and long restperiods

Higher specific energy for a given specific

power ideally, want specific energy = theoretical capacity

depends on pulse and rest periods


40/74

Exploiting Pulse Discharge

Gain in battery life if system shutdown is done

taking into account the pulse discharge

Examples: protocols in case of radios where power during

transmission is a lot higher than during receive and idle

periods

shutdown of CPUs and variable speed CPUs

shutdown of disks


41/74

Alternatives to Batteries?

Small batteries are the only choice forconsumer products upto 20W

But

heavyexpensive

expire without warning

require replacement (disposal problem) orrecharging (time problem)

Are there alternatives?


42/74

No Batteries Needed!

Energy Harvesting/Scavenging

Power requirements for ICs continually getting lower

The requisite power may be supplied by sources in the

environment, instead of the battery

lots of energy sources around us: light, wind, vibration etc.

E.g. computers worn on ones person are jostled when one walks,

and electric power may be generated

Media Labs Parasitic Power Harvesting project for devices built

into a shoe http://www.media.mit.edu/resenv/power.html

piezoelectric shoe inserts, shoe-mounted rotary magnetic generator

20-80 mW of peak power during brisk walk, 1-2 mW average

a system had been built around the piezoelectric shoes that periodically

broadcasts a 12-bit digital RFID as the bearer walks
http://www.media.mit.edu/resenv/power.htmlhttp://www.media.mit.edu/resenv/power.html


43/74

Self-powered Chips

Power generated using motion or solar cells, and

stored in a backup source (e.g. large capacitor) no batteries needed

applicable to sensors on vehicles, body etc.

e.g.Embedded power supply processor from MIT

[Amirtharajan97]

Back-up Source(large capacitor)

Generator

Processor


44/74

Fuel Cells

Invented in the 1990s: liberate energy from Hatom

Theoretically, quiet and clean like batteries

Plus, amazing energetic potential up to 20x more than NiCd of comparable size

No length recharging: rapidly refueled Costs coming down considerably

sophisticated engineering, and reduced amount of expensiveplatinum required for catalysts

while, $/J have gone up with energy-dense batteries

example: NiCd weighs 0.5 kg, lasts 1 hr, and costs $20

comparable Li-Ion lasts 3 hrs, but costs > 4x more


45/74

Electrochemistry of Fuel Cells

ELECTROLYTE(specialized polymer

or other materialthat allows ions topass but blocks

electrons)

ANODE CATHODECATALYST

(e.g. platinum)

HYDROGEN

OXYGEN

+

+

+

+

+

ELECTRONS

WATER


46/74

Theoretical Energetic Potential of

Fuel Cells

Stored Chemical EnergyWh/Kg Wh/liter

FUEL CELLS

Decalin (C10H18) 2400 2100Liquid hydrogen 33000 2500Lithium borohydride (LiBH4 and4H20)

2800 2500

Solid metal hydride (LaNi5H6) 370 3300Methanol 6200 4900Hydrogen in graphite nanofibers 16,000 32,000

RECHARGEABLE BATTERIES

Lead acid 30 80NiCd 40 130Ni-metal hydride 60 200Lithium-ion 130 300


47/74

Also Important: Modeling the

DC-DC Converter Efficiency

The dependency of

efficiency on the output

current

cycleC

CCTV

EI =

DC

outbat

II

=

cyclebatbatDCbat TVIE =

outDCbatDC EEE =

from [Simunic01]

B tt h


48/74

Battery charger

Due to internal leakage between terminals, fully charged

battery will get discharged even if unused took place overperiod of weeks, leads to fully discharged of battery

Charged by constant voltage method quickest Fully discharged battery damaged beyond repair plates

heavily sulphated

Float / trickle charge charge battery when battery fullycharged state

Compensates loss of battery capacity due to internal leakagei.e. small make up current for topping up, ensure battery fullycharged at all times

Float charging voltage > rated battery voltage (27V) allowsufficient charging current to compensate internal currentleakages

B tt h t


49/74

Battery charger components MCCB for switching supply to charger & provide SC

protection SD transformer step down 3 phase supply from 440 to 35V Potentiometer varies charging voltage as necessary Silicon diode rectifier bridge convert AC supply to DC for

charging

Electronic filter smoothing DC output from rectifier Batteries & transformer protected against SC by fuses or CB Keep battery on float condition & supplies power to all 24V

DC loads, as automatic switching system Indication provided on main swbd, if battery are discharged

B tt h ti


50/74

Battery charger operation

When black out occur, charger cannot supplythe DC 24V load due to no power input

So batteries automatically supply all the 24 Vloads

When power restored, charger gets normal AC powerinput

Charger automatically supplies quick charge tocharge the discharged battery

At same time, supply to all 24V DC loads At end of quick charge, charger automatically adjusts

the voltage to float charge the battery


51/74

Quick charge

When battery discharged, needs to charge ASAP &shortest time possible without damaging the battery

30V (2.5V/cell) applied to lead acid battery duringquick charging

Charging current is initially high, but reduces asbattery voltage rises

After quick charge completed, resume to float charge

For nickel cadmium battery, float charge is 1.4V/cell& quick charge is 1.7V/cell


52/74

Methods of control

Charge discharge

Float charge

Ch di h


53/74

Charge discharge

Battery initially charged from mains When fully charged, allowed to discharge to load If load is continuous type, two sets of batteries are

provided one on charge whilst the other ondischarge

Rectifiers besides supplying DC to battery, alsoensure battery on charge does not feed back into mainsupply network, if supply failure occur

Essential to have individual c/o switch operatedindependently i.e. each has an off position


54/74

Charge discharge (cont/)

This enables both batteries working in parallel to loadduring c/o period ensuring supply continuity at alltimes

Off positions essential to avoid excessiveovercharging

Each battery should off charge once adequate, left onopen circuit until required for another discharge

Excessive charging - electric power wasteful,shortened battery life & more frequent cell topping up

Battery charging system


55/74

Battery charging system Use transformer/rectifier arrangement to supply required DC voltage to cells Voltage size depends on battery type & mode of charging, e.g. charge/discharge cycle, boost

charge, trickle or float charge Do not allow electrolyte temperatures to exceed about 45C during charging. A lead acid cell will gas freely when fully charged but an alkaline ceil gases throughout the

charging period. The only indication of a fully charged alkaline cell is when its voltageremains at a steady maximum value of about 1.6 to 1.8V.

Generally, alkaline cells are more robust, mechanically and electrically, than lead acid cells.Nickel cadmium cells will hold their charge for long periods without recharging so are idealfor standby duties. Also they operate well with a float charge to provide a reliable emergency

supply when the main power fails. For all rechargeable batteries (other than the sealed type) it is essential to replace lost water

(caused during gassing and by normal evaporation) with the addition of distilled water to thecorrect level above the plates. Exposure of the cell plates to air will rapidly reduce the life ofthe battery.

On all ships and offshore platforms there are particular essential services which are vitalduring a complete loss of main power. Such services include switchgear operation, navigationlights, foghorns, fire and gas detection, internal communications, some radio communications,alarm systems. To avoid the loss of essential services they are supported by an uninterruptiblepower supply or UPS.

These can be for battery supported DC supplies or AC supplies both of which can beconfigure as continuous UPS or standby UPS.

UPS DC battery charger


56/74

UPS DC battery charger


57/74

System description

Shows typical continuous UPS DC supported supply system

Essential DC services supplied from 440V through charger 1 -continuously in trickle charges

During power loss, battery 1 maintains transitional supply

while emergency generator restores power to emergency board& charger 2

Either battery is available for few hours if both generators areunavailable

Some critical emergency lights - have internal batterysupported UPS i.e. battery charge continuously during nonemergency conditions

C & h dli


58/74

Care & handling

Main hazards hydrogen explosion in batterycompartment & short circuits Release hydrogen & oxygen when in charged Hydrogen easily ignited in concentrations 4~75% in

air Short circuit cause burns due to arcing, heavycurrent flows & flash may cause explosion

To avoid explosions & other hazards, proper care,handling & maintaining batteries should strictlyadhered

C & h dli ( t/ )


59/74

Care & handling (cont/)

1. Kept compartments adequately ventilated removedangerous gases

2. Smoking & any type of open flame prohibited incompartment no smoking & naked light sign displayed atentrance

3. Battery circuits should dead when leads connected ordisconnected avoid sparks

4. If battery in section, advise to disconnect jumper leadsbetween sections before commence works

5. Vent plugs should screwed tight while making or breakingconnections

6. Light bulbs in battery compartments - protected by gas tightglasses

C & h dli ( t/ )


60/74


1. Never lay metal tools (spanners, wrenches etc) on top ofbatteries sparking & short circuiting may occur +explosions

2. Battery connections clean & tight, dirty & looseconnections lead to local sparking

3. Compartment should never used as storage place forinflammable material or gas

4. Rings should removed from fingers or heavily taped shortcircuit through ring will heat it rapidly & cause severe burns

5. Always transported in horizontal position with sufficientmanpower heavy concentrated load & cause painful strainsor injury to individual handler

Care & handling (cont/ )


61/74

Care & handling (cont/) All cables / wires should adequately insulated & guarded

any open high current transmission equipment ispotential danger When preparing electrolyte, concentrated acid should

added slowly to water If water added to acid heat generated cause steam

explosions, acid spattering over handler To neutralize acid on skin / clothes, thoroughly &

frequently clean with fresh water Only fresh water should be used for eyes

Eyewash bottles & container of FW should kept incompartment for immediate use clearly label to avoidused by acid

Care & handling (cont/ )


62/74


1. Goggles & rubber gloves should worn when handling acid

2. Corrosive products may formed round the terminals injurious to skin &eyes, use brush to remove them

3. Protect the terminals with petroleum jelly

4. Excessive charging rate causes acid mist to be carried out of the vents intoadjacent surfaces, contact with which may burn the skin. If this happens,the affected areas should be cleaned off with diluted ammonia water or

soda solution.5. The general safety precautions with this type of battery are the same asthose for the lead acid battery with the following exceptions:

The electrolyte in these batteries is alkaline and corrosive. It should beallowed to come into contact with the skin or clothing. In the case of burnsto the skin, the affected part should be covered with boracic powder orsaturated solution of boracic powder if available.

Eyes should be washed out thoroughly with plenty of clean fresh waterfollowed immediately with a solution of boracic powder. This solutionshould always be readily available when the electrolyte is handled.

C & h dli ( / )


63/74


19. Unlike lead acid batteries, the metal cases of alkalinebatteries remain live at all times and care must be taken not totouch them or allow metal tools to come into contact withthem.

20. Alkaline and lead acid batteries should never be kept in thesame compartment. (this is because rapid electrolyte corrosionto metal work and damage to both batteries is certain).

21. Instrument and utensils (hydrometer, topping up jars andbottles) used for lead acid batteries should not be used on an

alkaline installation and vice versa or else thoroughly washedbefore using.

Wh b ?


64/74

Why worry about power?

Intel vs. Duracell

No Moores Law in batteries: 2-3%/ ear

P

roce

ssor

(MIPS)

HardDisk

(cap

acity

)

Memo

ry(ca

pacity)

Battery (energystored)

0 1 2 3 4 5 6

16x

14x

12x

10x

8x

6x

4x

2x

1xImprove

ment(comparedtoyear0)

Time (years)

S D i f L P


65/74

System Design for Low Power

Need to explicitly design the system with

power consumption or energy efficiency in

mind

Fortunately, IC technology still continue tohelp indirectly by increasing level ofintegration

more and faster transistors can enable low-powersystem architectures and design techniques

e.g. system integration on a chip can reduce the significant

circuit I/O power consumption

Energy efficient design of higher layers of the

S t D i f L P


66/74

System Design for Low Power

(contd.) Energy efficiency cuts across all system layers

entire network, not just the node

everything: circuit, logic, software, protocols, algorithms, user

interface, power supply... complex global optimization problem

Need to choose the right metric

e.g. individual node vs. network lifetime

Trade-off between energy consumption & QoS

optimize energy metric while meeting QoS constraint

Power-awareness, and not just low power

right energy at the right time and place

Wh d th P G ?


67/74

Power Supply

Where does the Power Go?

Batter

y

DC-DCConverter

Communication

RadioModem

RFTransceiver

Processing

Programmable

Ps & DSPs(apps, protocols etc.) Memory

ASICs

Peripherals

Disk Display

P C ti f


68/74

Power Consumption for a

Computer with Wireless NIC

Display36%

Wireless LAN

18%

Hard Drive

18%

CPU/Memory

21%

Other

7%

E C ti f


69/74

Energy Consumption of

Wireless NICs (Wavelan)

10 mA

156 mA190 mA

284 mA

10 mA

--------180 mA

280 mA

Sleep Mode

Idle ModeReceive Mode

Transmit Mode

11 Mbps

(Silver)

14 mA

178 mA

200 mA280 mA

9 mA

--------

280 mA

330 mA

Sleep Mode

Idle Mode

Receive Mode

Transmit Mode

2 Mbps

(Bronze)

MeasuredSpecs

P C ti i P t PC


70/74

Power Consumption in Post-PC

Devices Pocket computers, PDAs, wireless pads, wireless

sensors, pagers, cell phones

Energy and power usage of these devices is markedly

different from laptop and notebook computers much wider dynamic range of power demand

share of memory, communication and signal processing

subsystems become more important

disk storage and displays disappear or become simpler

Design of power-aware higher layer applications and

protocols need to be re-evaluated

E l P C ti f


71/74

Example: Power Consumption for

Berkeleys InfoPad TerminalDC/DC

25%

LCD

6%

I/O1%

Video

Display40%

Wireless

18%

Proc.

6%

Misc

7%

With Optional Video DisplayTotal = 9.6W

(with processor at 7% duty cycle)

DC/DC

42%

LCD

10%

I/O

2%

Wireless29%

Proc.

6%

Misc

11%

Without Optional Video DisplayTotal = 6.8W

(with processor at 7% duty cycle)

E l P C ti f


72/74


Compaq WRLs Itsy Computer System power < 1W

doing nothing (processor 95% idle) 107 mW @ 206 MHz

77 mW @ 59 MHz

62 mW @ 59 MHz, low voltage

MPEG-1 with audio 850 mW @ 206 MHz (16% idle)

Dictation 775 mW @ 206 MHz (< 0.5% idle)

text-to-speech

420 mW @ 206 MHz (53% idle) 365 mW @ 74 MHz, low voltage ( < 0.5% idle)

Processor: 200 mW 42-50% of typical total

LCD: 30-38 mW 15% of typical total

30-40% in notebooks

Itsy v1StrongARM 110059206 MHz (300 us to switch)2 core voltages (1.5V, 1.23V)64M DRAM / 32M FLASHTouchscreen & 320x200 LCDcodec, microphone & speakerserial, IrDA

E l P C ti f


73/74


Compaqs iPAQ

206MHz StrongArm SA-1110

processor

320x240 resolution color TFT

LCD

Touch screen

32MB SDRAM / 16MB Flash

memory

USB/RS-232/IrDA connection

Speaker/Microphone

Lithium Polymer battery

* Note

CPU is idle state of most of its time

Audio, IrDA, RS232 power is measured when

each part is idling

Etc includes CPU, flash memory, touch

screen and all other devices

Frontlight brightness was 16

M t i f P


74/74

Metrics for Power

Power sets battery life in hours

problem: power frequency (slow the system!) Energy per operation

fixes obvious problem with the power metric

but can cheat by doing stuff that will slow the chip

Energy/op = Power * Delay/op

Metric should capture both energy and

performance: e.g. Energy/Op * Delay/Op

low volatge and battery

Documents