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8/14/2019 Low Volatge and Battery
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ELECTROTECHNOLOGY I
By
Sulaiman Olanrewaju, Oladokun
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Objectives
Differentiate between primary & secondary
cell
Operation (with aid of sketches):Lead-acid battery
Alkaline battery
Battery charging system
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Sources of Power: Batteries
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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/Voltage8/14/2019 Low Volatge and Battery
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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/1780s8/14/2019 Low Volatge and Battery
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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/18368/14/2019 Low Volatge and Battery
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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_cell8/14/2019 Low Volatge and Battery
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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/Volt8/14/2019 Low Volatge and Battery
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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.
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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_reactions8/14/2019 Low Volatge and Battery
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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.
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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_law8/14/2019 Low Volatge and Battery
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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/Recycling8/14/2019 Low Volatge and Battery
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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.
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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.
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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:
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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).
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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
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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
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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
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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
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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
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Lead acid
battery
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Hygrometer tester
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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
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Alkaline battery
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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
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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
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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
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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]
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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
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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+)
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Ragone Plots (log-log plot)
Specific Power
W/kg
Specific Energy
Wh/kg
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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
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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
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Modeling Battery Efficiency
rated
aveI
I
IR =
cycle
batT
N
=
=
=batN
cycle
system
bat
ave cycleIN
I0
)(1
cyclebatavebatbat TVIE )1( =
from [Simunic01]
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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
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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
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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
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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
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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?
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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.html8/14/2019 Low Volatge and Battery
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Methods of control
Charge discharge
Float charge
Ch di h
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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
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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
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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
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UPS DC battery charger
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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
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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
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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
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Care & handling (cont/)
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/ )
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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/ )
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Care & handling (cont/)
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.
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Care & handling (cont/)
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.
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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
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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
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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
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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
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Power Consumption for a
Computer with Wireless NIC
Display36%
Wireless LAN
18%
Hard Drive
18%
CPU/Memory
21%
Other
7%
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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
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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
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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)
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Example: Power Consumption for
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
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Example: Power Consumption for
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
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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