23144916 Ultra Capacitors

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ULTRACAPACITORTECHNICAL DETAILS & APPLICATIONS

Report by:

Vivek Nandan

Emtech Foundation

http://en.wikipedia.org/wiki/File:Maxwell_MC_and_BC_ultracapacitor_cells_and_modules.jpg



Table of contents

1.Introduction.

2.Attractive Features.

3.Advantages to conventional Energy

Storing Devices.

4.Inside a

Supercapacitor/Ultracapacitor.

5.Working.

6.Applications.

7.Drawbacks.



Introduction

What is a Ultracapacitor?

A charge storing device(Capacitor) .

Differ in constructional features with

respect to simple capacitors. Has ability to store tremendous charge.

Capacitance ranges up to 5000F!

Also called Super capacitor or Double-layered capacitor.

Invented by Engineers at Standard

Oil,1966.



Attractive Features

Capacitance ranges to 5000 F.

No chemical reaction involved.

Much more effective at rapid, regenerative energy

storage than chemical batteries .

Works even at low temperatures -40 degrees Celsius. Ultracapacitors can store 5 percent as much energy as

a modern lithium-ion battery.

5000 farads measure about 5 centimeters by 5 cm by

15 cm, which is an amazingly high capacitance relativeto its volume.

Can effectively fulfill the requirement of High current

pulses that can kill a battery if used instead.



Advantages to conventional energy storing

devices.

Batteries: Degrade within a few thousand charge-discharge cycles. Ulracapacitors can have

more than 300 000 charging cycles, which is far more than a battery can handle.

Ultra capacitor charges within seconds whereas batteries takes hrs.

Because no chemical reaction is involved, ultracapacitors--also known assupercapacitors and double-layer capacitors--are much more effective at rapid,regenerative energy storage than chemical batteries are.

Batteries fail where high charging discharging takes place whereas ultracapacitor fares extremely well.

Ordinary Capacitors:

Higher capacitance.

Put two ordinary capacitors the size of a D-cell battery in your flashlight,

each charged to 1.5 volts, and the bulb will go out in less than a second, if itlights at all. An ultracapacitor of the same size, however, has a capacitanceof about 350 farads and could light the bulb for about 2 minutes.

Ultra Capacitors are Expensive.



Inside a Super Capacitor

Two Electrodes coated with sponge like activated carbon.

Electrolyte :Contains free mobile ions.

Porous Seprator-:Prevents electrodes from shoritng out.



•The combination of

enormous surface

area and extremely

small chargeseparation gives the

ultracapacitor its

outstanding

capacitance relative toconventional

capacitors.



Constructional Features

Originally electrodes were made of aluminum.

Standard Oil engineers coated these aluminum with 100-micrometer-thick

layer of carbon.

The carbon was first chemically etched to produce many holes that extended

through the material, as in a sponge, so that the interior surface area was

about 100 000 times as large as the outside. (This process is said to

”activate” the carbon.)

They filled the interior with an electrolyte and used a porous insulator, one

similar to paper, to keep the electrodes from shorting out.

carbon is inert and does not react chemically with the ions attached to it. Nor

do the ions become oxidized or reduced, as they do at the higher voltages

used in an electrolytic cell.



Working

When a voltage is applied, the ions are attracted to theelectrode with the opposite charge, where they cling

electrostatically to the pores in the carbon.

At the low voltages used in ultracapacitors, carbon is inert

and does not react chemically with the ions attached to it. Nor

do the ions become oxidized or reduced, as they do at thehigher voltages used in an electrolytic cell.

As the effective area where ions are stuck is much larger,

appreciably high value of capacitance is obtained.



Modern Ultracapacitors

Nanotechnology is being employed inthe design.

The active carbon is replaced by a thin

layer of billions of Nanotubes . Each Nanotube is like a uniform

hollow cylinder with 5nm and 100 µm

long. These Nanotubes are verically grown

over the conducting electrodes.



NANOTUBES STRUCTURES



Benefits of Nanotubes

Several Advantages over Activated carbon.

Limitations of Actiavated carbon are

The high porosity means there isn't much carbon material to

carry current.

The material must be ”glued” to the aluminum current

collector using a binder , which exhibits a somewhat highresistance.

• Carbon Nanotubes

Depending on their geometry, can be excellent

conductors .Thus they can supply more power than

ultracapacitors outfitted with activated carbon.

Their structure makes them less chemically reactive, so

they can operate at a higher voltage.



Applications

Military projects — for example, starting the engines of battle tanksand submarines or replacing batteries in missiles.

Common applications today include starting diesel trucks andrailroad locomotives, actuators, and in electric/hybrid-electricvehicles for transient load leveling and regenerating the energy of braking.

A bank of ultracapacitors releases a burst of energy to help a craneheave its load aloft; they then capture energy released during thedescent to recharge.

They're being explored as replacements for the batteries in hybridcars.

In ordinary cars, they could help level the load on the battery by

powering acceleration and recovering energy during braking.

Delivering or accepting power during short-duration events is theultracapacitor's strongest suit.

ultracapacitors function well in temperatures as low as –40 C, theycan give electric cars a boost in cold weather, when batteries are attheir worst.



Drawbacks of Ultracapacitors

Linear discharge voltage prevents use of thefull energy spectrum

Low energy density - typically holds one-fifth toone-tenth the energy of an electrochemical

battery Cells have low voltages - serial connections

are needed to obtain higher voltages. Voltagebalancing is required if more than three

capacitors are connected in series High self-discharge - the rate is considerably

higher than that of an electrochemical battery.

Requires sophisticated electronic control andswitching equipment

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