Power Supplies

GCSE Electronics

Assignment 1

Batteries

Batteries and Cells

Zinc carbon Low current suitable for infrequent use

Low cost

Zinc Chloride Medium currentsuitable for regular use

Medium cost

regular use

Alkaline High current suitable for regular use

High cost

Nickel cadmium Medium and high(not low) current

High outlay, low lifetime cost. Rechargeable

Solar Cells

Powered by lightenergy Most effective in sunlight

Suitable for low current, low voltage applications

High outlay, zero running costs

Lead Acid Battery

Rechargeable whilst in useTypical 5 year life

For high current, constant use 6V, 12V voltage

High outlay, low running costs

Generator

Power by rotation

For low current, and suitable for low voltage applications

High outlay, zero running costs

Low voltage supply

Mains powered therefore not portable

For high current, suitable for constant use, and with adjustablevoltage

High outlay, low running costs

Battery Capacity

• How long a battery will last for is called the capacity, it can be measured and depends on the voltage output required

• The capacity of battery to deliver • The capacity of battery to deliver electric current is measured in ampere hours (Ah)

Calculating Battery Capacity

• Multiplying the current (in amperes) by the time is a measure of the amount of charge which the battery can deliver to a circuita circuit

• For example, if a battery has a capacity of 20Ah and a specified discharge time of 8 hours, it will provide:

• 20/8 = 2.5 A for 8 hours, or less current for proportionately longer time

Calculating with Power Supplies• When power supplies are connected in series the voltage increases and the current is not affected

• v = v1+v2+v3+v4

• When power supplies are connected in parallel the available current increases and the voltage remains the same

• v = 1/v1+ 1/v2+1/v3+1/v4

AC and DC

• AC means Alternating Current

• DC means Direct Current

• AC and DC are also used when referring to voltages and electrical signals which to voltages and electrical signals which are not currents!

Alternating Current - AC

• Alternating Current (AC) flows one way, then the other way, continually reversing direction. An AC voltage is continually changing between positive (+) and negative (-)and negative (-)

• The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second

• Mains electricity in the UK and in Hong • Mains electricity in the UK and in Hong Kong has a frequency of 50Hz.

• An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic circuits require a steady DC supply

Direct Current - DC

• Direct Current (DC) always flows in the same direction, but it may increase and decrease

• A DC voltage is always positive (or • A DC voltage is always positive (or always negative), but it may increase and decrease

• Electronic circuits normally require a steady DC supply which is constant at one value or a smooth DC supply which has a small variation called ripple.

• Cells, batteries and regulated power supplies provide steady DC which is supplies provide steady DC which is ideal for electronic circuits.

Types of Power Supply

• There are many types of power supply

• Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for suitable low voltage supply for electronics circuits and other devices

• A power supply can by broken down into a series of blocks, each of which performs a particular function.

• For example a 5V regulated supply:

• Transformer - steps down high voltage AC mains to low voltage AC.

• Rectifier - converts AC to DC, but the DC • Rectifier - converts AC to DC, but the DC output is varying.

• Smoothing - smooths the DC from varying greatly to a small ripple.

• Regulator - eliminates ripple by setting DC output to a fixed voltage.

Mains Electricity in Hong Kong

• Mains supply electricity coming into our Hong Kong homes is alternating current (AC) with a peak value of 354 volts.

• The frequency of the AC in Hong Kong • The frequency of the AC in Hong Kong is 50 Hertz

10

period

-354 V

+354 V

peak volts

0 VTime (ms)

20

Root Mean Square Value

• As the voltage of the AC supply is constantly changes in one complete cycle (period) between the peak voltage of +354v to -354v

• This happens 50 times per second (50 • This happens 50 times per second (50 Hz)

• The voltage changes continuously and the average voltage is 0v over a complete period

Calculating the r.m.s voltage

• A Root Mean Square (RMS) voltage gives the same heating effect as a DC voltage of the same value

• r.m.s = peak value r.m.s = 354• r.m.s = peak value

• Using this formula gives a mains supply voltage of 250v (r.m.s)

√ 2r.m.s = 354

1.414

Photovoltaic & Solar Cells

• Photovoltaics (PV) is the field of technology and research related to the application of solar cells for energy by converting sunlight directly into converting sunlight directly into electricity

• Due to the growing need for solar energy, the manufacture of solar cells and photovoltaic arrays has expanded dramatically in recent years.

Environmental Concerns

• Batteries have been identified by the EU as a priority waste stream needing action to lessen their impact on the environment.

• As a result, a new Batteries Directive came into force on 6 September 2006.

• As a result, a new Batteries Directive came into force on 6 September 2006.

• Consumers will be able to hand in used batteries from household items such as toys, computers and phones to shops and at collection points.

• The directive aims to reduce the environmental impact of the manufacture, distribution, use and disposal and recovery of batteries. It will reduce the quantity of hazardous and non hazardous waste batteries going to landfill and increase the recycling of the materials they contain.

• Recycling schemes are also to be put in place, with at least three-quarters of nickel-cadmium batteries, 65 per cent of lead acid batteries and half of other least three-quarters of nickel-cadmium batteries, 65 per cent of lead acid batteries and half of other batteries being recycled.

• The disposal of untreated car and industrial batteries in landfill or by incineration will be banned.

• Battery producers will be listed on a register. They will be required to label batteries and make sure batteries that can be removed from equipment and products.

• The directive will limit the mercury content of all batteries and of cadmium in portable batteries. Exemptions will apply to mercury in button cells and cadmium in some products, for example cordless power tools, medical equipment and emergency and alarm systems.

• Producers are to meet the cost of collecting, treating and recycling used batteries. Alternative financial agreements could be made for industrial and agreements could be made for industrial and automotive batteries and exemptions will apply for small producers.

www.environment-agency.gov.uk