Silicon ChipElectric Vehicles; Pt.2 - February 1991 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Extolling the virtues of fluorescent lights
  4. Feature: Electric Vehicles; Pt.2 by Gerry Nolan
  5. Feature: A Practical Approach To Amplifier Design by David Eather
  6. Project: A Synthesised Stereo AM Tuner, Pt.1 by John Clarke & Greg Swain
  7. Feature: Computer Bits by Jennifer Bonnitcha
  8. Vintage Radio: One thing leads to another by John Hill
  9. Project: Three Inverters For Fluorescent Lights by Otto Priboj
  10. Project: Build A Low-Cost Sinewave Oscillator by Darren Yates
  11. Back Issues
  12. Project: Fast Charger For Nicad Batteries; Pt.2 by John Clarke & Greg Swain
  13. Serviceman's Log: Now look what ya gorn an' done! by The TV Serviceman
  14. Feature: Remote Control by Bob Young
  15. Feature: Amateur Radio by Garry Cratt, VK2YBX
  16. Feature: The Story Of Electrical Energy; Pt.8 by Bryan Maher
  17. Order Form
  18. Market Centre
  19. Advertising Index
  20. Outer Back Cover

This is only a preview of the February 1991 issue of Silicon Chip.

You can view 47 of the 104 pages in the full issue, including the advertisments.

For full access, purchase the issue for $10.00 or subscribe for access to the latest issues.

Articles in this series:
  • Electric Vehicles: The State Of The Art (January 1991)
  • Electric Vehicles: The State Of The Art (January 1991)
  • Electric Vehicles; Pt.2 (February 1991)
  • Electric Vehicles; Pt.2 (February 1991)
  • Electric Vehicles; Pt.3 (March 1991)
  • Electric Vehicles; Pt.3 (March 1991)
  • The World Solar Challenge (April 1991)
  • The World Solar Challenge (April 1991)
  • Motors For Electric Vehicles (May 1991)
  • Motors For Electric Vehicles (May 1991)
  • Electric Vehicle Transmission Options (June 1991)
  • Electric Vehicle Transmission Options (June 1991)
Articles in this series:
  • A Practical Approach To Amplifier Design (February 1991)
  • A Practical Approach To Amplifier Design (February 1991)
  • A Practical Approach To Amplifier Design; Pt.2 (April 1991)
  • A Practical Approach To Amplifier Design; Pt.2 (April 1991)
Articles in this series:
  • A Synthesised Stereo AM Tuner, Pt.1 (February 1991)
  • A Synthesised Stereo AM Tuner, Pt.1 (February 1991)
  • A Synthesised Stereo AM Tuner, Pt.2 (March 1991)
  • A Synthesised Stereo AM Tuner, Pt.2 (March 1991)
  • A Synthesised Stereo AM Tuner, Pt.3 (April 1991)
  • A Synthesised Stereo AM Tuner, Pt.3 (April 1991)
Articles in this series:
  • Computer Bits (July 1989)
  • Computer Bits (July 1989)
  • Computer Bits (August 1989)
  • Computer Bits (August 1989)
  • Computer Bits (September 1989)
  • Computer Bits (September 1989)
  • Computer Bits (October 1989)
  • Computer Bits (October 1989)
  • Computer Bits (November 1989)
  • Computer Bits (November 1989)
  • Computer Bits (January 1990)
  • Computer Bits (January 1990)
  • Computer Bits (April 1990)
  • Computer Bits (April 1990)
  • Computer Bits (October 1990)
  • Computer Bits (October 1990)
  • Computer Bits (November 1990)
  • Computer Bits (November 1990)
  • Computer Bits (December 1990)
  • Computer Bits (December 1990)
  • Computer Bits (January 1991)
  • Computer Bits (January 1991)
  • Computer Bits (February 1991)
  • Computer Bits (February 1991)
  • Computer Bits (March 1991)
  • Computer Bits (March 1991)
  • Computer Bits (April 1991)
  • Computer Bits (April 1991)
  • Computer Bits (May 1991)
  • Computer Bits (May 1991)
  • Computer Bits (June 1991)
  • Computer Bits (June 1991)
  • Computer Bits (July 1991)
  • Computer Bits (July 1991)
  • Computer Bits (August 1991)
  • Computer Bits (August 1991)
  • Computer Bits (September 1991)
  • Computer Bits (September 1991)
  • Computer Bits (October 1991)
  • Computer Bits (October 1991)
  • Computer Bits (November 1991)
  • Computer Bits (November 1991)
  • Computer Bits (December 1991)
  • Computer Bits (December 1991)
  • Computer Bits (January 1992)
  • Computer Bits (January 1992)
  • Computer Bits (February 1992)
  • Computer Bits (February 1992)
  • Computer Bits (March 1992)
  • Computer Bits (March 1992)
  • Computer Bits (May 1992)
  • Computer Bits (May 1992)
  • Computer Bits (June 1992)
  • Computer Bits (June 1992)
  • Computer Bits (July 1992)
  • Computer Bits (July 1992)
  • Computer Bits (September 1992)
  • Computer Bits (September 1992)
  • Computer Bits (October 1992)
  • Computer Bits (October 1992)
  • Computer Bits (November 1992)
  • Computer Bits (November 1992)
  • Computer Bits (December 1992)
  • Computer Bits (December 1992)
  • Computer Bits (February 1993)
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  • Computer Bits (April 1993)
  • Computer Bits (April 1993)
  • Computer Bits (May 1993)
  • Computer Bits (May 1993)
  • Computer Bits (June 1993)
  • Computer Bits (June 1993)
  • Computer Bits (October 1993)
  • Computer Bits (October 1993)
  • Computer Bits (March 1994)
  • Computer Bits (March 1994)
  • Computer Bits (May 1994)
  • Computer Bits (May 1994)
  • Computer Bits (June 1994)
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  • Computer Bits (July 1994)
  • Computer Bits (July 1994)
  • Computer Bits (October 1994)
  • Computer Bits (October 1994)
  • Computer Bits (November 1994)
  • Computer Bits (November 1994)
  • Computer Bits (December 1994)
  • Computer Bits (December 1994)
  • Computer Bits (January 1995)
  • Computer Bits (January 1995)
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  • Computer Bits (February 1995)
  • Computer Bits (March 1995)
  • Computer Bits (March 1995)
  • Computer Bits (April 1995)
  • Computer Bits (April 1995)
  • CMOS Memory Settings - What To Do When The Battery Goes Flat (May 1995)
  • CMOS Memory Settings - What To Do When The Battery Goes Flat (May 1995)
  • Computer Bits (July 1995)
  • Computer Bits (July 1995)
  • Computer Bits (September 1995)
  • Computer Bits (September 1995)
  • Computer Bits: Connecting To The Internet With WIndows 95 (October 1995)
  • Computer Bits: Connecting To The Internet With WIndows 95 (October 1995)
  • Computer Bits (December 1995)
  • Computer Bits (December 1995)
  • Computer Bits (January 1996)
  • Computer Bits (January 1996)
  • Computer Bits (February 1996)
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  • Computer Bits (March 1996)
  • Computer Bits (March 1996)
  • Computer Bits (May 1996)
  • Computer Bits (May 1996)
  • Computer Bits (June 1996)
  • Computer Bits (June 1996)
  • Computer Bits (July 1996)
  • Computer Bits (July 1996)
  • Computer Bits (August 1996)
  • Computer Bits (August 1996)
  • Computer Bits (January 1997)
  • Computer Bits (January 1997)
  • Computer Bits (April 1997)
  • Computer Bits (April 1997)
  • Windows 95: The Hardware That's Required (May 1997)
  • Windows 95: The Hardware That's Required (May 1997)
  • Turning Up Your Hard Disc Drive (June 1997)
  • Turning Up Your Hard Disc Drive (June 1997)
  • Computer Bits (July 1997)
  • Computer Bits (July 1997)
  • Computer Bits: The Ins & Outs Of Sound Cards (August 1997)
  • Computer Bits: The Ins & Outs Of Sound Cards (August 1997)
  • Computer Bits (September 1997)
  • Computer Bits (September 1997)
  • Computer Bits (October 1997)
  • Computer Bits (October 1997)
  • Computer Bits (November 1997)
  • Computer Bits (November 1997)
  • Computer Bits (April 1998)
  • Computer Bits (April 1998)
  • Computer Bits (June 1998)
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  • Computer Bits (July 1998)
  • Computer Bits (July 1998)
  • Computer Bits (November 1998)
  • Computer Bits (November 1998)
  • Computer Bits (December 1998)
  • Computer Bits (December 1998)
  • Control Your World Using Linux (July 2011)
  • Control Your World Using Linux (July 2011)
Articles in this series:
  • Fast Charger For Nicad Batteries; Pt.1 (January 1991)
  • Fast Charger For Nicad Batteries; Pt.1 (January 1991)
  • Fast Charger For Nicad Batteries; Pt.2 (February 1991)
  • Fast Charger For Nicad Batteries; Pt.2 (February 1991)
Articles in this series:
  • Remote Control (February 1991)
  • Remote Control (February 1991)
  • Remote Control (March 1991)
  • Remote Control (March 1991)
Articles in this series:
  • Amateur Radio (November 1987)
  • Amateur Radio (November 1987)
  • Amateur Radio (December 1987)
  • Amateur Radio (December 1987)
  • Amateur Radio (February 1988)
  • Amateur Radio (February 1988)
  • Amateur Radio (March 1988)
  • Amateur Radio (March 1988)
  • Amateur Radio (April 1988)
  • Amateur Radio (April 1988)
  • Amateur Radio (May 1988)
  • Amateur Radio (May 1988)
  • Amateur Radio (June 1988)
  • Amateur Radio (June 1988)
  • Amateur Radio (July 1988)
  • Amateur Radio (July 1988)
  • Amateur Radio (August 1988)
  • Amateur Radio (August 1988)
  • Amateur Radio (September 1988)
  • Amateur Radio (September 1988)
  • Amateur Radio (October 1988)
  • Amateur Radio (October 1988)
  • Amateur Radio (November 1988)
  • Amateur Radio (November 1988)
  • Amateur Radio (December 1988)
  • Amateur Radio (December 1988)
  • Amateur Radio (January 1989)
  • Amateur Radio (January 1989)
  • Amateur Radio (April 1989)
  • Amateur Radio (April 1989)
  • Amateur Radio (May 1989)
  • Amateur Radio (May 1989)
  • Amateur Radio (June 1989)
  • Amateur Radio (June 1989)
  • Amateur Radio (July 1989)
  • Amateur Radio (July 1989)
  • Amateur Radio (August 1989)
  • Amateur Radio (August 1989)
  • Amateur Radio (September 1989)
  • Amateur Radio (September 1989)
  • Amateur Radio (October 1989)
  • Amateur Radio (October 1989)
  • Amateur Radio (November 1989)
  • Amateur Radio (November 1989)
  • Amateur Radio (December 1989)
  • Amateur Radio (December 1989)
  • Amateur Radio (February 1990)
  • Amateur Radio (February 1990)
  • Amateur Radio (March 1990)
  • Amateur Radio (March 1990)
  • Amateur Radio (April 1990)
  • Amateur Radio (April 1990)
  • Amateur Radio (May 1990)
  • Amateur Radio (May 1990)
  • Amateur Radio (June 1990)
  • Amateur Radio (June 1990)
  • Amateur Radio (July 1990)
  • Amateur Radio (July 1990)
  • The "Tube" vs. The Microchip (August 1990)
  • The "Tube" vs. The Microchip (August 1990)
  • Amateur Radio (September 1990)
  • Amateur Radio (September 1990)
  • Amateur Radio (October 1990)
  • Amateur Radio (October 1990)
  • Amateur Radio (November 1990)
  • Amateur Radio (November 1990)
  • Amateur Radio (December 1990)
  • Amateur Radio (December 1990)
  • Amateur Radio (January 1991)
  • Amateur Radio (January 1991)
  • Amateur Radio (February 1991)
  • Amateur Radio (February 1991)
  • Amateur Radio (March 1991)
  • Amateur Radio (March 1991)
  • Amateur Radio (April 1991)
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  • Amateur Radio (May 1991)
  • Amateur Radio (May 1991)
  • Amateur Radio (June 1991)
  • Amateur Radio (June 1991)
  • Amateur Radio (July 1991)
  • Amateur Radio (July 1991)
  • Amateur Radio (August 1991)
  • Amateur Radio (August 1991)
  • Amateur Radio (September 1991)
  • Amateur Radio (September 1991)
  • Amateur Radio (October 1991)
  • Amateur Radio (October 1991)
  • Amateur Radio (November 1991)
  • Amateur Radio (November 1991)
  • Amateur Radio (January 1992)
  • Amateur Radio (January 1992)
  • Amateur Radio (February 1992)
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  • Amateur Radio (March 1992)
  • Amateur Radio (March 1992)
  • Amateur Radio (July 1992)
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  • Amateur Radio (November 1992)
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  • Amateur Radio (January 1993)
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  • Amateur Radio (December 1993)
  • Amateur Radio (December 1993)
  • Amateur Radio (February 1994)
  • Amateur Radio (February 1994)
  • Amateur Radio (March 1994)
  • Amateur Radio (March 1994)
  • Amateur Radio (May 1994)
  • Amateur Radio (May 1994)
  • Amateur Radio (June 1994)
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  • Amateur Radio (September 1994)
  • Amateur Radio (September 1994)
  • Amateur Radio (December 1994)
  • Amateur Radio (December 1994)
  • Amateur Radio (January 1995)
  • Amateur Radio (January 1995)
  • CB Radio Can Now Transmit Data (March 2001)
  • CB Radio Can Now Transmit Data (March 2001)
  • What's On Offer In "Walkie Talkies" (March 2001)
  • What's On Offer In "Walkie Talkies" (March 2001)
  • Stressless Wireless (October 2004)
  • Stressless Wireless (October 2004)
  • WiNRADiO: Marrying A Radio Receiver To A PC (January 2007)
  • WiNRADiO: Marrying A Radio Receiver To A PC (January 2007)
  • “Degen” Synthesised HF Communications Receiver (January 2007)
  • “Degen” Synthesised HF Communications Receiver (January 2007)
  • PICAXE-08M 433MHz Data Transceiver (October 2008)
  • PICAXE-08M 433MHz Data Transceiver (October 2008)
  • Half-Duplex With HopeRF’s HM-TR UHF Transceivers (April 2009)
  • Half-Duplex With HopeRF’s HM-TR UHF Transceivers (April 2009)
  • Dorji 433MHz Wireless Data Modules (January 2012)
  • Dorji 433MHz Wireless Data Modules (January 2012)
Articles in this series:
  • The Technology Letters, Pt.2 (January 1989)
  • The Technology Letters, Pt.2 (January 1989)
  • The Story Of Electrical Energy (July 1990)
  • The Story Of Electrical Energy (July 1990)
  • The Story Of Electrical Energy; Pt.2 (August 1990)
  • The Story Of Electrical Energy; Pt.2 (August 1990)
  • The Story Of Electrical Energy; Pt.3 (September 1990)
  • The Story Of Electrical Energy; Pt.3 (September 1990)
  • The Story Of Electrical Energy; Pt.4 (October 1990)
  • The Story Of Electrical Energy; Pt.4 (October 1990)
  • The Story Of Electrical Energy; Pt.5 (November 1990)
  • The Story Of Electrical Energy; Pt.5 (November 1990)
  • The Story Of Electrical Energy; Pt.6 (December 1990)
  • The Story Of Electrical Energy; Pt.6 (December 1990)
  • The Story Of Electrical Energy; Pt.7 (January 1991)
  • The Story Of Electrical Energy; Pt.7 (January 1991)
  • The Story Of Electrical Energy; Pt.8 (February 1991)
  • The Story Of Electrical Energy; Pt.8 (February 1991)
  • The Story Of Electrical Energy; Pt.9 (March 1991)
  • The Story Of Electrical Energy; Pt.9 (March 1991)
  • The Story Of Electrical Energy; Pt.10 (May 1991)
  • The Story Of Electrical Energy; Pt.10 (May 1991)
  • The Story Of Electrical Energy; Pt.11 (July 1991)
  • The Story Of Electrical Energy; Pt.11 (July 1991)
  • The Story Of Electrical Energy; Pt.12 (August 1991)
  • The Story Of Electrical Energy; Pt.12 (August 1991)
  • The Story Of Electrical Energy; Pt.13 (September 1991)
  • The Story Of Electrical Energy; Pt.13 (September 1991)
  • The Story Of Electrical Energy; Pt.14 (October 1991)
  • The Story Of Electrical Energy; Pt.14 (October 1991)
  • The Story Of Electrical Energy; Pt.15 (November 1991)
  • The Story Of Electrical Energy; Pt.15 (November 1991)
  • The Story Of Electrical Energy; Pt.16 (December 1991)
  • The Story Of Electrical Energy; Pt.16 (December 1991)
  • The Story Of Electrical Energy; Pt.17 (January 1992)
  • The Story Of Electrical Energy; Pt.17 (January 1992)
  • The Story Of Electrical Energy; Pt.18 (March 1992)
  • The Story Of Electrical Energy; Pt.18 (March 1992)
  • The Story Of Electrical Energy; Pt.19 (August 1992)
  • The Story Of Electrical Energy; Pt.19 (August 1992)
  • The Story of Electrical Energy; Pt.20 (September 1992)
  • The Story of Electrical Energy; Pt.20 (September 1992)
  • The Story Of Electrical Energy; Pt.21 (November 1992)
  • The Story Of Electrical Energy; Pt.21 (November 1992)
  • The Story Of Electrical Energy; Pt.22 (January 1993)
  • The Story Of Electrical Energy; Pt.22 (January 1993)
  • The Story of Electrical Energy (April 1993)
  • The Story of Electrical Energy (April 1993)
  • The Story Of Electrical Energy; Pt.24 (May 1993)
  • The Story Of Electrical Energy; Pt.24 (May 1993)
  • The Story Of Electrical Energy; Pt.24 (June 1993)
  • The Story Of Electrical Energy; Pt.24 (June 1993)
ectr,c he size, weight, shape and technical characteristics of the energy source affect almost every other vehicle attribute. Energy density is the most important consideration but choice of the energy source will depend on a host of factors including: power density, cycle life, initial cost, maintenance cost, energy efficiency, output voltage, internal impedance, charge rate, byproducts, shelf life, temperature characteristics and overall safety. However, energy density is what really matters. This is simply the total source energy divided by the source weight to give a result in watt-hours per kilo~ gram (Wh/kg). Naturally, the source weight must include any subsystems required by the source, such as cooling fans and so on. Table 1 shows the energy densities of various fuels and other energy sources and makes it clear how very low the energy densities of man-made sources are. The values listed are nominal and may vary considerably under certain conditions but the much lower energy densities of the man-made sources relative to the natural sources are obvious. It is also important to realise that energy density may vary considerably with the rate at which the energy is used. For example, an energy density of 60Wh/kg may be claimed by the manufacturer of a particular type of T By GERRY NOLAN When you consider that one kilogram of petrol stores the equivalent of 12,000 watt-hours of energy, any electric storage medium falls a long way short. The best alternative is the aluminium-air fuel cell which has an energy density of up to 360 watt-hours per kilogram, so it is obvious that the field of energy storage is wide open to innovation. 8 SILICON CHIP battery weighing 30kg, so we would expect to obtain 1800Wh of energy. What the manufacturer may neglect to tell us, however, is that if we use the energy at double the normal rate, the energy density drops to 45Wh/kg, giving us a total energy availability of only 1350Wh. The moral of this, of course, is to specify energy density at a specific power level. As anyone reading this article probably already knows, the most common energy source for electrical vehicles is the lead acid cell. The currently obtainable energy densities of these is up to 50Wh/kg. Other batteries, fuel cells and flywheels are shown in Table 2 along with their theoretically obtainable energy densities. Power density vs acceleration An energy source with a very high energy density is highly desirable but, as with conventional engines, the rate at which the energy may be used is also very important. This rate is determined by the power density which is measured in watts per kilogram. A good example of a battery with a high energy density but a low power density is the aluminium-air fuel cell developed by Alupower in Ontario, Canada. Because it takes up to half an hour to reach its full power capacity, it needs to be used with lead acid cells which supply short term demands. Pt.2: energy storage - THE GENERAL MOTOR'S IMPACT car uses high-power sealed-lead acid batteries & shatters the perception thai electric vehicles are slow-moving golfbuggies. During trials, it beat a Nissan 300ZX in 0-100km/h acceleration tests. Power densities of up to 150W/kg may be obtained from lead acid batteries , around 200W /kg for nickel zinc, 100W /kg for nickel iron, 65W / kg for zinc chloride, 160W /kg for lithium iron and up to 200W /kg for sodium sulphur. On the basis of this comparison, the ordinary lead acid battery isn 't too bad. Replacement cost How many times can you charge and discharge (cycle) the batteries before they have to be replaced? The General Motors Impact car is designed to be powered by 32 10-volt batteries. These have an expected life of about 40,000km and a replacement cost of around $3500, or a little less than nine cents per kilometre. This is a much higher cost than the energy itself, which could be taken from the power grid for as little as 0.3 cents per kilometre. Increasing cycle life will obviously reduce the replacement cost per kilo- metre and research over the past decade has greatly improved the number of cycles possible, in some cases almost doubling it. Now lead acid batteries have a cycle life approaching 800 cycles, up from 500 in 1980, while nickel iron and sodium sulphur may be cycled (ie, fully charged and fully discharged) more than a thousand times. Another factor which needs to be taken into consideration when selecting an energy source is cell voltage , which will determine how many cells need to be hooked up and the type of array to obtain the voltage necessary to run the motor and battery efficiently. The available voltage will also be affected by the internal impedance, which generally increases as charge decreases. Battery maintenance is also an important consideration from time, material costs and skills points of view - your average EV user may not feel too comfortable topping up the battery with some exotic electrolyte every second day. Flat batteries One of the things that will worry EV users , at least until there are enough recharging stations handy, is the fear of the batteries going flat without warning. In your present vehicle, a glance at the fuel gauge and a quick mental calculation will ef\able you to work out roughly how far you can go before you need to stop for fuel. However, replacing the fuel gauge Table 1 Energy Source Nominal Energy Density (Wh/kg) Petrol 12,300 9,350 Natural gas Methanol 6,200 Hydrogen 28,000 Coal 8,200 Lead-acid battery: up to 50 Sodium-sulphur battery: 150-300 an Eldorado for innovators FEBRUARY1991 9 ELECTROLYTE STORAGE TANK \ LEAD-ACID BATTERY PACK ELECTRIC DRIVE ALUMINIUM-AIR HYBRID ELECTRIC PROTOTYPE - because the aluminiumair battery takes half an hour to build up to peak power, a lead-acid battery pack is used to supply start-up and acceleration energy. Excess energy from·the Al-air battery can then be used to recharge the lead-acid pack while the vehicle is moving. with a "charge gauge" is not such a simple matter in an electric vehicle. The definitions of a fully charged battery and the way to measure its charge vary considerably with the type of battery. The no-load voltage level may give a reasonable indication in some cases but will vary with the history of the battery, temperature and so on. Measuring the electrolyte specific gravity also gives an indication but few EV users would appreciate the inconvenience. A type of "charge gauge", which integrates the current into and out of the battery to give an actual state-ofcharge, would be a great comfort. An additional selling point would be a "range-at-present-speed" readout. Charge acceptance The capability of the energy source to take a charge is also an important ALUMINIUM-AIR CELL - an aluminium-air cell usually has 20 individual cells, a condenser and a heat exchanger at the centre of which are located the pump motor and air blower. The condenser removes oxygen depleted air from the system and the heat exchanger keeps the electrolyte temperature at about 60°C. The blower circulates air through the cathodes. 10 SILICON CHIP consideration, as it should be able to absorb high rates of energy input (eg, under regenerative braking) without exceeding acceptable temperature levels. Nickel-cadmium batteries, in particular, are able to handle high charge rates and Audi is using these in a hybrid 4-wheel drive car. The front wheels of the "duo" are driven by the normal Audi 2.3 litre, 5-cylinder petrol engine and the rear wheels by a pack of 49 nicad cells, each of 1.2 volts, powering a 9.4kW electric motor which fits into the transmission tunnel. Safety considerations The sheer weight of batteries, especially when lead acid cells are used, requires special strengthening in the design and construction of EVs from scratch or when converting conventional vehicles to EVs or hybrids. 400kg of batteries suddenly coming loose during a crash stop would be a major hazard, to say the least. "Gassing" and high temperatures during charging can also lead to problems, particularly at high rates of charge, and effective ventilation must be built-in. Silver zinc batteries Twelve of the first 13 cars in the recent World Solar Challenge used silver zinc batteries, while roughly the same number of vehicles used DUAL POWER FOR AUDI - a 180kg, high performance nickel-cadmium battery pack fits into the spare wheel-well of the Audi 100 to power the 9.4kW electric motor which fits into the transmission tunnel. Because the petrol engine is retained to drive the front wheels, a 4WD vehicle with two completely independent drive systems is the result. lead acid batteries. Although they are much more expensive than lead acid batteries, with their high energy density (100Wh/kg), superior power density and lighter weight, silver zinc batteries give an electric vehicle a decided performance advantage. So far we've talked mostly about batteries and their close relatives, fuel cells, but flywheels have been around for a long time, much longer than batteries in fact, and could conceivably have even greater potential than batteries or fuel cells as energy storage systems for EVs. Flywheel research Your silky smooth BMW, Mercedes, even the Rolls, would run very roughly, if at all , without a flywheel to maintain the crankshaft rotation through to each ignition stroke. Apart from smoothing out the staccato power delivery of the piston engine, flywheels have also been used in vehicles for energy storage since the 1930s in everything from torpedoes to draglines and helicopter hoists. Archaeologists have found one in the Middle East that they believe was used as a potter's wheel in ancient Ur of Chaldea 5,500 years ago. As far back as 1973 , researchers were predicting energy densities of 870 watt-hours per kilogram using fused silica as a material for super flywheels. What some people didn't seem to Exotic Energy Storage For EVs Zinc-hydroxide, aluminium-air, vanadium and sodium-sulphur electro-chemical batteries and fuel cells, some being recharged simply by replacing the electrolyte, are all current areas of research . Energy densities of up to 200Wh/ kg are being claimed for the zinchydroxide electrochemical cells which are being researched by a team headed by Jim Evans at the Lawrence Livermore Laboratories near San Francisco. Zinc is often used as a material for electrodes - remember the zinccopper-acid cell we all experimented Table 2 Source Lead acid Nickel zinc Nickel iron Nickel cadmium Silver zinc Zinc chlorine Energy Density (Wh/kg) Now Available Theoretical 110 50 90 60 30 100 500 90 High Temperature Batteries Lithium metal sulphide: Sodium sulphur: 170 300 Fuel cells Aluminium air: Flywheel (steel): Super flywheel (fibre): realise until much more recently was that, while the energy storage capacity is directly proportional to the mass , it is proportional to the square of the rotational velocity - so triple the speed ofrotation and you get nine times the energy storage capacity. Concentrating the mass near the circumference, where the rotational velocity is highest, also increases the energy storage capacity for a given overall weight. For a time, lightweight high-speed flywheels appeared to have real potential and a great deal of research was carried out during the early 70s with at school? - but it is generally in the form of a sheet or slab. By using the zinc as particles, the slurry of anode and electrolyte can be continuously replaced from a reservoir with the used material being stored for later replacement and recycling at a "service station". The aluminium-air cells being developed by Alupower have a claimed energy density of 360Wh/kg. Alupower is an Alcan subsidiary which is combining its technology with Moli Energy's rechargeable lithium battery knowledge. Alupower's fuel cell generates electricity by an electrochemical reaction between aluminium and oxygen , using an alkaline solution or saltwater as an electrolyte. An air 350 12-30 up to 40 870 when the Middle East put up oil prices. Unfortunately, when oil prices dropped again, flywheel research lost its momentum. Now, although research is gaining speed again, the high expected energy densities haven't materialised. Nevertheless, the availability oflight, high-tensile fibres such as Kevlar, magnetic levitation bearings, high vacuum enclosures and electronic commutation and control have enabled densities of more than 40 watthours per kilogram to be obtained. Because they are so light, relatively maintenance free and could be made stream is blown through the cell stack to supply the oxygen for the electrochemical reaction, while the electrolyte is pumped through the cell stack between the aluminium anodes and air cathodes. Electricity is produced as the alu minium oxidizes, forming aluminium hydroxide as a byproduct which precipitates out and is collected in a sump. This can be collected and recycled back into aluminium, making it a clean and non-polluting renewable power source (see illustration). Some of these research paths will be blind alleys, others will lead to developments in directions quite different from that originally intended, but that is the way of research. FEBRUARY1991 11 i THE CLEAN AIR TRANSPORT LA301 - a 4-passenger or 2-seat microvan - uses lead-acid batteries & an aluminium-air fuel cell to power an 11.9kW DC motor. It also has a propane-fuelled auxiliary power unit to achieve a maximum range of 240km and a top speed of lO0km/h. for change over at service stations instead of waiting for a recharge, the possibilities for fruitful research are very high. Another advantage of the lightweight fibres is that if the flywheel disintegrates, perhaps because of overspeeding, it just becomes a pile of fluff instead of potentially lethal chunks of high grade steel. Where are we going? One of the mistakes EV designers and builders seem to be making is to compete head on with existing fam- ily cars by designing for ranges of at least 100km at speeds up to 100km/h. You may remember from last month's article that 90% of all daily one way trips are less than 35km long. So why not design for a trip range of 50km at speeds of up to 80km/hr, at least until the technology_ is more widely accepted. For a start, this would reduce battery weight to less than half. Less than half? Yes - with a lighter battery load and the consequent reductions in strengthening required - the overall vehicle weight would be much EXPERIMENTAL ELECTRIC vehicles have been produced in Australia. This one is a converted Mazda utility powered by a tokW forklift motor & a 48V battery bank. Solar cells on the roof top up the batteries during the day. less and not so much energy would be required to push it around. The combined results would be reduced manufacturing, running and maintenance costs, making EVs a much more immediately attractive alternative, thereby greatly accelerating their acceptance by the public. sc Outside chamber liquid-filled for cooling Fibre-glass shielding · Contra-rotating flywheel rotors Gimball ing spring assembly Electrical leads to motor/generator 12 SILICON CHIP THE ADVENT OF THE "ENERGY WH~EL" an energy pack of super flywheels built as a combined motor/generator with electronic commutation and magnetic levitation bearings, running in a high vacuum, would provide very efficient energy storage. Because of the enormous speed at which the flywheels rotate, the energy would be used to power an electric motor to drive the wheels, rather than using a mechanical drive train. The pack would be self-contained so that it could be quickly replaced by a fully charged one when discharged. Flywheels used for energy storage in moving vehicles would need to be contrarotating and gymballed to dampen out gyroscopic precessing forces.