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25th August 1967, Page 59
25th August 1967
Page 59
Page 60
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Page 59, 25th August 1967 — ELECTRIFYING. . . BUT WHAT NEXT?
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by P.A.C. Brockington, AMIMechE

Vki NILE recent advances in the design of v v control equipment for electric vehicles, use of lightweight body structures, the development of chargers that can safely be used to charge batteries at a high rate, employing portable auxiliary generators and progressive battery improvements have given the battery electric delivery vehicle greater operational scope rather than a role representing a new concept, battery developments could possibly within a few years revolutionize its role in the transport industry. And in the background the very large expenditure by organizations in America and in this country on electrical power storage systems (including equipment for space vehicles) promises fruitful results that could well promote revolutionary developments in road vehicle applications.

The eventual depletion of hydrocarbon fuel reserves, including crude oil and coal, moreover, will probably result ultimately in the elimination of all forms of prime mover other than electric vehicles of the battery or fuel-cell type.

Of directly related importance, nuclear power stations will at some future date supersede conventional stations and the authorities will be seeking a means to dispose of surplus current at a cheap rate during the night and possibly at other off-peak periods. In contrast to conventional power stations, nuclear stations cannot be closed down as a routine exercise to cater for changes in demand It is noteworthy that the majority of technicians dismiss the electric car as a practical proposition for more than very limited application pending the production of a battery or power source that could provide a speed and range of, say, 50/60 m.p.h. and 100 miles respectively. Obviously, progress in the design of electric cars would be of direct importance to the makers and users of electric delivery vehicles Although it is unlikely that a "super" battery will be evolved overnight that would provide a speed and range well in excess of these figures and weigh half as much as existing types of lead-acid battery, such a development is not impossible and in the event it would mark the beginning of the relatively quick end of the internal combustion engine for 60/70 per cent of the private-car and road-vehicle market, whatever the prospects offered by new sources of hydrocarbon fuel.

This then is the general picture of electric vehicle development and prospects, the larger current types of delivery vehicle offering payloads up to 3 tons or more, a speed of about 20 m.p.h. and a range of around 40 miles on stop/start work. In part, design is allied to the changing pattern of deliveries dictated by town-planning programmes and the increasing demand for fumeless vehicles operating at a very low noise level.

Dealing first with controllers, Austin Crompton Parkinson Electric Vehicles Ltd., Morrison Works, South Wigston, Leicester, has prepared an assessment of the cost and payload savings provided by the Powermiser electronic controller when applied to a Mar

rison 20 cwt battery-electric engaged on daily runs of 30 miles with an average of 300 stops, which shows that the annual saving would be about £27 and that the useful payload would be increased from 18cwt to 21cwt. The Powermiser was developed by Austin Crompton Parkinson in co-operation with Electro-Voice Products Ltd. and adds about £110 to the first cost of the vehicle.

Hidden savings should include a considerable reduction in maintenance costs which would be derived from controlled acceleration and the use of an overload safety device. Compared with a typical resistance controller the Powermiser gives smooth stepless control at all times, eliminates the use of contactors, gives a 13 per cent reduction of operational An ano provides a 16.6 per cent reduction in the required Ah capacity of the battery. A charger with a 35amp capacity may be employed in place of one with a capacity of 40amp and mains units in Ah required to recharge the battery are reduced from 33.3 to 28.9.

The controller is of the thyristor "pulse" type, in which the pulse rate of the current being fed into the motor is varied by a silicon-controlled contactorless rectifier to increase or reduce the current load of the motor, the average time for switching-on and switching-off a rectifier of this type being 0.000005 sec. and 0.00005 sec respectively. No starting resistances are used, starting losses are virtually eliminated and more efficient utilization is made of battery power. Maximum pulse rate is limited, and it is therefore impossible to overload the motor by rapid depression of the foot pedal. A heat sink is fitted to the rectifier which integrates the power drawn from the motor with time and thus obviates persistent overloading of the motor or other electrical components. There are no moving parts in the controller.

Equipped with a battery of normal size and carrying the same payload, a substantial increase in operating range is afforded by an electronic controller, an increase of 25 per cent being claimed by a number of vehicle makers and operators when multiple stops are involved.

The silicon-controlled rectifier of the Powermiser comprises an anode, a cathode and a gate and the device provides an open circuit until a discreet signal of a few thousandths of an ampere is applied to the gate terminal which in effect -closes the circuit". A signal can control currents of many hundreds of amperes and as there are no moving parts the device is capable of performing an infinite number of operations without deterioration.

Manufacturer of the Pulsomatic thyristor control, Cableform Ltd., Romily, Cheshire, emphasises that the absence of contactors virtually eliminates maintenance and it is notable that the speed control unit of the system has been life tested to 5m operations. The Pulsomatic is employed by the Stanley Engineering Co. Ltd., The Airport, Exeter, Devon, for applications to Manulectric batteryelectric delivery vehicles and trucks, and tests of vehicles on stop-start work have confirmed that the controller extends the range 25 per cent on a typical route.

Known as the Weever, the electronic pulsecontrol unit produced by the Westinghouse Brake and Signal Co. Ltd.. Semiconductor Division, 82 York Way, King's Cross, London Ni. is conventional in that it comprises a foot pedal unit, a pulse generator, a power unit and a commutation unit, servicing being simplified by the employment of plug-in electronic modules. Auxiliary braking is provided by a combination of plug braking, which is directly controlled by the driver, and dynamic or regenerative braking which is wholly or partly automatic.

An increase in useful range comparable to that provided by an electronic controller is claimed for the Rectator series/parallel fourstage control developed by the Harborough Construction Co. Ltd., Market Harborough, Leics.. for the company's Harbilt batteryelectric road vehicles and trucks, and although the DVD series/parallel control system, evolved by Coventry Climax Engines Ltd., Widdrington Road Works, Coventry, has only been applied to fork-lift trucks and a towing tractor test results show that application to stop-start delivery vehicles could give a similar advantage.

In the case of the Rectator System (which is designed for single motor vehicles) the battery is divided into four parts and the four stages give a voltage of 25 per cent when the four sections are in parallel; of 50 per cent when two parallel sections are in series with the remaining two sections, also in parallel; of 75 per cent when two sections in series are connected in series with the remaining sections connected in parallel; and 100 per cent when the four sections are in series. Conventional switchgear is used in conjunction with heavyduty silicon rectifiers, and once the first stage is switched on the motor remains connected at all times to all the battery sections, and successive switching operations do not opencircuit either the motor connections or any of the connections to the battery.

Harborough Construction technicians refer to the electronic system as expensive, of complex circuitry and of questionable reliability and point to a number of faults in the normal type of series/parallel contactor equipment, including wear and tear on the switchgear during change-over operations and the adverse effects of temporary interruptions of current supply to the motor.

Developed from the Coventry Climax series/ parallel field system, the DVD control connects the two halves of a 36V battery in parallel for operation at lower speeds and in series for higher speed operation, which enables lowvalue resistors to be employed and reduces arcing because operation of the contactors for battery or field switching does not involve breaking the current circuit, the current being diverted through the power diodes.

Whilst the advantages of rapid battery charging cannot readily be exploited by a battery-vehicle user operating a service that occupies a full working day (and charges the battery at a low rate during the night) the availability of a boost charger at an appropriate point on a route could enable a high-performance vehicle to be employed or the range to be increased. Charging time per degree of charge increases disproportionately as the fully-charged state is approached, and whereas it is possible to charge a battery 50 per cent in half-an-hour and 90 per cent in less than one hour with the appropriate charging equipment. 100 per cent charging occupies more than 5 hours. For these rates of charging a rec tifier is required having the same Ah capacity as the battery and is therefore very large and costly.

The ability of a charger safety to charge at a high rate is dependent upon a number of factors and the makers of Cyclocat equipment, Harmer and Simmons Ltd., 97/101 Peregrine Road, Hainault, Ilford, Essex, point out that recharging can only be achieved in the shortest time with the minimum damage to the battery if, throughout the charging period, the current is automatically adjusted to the maximum value compatible with maintaining an electrolyte temperature below 120 deg F and obviat

ing excessive gassing. The company claims that their gas-electronic battery-charging system has advantages over all other charging methods, including constant-current, multirate, constant-potential and taper charging.

A gas probe is incorporated in the Cyclocat system which monitors the gases liberated during the later stages of charging and produces an electric signal at a pre-determined rate of hydrogen release, which is used to control the voltage/current characteristics of the charging system. The probe is fitted on one of the cell terminals and is encased in a plastics cover to ensure that it is not affected by variations in ambient temperature. Any gases liberated from the cell pass over a pre-heated plasticized negative-coefficient resistor in the probe, the resistance of which varies according to the cooling effect of the hydrogen to produce a signal that adjusts the charging rate in inverse proportion to the amount of hydrogen produced. A heat-conductive collar, fitted to the probe, overrides the gas control should the battery temperature become excessive.

Reducing routine battery maintenance to a minimum is an important adjunct to obtaining optimum vehicle ultilization and special mention is made by Wales and Edwards, Hadescott, Shrewsbury, of automatic topping up as a valuable maintenance aid, such a device being available for fitting to the company's largest vehicle, the Freightleader 50cwt fourwheeled dairy truck. The device comprises a non-siphoning system connected to a reservoir which maintains the correct level of electrolyte at all times, replenishment of the reservoir being only required at long intervals.

Whether or not the use of a portable generator driven by an auxiliary engine to increase the speed and/or range of a battery electric is "sound practice" is a matter of controversy among vehicle makers and users, but is certainly justified in certain types of application. Austin Crompton Parkinson, for example, states that fitting a booster set can increase the scope of a battery electric by raising its useful speed from, say, 15 m.p.h. to 20 m.p.h. and thus enable it to operate on delivery rounds previously outside its capacity, and they point out that operating conditions favour the generating set in that it can be designed to run economically and to give a long engine life.

Makers of the Gainmaster propane-fuelled booster unit, the G and M Power Plant Co. Ltd., Magnet Works, Whitehouse Road, Ipswich, claims that a series of trials has been successfully completed which is "bound to revolutionize electric-vehicle transport", and in answer to the question "why not employ a larger engine and dispense with the electrics?" they emphasize tnat the batteries should be employed to the maximum extent, the generator providing a means of "extending the desirable characteristics" of the electric vehicle. The Gainmaster 2kW generator costs £286 and weighs less than 300lb, power being provided by a 5 h.p. engine. Housed in a sound-proofed welded-steel compartment, the set can conveniently be located under the working platform of the vehicles attached to a simple angle-iron support. Operation on propane gas gives a non-toxic exhaust, reduces the formation of carbon in the engine cylinder and eliminates dilution of the lubricating oil, The Stanley Engineering Co. does not favour the use of an auxiliary generator for its Manu lectric vehicles, but would fit a set if specified by a customer. A well-known operator of dairy vehicles states that while auxiliary sets afford a range increase of 30 per cent an equivalent increase is obtainable more cheaply by employing an electronic pulse-type controller, The "get-you-home" advantage of the auxiliary generator is, of course, of special merit in some applications.

Progress in the development of conventional lead-acid batteries is spasmodic, according to Electric Power Storage Ltd., Bakewell, Derbys, the makers of Exide and Kathanode batteries, the average annual improvement that can be expected in the power-to-weight characteristics of batteries being given as 1 per cent. In 1959, the very

substantial improvement of around 35 per cent was obtained "overnight-, since when

progress has been slow. In the design of a battery it is necessary (in this company's view) to equate life, cost, weight and reli ability to cater for commercial demand, an increase in energy being obtainable by sacrificing life expectancy. or by using more costly production methods. While the silverzinc battery (as used in space vehicles) gives a phenomenal improvement in power-toweight ratio, its application to road vehicles is entirely impractical.

In an assessment of development progress in the design of lead-acid batteries, Joseph Lucas Ltd., Great King Street, Birmingham 19, points out that some years ago batteries yielded about 5 Wh per lb and had a bulk ratio of approximately 2.3 cu. in. per Wh, whereas current types give up to 8.4 Wh per lb and a ratio of 1.38 cu. in. per Wh.

As intimated earlier in this article, the future of the electric vehicle gives rise to hopeful possibilities to a greater extent than any other type of vehicle and of these possibilities the potential role of the fuel cell is possibly of greatest interest in the longterm view.

Electric Power Storage observes that size and weight are still factors that inhibit the commercial use of fuel cells for traction purposes in competition with conventional batteries. As design becomes more sophisti cated, however, reductions in size and weight should offer signficant advantages over existing types of battery and this should foster volume production at a lower cost. Events leading to traction applications could become evident in five to 10 years' time.

The incorporation of a small fuel cell having an output of about 3 h.p. in a conventional type of battery-electric vehicle is envisaged as a practical possibility by Austin Crompton Parkinson, the battery being employed for acceleration and higher speeds for which an output of 20/25 h.p. would be required. The fuel cell would be utilized to propel the vehicle at steady speeds up to about 10 m.p.h.. and this combination would, it is claimed, increase the effective range by at least 300 percent. the fuel cell being also used for recharging the battery when the vehicle was stationary.

The Electrovan experimental fuel-cell vehicle, developed by General Motors Corporation of Detroit, has an average operating range of about 150 miles, the continuous output of the cells being 32 kW. Of the alternating current type, the motor develops 115 h.p. at 13,000 r.p.m. and weighs only 150Ib.

Other alternatives include fuel-battery systems such as the zinc/air type which could increase the operating range of a battery-electric to 100/150 miles. The system is being developed in this country by the Joseph Lucas Co. in close co-operation with the General Atomic Division of General Dynamics of California, and it is anticipated that work will be directed towards commercial applications in the early 1910s. In the case of delivery-vehicle applications, the power source weight will be about 700Ib, which is equivalent to that of a petrol-engined vehicle.

A number of fuel battery systems has been developed by the Electric Power Storage Co.

in the past few years, including a hydrogenfuel type, but although it is possible that a system economically suitable for vehicle trac tion may be produced in the next 5/10 years, the fuel cost of existing systems is too high for vehicle application. Progress may well depend on a means being found economically to extract oxygen from the air to use with the hydrogen.

A spokesman of Ross Auto Engineering Ltd., Banastre Road. Southport, makers of electric delivery vehicles, ambulances and trucks, forecasts that there could be spectacular developments of new power sources over the next 10 years and that the strategic problems associated with the purchase and transport of liquid fuel are likely to increase its cost.

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