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Jew Smith's electric o be shown
Page 130
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`IF outstanding battery-electric interest J at Earls Court this year, a new Roundsin 1.5-ton electric truck will be shown by lith's Delivery Vehicles Ltd., Gateshead-Tyne 11, which in chassis form will nure a new Powerflow solid-state controller d in dairy truck form will be equipped with new Powerstep resistance-type controller. The Roundsman has a range of up to 50 les a day on stop-start delivery work and riants are available covering many types operation including the transport of bagge and freight. The brakes, wipers and adlamps comply with the proposed iendments to the regulations relating to ch equipment, and body details of the dairy ick will include Smith's Stowaway cab ors.
The The Powerflow controller incorporates thyrister which provides a mean voltage low that of the line voltage by applying ry short pulses of line voltage interposed • periods of no voltage, the magnitude of e mean voltage of the motor being deterined by adjustment of the ratio of "on" "off" periods. By this means it is posile to provide a smooth and noiseless Intro' of speed with negligible losses.
The company's technicians point out at, in the case of a conventional control
system, up to a third of the total battery power may be lost in stopping and restarting on house-to-house deliveries. They claim that the Powerflow thyrister control reduces this loss to a bare minimum, with a consequent material gain in the miles-percharge obtainable. Moreover, the Powerflow facilitates "inching" of the vehicle and offers smooth progressive acceleration from rest to full speed. Additionally, it is claimed, the vehicle can be operated continually at any speed without danger of overheating or wastage of energy.
The controller replaces a considerable number of contactors and associated mechanically-operated auxiliary components, all of which are prone to electrical erosion and mechanical wear. Because the Powerflow is not based on moving parts it enables inspection and maintenance costs to be reduced considerably. Components liable to wear are produced in the form of plug-in units which can be readily replaced. The approximate weight of the controller is 40 lb. It measures 1 ft. 8.5 in. by 1 ft. 0.5 in. by 9.5 in.
Incorporating a double-interlock system, the Powerstep controller represents a valuable safety feature in that a vehicle fitted with the unit is extremely difficult to start (by a child or unauthorized person) even if the ignition switch has been left in the "on" position.
Of the series-resistance type, the controller features main and reversing circuit breakers of the electrically-controlled type, a pair of heavy-duty contactors acting as circuit insulators and as a forward-andreverse selector. When the selector switch is in the neutral position, power is switched off to both the control and main circuits, and as a means of enhancing safety a new type of foot controller is fitted having a safety interlock switch. This isolates all power and control circuits until the pedal is depressed to the "first" position. A "dead-man's" switch, operated by the left foot, is offered as an optional extra.
The four speeds are selected to give a smooth take-off and drive, and the standard unit incorporates a delay-timer which obviates undue strain on the motor and battery if the vehicle is driven inexpertly. Two heavyduty contactors with magnetic-arc blow-out actuate the four stages, and maintenance is thus reduced to a minimum. Because of its compactness the controller can be mounted relatively close to the motor, compared with a conventional unit, which reduces power losses in the main cables and eliminates the use of heavy cables in the driving cab. Weighing approximately 32 lb. the unit measures 1 ft. 2.5 in. by 9.5 in. by 6 in.