Equipment for Efficient Charging
Page 69
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The Economy of the Electric Vehicle ehicle Largely Depends Upon the Means for Charging the Battery
HE efficiency of an electric vehicle depends to a large extent upon the economy and well-controlled charging of its battery. For this purpose several classes of equipment are made The Davenset automatic type, made by Partridge. Wilson and Co., Ltd., Davenset Works, Evington Valley Road, Leicester, is for A.C. mains, for either single or three-phase current supply, using the hot-cathode principle. The single-phase equipment for voltages between 200 and 250 at 50 cycles includes a core-type vacuum-impregnated transformer, a rectifying valve, an A.C. mains contactor and terminal connectors housed in a louvred steel case.
An output-control switch gives positions for normal and " equalizing " charging rates. Adjustment of the taper rate and equalizing value is governed by ballast resistances. An automatic time-delay switch ensures that the cathode is adequately heated before rectification of current occurs.
When a fleet requires charging regularly it is beneficial to use the Davenset group charging system, operating from three-phase mains; this, again, is entirely automatic. The central static rectifier feeds distribution panels up to a maximum of, sny, five. It is claimed to save about 18
per cent, of the cost of electricity and has an electrical efficiency of 84 per cent.
Efficient rectifiers for industrial needs, including the charging of electric vehicles, can be supplied by Philips Industrial (Philips Lamps, Ltd.), 145, Charing Cross Road, London, W.C.2.
Oxide-cathode rectifying valves are employed. A difficulty with rectifiers of large capacity is the question of heat dissipation. Water cooling is the most efficient method, but in the case of an all-glass valve it is impossible to provide this, so that a metal container becomes necessary.
Owing to the development of the chrome-steel-to-glass seal it is possible to design a hermetically sealed metal rectifying valve of extremely high efficiency, and the Philips metal-clad valve gives the advantage of the metaltank rectifier.
The cathode is a pool of mercury within a chrome-steel chamber cooled by a flow of water through a metal jacket. The main anode is a special graphite compound, and striking of the arc is caused by an auxiliary anode which is withdrawn magnetically from the mercury pool.
A. Morrison and Sons, Ltd., Brunswick Works, South Wigston, Leicester, supplies a patented multi-circuit charger for D.C. supplies, and built to deal with from one to four vehicles simultaneously, although each can be charged individually, and automatically switched off.
The equipment embodies a combined dynamo-motor unit with fully automatic taper off.
For A.C. supplies the company finds that the most satisfactory means is the metal rectifier, which has an efficiency of some 75 per cent.
The Westinghouse charger is giving
great satisfaction to users. It incorporates metal rectifier units, has an extremely long life and requires no replacements, maintenance or attention.
Two designs are marketed, the smaller including all components in one framework, the larger having separate recti fier and control-gear sections. They are, of course, only for AC. supply. The standard transformer covers a range of 200-250 volts, 40-60 cycles, single phase A.C.