From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Evaluation of Patent 515731 for boosting ignition coil voltage, comparing dry cell and accumulator options, and proposing a simpler alternative using a ballast resistance.
| Identifier | ExFiles\Box 147\2\ scan0354 | |
| Date | 27th June 1940 guessed | |
| COPY FOR FILES: PATENTS ELECTRICAL FILE STARTING. 1247. Patent 515731 by Witcomb & Blackwell Ltd. is a scheme for boosting the voltage across the primary winding of the ignition coil during the time taken to start the engine, thereby making up for the Volt drop on the system due to the large current taken by the starter motor. This is effected by switching extra cells into the circuit by means of a solenoid switch, the latter being controlled by the starter push button switch. Either dry cells or accumulators may be used as the auxiliary battery. The use of dry cells would provide the cheaper scheme. The extra equipment would consist of three dry cells, a container, and a solenoid switch costing, in all, about 7 shillings. However, unless the cells were replaced when exhausted, their inclusion would be detrimental instead of helpful. If accumulators are used, the solenoid switch is arranged so as to provide a trickle charge to the auxiliary cells during normal running. Here, the necessary extras would consist of two lead-acid cells of about 10 amp-hour capacity, and a six-contact solenoid switch. - The whole costing about £1. Although the principle of the above scheme is sound, and will, as claimed, provide a boost at starting, we feel that to use it would be unnecessarily adding parts to our electrical system, which, due to lack of attention, would lead to failures in service. If it is found that a boost on the coil circuit is necessary for good starting, we can provide for it in a much simpler manner by designing the coil to run with a ballast resistance, and to utilise the volt drop across the latter by short circuiting it when using the starter, the push button can, besides passing current to the starter switch solenoid, short circuit the ballast. This may be tried out on the Wraith by tapping the ballast at a suitable point. Alternatively we can, by providing a ballast resistance, use any stock 6 volt coil and obtain the desired boost at starting by tapping the resistance at a suitable point and, as above, short circuiting it when starting. | ||