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).
Experiments to suppress regulator interference using a choke coil filter unit on a 7.B.V. car.
| Identifier | ExFiles\Box 168b\1\ img276 | |
| Date | 6th May 1938 guessed | |
| -4- Regulator Interference. As it has previously been discovered the best method of removing interference due to the regulator was to fit a roof aerial. It was now decided to adopt another method of suppression whilst using an underslung chassis aerial. The car which these experiments were carried out on was 7.B.V. as it was a particularly bad offender. A filter unit was constructed, consisting of four choke coils. These coils were wound with heavy gauge copper wire and were constructed multi-layer fashion, the inductance of each was 70 H.{Arthur M. Hanbury - Head Complaints} These coils were then mounted inside a metal box and were divided into two pairs, each coil of the pairs being connected in series. The coils were then inserted between the leads connecting the main switch and ammeter to the regulator, the whole unit being mounted on the metal dash and thoroughly earthed. By this method a certain percentage of interference was removed. The next step was to ascertain what effect this filter unit had upon the charging of the battery and also upon the voltage on the ignition coil. For this experiment a specially discharged battery was fitted to the car so that there would be a heavy charging current flowing from the dynamo. A voltmeter was then connected across the battery and an ammeter in series with the same instrument upon the car. The first set of figures were obtained with the car running without the filter and the second set were taken with the filter unit in circuit; for each of these individual readings an additional load was imposed upon the battery such as the side and head lights & the side, head and fog light, etc. The car was then let run for a lengthy time so as to allow the battery to charge, and to obtain a set of figures at a lower charging rate the car was running at 30 m.p.h. while all these readings were taken. These two sets of figures were obtained in a similar manner with and without the filter unit. A graph was then plotted & a curve obtained showing the relationship between the normal charging current & voltage, a second curve was also drawn showing the same relationship with the chokes in circuit. From the curve with the chokes in circuit it will be seen that the charging current will rise up to a 6 amp charge and will remain at that figure, i.e. if the battery of the car was at all run down it would never become fully charged as long as the chokes were in the circuit. It will thus be seen that if these chokes are to be used they must consist of very heavy gauge wire to counteract for voltage drop owing to their resistance. The above chokes were wound with 14 B.S.W copper wire. | ||