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).
Test report on a dimmer switch resistance wire, noting high temperatures and suggesting design improvements.
| Identifier | ExFiles\Box 163\1\ img033 | |
| Date | 18th November 1936 | |
| To E.{Mr Elliott - Chief Engineer} c. to Hs.{Lord Ernest Hives - Chair} c. to Sg.{Arthur F. Sidgreaves - MD} c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} Rm{William Robotham - Chief Engineer}/Wst.3/JH.18.11.36. The resistance tested consisted of 7 1/2 ft. of 24 S.W.G. .022 dia. Dullray wound on a Pressphan barrel with thread between the turns. Res. 8.63 ohms. The dimmer switch was tested in series with six 16-Bv. 3w. MES. bulbs connected in parallel, and the temperature of the wire was obtained by means of a thermocouple. Variation in temperature with varying amounts of the resistance in circuit was negligible. With a supply of 14 volts the maximum temperature recorded was 62°C. the current being .8 amp. This temperature was reached on the bench and if fitted in a position with restricted ventilation it would probably be considerably higher. It is considered that this temperature, is too high for the resistance to be left exposed as it is too hot to touch. A larger gauge of wire could be tried, or the present switch could be enclosed in a well ventilated cover. Another item requiring attention is that there is no definite 'off' position for the switch and the arm would tend to wander under vibration and cause the lights to flicker. Rm{William Robotham - Chief Engineer}/Wst. | ||