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).
Analysis of the resistance of a dimmer switch from T.H. Gill & Sons and its suitability for dimming lamps.
| Identifier | ExFiles\Box 61a\1\ scan0110 | |
| Date | 6th June 1921 | |
| X.4291 EFC. PB.2. June 6th 1921. X.4291 X.1369 DIMMER SWITCH FROM T.H. GILL & SONS. The resistance of this switch is .33 ohms, which is much too low. Two similar 12 volt 36 watt O.M.F. lamps take 2.9 amperes each when in parallel, total 5.8 amperes. When in series on 12 volts they take 2.0 amperes and the brilliency is not quite as low as might be for dimming purposes. About 3.2 amperes, i.e. (1.6 each) instead of 4.0 amperes (2.0 each) would be right and would necessitate a resistance of 3.2 ohms in series with the lamps in parallel. Two similar 12 volts 24 watt half watt lamps take 2.65 amperes each when in parallel, total 5.3 amperes. When in series on 12 volts they take 1.9 amperes and the brilliency is also not quite as low as might be for dimming purposes. About 3.2 amperes, i.e. (1.6 each) instead of 3.8 amperes (1.9 each) would be right and would necessitate a resistance of 3.4 ohms in series with the lamps in parallel. The resistance of the Rex head light dimmer was 9.4 ohms. C.A.P. (Copy handed to De/Thr). 7.6.21. | ||