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).
The characteristics of carbon contacts and open circuit results in a dynamo and regulator system.
| Identifier | WestWitteringFiles\E\August1920\ Scan6 | |
| Date | 17th August 1920 | |
| EFC4/T17.8.20. -3- Contd. current to the field winding at all. The carbon contacts introduce a slight amount of resistance, even when no current is passing through the operating coils, and this resistance is increased as the pressure between the contacts is reduced due to currents in the coils. This causes the field to be slightly weaker than it would otherwise be, even at speeds lower than the speed at which the contacts begin to tremble. It results in the characteristic of these contacts that there is really no very definite point at which it can be said that the vibrator begins to operate, as is the case when metallic contacts are used. Above this rather indefinite point the resistance introduced in the field circuit is of the nature of a hot carbon contact with a tendency towards an arc. So far, we have only completed open circuit results which are exhibited on the curves given. These curves show first, the open circuit voltage in the cold and hot conditions when running as a shunt machine with the carbon contacts short circuited, and secondly, open circuit voltage curves with the controller in action. It will be noticed before the vibrator begins to operate, the voltage curve bends away from that for plain shunt owing to the resistance of the contact itself, and afterwards how the voltage curves rise from the points at which the vibrator begins. The speed at which the vibrator begins to operate hot, is somewhat higher than for the cold condition, further, the open circuit voltage of the combined dynamo and regulator is greater for the Contd. R.R. 199 (250r) (SD676 19-7-17) MP 180865 | ||