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 Smith cutout operation under varying temperature and battery conditions.
| Identifier | WestWitteringFiles\F\April1921\ Scan89 | |
| Date | 18th April 1921 | |
| Contd. -2- EPC4/T18.4.21. variation and battery E.M.F. variation. We have tried to prove whether this has been due to retentivity in the magnetic circuit, but so far as we have been able to ascertain, this also does not account for it. The Smith cutouts, however, seem to be more consistent in their operation from time to time. The following table gives the operation of these cutouts in the cold and hot conditions:- Numerical operation of Smith cutouts Nos. 7914 (half of whose shunt coil resistance is of copper wire and half eureka) and 11846 (whose shunt coil is all copper). | CUT-OUT | CONDITION | Battery disconnected. Operated at | Battery disconnected. Deoperated at | Battery connected. Deoperated at | Remarks. | |----------------------|-----------| Volts. | Amperes. | Volts. | Amps. | Volts. | [Unlabelled] | Discharge amps. (shunt & series amps) | | 7914 Copp-er & Eureka| COLD | 13.2 | .050 | 7.8 | .030 | 12.2 | .047 | -.5 | Battery E.M.F. 12.4 approx.| | 11846 copp-er only | | 13.0 | .055 | 8.7 | .055 | 12.3 | .080 | -1.0 | | | 7914 copper & Eur-eka| HOT | 14.1 | .050 | 8.6 | .030 | 12.7 | .046 | -.5 | Battery E.M.F. 13.0 approx.| | 11846 | | 15.0 | .050 | 9.4 | .050 | 12.2 | .067 | -.7 | | It will be seen on examination of this table that in a cold condition the operating point is very slightly above our limit (this, however, can easily be rectified by adjusting the control spring). The particular point to notice is that in the hot condition the one wound with half Eureka wire Contd. | ||