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 operational characteristics of a dynamo cutout system and the Bleriot Phi cutout.
| Identifier | ExFiles\Box 48\3\ Scan252 | |
| Date | 10th May 1921 guessed | |
| EFC {E. Fowler Clarke - Electrical Engineer} 2/T. -2- Contd. cutout is hot. It will also be appreciated that the moment the cutout comes into operation it will begin to heat up and the cutting in voltage will increase almost immediately so that, all things considered, it really amounts to this, that our specification of operation is not so far from agreement with yours as might at first sight be imagined. 2. The Bleriot Phi cutout incorporates a principle which, if properly taken advantage of, enables the dropping out voltage (on open circuit) to be very nearly as large as the cutting in voltage. The exact reason for this was carefully explained to your representative graphically during our visit. As a result of this it was possible to so arrange the cutout that very little reverse current is necessary, but in order not to cut this too fine, we have allowed in our specification a reverse current not exceeding 1 ampere, whereas in the specification of an ordinary type of cutout, this would be 2 amps. 3. If the cutout is set late when it is cold, it will be relatively still more late when hot, as the change in voltage of operation of cutout is more than the change in the voltage of the battery from normal to fully charged. Hence, in the cold condition it is an advantage to specify the cutting in operation to be fairly early, especially in the case of the Bleriot Phi cutout where such early operation does not necessarily imply a large reverse current to effect the cutout. 4. Another point is that if a dynamo is used in which the speed of balancing a battery is even a little later than is desirable, it is important to secure every little bit of output which is given by the dynamo in the early stages, especially in Town work. If the cutout is late in operation, especially when it is hot, quite a portion of the output of the dynamo in the earlier stages is lost. The proportion of that portion may not look large on the curve of dynamo output, but is relatively of more importance owing to the fact that more running may be being done in town at just about this speed than at speeds a little higher up the scale. Further to this, it is desirable that the cutout shall connect the dynamo to the battery when the dynamo is ready to give any current, as otherwise a false impression of the lateness of the dynamo cutting in is given and the dynamo is blamed for not charging at all at a certain speed, owing to a fault of the-cutout, whereas the dynamo might be giving perhaps 2 or 3 amperes. Contd. | ||