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).
Technical note on dynamo fuse protection under various operating conditions.
| Identifier | ExFiles\Box 61\2\ scan0299 | |
| Date | 1st February 1920 | |
| Ck{Mr Clark}1/T3.2.20. -4- Contd. therefore smaller than occurs in normal running and will do no harm, so that good protection is afforded. (5). Running with battery disconnected with main negative fuse only, this fuse goes at about 720 R.P.M. with the dynamo cold and 840 R.P.M. with the dynamo hot. (A 15 or 20 ampere fuse would also go at higher speeds). After which the control brush becomes the main negative and the dynamo is still highly excited and will run up to about 55 (or 60) Volts at 3000 R.P.M. with a corresponding field current of about 7 amperes, which, in time, will roast the field winding. (6). If, however, both field and main negative fuses be there, the main negative fuse (if of 15 amperes or less capacity) will go first and the field fuse will subsequently go at a dynamo speed of about 1920 cold and 2430 hot, and the result, if this speed be reached, will be complete protection of the dynamo, but if not quite reached, over-heating of the field winding will take place. (If the negative fuse be of 20 amp. capacity, the field fuse would go first and conditions would be as in (4)). (7). It will be seen by comparison of (6) and (4) that complete A protection of the dynamo is better secured, and at slower speeds, if the field fuse only is provided than if both field and main negative fuses are there, unless the negative fuse be of large capacity in which case it becomes useless for B protection. Contd. | ||