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 testing and electrical characteristics of a 20 HP dynamo with two coils per slot.
| Identifier | WestWitteringFiles\L\2Jan1924-March1924\ Scan86 | |
| Date | 11th March 1924 | |
| EFC. AC.7. X.4610. 20 HP. DYNAMO WITH TWO COILS PER SLOT. Three machines of this type have so far been made; the first No.161. was fitted to 5GII last October; the Others, B and E, have been more fully tested. As regards electrical characteristics, the B machine is somewhat inferior in performance than when fitted with the standard armature. The hot cutting-in speed is about 25 r.p.m. higher (675 r.p.m.) the peak output, (the machine being set for a final temperature of 75°C) occurs earlier and is therefore lower, the figures being 10.35 amps. at 1320 r.p.m.* Some improvement was effected on this machine by using thinner brushes (see report AB.100 24.1.24) when set to the general specification, the cutting in speed was 670 r.p.m., a peak output of 11.0 amps. being obtained at 1340 r.p.m.* as compared with 12 amps. at 1640 r.p.m. The machine E performance showed very little difference from that when fitted with the standard armature, which latter was not, however, better than that of the B machine (with two coils per slot), for cutting in. This occurred at about 680 r.p.m. hot, and the output reached 11.3 amps. in each case, the speeds being 1660 r.p.m. with the old armature and 1610 r.p.m. with the new. In all cases with the two coil per slot armatures commutation was excellent there being very little sparking, and much smaller brush-wear than on the standard machines, though this was not so much reduced when the thinner brushes were used (see report AB.103 15.2.24). So far, no differences in noise-producing qualities have been observed between the two machines (see report AB.104 20.2.24). Machine E has now been allotted to chassis 5GII. On the armatures received being assembled in the standard carcase and brush gear, the main brushes were found to be 3.5° less retarded (i.e. a retard of 5.5° instead of 9°) than was the case with the standard armatures, the position indicated being the same as found on either of two adjacent segments. when In all tests carried out, the brushes were first set to the 9° retard position which is standard on present production machines. Contd. | ||