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 dynamo coil performance, comparing output curves and magnetic circuit modifications.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan128 | |
| Date | 8th January 1931 | |
| -2- EPC3/AD8.1.31 contd. The curves on sheet 1. represent progressive stages from early cutting in with low output to late cutting in with high output. I. Being for the standard 56 coil dynamo. II. For the 48 coil dynamo. III. For the 48 coil dynamo modified by tapering away the trailing edges of the pole pieces. This modification increases the reluctance of the magnetic circuit and results in later cutting in but a higher output and better control at speed. On sheet 2. there are two curves, the top one being for a similar machine to that for which II on sheet 1. was drawn, but one in which the output has been purposely pushed up (by allowing a slightly higher temperature rise) in view of the fact that this machine represents the latest proposal, see our EPC1/AD6.1.31 for operation with the two-rate charge scheme, whereas as set for II on sheet 1 it was for operation without that scheme. The bottom curve on sheet 2. represents the curve as modified by the insertion of the lowest resistance (called the 6" resistance) in the dynamo field circuit. This actual machine has been fitted to Sg{Arthur F. Sidgreaves - MD}'s car 58-GN and is considered to represent the best immediately available proposal for the purpose of the two-rate charge scheme. Now answering FN's note PN{Mr Northey}4/PH7.1.31, it will be clear from the above that the earlier cutting of the 48 coil medium output dynamo is not on account of the greater number of armature conductors, this number being the same, but on account of the lower reluctance of the magnetic circuit. The lower such reluctance the earlier the cutting in and the greater the peakiness of the output curve. Our latest idea, as already referred to, is to have the best magnetic circuit possible everywhere but where the flux passes through the armature conductors and at that point to put the big reluctance as by so doing the conductor size and/or number may be increased. In regard to the point mentioned by FN. of the P.D. of a fully charged battery, please find also attached | ||