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).
Various technical points regarding a generator, including polarity, air gap, and operating temperatures.
| Identifier | ExFiles\Box 43\1\ Scan028 | |
| Date | 15th December 1927 | |
| To CY. from EFC. X3948 EFC3/T15.12.27. RE GENERATOR. X5280 X8671 Answering the various points in your letter of October 26th. - page 2. :- (1) We do not consider there is any disadvantage of an earthed positive from an ignition point of view. The actual polarity at the H.T. plug points is a matter of coil connection, and we supply positive H.T. to these, but the polarity does not seem to matter. (2) Par.4. Our tendency has been to increase the air gap because by so doing we get as bigger output for the same degree of heating, and a more rounded peak output with a larger gap. (3) Par.5. The conditions under which a generator is run very largely affect the temperatures reached, e.g. (a) Voltage of operation. (b) Nature of machine clamping, i.e. whether to cast iron table or wooden bed. (c) Ambient temperature. 75°C as quoted by you with an ambient temperature of 20°C is a figure for our own approximate testing conditions in which the machine is quite safe. (4) Par.10. We think your density of 58.6 amps/sq.in. is approaching the high side. Our maximum density is on the positive brush of the 20 HP. machine and is 53-1/2 amps/sq.in. EFC. | ||