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 20 HP dynamo brush spring pressures and related test results.
| Identifier | ExFiles\Box 50\5\ Scan201 | |
| Date | 17th July 1923 | |
| a.{Mr Adams} & E.{Mr Elliott - Chief Engineer} To R.{Sir Henry Royce} from EFC. c. CJ. c. DA.{Bernard Day - Chassis Design} c. BY.{R.W. Bailey - Chief Engineer} By/Ds. c. Sft.{Mr Swift} for Mr. Brock. X4333 EFC3/T17.7.23. X.4333 - 20 H.P. DYNAMO BRUSH SPRING PRESSURES. ------------------------------------------ The spring pressures on the Goshawk dynamo brush spring are specified to be 1 lb. at each of the main brushes and .75 lb. at the control brush springs, without wear having taken place. Actually the pressures found on present production and on the various machines on experimental cars agree well with these figures. Due to wear to the extent allowed by the brush holder, the pressures will fall to about half this amount, thus the pressure per square inch on the main brushes would be 4.85 lbs. and 6.7 lbs. on the control brushes. With the soft graphitic brushes on the R.{Sir Henry Royce} Bosch dynamo, a pressure of 4.25 lbs/sq." is used, in the initial position, which falls to half this amount when the brushes are worn. The Scintilla dynamo which has very similar brushes is arranged with only 2 lbs. per sq/" brush pressure, which falls to 1.3 lbs. with brush wear. Regarding tests with alternate polarity on the brushes and further to our EFC1/T30.6.23, one of the dynamos there referred to has now been run for a further five days (average 8 hours each) with changing polarity on alternate days. The machine was not this time running continuously, but a mechanically operated carbon resistance was arranged in the motor circuit to complete a cycle of starting, running on peak output, working up to a high speed, running for a | ||