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).
Endurance test investigating excessive brush wear on dynamos operating at high speeds.
| Identifier | ExFiles\Box 166\1\ img098 | |
| Date | 20th April 1937 | |
| 6093. Hs.{Lord Ernest Hives - Chair} from Rm{William Robotham - Chief Engineer}/Wst. c. Sg.{Arthur F. Sidgreaves - MD} c. E.{Mr Elliott - Chief Engineer} c. By.{R.W. Bailey - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. RHC.{R. H. Coverley - Production Engineer} c. Mx.{John H Maddocks - Chief Proving Officer} Rm{William Robotham - Chief Engineer}/Wst.1/AP.20.4.37 BRUSH WEAR ON DYNAMOS AT HIGH SPEED. If our dynamos are run for any length of time at speeds above 5000 r.p.m. with full output the brush wear is excessive. This is shewn up on most 10,000 mile tests in France during the winter months. We have recently carried out an endurance test on our small dynamo running continuously at 5,500 r.p.m. and the following copy of our Laboratory report shews how serious this brush wear is when the voltage regulator permits the current to remain at a high value for any length of time at the high speeds. 'A high speed endurance test has been carried out on a set of standard Morganite E.O.O. brushes, fitted to a small dynamo No.S.F.1. (25/30.type) The machine was run at a constant speed of 5,500 r.p.m. in conjunction with a Lucas L.R.7.T. type regulator. The volts, measured at the regulator terminals, were maintained at about 13.0, while the current, commencing at about 16 amperes with the regulator cold, varied down to 9 or 10 amperes, as it warmed up. The greater part of the running was done at the lower current values. Under these conditions the machine ran for 131 hours, when it failed in output, due to the positive brush wearing right down into the holder, and not bearing on the commutator properly. The distance travelled, corresponding to the time run at 5,500 r.p.m., was 8,490 miles on the 25/30, and 10,240 miles on the Bentley. When measured, the wear of the brushes was found to be .341" on the positive and .086" on the negative. The commutator was blackened and had rather a deep track worn in it. There is little doubt about the severity of commutating conditions at this high speed and either less turns per coil or compensating turns might be considered. continued. | ||