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).
Test report on a Goshawk dynamo with reduced output, investigating the effect of current density on dynamo brushes.
| Identifier | ExFiles\Box 50\5\ Scan213 | |
| Date | 18th August 1923 | |
| EFC. AB.79. 18th August, 1923. X.4383- GOSHAWK DYNAMO WITH REDUCED OUTPUT A test to find the effect of current density on the the condition of the dynamo brushes (especially the positive), has been made by running dynamo E on the bench at a reduced output. The machine commenced with the positive brush characteristically roughened and was run at three-quarters of its normal voltage, the current being (maximum) about 7.0 amps. and the temperature forced pp to 75°C. After a few hours, it was found that the positive brush surface was not changed. It was therefore cleaned up and given a fresh start. field This time it acquired and retained a good polish. The positive terminal on the dynamo was now connected through the main ammeter, so that the total current passing at the positive brush might be observed. The normal working voltage was resumed (or exceeded as required) and the output was gradually increased, by raising the speed of the dynamo. In this way up to almost 12 amperes (about 10 amps going to the battery) could flow at the positive brush, without serious roughening. By obtaining this output at above the peak output speed of the machine, however, the brush showed a greater tendency to roughen. When slightly roughened, the polish of the brush surface could generally be restored by again running at a low speed and output, but this did not seem possible, at least in any very short time, if the roughening had been carried too far. Dynamo R3 on 3GII runs with a polished positive brush, though set to the 12 amp. specification. A bench test of this machine, might show whether this is due to the machine itself or to some difference in the brush material. The brush tests now proceeding on machine No.288 show that some qualities will remain bright where ordinary Z brushes will not. FJA | ||