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).
Letter to S. Smith & Sons detailing the test results of a Type 3A dynamo and its subsequent return.
| Identifier | ExFiles\Box 3\5\ 05-page066 | |
| Date | 19th May 1919 | |
| X.295 EPCL/T. 19th May 1919. Messrs. S. Smith & Sons, 179-185 Great Portland Street, London, W.1. Dear Sirs, RE DYNAMO LIGHTING EQUIPMENT. Having now made some tests of the two dynamos which you submitted to us, we are now arranging to return to you the smaller one of the two, namely, the type 3A. We are also giving instructions for the return of the special Bezel operated switch. We are arranging to keep the larger of the two dynamos, also the cut-out supplied, and have instructed that these shall be paid for in accordance with our invoice. Regarding the cut-out, in many respects we are pleased with this and we think it should be quite a reliable piece of apparatus. Its bulk and weight are, however, points rather in its disfavour. DYNAMO - Type 3A. - We find on test that the smaller dynamo when cold, attains a voltage of 12.4 at 640 R.P.M. When at normal running temperature (i.e. after running for about 1 1/2 hours on load), we find a voltage of 13.6 to be obtained at a speed of 725 R.P.M. These are the true cut-in points, because the ideal cut-out would operate exactly when the E.M.F. of the dynamo is equal to that of the battery, (the actual figures given being quite independent of any particular cut-out). The two particular figures 12.4 and 13.6 are given, as the first represents the E.M.F. of a battery well charged, but after standing, and the second represents that of a battery which has been just gassing up on charge. We might say, therefore, that these two speeds of 640 and 725 R.P.M. represent the minor and major limits of cuttin in speeds for practical conditions. We find the current rises fairly rapidly at first after these points, and for the hot condition attains a maximum value of nearly 9 1/2 amperes at about 1700 R.P.M., after which it gradually falls to a value of about 8 1/2 amperes at 4000 R.P.M. We found the runnin and commutation of this dynamo to be very sweet at all speeds. This smaller dynamo, however, would not give us either the low cutting in speed or the out-put we require, and we are, therefore, returning this. Contd. | ||