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).
Production testing and performance of a 20 HP Dynamo with pole modifications.
| Identifier | ExFiles\Box 165\6\ img125 | |
| Date | 21th March 1927 | |
| X5660 To EY. from EFC. c. Mx.{John H Maddocks - Chief Proving Officer} c. Mr.Brock. EFC2/T21.3.27. 20 HP. DYNAMO P.6.KM. WITH POLE MODIFICATION. Answering your EY19/H17.3.27 we have not so far issued a specification of production inspection and test of 20 HP. dynamos modified from standard, and since the modification of these machines involves removing some of the iron from the pole pieces, it is unlikely that any of the machines so modified would pass our production specification on the open circuit voltage of 13.6 at 720 r.p.m. after 3 1/2 hours running. That means that any of these machines which have been passed to the Test Dept. have been so passed largely on the peak output, and that is why we have been anxious to have one or two more of these machines ourselves to check and pass off if up to a standard which we ourselves decided upon. The figures in our EFC6/T8.3.27 were given as relatively comparative. On the new schedule of volt-ampere output to which we work our cutting-in is reckoned as at 14.0 volts with the carcase temperature, as measured by a thermometer in the usual way, at 800C. Your quoted figure of 12.8 at 840 r.p.m. would appear to agree with your own figures as nearly as can be gauged, taking into account the fact that the temperature of the machine on Mr. Brock's test, as it would be measured by our thermometer, was probably only about 650C, as it would probably have been running with the end cover removed. Therefore there appears to us to be little to suggest the desirability of a check of the instrument used by Mr. Brock. Any doubt we might have as to the value of outside figures does not imply any doubt as to the actual observations, but as to the exact conditions under which the observations are taken. The actual performance of a dynamo is subject to so many variations that it has taken ourselves a year or two to arrive at an entirely logical method of comparative test. As in the case of the 40/50 machine, see our EFC1/T19.3.27 there is, though perhaps to a lesser degree, a fair variation in the output characteristics of these modified machines from one machine to another, e.g. of two we have received we were able to pass one while the other was considerably down. We should like to know in this 20 HP. case if, as we understand to be the case with the 40/50, this pole modification causes the dynamo to satisfy Mx.{John H Maddocks - Chief Proving Officer} on the question of noise, as in that case it would appear to be worth while continuing the modification, though I note from one of your paragraphs that apparently this is not the case with the 20 HP. machine. | ||