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 discussing starter motor brake tests and comparing performance curves.
| Identifier | ExFiles\Box 168b\2\ img050 | |
| Date | 17th July 1921 | |
| X 802 OY-1-C.16721. July 17, 1921. X.4298. X.4206. X.802. X.1198. X.3309. Mr. Claude Johnson, Managing Director, Rolls-Royce Ltd., London, England. Attention: Messrs. F.H. Royce and E.F.Clarke. Dear Sir:- X.3082. Re Starter Motor Brake Tests. (1) Replying to Mr. Clark's memo EFC1/T22.6.21 on this subject, we note that the curve for the production motor agrees closely with the curves sent to Mr. Hives with our letter OY1/G3621 on 4 EX (copies of which are attached). The torque rise with increase of amps. is practically identical, but the speed is less, because of the less terminal volts assumed. This decrease of speed, however, does not appear to give results quite in proportion to the drop in volts, and hence Mr. Clark gets a maximum efficiency of 68% at 19 lbs. ins. torque, whereas our curve would give a maximum efficiency of 64% at 36 lbs.ins. torque. The curve we gave was from tests of a production motor without epicyclic gear made by the Westinghouse Co. Other copies of this curve, as sent us by the Westinghouse Co. were sent to Mr. Hives. (2) Mr Clarke mentions that he proposes plotting all future starting motor curves against a torque base. We wish to mention that the practice which is almost standard in this country is to plot against an ampere base. The only exception which we have met is the Bijur, who sent us some preliminary curves on a torque base. For comparison it is therefore convenient, at least in the United States, to have curves plotted on an ampere base. (3) With regard to the voltage drop mentioned by Mr.Clark of 1 volt per 50 amps, we would ask him to refer Contd. | ||