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).
Comparison of the charging internal resistance and voltage between P & R and Exide batteries.
Identifier | ExFiles\Box 54\1\ Scan041 | |
Date | 21th November 1925 guessed | |
-2- Contd. say the statement would hold with a complete P & R battery. at the same time I have never yet seen or been shown in the Test Dept. an output in excess of 13.5 amperes in these circumstances. so feel sure that if it exists, either :- (1) It must be a P & R battery or (2) There must be something definitely wrong with the system. I am coming now to the definite point at which I have arrived and which I admit I had not fully appreciated until the present, and that is, that the charging internal resistance of the P & R battery is considerably greater than that of the Exide, and I want to say that it is much greater than we would like it to be. For the moment I can only give you the results of one or two preliminary observations, but we are working on the matter and in a day or two I am going to provide you with some definite figures to prove this point. It is not so much a question of the internal resistance of the battery on discharge - if it had been we should have found this out long ago on our high rate discharge tests - as a matter of fact on the high rate discharge tests, the voltage of the P & R cells in the sandwich battery is only slightly less than that of the Exide, and the high rate effective discharge of the complete P & R battery is to all intents and purposes as lively as that of the Exide. When, however, the batteries are in the last stages of charge, the P.D. on the P & R cells is very considerably higher than the P.D. on the Exide cells. For instance, our observations on the chassis under actual running conditions yesterday showed the voltages on each of the three Exide cells to be 2.5, and on each of the P & R cells to be 3.0. There would be no reason to suppose that the true E.M.F's of the P & R cells were any more than those of the Exide, and particularly so as the density in the P & R's is less than that in the Exide. We can, therefore, assume that at least half a volt per cell represents an additional resistance in the P & R cells which does not exist in the Exide, and we can say (since the charging current is about 12 amperes) that the resistance of six P & R cells, as compared with six Exide cells, is at least 3Vs{J. Vickers}/12a = .25 ohm. greater. Contd. | ||