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 battery performance data, concluding on their suitability for the Wraith model.
| Identifier | ExFiles\Box 151\3\ scan0368 | |
| Date | 4th February 1938 | |
| -2- Rm {William Robotham - Chief Engineer} /RC. {R. Childs} 1/MH. {M. Huckerby} 4.2.38. The figures above prove that there is nothing to choose between the two batteries. This is confirmed by the maker's figures :- | Type. | Capacity AMP. HOURS. | Comparative starting effort taking the P.III battery as 100. | |---|---|---| | | 20 hour rate. | 10 hour rate. | | | Bentley 6.HZD.9-S. | 54 | 49 | 68 | | Wraith 6.LZLD.13-S. | 60 | 54 | 72 | | 25/30 6.HZD.11-S. | 68 | 61 | 83 | | 6.HZD.13-S. | 81 | 73 | 100 | It is concluded that neither the Bentley type nor the Wraith type battery is suitable for fitting to the Wraith car, as the heavy current required to start the engine, under cold conditions results in too big a voltdrop across the battery: thereby causing poor carburation due to insufficient speed, and a weak spark due to insufficient voltage across the ignition coil. Obviously a battery of larger capacity would have less internal resistance and therefore would show less voltdrop for a given current. Inorder to prove this point, further tests were carried out using a standard P.III battery, this battery gave a definitely improved performance, both with regard to engine speed and voltage across the coil. But as this battery is out of the question, both from a size and weight point of view, further tests were carried out using a 25/30 type battery which according to the maker's figures has a starting effort of 83% compared with the figure of 72% given for the Wraith. The performance of this battery is very promising giving an increased engine speed 60:40 and an increase of approximately 1 volt across the coil. Following this comparative tests were taken using a standard 25/30 chassis and a Wraith chassis, these were subjected to the same cold conditions as in the former tests. The results obtained once again proved the Wraith type battery of insufficient capacity for good cold | ||