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).
Dynamo's output, battery discharge rates, and the inadequacy of headlamp bulbs for night driving.
| Identifier | ExFiles\Box 5a\3\ 03-page120 | |
| Date | 23th November 1931 | |
| X5840 To Hs.{Lord Ernest Hives - Chair} from G.W.H. c.c. to Hs{Lord Ernest Hives - Chair}/Wst. Hotel de France, Chateauroux, FRANCE. 23/11/31. X6005 Re. 18.G.IV. DYNAMO. In reply to Hs{Lord Ernest Hives - Chair}/Wst.4/AD20.11.31. We spent some considerable time with the dynamo and obtained approximately an increase of one amp. on the output. There appears to be a misunderstanding with regard to the discharge that has been taken from the battery during the day's mileage. The approx. time the headlamps are used is 2.1/2 hours, the discharge resistance that we fitted was therefore only used for 2.1/2 hours which made the total time, of current being taken out of the battery, 6 hours. The difference therefore between this car and 19.G.IV. is that the amount of discharge being taken from the battery on 18.G.IV. is approx. 12 amps. for 6 hours, whereas on 19.G.IV. it was approx. 7 amps. This figure may not be correct as the references of this dynamo are at Derby, and I have not got any here. It will be seen therefore, that the failure of the dynamo to keep up the battery charge is due to the 12 amp. discharge. In your memo; you have evidently forgotten that the figures we have sent you are Half Charge figures as we do not interfere with the resistance in the field of the dynamo when obtaining the dynamo output. Therefore, we can only give you the output of the dynamo with the full lights on, that is, the dynamo working at its maximum output, and with the lamps off, the half charge figures, which instead of being as you say roughly 8 amps. would be approx. 12 amps, as your bench tests shew. We are not interested in the differences between 19.G.IV. and 18.G.IV. and we are aware that we had only 36 watt. headlamp bulbs in 19.G.IV., but as that car was not used at all during darkness, the question of night driving did not enter; it is now a very different undertaking, and we are taking up the attitude of the owner driver. We have had experience in France using 36 watt headlamp bulbs, and with the conditions over here which are entirely different to any in England, the 36 watt lamps are useless, and an owner would not put up with them for 5 minutes. There are miles upon miles of roads here that have no hedging, are of a black surface, and with poor headlamps it would be dangerous to drive at anything more than 50 m.p.h. This condition an owner would not tolerate. It is therefore up to us to provide a dynamo that will give satisfaction to an owner who buys that car, and we are reporting from this view only. To tell a customer who has bought what is supposed to be the world's best car, that he must not use more than 36 watt bulbs in his headlamps is beyond apprehension. | ||