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 cutting-in speeds, electrical loads, and performance issues.
| Identifier | WestWitteringFiles\D\January1920\ Scan16 | |
| Date | 26th January 1920 | |
| ORIGINAL. D To DN. from R.{Sir Henry Royce} Copy to CJ. " " CK.{Mr Clark} " " HS.{Lord Ernest Hives - Chair} " " PN.{Mr Northey} X.3014 RE DYNAMOS. I have received your memo BN{W.O. Bentley / Mr Barrington}12/W16/1/20 relating to cutting in speed of dynamos. Our specification is that the dynamo should cut in at a speed of 10 miles an hour which, with the present back axle ratio, is 330 on the engine, and with a belt drive of 1.5 is about 500 on the dynamo. I believe if it did this, that for ordinary uses and for ordinary cars no trouble would occur, providing moderate sized lamps of good efficiency are used. X.1114 For instance, there is no need for side lamps of a car to be more than about 8 to 12 c.p. and the tail lamp 4 to 8 c.p. Head lamps are not used much in town, but in the country they certainly ought to be high efficiency (1/2 watt) lamps not exceeding 24 watts, i.e. 48 c.p. There is also the Klaxon and ignition current to be provided, but even with this it would seem that with ordinary average use the cells should not be discharged. It is very certain that owing to the use of the electrical starter it will be necessary for the dynamo to either cut in earlier or provide more current, but as most of the batteries will not bear a greater rate of charging than we have arranged, it only seems possible to be sure that the dynamo should give a good current at the lowest speed the car is likely to run. It is my impression that with the present system, such as the Lucas, the dynamo cuts in all right when it is cold, but it may be very different when it becomes heated and the cutout also becomes heated. Mr. Northey reports variation between the Hanbury trials car and the Prince of Wales car, the latter being quite satisfactory, giving a good current at quite a slow engine speed; can CK.{Mr Clark} account for this? X.576 The accessibility of the adjustment of the belt drive is very unsatisfactory on a finished car, i.e. on 1 EX. - what can be done to make this better? See other memo. In addition to change of temperature we have the fault that the dynamo belt may be allowed to slip and give very little charging for a long time, before it is noticed. All these things appear to make it imperative that wherever possible there should be means of charging the battery in the garage, which can be so easily done providing the lighting of the garage is by continuous current. It is only necessary then to arrange for the connection socket (of which the positive and negative plugs on the connector should be of different diameter) belonging to the portable light to have an extra plug. (Contd.) | ||