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).
Design of a distributing board and the potential for a dynamo to burn out under open circuit conditions.
| Identifier | WestWitteringFiles\E\August1920\ Scan54 | |
| Date | 30th August 1920 | |
| To EFC. from R.{Sir Henry Royce} Copy to CJ. " " HS.{Lord Ernest Hives - Chair} " " DA.{Bernard Day - Chassis Design} " " EP.{G. Eric Platford - Chief Quality Engineer} X.4173 X.2575 ORIGINAL RE DISTRIBUTING BOARD. R8/G27/8/20. 6 X.3936 X.295 30 AUG 1920 RECEIVED When a fuse blows and nothing is found wrong with the circuit, a man naturally puts in a bigger fuse. It is impossible to prevent this happening, so that any fuse system is dangerous, if by incorrect sizes some of the apparatus can be burnt out. I have arranged our distributing board without dynamo fuses (as in the Lucas scheme) but it would be quite easy to introduce one as your diagram (2) i.e. so that dynamo would only be excited by 12 volts if battery cut off by fuse, but one would have to prove if such excitation is enough to roast the dynamo if on open circuit. I am not sure about this, but certainly it would be far different from allowing the excitation voltage to run up to may be 100 volts, in case the machine is run at 4,000 revs. without an external circuit. Our engine runs with 3.5 back axle ratio up to close on 2700 revs. and dynamo will then be 4,000 revs. which should be your tested speed. I shall await such a test, i.e. dynamo speed 4,000 open circuit, field excited by battery at 12/14 volts. Will dynamo roast ? It does not matter in the least if battery is slowly discharged, ammeter would shew if this is going on and hand switch on instrument board would naturally stop this. Therefore, fig. 2 arrangement may be the good one, and is the only one we can consider. (Contd.) K E' 5327 (200 L) (E'D' 408 89-1-1) LW' S12213 | ||