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).
Technical report discussing the design, operation, and issues with a single-stage dynamo voltage regulator.
Identifier | ExFiles\Box 142\1\ scan0018 | |
Date | 28th October 1937 | |
-2- Rm{William Robotham - Chief Engineer}/CAP.11/MH.{M. Huckerby}28.10.37. (a) This regulator is of the single-stage type, wherein a resistance is intermittently inserted in the field circuit of the dynamo; thus limiting the dynamo voltage with rise in engine speed. From the principle of its design, there must come a point, as the speed rises, when the resistance will be permanently inserted, and above which the regulator ceases to have any control over the voltage. This point occurs, with the dynamo on open circuit, at about 3,500 to 4,000 r.p.m. of the dynamo. Should, therefore, our armature fuse be "blown", putting the dynamo on open circuit, it would be possible with fast driving for the dynamo voltage to rise to 35 volts or more. The maker's reply to this criticism is that the fuse should be removed, and the dynamo rigidly linked to the battery. While we hesitate to do this, we must admit that we have had very few cases of breakdown bringing this fuse into operation. Moreover, in the event of such a breakdown, it would most likely be definite, and consequently (in the absence of an armature fuse) blow the 90-ampere main fuse. Our fear is, that the fault may be of such a nature, as to cause a heavy current, something less than 90 amperes, to flow and so burn out the smaller cables. In order, however, not to turn the regulator down at the outset, we have tacitly agreed to this, and modified our specification accordingly. (b) (d) Since increase in the temperature of the windings of the units, is normally accompanied by an increase in the operating values, it is necessary to reduce the internal heating to a minimum. We think that in order to keep the size of the unit down, the shunt windings on these regulators have been made smaller than they should be, with the result that internal heating, and consequent variation in operating values, is unduly high. In an attempt to reduce the extent of this rise with temperature, two units were fitted with a bi-metal compensating spring, which had a falling characteristic with temperature. The net result was a fall in operating values, with rise in temperature which was too much the other way. These characteristics are indicated in the figures given below, where representative currents, at 13 volts, in the cold and hot conditions, given by the Lucas units, are compared with our specified requirements. continued. | ||