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).
Critique of a dynamo's voltage regulator and a starter motor unit with a Bendix drive.
| Identifier | ExFiles\Box 35\3\ scan 072 | |
| Date | 18th March 1922 | |
| EFC2/T18.3.22. -2- Contd. winding of the dynamo and the dynamo output reduced. In principle this is of course a sound scheme, as no doubt many batteries have been spoilt by continuous overcharging at touring speeds. Although the actual point of cutting this resistance in and out must vary somewhat with temperature conditions, we are of the opinion that the extra complication of this unit is justifiable in that it allows a generator to be used whose output normally keeps up a high value at high speeds, that is, when the demand is there, or when all lights are on, but at any time when there is little or no demand this high output is reduced. If such a unit is not used a compromise has to be made in the output curve at open road speeds so that whereas the dynamo shall give a reasonable amount of current to cope with the whole lighting load, it shall not give too much current under daytime conditions. The makers, in comparing their system with what they term the voltage regulator system, by which they mean the system in which the output of the dynamo in volts or amperes, or a combination of the two, is controlled by means of vibrator regulator control of the field current, make certain statements about this other system with which we do not agree, the criticism of which statements, however, would be out of place in this report. Starter Motor Unit. This is fitted with the ordinary bendix drive, the good and bad points of which are well known. A starter switch is dispensed with, but in place of this, when it is desired to operate the motor, one of the starter motor brushes is brought into contact with the commutator by a Bowden wire control. In the first place we consider that the Bowden wire control would be out of place on a high class car, as they are liable to give trouble. In the second place, we do not consider it good electrical practice, from the point of view of commutation, to adopt this method of making the circuit. Thirdly, one of their arguments is that a starter motor switch robs the motor of quite an appreciable proportion (they say 10% or 15%) of the energy given by the battery. We do not agree with this, in fact we know it to be untrue provided the switch is in ordinarily good condition. We have on several occasions measured the volt drop across switches in ordinarily good condition, carrying currents of starter motor magnitude, and have found this to be unappreciable. It is true that they may avoid a little loss by reducing the length of cable, but with cables of the size they specify, the smallest of which is about 35% greater than our present standard, the reduction of circuit resistance, due to the shortening of the cables owing to the omission | ||