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).
Journal page discussing the voltage regulation of electrical systems, with a comparison of generator types using performance graphs.
| Identifier | ExFiles\Box 31\1\ Scan175 | |
| Date | 1st June 1925 | |
| Vol. XVI June, 1925 No. 6 577 VOLTAGE REGULATION OF ELECTRICAL SYSTEMS Two adjustments are provided on the regulator: (a) the adjustment of the contact point G by the screw O and its locking nut and set screw; and (b) adjustment of the spring tension of the armature spring P by the knurled locking-nut Q. It should be remembered that, on voltage-regulated systems, batteries automatically will take different ampere-hour charging-rates at various conditions of charge. If the specific gravity of the battery is low, the charging rate will be comparatively high, and will taper off to a lower value as the battery takes its charge. Battery specific-gravity and condition should be considered carefully before adjustment is pronounced as to whether a charging rate is too high or too low. It is being found necessary to educate users as well as service-station attendants on this point. Frequently, a voltage-regulated system will keep the battery fully charged to a point such that only a trickling current is passing and the user becomes disturbed, thinking the generator is not charging as it should. A check almost invariably shows the battery to be fully charged. If the points of a voltage regulator are held together, no regulating action takes place; the generator then operates under full field-strength at its maximum voltage for the given speed and load as a third-brush-controlled generator or a straight shunt-wound machine, as the case may be. The curves in Fig. 4, furnished by a representative battery manufacturer, illustrate the desired tapering charge. These curves were taken in the laboratory of the battery manufacturer, the voltage being regulated manually at a very constant value; they are very similar to curves obtained from vehicle application of voltage-regulated systems. FIG. 4—CURVES ILLUSTRATING THE DESIRABLE TAPERING BATTERY-CHARGE The Data Were Obtained in the Laboratory of the Battery Manufacturer, the Voltage Being Regulated Manually at a Very Constant Value. The Curves Are Very Similar to Those Obtained from Vehicle Applications of Voltage-Regulated Systems CHARGING ECONOMICS The curves taken while a generator was running as a third-brush machine are shown in Fig. 1, and those taken when running as a voltage-regulated machine are shown in Fig. 2. These are simply specimen performances and apply to tests taken at certain brush and regulator-settings and under certain battery conditions; but, while the conditions were similar in the two tests and the curves illustrate the difference in operation, these must not be taken as applying specifically to all conditions. Many variables must be taken into account in the analysis of generator-performance curves, such as battery size and conditions, speed, temperature, brush settings and regulator settings. A generator designed to handle certain loads through certain speed ranges is built to meet specific conditions; so, the exact conditions under which tests are conducted are important if any intelligent analysis of performance is to be made. These curves were taken at constant speed on a large battery and show no rise in the third-brush-generator voltage which often results on protracted charging. FIG. 5—COMPARATIVE CURRENT AND VOLTAGE CURVES Data Were Obtained on Two Different Types of Machine, As Stated in Table 1 No reference has been made to generator efficiencies, but it will be appreciated that they vary with load, speed and design. In general, efficiencies on automotive generators are not important, because the amount of material it is possible to use is closely restricted and this naturally is reflected in the efficiencies. Likewise, little has been said with reference to generator temperatures. Usually, a manufacturer will rate the generator output on the vehicle while it is subjected to favorable cooling conditions and such a generator, if run at full rated-load on the block, is very likely to overheat. In Fig. 5, the current and the voltage curves for the two types of machine have been plotted for comparison. The curves were plotted from the data in Table 1. The average number of watts input for the two tests is shown by the curves in Fig. 6. FIG. 6—AVERAGE NUMBER OF WATTS INPUT FOR THE TWO TESTS OF FIG. 5 For the Same Period, the Total Watt-Hour Input of the Voltage-Regulated Generator Was 1388 and for the Third-Brush Generator It Was 2388 Watt-Hours. That is, the Third-Brush Machine Delivered About 73 per Cent More Power in the Same Time Than Did the Voltage-Regulated Generator. The Two Tests Were Made on the Same Battery at Approximately the Same Condition of Discharge on Starting. Beyond a Certain Point, Electrical Energy Cannot Be Used in Charging the Battery and Represents a Direct Loss. | ||