« НазадПродовжити »
the battery from the half of the secondary that has previously been idle. As the current flow is in the same direction as that previously supplied, the battery is charged exactly the same as if uni-directional current from a generator was used.
The element upon which the success of the outfit depends is the vibrating mechanism, upon which devolves the duty to reverse connections in synchronism with the voltage and also exactly in step with the transformer secondary voltage in such a manner as to open the current character circuit at the instant of zero current and prevent injurious wear of the contacts by sparking. The following description of the action of this rectifier is repro
duced from the Electric Journal, and the action of the device may be understood by studying the wiring diagram shown at Fig. 42 B. “Two small laminated iron magnets, marked A.C. magnets, are connected in series across one-half of the transformer secondary, connections being made so that the corresponding ends of the magnet are of the same magnetic polarity. A direct-current magnet, polarized by shunt current from the battery, is so placed as to bring its ends within the effective field areas of the A.C. magnets. Since the ends of the D.C. magnet are of opposite polarity, they are forced at any instant in opposite directions by the fields of the A.C. magnets and one pair of contacts is closed. During the succeeding half cycle the A.C. mag
nets are reversed in polarity, while the D.C. magnet is not, the impelling force is reversed, and the armature takes such a position as to close the other pair of contacts. One side of the battery is thus connected alternately to the opposite ends of the secondary of the transformer in synchronism with the alternating voltage, while the other side is permanently connected to the center point. Exact timing to insure sparkless operation, by
Fig. 41.—Devices for Rectifying Alternating Current. A— Vibrator
Type Rectifier. B-Small Rotary Converter Set.
breaking the current-carrying circuit at the time when the battery and transformer voltages are equal and opposite and no current is flowing, is secured by connecting in series with the A.C, magnets, a resistance which alters the power-factor of the current in the magnets without affecting that of the load current in the transformer. This change in power-factor translates in time the impelling force, with respect to the current in the contacts, and secures the result of sparkless operation. This phase-controlling resistance is made variable, in order that the outfit will be ap
plicable on circuits of which the wave form is not a true sine wave, and on circuits on which the voltage is not of normal value. The condensers connected around the contacts reduce to a negligible amount the unavoidable slight sparking, due to fluctuations in the line voltage, variation in wave form and change in battery voltage.
“The regulating resistance, which is connected in each side of the secondary circuit between the transformer and the stationary contact, is for the purpose of giving the outfit high or low regulation, in order that the change in battery voltage, as the charge progresses, will make only a small change in the current delivered. The standardization of lighting batteries in general use has resulted in the selection for the commercial form of this apparatus of such transformer voltage and resistance value as to make the charging current under normal conditions approximately 8.5 amperes at the start of charge and 6.5 amperes at the finish. The features above mentioned result in an outfit which can be connected to an ordinary alternating-current lighting circuit and to a battery, without attention to polarity, owing to the polarization of the D.C. magnet by the battery, and which will then, after a single adjustment of the phase-controlling resistance, give a full charge to the ordinary lighting battery without further attention. The cost of power for such a charge at the common rate of 10 cents per kilowatt hour is roughly 6.5 cents, as compared to the ordinary charge of 75 cents to $1.25 per charge by a public garage.
Battery-Charging Apparatus.—The apparatus to be used in charging a storage battery depends upon the voltage and character of the current available for that purpose. Where direct current can be obtained the apparatus needed is very simple, consisting merely of some form of resistance device to regulate the amperage of the current allowed to flow through the battery. The internal resistance of a storage battery is very low, and if it were coupled directly into a circuit without the interposition of additional resistance, an excessive amount of current would flow through the battery and injure the plates. When an alternating current is used it is necessary to change this to a uni-directional flow before
Fig. 42.-Construction of Westing house Vibrator Type Alternating-Current Rectifier at A, and Wiring
Diagram Showing Operation at B.
it can be passed through the battery. Alternating current is that which flows first in one direction and immediately afterward in the reverse direction. When used in charging storage batteries some form of rectifier is essential. The rectifier may be a simple form, as shown at Fig. 43 A, which is intended to be coupled directly into a lighting circuit by screwing the plug attached to the flexible cord in the lamp socket. A rotary converter set, such as shown at B, or at Figs. 39 and 41, may also be used; in this the alternating current is depended on to run an electric motor, which drives the armature of a direct-current dynamo. The current to charge the battery is taken from the dynamo as it is suitable for the purpose, whereas that flowing through the motor cannot be used directly.
The view at Fig. 43 C shows a usual form of hydrometer syringe which is introduced into the vent hole of the storage battery, such as shown at Fig. 44, and enough electrolyte drawn out of the cell to determine its specific gravity. This is shown on the hydrometer scale, as indicated in the enlarged sections. A very useful appliance where considerable storage-battery work is done is shown at Fig. 45 A. This is a stand of simple form, designed to carry a carboy containing either acid, distilled water or electrolyte. In fact, it might be desirable to have three of these stands, which are inexpensive, one for each of the liquids mentioned. In many repair shops the replenishing of storage batteries is done in a wasteful manner, as the liquid is carried around in a bottle or old water pitcher and poured from that container into the battery, often without the use of a funnel. The chances of spilling are, of course, greater than if the liquids were carefully handled and more time than necessary is consumed in doing the work. The stand shown is about 5 feet high and is fitted with castors so it may be easily moved about the shop if necessary. For example, in taking care of electric vehicle batteries, it may be easier to move the carboy to the battery than to remove the heavy battery from the automobile. The container for the liquid is placed on top of the stand and the liquid is conveyed from it by a rubber tube. The rubber tube is attached to a glass tube extending down nearly to the bottom of the liquid. At the bottom