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Fig. 76.–Mercury Rectifier Bulbs and Methods of Wiring to Charge
Storage Battery from Alternating Current Main.
not provided to maintain a flow continuously toward the negative electrode. In the General Electric rectifier tube there are two anodes and one cathode. Each of the former is connected to a separate side of the alternating current supply and also through reactances to one side of the load and the cathode to the other. As the current alternates, first one anode and then the other becomes positive and there is a continuous flow toward the mercury cathode thence through the load (in this case the battery to be charged) and back to the opposite side of the supply through a reactance. At each reversal the latter discharges, thus maintaining
Fig. 77.—Simplified Wiring Diagram, Showing Method of Using Rectifier
the arc until the voltage reaches the value required to maintain the current against the counter E. M. F. and also reducing the fluctuations in the direct current. In this way, a true continuous flow is obtained with very small loss in transformation.
A small electrode connected to one side of the alternating circuit is used for starting the arc. A slight tilting of the tube makes a mercury bridge between the terminal and draws an arc as soon as the tube is turned to a vertical position. The ordinary form used for vehicle batteries has a maximum current capacity of 30 amperes for charging the lead plate type and a larger form intended for use with Edison batteries yields up to a limit of 50 amperes. Those for charging ignition batteries will pass 5 amperes for one to charge six cells and a larger one that will pass 10 amperes for from three to ten batteries. As is true of the electrolytic rectifier complete instructions are furnished by the manufacturer for their use.
The Wagner device, which is shown at Fig. 74, A, operates on a new principle and comprises a small two coil transformer to reduce the line voltage to a low figure; the rectifier proper which consists of a vibrating armature in connection with an electro magnet and a resistance to limit the flow of the charging current. A meter is included as an integral part of the set for measuring the current flow. All sets are sold for use with ignition or lighting batteries of low voltage with a lamp socket plug and attaching cord, the idea being to utilize an ordinary lighting circuit of 110 volts A. C. The magnet and vibrating armature accomplish the rectification of the current with little loss, the action after connection to the battery which is to be charged proceeding automatically. By a simple device, the current stoppage throws the main contacts open so the partially charged battery cannot be rapidly discharged. While the rectifiers are constructed to use 60 cycle, 110 volt alternating current they will work at all frequencies from 57 to 63. The size made will pass three to five amperes, the voltage being sufficient to recharge a three cell battery.
When batteries are to be charged from a direct current it is possible to use a rheostat to regulate the voltage at the terminals. The construction of a rheostat is very simple as it consists only of a group of high resistance coils of wire mounted in insulating material and having suitable connections with segments on the base plate upon which is mounted the operating arm that makes the contact. According to the manner in which these are made and wired a large resistance is introduced at first, gradually decreasing as the lever is moved over or it may operate in the reverse fashion, a large amount of current being allowed to pass at the first contact and less as the handle progresses across the path. Rheostats should only be purchased after consulting a capable electrician as the required resistance must be figured out from the voltage of the circuit to be used, the maximum battery
Fig. 78.—How to Charge Storage Battery by Direct Current Through
Simple Lamp Bank Resistance.
current, the charging rate in amperes and the number of cells to be charged at one time.
By far the simplest method of charging storage batteries is by interposing a lamp bank resistance instead of the rheostat. These are easily made by any garage mechanic and are very satisfactory for charging ignition or lighting batteries. Standard carbon lamps of the voltage of the circuit shown should be used and the amperes needed for charging can be controlled by varying the candle power and the number of lamps used. If the lamps are to operate on 110 volt circuit, a 16 candle power carbon filament
lamp will. permit one-half ampere to pass; a 32 candle power will allow 1 ampere to pass. If it is desired, therefore, to pass three amperes through the battery, one could use 3-32 candle power lamps, or 6-16 candle power lamps. If the lamps are to burn on 220 volts it should be remembered that when the voltage is doubled the amperage is cut in half, therefore the 32 candle power, 220 volt carbon filament bulbs will only pass half an ampere. The method of wiring is very simple as may be readily ascertained by referring to Fig. 78. The line wires are attached to a fuse block and then to a double knife switch. The switch and fuse block are usually mounted on a panel of insulating material such as slate or marble. One of the wires, the positive of the circuit, runs from the switch directly to the positive terminal of the storage battery. The negative wire from the switch passes to the lamp bank resistance. The lamps are placed in parallel connection with respect to each other but in series connection in respect to the battery. When coupled in this manner the current must overcome the combined resistance of the storage battery which is very low and that of the lamps. This prevents the battery being charged with current of too high voltage.
A complete commercial installation which has been used successfully with a direct current of 110 volts pressure and which has a capacity for charging 30-6 volt batteries simultaneously is composed of two charging sets either of which may be employed independently or both may be used at the same time. The method of wiring is clearly shown at Fig. 79. In this a three wire system is employed for lighting. This consists of one positive wire and two negative conductors, forming in reality two separate circuits so that one half of the installation is on one wire, while the remainder is on the other two. An upper branch is used merely for illumination. On either half of the three wire double circuit is placed a bank of lamps, these being in series with the batteries but the lamps are in multiple with each other. The board at the left has 9 sockets, that at the right 12 sockets. The number of lamps placed in these and their candle power regulate the amount of current in amperes that will pass through the battery. As we have seen, battery manufacturers advise that certain minimum and