How and When to Adjust Charging Rates
A correct charging rate is one which keeps a battery fully charged, but does not overcharge it, and which does not cause either the generator or the battery to become overheated. The only way to determine whether a certain charging rate is correct on any particular car is to make an arrangement with the car owner to bring in his car every two weeks. On such occasions hydrometer readings should be taken and water added, if necessary, to bring the surface of the electrolyte up to the proper level. The hydrometer readings will show whether the generator is keeping the battery charged, and if a change in the charging rate is necessary, the necessary adjustments may be made. If a customer does not bring in his car every two weeks, call him up on the phone or write to him. The interest which you show in his battery by doing this will generally result in the customer giving you all his repair business, and he will also tell his acquaintances about your good service. This will give you considerable “word of mouth” advertising, which is by far the best form of advertising and which cannot be bought. It must be earned by good battery service.
Adjusting a third brush generator. The best rule to remember for changing the output of a third brush machine is that to increase the output, move the third brush in the direction in which the commutator rotates, and to decrease the output, move the third brush in the opposite direction. Move the third brush only 1/16 inch and then sandpaper the brush seat with 00 sandpaper. Allow the generator to run for about twenty minutes to “run-in” the brush. Then vary the speed to see what the maximum charging rate is. If the change in the charging rate is not sufficient, move the third brush another 1/16 inch and proceed as before until the desired charging rate is obtained.
Adjusting Vibrating Regulators. The output of generators which use a vibrating regulator is adjusted by changing the tension of the spring fastened to the regulator arm. In many cases this adjustment is made by means of a screw which is turned up or down to change the spring tension. In other cases a hook or prong is bent to change the spring tension. Where a coil spring is used, lengthening the spring will decrease the tension and lower the output, while shortening the spring will increase the tension and raise the output.
Vibrating regulators are of the “constant” current or the “constant-voltage” types. The constant current regulator has a winding of heavy wire which carries the charging current. When the charging current reaches the value for which the regulator is set, the electromagnet formed by the coil and the core on which it is wound draws the regulator armature toward it and thereby separates the regulator points, which are in series with the shunt field. A resistance coil, which is connected across the regulator points and which is short-circuited when the points are closed, is put in series with the shunt field when the points separate. This reduces the shunt field current, causing a decrease in generator voltage and hence current output. As the current decreases, the pull of the electromagnet on the regulator armature weakens and the spring overcomes the pull of the electromagnet and closes the regulator points. This short-circuits the resistance coil connected across the regulator points and allows the shunt field current to increase again, thereby increasing the generator output. This cycle is repeated at a high rate of speed, causing the regulator points to vibrate rapidly.
The action of a vibrating “constant-voltage” regulator is exactly the same as that of the “constant current” regulator, except that the coil is connected across the generator brushes. The action of this coil therefore depends on the generator voltage, the regulator points vibrating when the generator voltage rises to the value for which the regulator is set.
Adjusting Reverse-Series Generators. The regulation of the output of this type of generator is accomplished by means of a field winding which is in series with the armature, and which therefore carries the charging current. These series field coils are magnetically opposed to the shunt field coils, and an increase in charging current results in a weakening of the field flux. A balanced condition is reached at which no increase of flux takes place as the generator speed increases, the tendency of the increased shunt field current to increase the total flux being counterbalanced by the weakening action of the flux produced by the series field current.
To increase the output of a reverse series generator, it is necessary to weaken the opposing series field flux. The only way of doing this is to short-circuit the series field coils, or connect a resistance across them. To decrease the output of a reverse series generator, a resistance coil may be connected in series with the shunt field winding. Neither of these schemes is practicable, and hence the reverse series generator may be considered as a “non-adjustable” machine. Under-charging may be prevented by using the starting motor and lights as little as possible, or by giving the battery a bench charge occasionally. Over-charging may be prevented by burning the lights whenever the engine is running, or leaving the lights turned on over night.
Other forms of regulation have been used on the older cars, but the majority of the cars now in use use one of the four forms of regulation described in the foregoing paragraphs. If adjustments need to be made on some car having a system of-regulation with which the battery man is not familiar, the work should be done in a service station doing generator work.
If generator outputs are changed because of some special operating condition, such as summer tours, the rate should be changed to normal as soon as the usual driving conditions are resumed.