Зображення сторінки

through and the battery capacity will be quickly depleted. The same condition may exist in the windings of the generator, and if a short circuit is present the current produced by the rotation of the windings will not flow through the external circuit, but will take the shortest way to the ground. A complete open circuit, as indicated at B, permits absolutely no current to reach the lamp. This is because of a positive break in the conductor, which may be produced because of a loose connection or a broken wire. When there is a short circuit, as shown at A, some of the current may reach the lamp filament and cause it to burn dimly.

The location of a fault in a double-function (two commutator) armature is more difficult than finding trouble in a single-function armature, because more things can happen. The method of testing for grounds and shorts has been described. The symptoms and the troubles they indicate in the windings are summarized as follows under the heading of the defective conditions:

Shorted Generator Coil.—Charging rate low; meter vibrates when motoring the generator, or possibly the generator will only turn for a part of a revolution; meter vibrates when engine is running at low speeds; two or more adjacent commutator bars burn and blacken; cranking is slower than normal, but if only one coil is shorted this latter will not be noticed.

Grounded Generator Coil.—This will very seriously affect the cranking, causing it to be slow, and will soon discharge the battery with practically no charge from the generator; will cause burning of the commutator bars; is tested by insulating all brushes from the commutator and testing with the test points from the generator commutator to the frame of the machine. If grounded the test light will burn.

Open Generator Coil.—Charging rate is low; meter vibrates when motoring the generator, and when running at low speeds, the same as with the shorted generator coil; severe sparking at the generator brushes when the engine is running which causes serious burning at one commutator bar. This will not affect the cranking.

Grounded Motor Winding.--This will rapidly discharge the storage battery; is tested by insulating the motor brushes from the commutator and test with the test points from the motor commutator to the frame. The light will burn if the winding is grounded.

If the cut-out relay points stick, the generator armature will continue to revolve even when the engine is stopped. Smooth the contacts by drawing a piece of very fine emery cloth between them, and be sure that the pivot bearings are free. This will usually cure

[merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][merged small][merged small][merged small][merged small][merged small]

Fig. 271.-Diagram Showing Method of Testing Armature Winding with

Test Points for Grounds or Short Circuits.

the trouble, although a sticking roller driving clutch at the forward end of the generator may cause a flow of sufficient current through the relay to give a similar result. The adjustment of the spring tension of the cutout relay should never be made without connecting a volt meter between the proper terminal on the cutout relay and the ground. Start the engine and gradually increase its speed, and if the spring tension is properly set the relay contacts will close when the meter indicates seven volts. If the relay does not close the contact at seven volts, adjust the spring tension, which may be done by bending the arm at the top to which the spring is attached, using a small pair of pliers for this operation.

If there is any trouble in the voltage regulator the generator will not turn when the starter button is pressed, and the generator will not generate current. To test out the voltage regulator depress the starter button, and if there is sufficient current in the battery and no broken wires and the armature does not revolve, remove the connection to the bottom terminal and voltage regulator and connect it to the terminal above. The armature will now revolve when the starter button is depressed. In order to make repairs replace the regulator tube complete. This can be checked out in another way. When the engine is running at normal speed, see if the cutout remains open. If it does this will indicate a burnt out voltage regulator resistance. If the resistance is burnt out when the lead connecting with the binding post at the bottom of the tube is moved to the upper connection the cutout will immediately be drawn closed and the generator will start to charge the battery. The voltage regulator is not used on all Delco systems, as the third brush system of regulation is used on some cars. The voltage regulator system is used on the 1914 Cadillac, as shown in wiring diagram in preceding chapter, and also in the Cole and Moon cars for the same year. A voltage regulator is found on the 1914 Hudson Six-54, on the 1914 Oakland, Models 43, 48 and 62, on the 1914 Oldsmobile, Model Six-54; the 1915 Oldsmobile Six-55. On the 1915 Buick, Cole, Hudson, Moon, Patterson, and Oakland cars the third Brush System of regulation is used, and is practically the system in general use on 1916 cars because it is a simpler system than that using the voltage regulator.

Ammeter Reading When Motoring Generator.—During the motoring of the generator the pole pieces are magnetized by the current through the shunt field winding. The armature is magnetized by the current through the brushes and generator winding on the armature. It is necessary that current flow through both of these circuits before the armature will revolve. It is a familiar mistake to think that when current is passing only through the armature the armature should revolve. The shunt field current can be easily checked by disconnecting the shunt field lead from the generator at the ignition coil terminal. The ammeter in this line should indicate approximately 144 amperes when the ignition button is pulled out. The ammeter on the combination, switch can be depended upon to determine the amount of current flowing through the generator winding during this operation. Both the ignition current and the shunt field current flow through this meter in addition to the current through the generator armature. The timing contacts should be open. This will cut off the ignition current and leave only the armature and shunt field current. Since the shunt field current is only 1/4 amperes the reading of the ammeter will readily indicate whether or not current is flowing through the generator armature winding.

Should it be found that the current through both the armature and the shunt field windings is normal and the armature still does not revolve the trouble may be caused by either (1) the armature being tight mechanically, due to either a sticking driving clutch, trouble in the bearings or foreign particles jammed between the armature and pole pieces. This can be readily tested by removing the front end cover of the generator and turning the armature from the commutator; (2) the shunt field winding or the generator armature winding may be defective in some manner, such as shorted, grounded, or connected to the motor winding. Any one of these would show an abnormal reading of the ammeter in some position of the armature when the armature is revolved by hand. If the ammeter vibrates at each revolution of the armature during the motoring of the generator, and when the engine is running at low speeds, this is very conclusive proof that the armature has either a ground, open coil, shorted coil, or is connected to the motor winding.

If the motor fails to turn the engine when the battery shows that it is properly charged either by specific gravity or meter reading turn on the head lights and then operate the starting lever. If the lights go out, this indicates either a bad cell in the storage battery or a poor connection either in the plate connectors in the battery itself or at either end of the large cable leading from the battery to the generator. If the light burns brightly, but the motor makes no effort to turn over the engine, the trouble may be caused either by poor contact between the motor brushes and the commutator due to the accumulation of dirt and grease or improper spring tension against the motor brushes. If either of these conditions exist, pressing the brushes more firmly against the commutator will usually result in the armature revolving, proving that the defects enumerated exist.

Voltmeter Test If Cranking Action is Weak.—This cranking current is a heavy discharge on the storage battery, the average car requiring approximately 12 horse power to perform the cranking operation. Nine-tenths of all cranking failures is due either to the storage battery or poor connections in the cranking circuit. The first rush of current from the storage battery during the cranking operation varies from 200 to 600 amperes, depending upon the condition of the engine and the storage battery. This is only a momentary flow of current, but a poor connection prevents this heavy flow of current and prevents the starter from breaking the engine loose. This heavy discharge will naturally cause the voltage of the battery to be decreased, and the amount that it is decreased depends to a great extent upon the condition of the charge of the battery. On a storage battery which is charged so that its specific gravity registers 1200 or more the voltage should not fall below 5 volts.

The voltmeter is the instrument to use to quickly locate the cause for failure to crank. The starter cannot be expected to crank the engine when the voltage falls below 3 or 4 volts. There fore, a voltmeter should be connected to the heavy terminal on the rear of the generator and to the ground and the starting pedal depressed. If the voltage falls below 4 volts the trouble is either a nearly discharged battery or a poor connection, or possibly a bad cell in the battery. Any one of these can be quickly located by taking individual voltmeter readings of the different cells when the starting pedal is still depressed. If the individual cells show a normal voltage when the starting pedal is depressed then each

« НазадПродовжити »