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nection. Remember, a loose, corroded or dirty connection on the battery can put both starting and lighting systems out of commission.

The description of the special volt-ammeter shown at Fig. 269, and the methods of using it in looking for derangements in the Delco-motor generator are reproduced from the 1916 Delco-Buick instruction book to insure accuracy in describing these tests. Too

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Fig. 269.—Interior Wiring Arrangement of Special Volt-Ammeter, an

Important Adjunct to the Testing Equipment of the Delco System

often the mechanic is handicapped by not having the proper tools to work with. No mechanic would attempt to overhaul an engine with the tools included in the car equipment, neither should he expect to make all of the practical tests on the electrical system without some additional equipment.

A voltmeter and an ammeter or a combination volt-ammeter is the one most important instrument that the mechanic can use in this work, and in order to explain the action of such a meter,

(Fig. 269) is included. This shows the internal circuits of such a meter with full scale readings of 30 Ampere, 3 Ampere, 15 Volts. The meter proper consists of a permanent magnet “M” between the poles of which is mounted a movable coil “K” which carries the pointer. This part of the meter is very sensitive and carries only a small amount of current. In the average meter with the scale readings as given the current in the different parts would be approximately as follows: With the meter connected to give a full scale reading of 30 amperes (connect the lines to the terminal marked + and to the one marked “30-A”) the current would divide at the + terminal, the main part of which flows to the terminal marked “30-A” 29%10 amperes flowing in this circuit and 110 ampere flowing through the coil to terminal 3-A through the shunt to 30-A terminal. The 110 ampere through the movable coil is the amount required to give a full scale reading of the pointer.

When the 3 ampere scale is used the current divides at the + terminal and 2%10 amperes flows through both shunts to 3-A terminal and 110 ampere through the coil as before. The difference in the proportions of the total current that flows through each circuit from the amount that flows through each circuit in the former case is due to the resistance of the 3-A shunt. When the instrument is used as a voltmeter connections are made to the positive terminal and the terminal marked “15 V” and the button must be pressed. This cuts out the shunts and connects in series the high resistance. This is a very high resistance and when the full voltage reading is taken there is 110 of an ampere flowing through the high resistance and the movable coil, which is the same amount of current that flows in it when it is used as an ammeter and it gives a full scale deflection.

The important points to remember when using an instrument of this kind are as follows: 1. Do not test the storage battery with an ammeter as dry batteries are tested. (This will positively ruin the meter.) 2. In taking an ammeter reading in the circuit where the approximate flow of current is not known, always use the highest scale on the meter and make the connection where it can be quickly disconnected in the event of a high reading. 3. If the meter reads backwards reverse the wires to the meter terminals. The meter will not be damaged by passing a current through it in the reverse direction as long as the amount of the current is not over the capacity of the meter. 4. No damage will be done by connecting a voltmeter as an ammeter so long as the voltage of the system is not above the range of the voltmeter, but the ammeter should not be used as a voltmeter. 5. A high-class instrument of this type will stand a momentary overload of from 200 to 400%. If the user is careful not to make his connections per





Fig. 270.—Wiring Diagram Showing Methods of Connecting Lamp and

Test Points in Lighting Circuit.

manently until the current is normal, he will very seldom injure the instrument.

Next to the combination volt-ammeter the most important testing arrangement for the mechanic is a set of test points to use in connection with the electric light circuit. This is very easily made as shown at Fig. 270 by tapping one wire of an ordinary extension lamp, splicing the wires on to which are attached suitable points with insulated handles in order that these may be handled with no danger of electrical shock. With a set of test points as described the lamp will burn when the test points are together or when there is an electrical connection between the points. This will give more satisfactory results for testing for grounds, leaks or open connections than will a bell or buzzer used with dry batteries, as the voltage is higher and it requires a small amount of current to operate the lamp. With a bell or buzzer, a ground or open connection may exist, but the resistance is so high that enough current will not be forced through it by the dry batteries to operate the bell or buzzer. No harm can be done to any part of the Delco or other apparatus by tests points as described above, when the ordinary carbon or tungsten lamp is used in testing purposes.

Indications of Delco Generator Troubles. If there is any derangement of the interior wiring of the Delco motor-generator unit, these defects will be made apparent by: 1st, failure to turn over at uniform speed when starter button is pushed down; 2nd, blackening and burning of the generator commutator or excessive sparking; 3rd, failure to keep battery charged; 4th, slow cranking, even with a well charged battery; 5th, vibration of cut-out relay; 6th, excessive heating of generator. If any of the above indications exist the first step is to go over all connections and make sure if these are made correctly in accordance with the wiring diagram furnished with the car. Examine the commutator to see if it has the same appearance at all points on its periphery or whether some of the segments are burnt more than others. See if the armature will revolve at a uniform speed when the starter button is depressed. If the commutator is burnt black on two or. more adjacent segments and it does not revolve uniformly or evenly when the starter button is pushed down, this will indicate that a short circuit exists in one or more of the armature coils which entirely eliminates the action of the winding, so that the armature will revolve only for a fraction of a revolution. It will usually cause the relay to vibrate when the generator is being driven by the engine. If an amperemeter is used in the circuit, the pointer of this will swing back and forth at each revolution both when the engine is turning the generator over and when the current from the storage battery is employed for the same purpose. While a short or open circuited winding is an extremely rare occurrence it may be well to detail the method of testing to see if any grounds or short circuits exist in the armature winding.

Testing for Defective Windings.-In order to make this test intelligently it is advisable to use a 110 volt circuit which includes a 16 candle power carbon filament lamp wired in series and a pair of test points as previously described. Each end of the wire is soldered to an insulated contact point composed of a piece of brass or copper rod having a tapered point attached to an insulating handle of fiber or other non-conductor. The test may be made with the generator in place on the car, if it is accessibly placed or the device may be removed from the chassis. If the armature is in place insulate all brushes from the commutator by placing sheets of waxed paper between them. Then with the test points test for a ground from each commutator segment to the frame or armature shaft as shown at A, Fig. 271. Obviously, if a short circuit exists between any wire and the ground this will complete the circuit and cause the lamp to light. Next with the brushes and commutator bars still insulated as in the first test make a trial for a “short” including the armature and generator windings holding one test point on the segment of the motor commutator and the other on one of the segments of the generator commutator. The lamp should not light during this test, if it does it indicates a short circuit between the two windings. The first test indicates a short circuit between one of the windings and the metal representing the ground, in this case the armature core and shaft.

It may be well at this point to outline the difference between a short circuit and an open circuit. Both of these are clearly shown at Fig. 266. At A, what is technically known as a short circuit is depicted. It will be observed here that the insulation is worn off of one of the wires and that the conductor is rubbing on the metal frame. The positive terminal of the battery is attached to the metal frame and the negative terminal of the battery goes to the current consuming unit, in this case an incandescent lamp. It will be apparent that with the bare wire in contact with the frame that the current will follow the course indicated by the arrows and will return to the storage battery through the ground connection with the bare or grounded wire. In this case no current can flow through the current consuming unit. Owing to the low resistance of the circuit a large amount of current will pass

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